kdmin, 
 
 Correlation of Concrete Tie 
 Track Performance in 
 Revenue Service and at the 
 Facility for Accelerated 
 Service Testing 
 
 >n, DC 20590 
 
 Volume I A Detailed Summary 
 
 'FRA 3t 1984 
 
 Report 
 
 This document is av 
 U.S. 
 
Technical Report Documentation Page 
 
 1. Report No. 
 
 FRA/ORD- 84/02.1 
 
 2. Government Accession No. 
 
 3. Recipient's Catalog No. 
 
 4. Title and Subtitle 
 
 Correlation of Concrete Tie Track Performance in 
 Revenue Service and at the Facility for Accelerated 
 Service Testing 
 
 5. Report Date 
 
 August 1984 
 
 6. Performing Organization Code 
 
 BCL (Battelle) 
 
 8. Performing Orgonization Report No. 
 
 7. Authors) h. D. Harrison* 
 F. E. Dean* 
 
 E. T. Selig** 
 H. E. Stewart** 
 
 9. Performing Orgonization Name and Address 
 
 *Battelle Columbus Laboratories 
 505 King Avenue 
 Columbus, OH 43201 
 
 10. Work Unit No. (TRAIS) 
 
 **University of 
 Massachusetts 
 Amherst, MA 01 003 
 
 11. Contract or Grant No. 
 
 D0T-FR-8164 
 
 12. Sponsoring Agency Name and Address 
 
 Federal Railroad Administration 
 400 Seventh Street, SW 
 Washington, D.C. 20590 
 
 13. Type of Report and Period Covered 
 
 Final Report 
 
 March 1979 - July 1982 
 
 14. Sponsoring Agency Code 
 
 RRD-10 
 
 15. Supplementory Notes 
 
 16. Abstract 
 
 This report is the first of three volumes which describe a comparative 
 study of concrete tie track in U.S. revenue service and at the Facility for 
 Accelerated Service Testing (FAST). The work was undertaken to develop an 
 understanding of the degree to which FAST represents the "real world" of revenue 
 service. The loading environment, structural characteristics and long-term 
 performance of concrete tie track at FAST were compared with corresponding 
 data from four concrete tie track segments in revenue service. 
 
 The major conclusions of the study include: 
 
 a. Impact loads of high magnitude relative to nominal wheel loads occur 
 because of small percentages of freight and passenger traffic in revenue 
 service. These impact loads are caused by wheel tread irregularities and pro- 
 duce bending cracks at the rail seats of concrete ties. Without detection and 
 removal of the worst wheel tread conditions or attenuation of the impact loads, 
 the service lives of the concrete ties may be significantly shortened. 
 
 b. While FAST has the highest mean loads of any site examined, crack- 
 producing impact loads do not occur at FAST because of the extremely good 
 (untypical) FAST consist wheel maintenance program. 
 
 c. Track surfacing maintenance (raising and tamping) loosens the 
 ballast structure, reduces the uniformity of support and contributes to 
 large variations in relative track settlement. Uniformity of initial track 
 support conditions is a key to good track performance. 
 
 17. Key Words 
 
 Concrete Ties, Track Loading, 
 Track Performance, FAST, Track 
 Structures, Permanent Deformation 
 
 18. Distribution Stotement 
 
 Document is available to the U.S. 
 public through the National Technical 
 Information Service, Springfield, VA 
 22161. 
 
 19. Security Classif. (of this report) 
 
 UNCLASSIFIED 
 
 20. Security Classif. (of this page) 
 
 UNCLASSIFIED 
 
 21. No. of Pages 
 
 148 
 
 22. Price 
 
 Form DOT F 1700.7 (8-72) 
 
 Reproduction of completed page authorized 
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PREFACE 
 
 This report is a summary of the research performed under contract DOT-FR- 
 8164 by Battelle's Columbus Laboratories (BCL) and its subcontractor, the 
 University of Massachusetts (UMass),and was sponsored by the U. S. Department 
 of Transportation, Federal Railroad Administration. The program manager for 
 this study was Howard G. Moody of the Federal Railroad Administration. 
 
 Harold D. Harrison, Senior Research Scientist of BCL, managed the prime 
 contract and the subcontracts with UMass and the four participating rail- 
 roads and was the principal investigator for the research performed at BCL. 
 The BCL team of researchers included Robert H. Prause, Manager of the Applied 
 Dynamics and Acoustics Section, and Francis E. Dean who were both heavily 
 involved in the initial planning of the program. James M. Tuten was 
 responsible for all data processing and analysis with help from W. Tony So 
 and Michael D. Kurre. Technical support was provided by Matthew S. Zelinski, 
 Kenneth Schueller, Gary Conkel , and Donald Skaggs. Administrative support 
 was provided by Constance Leavens and Audrey Knapp. 
 
 The University of Massachusetts research was conducted under the direction of 
 Ernest T. Selig, Professor of Civil Engineering, and Principal Investigator. 
 Donald R. McMahon served as Research Engineer. Graduate students also 
 participated in the UMass research. In particular, Harry E. Stewart, a 
 co-author, focused on the prediction methodology, presented in Volume II. 
 Additional technical support was provided by Ronald F. Bukoski , Deh C. 
 Ho, Gillian M. Norman, Donna M. Feng, Thomas J. Giller, Ching L. Kuo, Michael 
 C. McVay, and Robert S. Grout. Administrative support was provided by 
 Kristin J. Currier and Thomas E. Sikora. 
 
 Four railroads were subcontracted to support the field testing at their 
 respective test sites. The technical liaison was provided by the following 
 railroad personnel on behalf of their chief engineers: Mr. Steve Heath and 
 Mr. John Baker of the Atchison, Topeka and Santa Fe Railway (ATSF), Mr. Dan 
 Jerman of Amtrak, Mr. Bruce Dunseth of the Chessie System, and Mr. Robert 
 Catlett of the Norfolk and Western Railway (N&W). 
 
 Data acquired from the Facility for Accelerated Service Testing (FAST) 
 wereprovided through the efforts of Larry Daniels and Jack Heiss. 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://archive.org/details/correlationofcon84021harr 
 
TABLE OF CONTENTS 
 
 Page 
 
 1.0 SUMMARY 11 
 
 2.0 INTRODUCTION 13 
 
 3.0 SITE DESCRIPTIONS 15 
 
 3.1 The Facility for Accelerated Service Testing (FAST) Site 
 
 at Pueblo, Colorado 15 
 
 3.2 AT&SF Site Near Streator, Illinois 16 
 
 3.2.1 Location 16 
 
 3.2.2 Physical Layout 16 
 
 3.3 Chessie System Site Near Richmond, Virginia 21 
 
 3.4 Amtrak Northeast Corridor Site Near Aberdeen, Maryland .... 25 
 
 3.4.1 Location 25 
 
 3.4.2 Physical Layout 25 
 
 3.5 The Norfolk and Western Site Near Roanoke, Virginia 25 
 
 4.0 CORRELATION MEASUREMENT PLAN 31 
 
 4.1 Summary of Measurements 31 
 
 4.2 Measurement Locations 35 
 
 5.0 DYNAMIC MEASUREMENTS 36 
 
 5.1 Traffic Loads 36 
 
 5.1.1 FAST Loads 44 
 
 5.1.2 Streator Loads 44 
 
 5.1.3 Richmond Loads 45 
 
 5.1.4 Aberdeen Loads 45 
 
 5.1.5 Roanoke Loads 45 
 
 5.1.6 Load Summaries 46 
 
 5.1.7 Speed Effects 46 
 
 5.1.8 Effects of Vehicle Weight 50 
 
 5.2 Rail Seat Bending 51 
 
 5.3 Tie Center Bending 56 
 
 5.4 Ancillary Dynamic Measurements 56 
 
 5.4.1 Tie Bending Modes 56 
 
 5.4.2 Rail and Tie Accelerations 59 
 
 6.0 TRACK SYSTEM CHARACTERISTICS AND PERFORMANCE 62 
 
 6.1 Track Stiffness/Modulus 62 
 
 6.2 Track Settlement/Roughness 69 
 
 7.0 BALLAST AND SUBGRADE CHARACTERISTICS 79 
 
 7.1 Ballast Descriptions 79 
 
 7.2 Physical State Tests . 84 
 
 7.2.1 Ballast Density Tests 86 
 
 7.2.2 Plate Load Tests 90 
 
 7.2.3 Lateral Tie Push Tests 93 
 
 7.3 Subgrade Description 93 
 
 7.3.1 Standard Penetration Tests 93 
 
 7.3.2 Cone Penetration Tests 96 
 
 7.3.3 Water Content and Atterberg Limits 96 
 
TABLE OF CONTENTS (Continued) 
 
 Page 
 
 7.4 Moisture Instrumentation and Weather Data 99 
 
 7.5 Laboratory Stress-Strain and Strength Testing 102 
 
 8.0 COMPONENT PERFORMANCE 105 
 
 8.1 Rail Seat Flexural Cracks 105 
 
 8.2 Top-of-Tie Inspections and Fastener Performance 108 
 
 9.0 CORRELATIONS 115 
 
 9.1 Tie Loads vs. Tie Cracking 115 
 
 9.2 Predicted vs. Measured Track Vertical Load-Deflection 
 
 Response 120 
 
 9.3 Correlation of Track Modulus With Ballast Depth 125 
 
 9.4 Predicted vs. Measured Track Settlement 125 
 
 9.5 Track Roughness vs. Absolute Settlement 140 
 
 10.0 CONCLUSIONS 145 
 
 10.1 Wheel Loads vs. Tie Cracking 145 
 
 10.2 Bal last/Subgrade Support and Track Settlement/ 
 
 Roughness 145 
 
 10.3 Wood vs. Concrete Tie Track 146 
 
 REFERENCES 147 
 
 LIST OF TABLES 
 
 Table 1. Summary of Measurements and Data Reductions 32 
 
 Table 2. Dynamic Wheel/Rail Load Statistics Summary 48 
 
 Table 3. Vertical Track Stiffness and Modulus 68 
 
 Table 4. Effect of Disturbance of Ballast Support on Track 
 
 Stiffness and Modulus 70 
 
 Table 5. Summary of Ballast Index Test Results From Field Sites ... 86 
 
 Table 6. Summary of Cracked Ties 107 
 
 Table 7. Summary of the Tie Surface and Fastener Inspection at 
 
 Streator, 11/2/79 109 
 
 Table 8. Summary of Tie Surface and Fastener Inspection at 
 
 Streator, 4/22/81 110 
 
 Table 9. Summary of Tie Surface and Fastener Inspections at 
 
 Richmond, 12/18/79 112 
 
 Table 10. Summary of Tie Surface and Fastener Inspections at 
 
 Aberdeen 113 
 
 Table 11. Results and Computations for Concrete Tie Cracks 119 
 
LIST OF ILLUSTRATIONS 
 
 Pa^e 
 
 Figure 1. Reconstruction of Fast Section 22 at 425 MGT 17 
 
 Figure 2. Layout of Streator Test Sites 18 
 
 Figure 3. Cross-Sections of Track at Streator Site 19 
 
 Figure 4. AT&SF Concrete Tie Test Site, Streator (Leeds), 111., With 
 
 Westbound Geometry Car 20 
 
 Figure 5. Plan View of Chessie/Richmond Test Area 22 
 
 Figure 6. Chessie Concrete Tie Test Track, Richmond (Lorraine), VA., 
 
 (3 Degree Curve) 23 
 
 Figure 7. Cross-Section of Curve at Richmond Test Site 
 
 (Section A-A')(Ref. 3) 24 
 
 Figure 8. Location of Northeast Corridor Test Site at 
 
 Aberdeen, MD 26 
 
 Figure 9. View of Aberdeen Test Site Looking Northeast 28 
 
 Figure 10. Layout of Concrete Tie Test Section at Roanoke, VA 29 
 
 Figure 11. N&W Concrete Tie Test Site, Near Roanoke* Va, Looking 
 
 West 30 
 
 Figure 12. Rail and Tie Instrumentation for Dynamic Measurements ... 37 
 
 Figure 13. Typical Layout of Dynamic Measurements in a Test Section . . 33 
 
 Figure 14. Static and Dynamic Wheel Loads at FAST, Section 22 39 
 
 Figure 15. Static and Dynamic Wheel Loads at Streator (Santa Fe). . . . 40 
 
 Figure 16. Static and Dynamic Wheel Loads at Richmond (Chessie) .... 41 
 
 Figure 17. Combined Passenger and Freight Static and Dynamic Wheel 
 
 Loads at Aberdeen (Amtrak and Conrail) 42 
 
 Figure 18. Static and Dynamic Wheel Loads at Roanoke (N&W) 43 
 
 Figure 19. Summary Plot of Dynamic Wheel Loads at all Sites 47 
 
 Figure 20. Distribution of Train Speeds at Each Site 49 
 
 Figure 21. Summary of Tie Bending at All Sites 52 
 
 Figure 22. Statistical Rail Seat Bending Response at Streator- 
 
 Concrete 54 
 
 Figure 23. Statistical Rail Seat Bending Response at Roanoke 55 
 
 Figure 24. Summary of Tie Center Bending Response at All Sites .... 57 
 
 Figure 25. Tie Center Bending Response at Roanoke - Each Tie 58 
 
 Figure 26. Samples of First Three Bending Modes for CC-244-C 
 
 Concrete Tie 50 
 
 Figure 27. Transfer Function of Rail/Tie Acceleration for Three 
 
 Different Tie Pads 61 
 
LIST OF ILLUSTRATIONS (Continued) 
 
 Page 
 
 Figure 28. Summary of Track Stiffness at All Sites 63 
 
 Figure 29. Track Vertical Response to Point Load Application 
 
 at Streator-Wood 65 
 
 Figure 30. Track Vertical Response to a Point Load Application 
 
 at Streator-Concrete 66 
 
 Figure 31. Track Vertical Response to a Point Load Application 
 
 at Richmond 67 
 
 Figure 32. Concrete Tie Track Settlement at FAST 72 
 
 Figure 33. Concrete Tie Track Settlement at Streator 73 
 
 Figure 34. Concrete Tie Track Settlement at Richmond 74 
 
 Figure 35. Concrete Tie Track Settlement at Aberdeen 75 
 
 Figure 36. Summary of Mean Track Settlement 76 
 
 Figure 37. Track Geometry at Streator (Leeds) Wood and Concrete 
 
 Tie Test Sites 78 
 
 Figure 38. Ballast Profile for Streator Wood Tie Section 80 
 
 Figure 39. Ballast Profile for Streator Concrete Tie Section 81 
 
 Figure 40. Ballast Profile for Richmond Concrete Tie Section 82 
 
 Figure 41. Ballast Profile for Aberdeen Concrete Tie Section 83 
 
 Figure 42. Composite Gradation Curves for Under-Tie Ballasts 
 
 From Revenue Sites 85 
 
 Figure 43. Ballast Densities — Under Tie at Rail Seat 88 
 
 Figure 44. Ballast Densi ties--Crib Near Rail Seat 89 
 
 Figure 45. Plate Bearing Index—Under Tie at Rail Seat 91 
 
 Figure 46. Plate Bearing Index—Under Center of Tie 92 
 
 Figure 47. Lateral Tie Push Resistance 94 
 
 Figure 48. Standard Penetration Resistance Versus Depth for 
 
 Field Sites 95 
 
 Figure 49. Cone Resistance Versus Depth for Field Sites 97 
 
 Figure 50. Water Content and Atterberg Limits Versus Depth for 
 
 Field Sites 98 
 
 Figure 51. Moisture Content and Rainfall Data From Streator 100 
 
 Figure 52. Moisture Content and Rainfall Data From Aberdeen and 
 
 Richmond 101 
 
 Figure 53. Ballast Box Test Apparatus 103 
 
 Figure 54. Concrete Tie Transverse Rail Seat Cracks 105 
 
LIST OF ILLUSTRATIONS (Continued) 
 
 Page 
 
 Figure 55. Results of Final Inspections for Concrete Tie Cracks 116 
 
 Figure 56. Number of Axles Producing Rail Seat Moments Above 
 
 Cracking Strength at Aberdeen 118 
 
 Figure 57. Concept for Estimation of Tonnage at Which All Ties 
 
 Will be Cracked 121 
 
 Figure 58. Ballast and Subgrade Properties Used for Analytical 
 
 Predictions 122 
 
 Figure 59. Measured Versus Predicted Differential Rail Deflections 
 
 for 6- to 30-Kip Load Range 123 
 
 Figure 60. Measured and Predicted Track Moduli for Revenue Field 
 
 Sites, 6- to 30-Kip Load Range 126 
 
 Figure 61. Ballast Depth Versus Track Modulus for Revenue Field 
 
 Sites 127 
 
 Figure 62. Normalized First Cycle Strains as a Function of 
 
 Stress Ratios 129 
 
 Figure 63. Measurements and Predictions of Track Settlement for 
 
 Streator Wood Tie Section 131 
 
 Figure 64. Measurements and Predictions of Track Settlement for 
 
 Streator Concrete Tie Section 132 
 
 Figure 65. Measurements and Predictions of Track Settlement for 
 
 Richmond -j 34 
 
 Figure 66. Measurements and Predictions of Track Settlement for 
 
 Aberdeen 135 
 
 Figure 67. Measurements and Predictions of Track Settlement for 
 
 FAST Section 22 After Rebuild 136 
 
 Figure 68. Logrithmic Settlement of Section 22, FAST, After 
 
 Maintenance 139 
 
 Figure 69. Logrithmic Settlement at Aberdeen - Ballast Strain 
 
 Coil Data 141 
 
 Figure 70. Track Roughness (RMS) for 60-Foot MCO Values 142 
 
 Figure 71. Track Roughness for 95th Percentile Deviation 144 
 
1.0 SUMMARY 
 
 The Facility for Accelerated Service Testing (FAST) was created to make 
 comparative evaluations of track systems and components and of mechanical 
 systems and components over their service life cycles. These evaluations are 
 made under accelerated loading by measuring the rates of degradation and 
 failure of the systems and components. Some of these results may be influ- 
 enced by the specific environment in which they occur (such as the climate), 
 while others may be influenced by the accelerated testing process. The 
 accelerated test is not appropriate if, in the process of increasing the load 
 or changing the rate of loading, something is left out (such as impact load- 
 ing) or if the increase in loads creates other failure modes not seen in reve- 
 nue service. The purpose of the correlation study was to determine whether 
 the FAST results truly represent, in an accelerated manner, revenue 
 service. 
 
 The area of study chosen was concrete tie track, because there was not a great 
 deal of empirical information available about concrete tie performance for 
 North American conditions. After evaluating over sixty potential locations, 
 four distinctly different revenue service sites were selected because they met 
 a variety of requirements established for this program. In general, the test 
 sites contained prestressed monoblock concrete ties of equivalent length and 
 strength to those being tested at FAST (designed to the current AREA recom- 
 mended specifications). The fastener clips and pads were generally similar to 
 those at FAST. The ballast and subgrade types and conditions were different 
 at each site as were the climate, the traffic density and mix, and the track 
 construction. This tended to improve the correlation analysis by providing a 
 broader spectrum of service conditions to compare with the FAST results. 
 
 To understand the relationships between FAST and revenue service conditions , 
 extensive data were collected and analyzed. These data were broken down into 
 three basic groups: 
 
 a. Primary performance measures: track geometry and track component 
 degradation 
 
 b. Governing structural characteristics: vertical and lateral track 
 stiffness, transfer functions of the pads, subgrade moisture 
 content, subgrade elastic and plastic limits, ballast degradation 
 and general ballast condition 
 
 c. Loading and load response: wheel rail loads, tie strains, and 
 ballast strains. 
 
 The program was structured to compare data from the revenue service sites and 
 similar data from FAST and to determine the applicability of FAST tests to 
 revenue service conditions. 
 
 11 
 
The major conclusions from this study are: 
 
 a. There are significant differences in traffic loading at FAST and 
 the revenue service sites which affect the performance of con- 
 crete ties. Impact loads of high magnitude relative to nominal 
 wheel loads occur due to small percentages of freight and passenger 
 traffic at most revenue sites. These impact loads are caused by wheel 
 tread irregularities and produce bending cracks at the rail seats 
 
 of concrete ties. While FAST has the highest mean axle loads of 
 any site examined, crack-producing impact loads do not occur at 
 FAST because of the extremely good (atypical) FAST-consist wheel 
 maintenance program. The net result is few concrete tie cracks at 
 FAST. The importance of this finding is in discovering the poten- 
 tial damage and the shortened revenue life of concrete ties (and the 
 possibility of damage to other components such as rail, wheels, and 
 bearings) because of a few defective wheel treads that are found 
 in nearly all revenue traffic. 
 
 b. Track surfacing maintenance (raising and tamping) loosens the 
 ballast structure, reduces the uniformity of support and contri- 
 butes to large variations in relative track settlement. Average 
 track modulus does not change much after surfacing but the var- 
 iability in modulus increases considerably. The mechanical 
 resistance of ballast to deformation is principally dependent on 
 the state of ballast compaction, rather than on ballast material 
 properties. These findings, similar for FAST and revenue sites, 
 indicate that FAST is generally representative, except for a bi- 
 linear settlement rate (possibly caused by freeze/thaw) observed 
 at some of the revenue service sites. 
 
 c. Uniformity of initial track support conditions is a key to good 
 track performance. Newly constructed wood tie track at FAST 
 showed nearly identical performance to adjacent, newly construct- 
 ed concrete tie track, relative to track settlement and rough- 
 ness. In contrast, older mainline track having a typical mix of 
 wood ties of varied age and length, built on an old ballast bed 
 was not as uniform as an adjacent newly constructed concrete tie 
 section with a new, deeper ballast section. 
 
 12 
 
2.0 INTRODUCTION 
 
 This report is the first of three volumes that describe a comparative study 
 of concrete tie track in U.S. revenue service and at the Facility for Ac- 
 celerated Service Testing (FAST). Called the Concrete Tie and Fastener 
 Performance and Correlation Analysis, the work was undertaken to develop 
 an understanding of the degree to which FAST represents the "real world" 
 of revenue service. A measurement and analysis plan for the study is pre- 
 sented in [1] .* 
 
 This volume summarizes the results of the correlation study using data 
 from Volumes II and III. Volume II describes an analytical and experiment- 
 al investigation of long-term track deformation behavior and includes (a) 
 the development of the MULTA/GEOTRACK model of track deformation under 
 repeated loads, and (b) the methods used in a geotechnical evaluation of 
 the ballast and subgrade properties through laboratory tests [2]. Volume 
 III describes the field work and compiles the initial analyses of data 
 from seven track segments, which include four concrete tie segments in 
 revenue service, one wood tie control segment in revenue service, and a 
 segment of concrete ties and wood ties at FAST [3]. 
 
 The correlation is important to the economic justification for the use 
 of concrete ties in U.S. revenue service. Part of the justification is 
 based upon the assumption that they will last much longer than wood ties, 
 and that requirements for certain types of maintenance will be reduced. 
 While concrete ties have shown promise in reducing some of the chronic 
 problems of wood tie track (gauge widening, spike killing), they have also 
 encountered other problems, such as the development of bending cracks and 
 the dislocation and failure of fasteners. 
 
 One of the major activities at FAST has consisted of the collection and 
 evaluation of long-term performance data on concrete tie track. Since 
 FAST operations began in September 1976, tonnage has been accumulated at 
 an average rate of about seven times the nominal revenue service rate of 
 20 million gross tons per year. Portions of the track were constructed 
 with a large variety of concrete ties and fasteners. 
 
 However, the FAST environment differs in several important respects from 
 many revenue service environments. The climate near Pueblo is relatively 
 mild and dry in comparison with the extremely cold climates of the plains 
 states and the wet-cold climates of the midwestern and northeastern states. 
 The track subgrade is sandy and stable. Train speeds do not exceed 45 
 mph. Perhaps the most important, the track and train are maintained daily. 
 While the average axle load is high at 33 tons, wheel flats are not allowed 
 to develop to the point of producing serious impact loads. 
 
 These differences in operating environments have resulted in many dissim- 
 ilar performance results between FAST and revenue service test segments. 
 While all the concrete ties in the revenue service test segments examined 
 
 Brackets indicate references listed in back of report 
 
 13 
 
in this study have developed rail seat bending cracks, none was found at 
 FAST. On the other hand, the 5-degree curves at FAST have experienced 
 rates of tie movement and fastener clip fallout and fracture which have 
 not been approached, on a per-MGT basis, at any revenue service site. 
 
 Thus, the FAST concrete tie experiment is limited in its applicability 
 to many of the major problems that affect the economic feasibility of con- 
 crete tie track in U.S. revenue service. This program was designed to 
 define both the performance differences among the FAST and revenue service 
 operations and the causes for these differences. This information can 
 then be applied to the design of FAST experiments that accurately reproduce 
 the revenue service environment. 
 
 14 
 
3.0 SITE DESCRIPTIONS 
 
 When planning for this study began in 1979, there were over 60 concrete tie 
 installations in North American revenue service tracks [4]. These ranged in 
 size from 10 to over 300,000 ties. The designs of ties and fasteners, tie 
 spacing, preparation of ballast and subgrade, and loading conditions of these 
 installations varied widely. Since the first concrete ties were installed in 
 1960, bending strength requirements were increased in stages which culminated 
 in recommendations of the American Railway Engineering Association (AREA) 
 first published in 1973 (AREA Bulletin 644) and with minor changes in 1975 
 (AREA Bulletin 655). These developments are discussed in Reference [4]. Also 
 during this development period, tie spacings were reduced from as much as 30 
 inches to the current 24-26 inches. 
 
 Because many of the early installations had experienced structural failures of 
 ties and fasteners, it was decided to limit the correlation study to sections 
 built to 1975 strength requirements and to a relatively small range of tie 
 spacing (24-26 inches). It was also desirable to select locations with 
 moderate to heavy tonnage, cold or wet-cold climates, and accessibility to the 
 test site. These criteria limited the study to the following revenue service 
 locations: 
 
 (a) the Atchison, Topeka and Santa Fe (AT&SF) site near Streator, 
 II linois 
 
 (b) the Chessie System site near Richmond, Virginia 
 
 (c) the Amtrak Northeast Corridor (NEC) original installation near 
 Aberdeen, Maryland 
 
 (d) the Norfolk & Western (N&W) site near Roanoke, Virginia. 
 
 A segment of track just east of the concrete test site at Streator was 
 selected as a wood tie control section. Section 22 at FAST was selected for 
 study because it provided concrete and wood tie segments which duplicated the 
 Northeast Corridor track construction. Supporting data from the 5-degree 
 curve of the concrete tie Section 17 at FAST are also included. 
 
 3.1 The Facility for Accelerated Service Testing 
 (FAST) Site at Pueblo, Colorado 
 
 The FAST track is located at the Transportation Test Center, about 25 miles 
 northeast of Pueblo, Colorado. The track is divided into 22 subsections which 
 provide many combinations of track construction and tie/fastener comDonents. 
 The test train of GO -76 cars is operated 5 niahts a week at a maximum speed 
 of 45 mph. The speed generally ranqes from 40 - 50 moh, with 2-inch 
 underbalance in the curves. The exception to this is found in counter- 
 clockwise operation over the 5-degree curve and 2-percent upgrade of Section 
 17, where the consist speed can drop to 25 mph. 
 
 15 
 
In July 1979, train operations were suspended to rebuild several sections 
 of the track loop. Section 22 was allocated to provide accelerated 
 data on the Northeast Corridor construction which was then in progress. The 
 old ballast was removed and replaced with NEC traprock to a depth of 15 
 inches. The 300-tie test segments shown in Figure 1 reproduced the NEC tie/ 
 fastener construction for wood and concrete ties. These sections were sepa- 
 rated with transition zones, also shown in the figure. 
 
 Eight new segments of concrete ties and fasteners were added to two original 
 segments in the 5-degree curve of Section 17. Three segments of new AREA 3 
 ballast were combined with one segment of cleaned existing ballast and one 
 segment of NEC traprock. 
 
 3.2 AT&SF Site Near Streator, Illinois 
 
 3.2.1 Location 
 
 The track site near Streator, Illinois, is located in north-central Illinois, 
 approximately midway between Chicago and Peoria. The test section at Leeds, 
 which was once the location of a water stop and station platform is in the 
 farming area, southwest of Streator. Both wood and concrete tie test sections 
 were evaluated at this site. 
 
 3.2.2 Physical Layout 
 
 A plan view sketch of the test section in relation to surrounding topographi- 
 cal features is shown in Figure 2. Cross sections at the wood and concrete 
 tie test sites appear in Figure 3. Figure 4 is a photo of the site. 
 
 In the concrete tie test section, there are two types of ties: Gerwick RT-7S 
 and Conforce Costain CC244C, in equal numbers. Pandrol spring clip fasteners 
 are installed on all 200 of the Costain-type ties. There are three different 
 types of fasteners on the RT-7S ties, one of which is the Pandrol fastener. 
 To maintain as much uniformity as possible in the tie/ fastener types examined 
 at the various test sites, all dynamic measurements on concrete ties were 
 confined to the CC244C ties, when available. (Aberdeen and FAST tracks were 
 built with only the newer RT-7SS-2.) 
 
 The wood tie test section is located approximately 1500 ft east of the Leeds 
 Road grade crossing and approximately 500 ft east of milepost 102. Both the 
 wood and concrete sections are located on the north track of the Santa Fe's 
 Chicago to Topeka double-track mainline. While the concrete tie test site is 
 essentially at grade, the wood tie test site is located in a fill section. 
 The timetable speed over the site is 60 mph for freight trains and 80 mph for 
 passenger trains and T0FC/C0FC trains (truck-trailer piggyback). 
 
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 TRANSITION 
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 TRANSITION 
 
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 TRANSITION 
 WOOD TIES 
 
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 SECTION A-A - CONCRETE TIE TEST SITE 
 
 Test track 
 
 Access road 
 
 Farm 
 
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 SECTION B-B - WOOD TIE TEST SITE 
 
 FIGURE 3. CROSS-SECTIONS OF TRACK AT STREATOR SITE 
 
 19 
 
FIGURE 4. AT&SF CONCRETE TIE TEST SITE, STREATOR (LEEDS), ILL., 
 WITH WESTBOUND GEOMETRY CAR 
 
 20 
 
3.3 Chessie System Site Near Richmond, Virginia 
 
 The Chessie System concrete tie installation is located in central Virginia, 
 in the suburbs eleven miles west of Richmond. (Chessie calls this section 
 Lorraine.) The track is part of the C&O line between Richmond and Lynchburg. 
 The test site, located just east of the foot of Gaskins Road between mileposts 
 11 and 12, is on the north bank flood plain of the James River. The test site 
 area has reportedly been flooded several times since the railroad was built. 
 However, it has not flooded since the installation of the concrete ties in 
 1974. As shown in Figure 5, the concrete tie installation is located near the 
 middle of a reverse curve. The short tangent portion of the reverse curve is 
 intersected by the Gaskins Road crossing. Figure 6 is a photograph of the 
 test section leading west towards Gaskins Road. The James River Golf Club 
 lies just north of the right-of-way. 
 
 A conifer wooded area extends south of the right-of-way to the James River. 
 During the measurement period, water was standing throughout portions of this 
 area. A sketch of a typical cross-section of the track can be seen in Figure 
 7. 
 
 The concrete ties are installed in a 3.0-degree curve with 3.0-inch superele- 
 vation. The test zone is about 550 feet long and was divided into 3 sections; 
 counting west: 
 
 TIE NO. TIE TYPE FASTENER TYPE 
 
 001 - 106 Gerwick RT-7S CS-5 Clips, Rubber Pads, 
 
 Plastic Insulators 
 
 107 - 124 Gerwick RT-7S Pandrol 607 A Clips and Fabrika Pads, 
 
 Insulated with Epoxy-Coated Shoulders 
 
 125 - 224 Conforce-Costain Pandrol 607 A Clips and Rubber Pads, 
 CC244* Metal/Plastic Insulators 
 
 An additional 44-tie section at the west end contains RT-7S ties which were 
 originally installed at the Sabot test site. These were excluded from 
 detailed inspection per a request from Chessie. The tie spacing averaged 25 
 inches. At the time of the site visit in December 1979, the cumulative 
 tonnage over the test section was 150.9 MGT. 
 
 *The CC244 tie has 26 prestressing tendons, while the CC244C has 28 tendons, 
 The ties were designed to the same strength requirements. 
 
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FIGURE 6. CHESSIE CONCRETE TIE TEST TRACK, RICHMOND (LORRAINE), VA., 
 (3 DEGREE CURVE) 
 
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3.4 Amtrak Northeast Corridor Site Near Aberdeen, Maryland 
 
 3.4.1 Location 
 
 The Northeast Corridor site is located approximately three miles southwest of 
 Aberdeen, Maryland. The site lies. between mileposts 68.7 and 68.9, 
 where milepost zero is located in the center of Philadelphia. As shown 
 in Figure 8, the site is accessed from Michael svil le Road at Perryman and 
 is adjacent to a concrete pipe plant on the west side of the track. 
 The Aberdeen Proving Grounds border the east side of the track. Although 
 the railroad runs northeast-southwest through the test area, the traffic 
 directions are designated North (toward Aberdeen) and South (toward Baltimore), 
 
 Three mainline electrified tracks in the test area are numbered Track 2 
 (easternmost) through Track 4( westernmost). Track 2 carries predominantly 
 northbound traffic. The center Track 3 carries traffic in both directions 
 along with all daytime freight traffic, and the concrete tie Track 4 carries 
 mostly southbound traffic. North of the test site, the tracks are tangent for 
 about two miles. The first curve to the south is approximately one mile from 
 the test site. Timetable speeds through this area are 110 mph for Metroliner 
 service, 90 mph for other passenger trains, and 60 mph for freight trains. 
 
 3.4.2 Physical Layout 
 
 Figure 9 shows a photograph of the test site. The RT7SS-2 concrete ties are 
 equipped with Pandrol elastic clips, external nylon insulators and EVA pads 
 which are notched to fit around the fastener shoulders. These components are 
 the standard equipment of the original Northeast Corridor concrete tie 
 installation, which began in 1978 with a 10-mile section through Aberdeen. 
 
 The test site is essentially at grade, and the area surrounding the site is 
 
 rather flat. The track itself is on a small embankment of about 4 ft, which 
 
 is an old trackbed that has been raised and reballasted many times over the 
 years. 
 
 3.5 The Norfolk and Western Site Near Roanoke, Virginia 
 
 ""he Roanoke, Virginia test site, designated Kumis by the N&W Railway Company 
 is located to the west of an overpass on US Rt. 460 about 15 miles west of 
 Roanoke. The N&W has two mainlines in this vicinity allowing it to direct 
 eastbound, loaded coal trains down a long grade which is 0.38 percent at the 
 concrete tie test site. The eastbound traffic crosses from Montgomery to 
 Roanoke Counties about midway through the test site in this rural area. 
 Timetable speed is 45 mph through this area and because of the downgrade, 
 service braking is required. 
 
 25 
 
FIGURE 8. LOCATION OF NORTHEAST CORRIDOR TEST SITE AT ABERDEEN, MD 
 
 26 
 
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 FIGURE 9. VIEW OF ABERDEEN TEST SITE LOOKI 
 
 
 27 
 
As shown in Figures 10 and 11, the N&W test track is a 1666-foot section on 
 tangent track paralleled by a two-mile-long passing siding. This site is 
 bisected by a grade crossing and a culvert immediately to the east of the 
 crossing. To the west of the grade crossing, ties are spaced at 26-inch 
 intervals while to the east, ties are at 24-inch intervals. Each half of the 
 site contains 200 RT-7S and 200 CC244C ties. 
 
 The random selection of instrumented ties began at the eastern end of the zone 
 containing CC244C ties on 24-inch spacing and progressed westward. This 
 allowed selection of the seven instrumented ties under the same conditions 
 of tie length and spacing as the other test sites, while it avoided a rough spot 
 further west in that same zone near the culvert. 
 
 The concrete tie test section has not received any maintenance, such as sur- 
 facing or undercutting since it was built, except for some spot maintenance 
 around the culvert. Several long-wavelength undulations of the track surface 
 can be seen downstream of the grade crossing. These have been caused by car 
 motions induced at the crossing. 
 
 Prior to the beginning of this program, a hopper car with a broken wheel came 
 through this test site. Visual evidence remains from scalloping of the south 
 rail gage corner about every five ties. As discussed in Section 8.1, inspec- 
 tion for rail seat cracks showed no direct indication that this broken wheel 
 produced any unique failures in the concrete ties. Systematic inspection of 
 rail seats directly beneath the broken wheel impact location and comparison of 
 those results against locations not adjacent to the wheel impact were found 
 inconclusive because all inspected rail seats were cracked. 
 
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FIGURE 11. N&W CONCRETE TIE TEST SITE, NEAR ROANOKE, 
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 30 
 
4.0 CORRELATION MEASUREMENT PLAN 
 
 The general approach of the correlation analysis was to evaluate the 
 dependence of track degradation on loads, track structural characteristics, 
 climatic conditions, and maintenance practices at FAST and in revenue service. 
 An ultimate objective was to develop the ability to predict analytically long- 
 term performance from a given set of operating conditions. However, the 
 current state of the art in analytical prediction is limited, even for the 
 simulation of very short-term phenomena such as track response to given loads. 
 Therefore, the correlation test plan was designed to gather the information 
 which would permit the evaluation of long-term performance on two levels: 
 
 a. by direct comparison of the conditions that cause track degra- 
 dation (loads, ballast and subgrade support characteristics) with 
 measurements of track degradation (track geometry, settlement, 
 component wear) 
 
 b. by analytical simulation of long-term settlement. This objective 
 required the collection of ballast and subgrade samples on which 
 laboratory tests were performed to determine behavior under 
 repeated loads. 
 
 This report summarizes the results of the efforts under (a) and (b), for which 
 a detailed measurement and analysis plan was developed [1]. Volume II covers 
 in detail the work required to achieve (b). Volume III describes the field 
 measurements, data acquisition, and analyses needed to support the performance 
 evaluations. 
 
 4.1 Summary of Measurements 
 
 The data required for a correlation study at either of the previously 
 described levels can be grouped into the following categories: 
 
 a. construction and maintenance history 
 
 b. traffic data 
 
 c. track loading and response under load 
 
 d. mechanical and material properties of ballast and subgrade 
 
 e. performance indicators. 
 
 In Table 1 the types of data collected from the railroads and the measurements 
 conducted during the visits to each revenue service track site are summarized. 
 The data have been applied to the site descriptions which appear in Section 3. 
 Each measurement is defined in more detail in following subsections, as well 
 as in greater detail in Volume III. 
 
 31 
 
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4.2 Measurement Locations 
 
 Most of the measurements of Table 1 required the selection of discrete loca- 
 tions at the test site where instrumentation was applied, material samples 
 were collected, or observations were made. Tie surface and fastener inspec- 
 tions were performed on all ties in the designated test section. Crib inspec- 
 tions were performed at intervals through the site in sufficient number to 
 form a large statistical sample. However, cost constraints required the se- 
 lection of the fewest number of instrumentation and material sampling sites 
 that could satisfy the test objectives. 
 
 These numbers of measurement locations were summarized in Table 1. As an 
 example, wheel/rail loads were measured at only one crib per test section. 
 Care was taken to see that this location avoided unusual track conditions such 
 as battered welds or joints between welded rail strings. Previous experience 
 with this measurement had shown that when bad track conditions were avoided, 
 the effect of spatial variation on loads is small, on the order of ± 10 
 percent. Since the test objective was only to characterize the traffic loads 
 at the site, the single measurement site was deemed adequate. Additional 
 discussion of the choices of measurement location appear in the procedure 
 descriptions of Volume III, Sections 5-7. 
 
 All of the measurements listed in Table 1 were performed at three sites: 
 Streator, Richmond, and Aberdeen. The dynamic measurements of wheel/ rail load 
 and tie bending moment were made periodically in Sections 17 and 22 at FAST. 
 Due to cost constraints and conflicting test plans at the N&W, the 
 measurements at Roanoke did not include the ballast and subgrade studies. 
 
 35 
 
5.0 DYNAMIC MEASUREMENTS 
 
 Several measurements were made to characterize the dynamic behavior of the 
 track structure under service loading. Strain gauge circuits were applied to 
 the rail to measure vertical and lateral wheel/rail loads. Strain gauge cou- 
 pons were applied under the rail seats and the tie center of selected ties in 
 each section. These were calibrated in place to measure tie bending moments. 
 Because of the variability of support conditions which are known to occur 
 within the track structure, a total of seven, randomly selected ties were in- 
 strumented. To maintain a sufficient statistical base by which valid compar- 
 isons could be made between sites and within separate populations of events at 
 each site, a minimum of 20,000 axles were recorded for each test condition. 
 
 Accelerometers were attached to the rail base and to the adjacent tie surface 
 to simultaneously measure rail and tie accelerations. These were used to de- 
 fine the attenuation of vibratory loading offered by the tie pad. Transducer 
 installations are illustrated in Figure 12. Figure 13 defines a typical lay- 
 out of dynamic measurement locations in a test section. 
 
 Details of installation and calibration of the transducers, data acquisition, 
 and data reduction are all included in Volume III. 
 
 5.1 Traffic Loads 
 
 As discussed in Section 3.0, the traffic loads at each revenue test site were 
 expected to be sufficiently different in character to afford a comparison of 
 load conditions. These different loading conditions would produce differing 
 responses in the track structure, both in terms of tie performance as well as 
 track settlement. 
 
 Once characterized, selected values of traffic loads at each site could be 
 used for correlation of track settlement through laboratory tests and analy- 
 tical model runs. 
 
 Traffic density and cumulative tonnage data were acquired from each railroad. 
 Listings of the individual train consists were acquired through their compu- 
 terized data systems. 
 
 By acquiring consist lists throughout the period of the revenue data collec- 
 tion and tabulating the gross loads of the cars listed on these consists, it 
 was possible to develop static load distributions. By comparing these against 
 the dynamic wheel load distributions, it was possible to make direct compari- 
 sons between static and dynamic loads without direct knowledge of the static 
 weights of the individual axles. Figures 14 through 18 are the resulting 
 pairs of static and dynamic wheel load distributions for each of the 5 test 
 sites including FAST. The variation between the static and dynamic load 
 curves at any one point can be caused by four factors: (1) static weight dis- 
 tribution to each wheel on any car will rarely be exactly 1/8 of the gross 
 load listed on the train consist sheet. Uneven car loading as well as 
 imperfect load distribution within the trucks' suspensions will cause a 
 
 36 
 
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 FIGURE 12. RAIL AND TIE INSTRUMENTATION FOR 
 DYNAMIC MEASUREMENTS 
 
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 FIGURE 14. STATIC AND DYNAMIC WHEEL LOADS AT FAST, SECTION 22 
 
 39 
 
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 STATIC AND DYNAMIC WHEEL LOADS AT STREATOR (SANTA FE) 
 
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 FIGURE 16. STATIC AND DYNAMIC WHEEL LOADS AT RICHMOND (CHESSIE) 
 
 41 
 
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 FIGURE 17. COMBINED PASSENGER AND FREIGHT STATIC AND DYNAMIC WHEEL 
 LOADS AT ABERDEEN (AMTRAK AND CONRAIL) 
 
 42 
 
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 43 
 
variability in the loads seen at each wheel, (2) dynamic wheel impacts caused 
 by irregularities in either the wheels or rail surfaces, (3) variation of 
 wheel force due to vehicle/track interaction, such as curving imbalance and 
 pitch and bounce, (4) differences in calibration between the scales used to 
 measure the gross carloads and the circuits used to measure the dynamic wheel 
 loads. 
 
 As can be seen from examining Figures 14 through 18, there is a relatively 
 close matching of the loads determined statically and dynamically over 90 to 
 95 percent of the axles. On the static curves, the near vertical line seg- 
 ments represent subpopulations of vehicles which are listed in the consists as 
 having identical gross loads. The corresponding segments of the dynamic 
 curves typically have finite slopes indicating the normal scatter in actual 
 wheel loads about the average of these subpopulations. In the lower portion 
 of each plot, static and dynamic loads begin to diverge significantly, parti- 
 cularly in Figures 17 and 18, because of the superposition on the dynamic load 
 curve of an additional subpopulation of loads from wheels having irregulari- 
 ties including spalled and eccentric profiles, and slid flats. Although a 
 direct interpretation of the two curves in this low-probability, high-load 
 region would tend to imply that these higher loads caused by wheel irregulari- 
 ties are being superimposed only on the heaviest nominal wheels, a detailed 
 examination of the wheel load data shows that nominally lighter wheels con- 
 tribute equally to these incremental dynamic loads. 
 
 5.1.1 FAST Loads 
 
 As the lower portion of Figure 14 indicates, the FAST consist exhibits almost 
 no wheel tread irregularities, evident by only small differences between the 
 heaviest static wheel loads and the corresponding dynamic wheel loads. The 
 FAST train primarily consists of 100-ton cars loaded to capacity, with a few 
 selected cars switched in and out for specific tests. The break in the curve 
 at the 90th percentile level indicates that approximately 10 percent of the 
 vehicles carry less than the rated maximum loads including a few empty cars. 
 This is very close to the maximum unit train condition expected where all cars 
 are 100-ton capacity and fully loaded. 
 
 5.1.2 Streator Loads 
 
 The vehicles on the Sante Fe as seen at Streator consists primarily of trailer- 
 on-flat cars and container-on-flat cars (T0FC/C0FC). The large segment 
 of this population, indicated on the static curve in Figure 15 between 
 15 and 45 percent, represents the nominal, loaded capacity of the T0FC/COFC 
 cars. The actual mix of these cars along with the variation in empty condi- 
 tions (with and without two trailers, etc.) produces the uniform range of 
 wheel loads from about 7 to 27 kip per wheel. The remainer of the fleet is a 
 mix of general freight, both loaded and empty, which will range in load 
 between 5 and 35 kip per wheel. A very small percentage of flat wheels indi- 
 cated at the bottom of the curve in Figure 15 shows an overall hi ah quality of 
 wheel maintenance exceeded only by that at FAST. 
 
 44 
 
5.1.3 Richmond Loads 
 
 At the Richmond site, Chessie primarily runs unit coal trains: loaded in 
 one direction and empty in the opposite direction. This is characterized 
 in Figure 16 as two curve segments separated at the 50th percentile. The 
 empties are represented by the upper curve segment between 6 and 8 kip 
 and the loaded unit trains dominate the lower 50 percent. The rounded 
 off region between the 50th and about the 15th percentile includes smaller 
 capacity hopper cars and an occasional mixed freight. The divergence at 
 the bottom of the curve between the 0.1 and 0.5 percentile characterizes 
 the portion of the fleet with wheel irregularaties. 
 
 5.1.4 Aberdeen Loads 
 
 Figure 17 is a composite of the static and dynamic loads acquired at the 
 Aberdeen test site. Freight consist data were not acquired from Conrail 
 directly, however Amtrak provided detailed tonnage data used to document 
 the traffic over Track 4 at Aberdeen. Both passenger and freight loads 
 could therefore be characterized by reconstructing the statistics in a 
 form similar to the data acquired at the other sites. The dynamic data 
 were also apportioned in a manner to reflect the correct cumulative balance 
 between passenger and freight traffic over Track 4. This resulted in a 
 relatively close match between static and dynamic loads down to about the 
 2 percent level. The subpopulation of large wheel loads below the 2 per- 
 cent probability level are caused almost entirely by the passenger car 
 fleet. This is especially significant because the nominal wheel loads 
 of the passenger cars are relatively low at about 23 kips and the speeds 
 are relatively high; between 80 and 110 mph. These large dynamic wheel 
 loads compromised tie performance as discussed in detail in Section 8. 
 Another research program was initiated to determine, in detail, the causes 
 and solutions to the effects of wheel flats on concrete ties [5L 
 
 5.1.5 Roanoke Loads 
 
 Figure 18 shows the static and dynamic loads for N&W traffic at Roanoke. 
 These curves are unique in that the static loads are consistently shown 
 to be greater than the corresponding dynamic loads down to about the 3 
 percent level of exceedance. For this to occur, the last two of the four 
 previously discussed factors affecting static and dynamic wheel load measure- 
 ments may be causing some discrepancy. Either there was a small but ef- 
 fective dip in the running surface of the rail at the location that wheel 
 loads were measured dynamically or there was a fundamental discrepancy 
 between the scale used to weigh the gross loads of the vehicles and the 
 calibration of the rail circuit at the test site. The vehicle population 
 on the N&W consisted entirely of loaded hopper cars in the 70- and 85- 
 and 100-ton capacity range. The static curve clearly shows that 55 percent 
 of all the vehicles are the 100-ton class and, correspondingly, about 15 
 percent are 85-ton class and about 18 percent are 70-ton class. Comparing 
 this to the dynamic response curve would indicate that for the heavy loads 
 there exists about a 5 kip underestimation of the nominal static loads. 
 This is of little consequence, however, when compared to the strong influence 
 of wheel irregularities that affect the lower 3 percent of the exceedence 
 curve. If the error is in the dynamic wheel load circuit calibration, 
 there may be a corresponding underestimation of the dynamic loads at the 
 extreme values. 
 
 45 
 
5.1.6 Load Summaries 
 
 Figure 19 is a summary plot of the same five dynamic wheel load exceedence 
 curves allowing direct comparison of the five sites. In addition, Table 2 
 summarizes the statistical values at the median load level and at the 10, 
 1, and 0.1 percent levels of wheel load. By coincidence the large variation 
 in both the nominal wheel loads and the extreme value loads can be seen to 
 "cross over" at about the 2 percent level. It will be shown later that the 
 relatively large, median loads at FAST will have little effect on the tie 
 cracking performance, whereas the large, low probability loads seen at 
 Aberdeen and Roanoke will dominate the tie performance. 
 
 Because wheel circumferences are on the order of 9 to 10 ft and wheel loads 
 were measured only over a 10-12 in. zone, the actual population of wheel 
 irregularities can be assumed to be about 10 times greater. Generally, maxi- 
 mum dynamic wheel loads can range from as low as 1.5 times the static weight 
 on smooth tangent track (as seen in the statistics from FAST) to extreme 
 values between 3 and 5 times the static weight as seen on passenger equipment 
 at Aberdeen. (Although well beyond the linear range of the data system some 
 events have been estimated at greater than 125 kips.) 
 
 5.1.7 Speed Effects 
 
 All data were analyzed to determine the effect of speed on the loads measured 
 at the wheel/rail interface. The relatively narrow range of speeds encoun- 
 tered at most test sites (Figure 20) did not provide for a thorough examina- 
 tion of the speed effects. However, the results do indicate a small speed 
 effect for freiqht traffic between 20 and 50 mph, although this effect can be 
 ignored because of its minimal influence on the performance of the track 
 structure. The data acquired at Aberdeen, however, revealed a dramatic speed 
 effect for passenger traffic over that site. Originally, data were sorted for 
 the passenger equipment into two speed bands, above and below 70 mph. When a 
 significant speed effect was evident, a more detailed examination of the 
 speeds above 70 mph showed what appeared to be a peak response in the 80 to 90 
 mph band due to the wheel irregularities. Track model evaluations of wheel 
 impacts have supported the possibility of a resonance effect between the 
 unsprung mass of the vehicle and that portion of the mass in the upper track 
 structure which responds to the impact [6]. However, two groups of passenger 
 equipment are involved: the new Amfleet coaches and the older, "heritage" 
 equipment. It has been shown that these two clases of equipment exhibit 
 different types of wheel irregularities which, when combined with different 
 operating speed ranges, do not allow for a direct verification of the speed 
 effect. In particular, the "heritage" equipment generally runs between 80 and 
 100 mph, while the Amfleet equipment which exhibits lower extreme loads will 
 run up to 110 mph. 
 
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 FIGURE 20. 
 
 40 
 
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 SPEED, mph 
 
 DISTRIBUTION OF TRAIN SPEEDS AT EACH SITE 
 
 49 
 
 120 
 
Another observation made during other related tests at Aberdeen [5] indicates 
 that the effective dynamic stiffness of the track can be controlled by the tie 
 pad stiffness. When flexible pads were installed, there was a detectable 
 reduction in the magnitude of the wheel impacts measured at the wheel /rail 
 interface. This is consistent with basic mechanics principles which say that 
 more flexible support conditions will lower the impact loads. It can be 
 assumed that all data summarized in Figure 19 and Table 2 were collected on 
 comparable track structures having essentially rigid rail seat pads and track 
 moduli greater than 4000 lb/in/in. 
 
 5.1.8 Effects of Vehicle Weight 
 
 All statistically analyzed dynamic data were sorted by nominal weight classes: 
 empties, moderate loads, heavy loads, and locomotives. Classifying vehicles 
 by weight from the dynamic wheel loads is difficult because of the large 
 impact loads caused by wheel irregularities. Several techniques have been 
 used in other programs to minimize the effect of having lighter cars pushed 
 into heavier categories because of wheel impacts. These data were processed 
 by averaging the values acquired for each wheel on an axle, then testing for 
 the difference in left and right wheels. When the difference exceeded 7 kips, 
 the axle was assigned to the next lower weight class. While intuition might 
 indicate that impacts would occur at nearly the same instant, particularly 
 from slid flats, data from Aberdeen showed that whenever a large impact 
 occurred on one wheel, there was rarely a comparable impact on the opposite 
 wheel . 
 
 The results of this sorting process is not perfect, so that it is difficult to 
 have high confidence in comparisons of the influence of nominal car weight on 
 the wheel impact phenomenon. However, wheel impacts clearly dominate the 
 loading spectrum to the point of significantly reducing the importance of the 
 nominal weight classes. Only under conditions of wel 1 -maintained wheels would 
 nominal weight classes become significant. (No attempt was made to address 
 the effects of weight on rail wear and other related issues that clearly show 
 such trends.) 
 
 Although it has not been identified quantitatively, there is an apparent 
 effect of nominal wheel load on the response of a concrete tie. On well- 
 consolidated track there may be a small void under the rail seat which will 
 normally be squeezed out under the larger wheel loads. If a light wheel with 
 an irregularity impacts the rail over this tie, then the tie will respond by 
 "ringing" (prolonged vibrations) at one or more natural frequencies. Thus, the 
 clearances under the rail seat cause the tie to appear lightly damped. Alter- 
 natively, if a heavy wheel rolls over the tie and generates an impact, then 
 the small gaps under the tie will be eliminated, causing a constrained 
 response with a significant reduction in the duration of the tie vibration. 
 
 50 
 
5.2 Rail Seat Bending 
 
 Tie responses to wheel/rail loads were measured with full-bridqe strain gauge 
 coupons developed for this program. Techniques described in detail in 
 Volume III allowed for installation of these coupons on ties within the test 
 sections without appreciably disturbing the consolidation* naturally occurring 
 around the test ties. At each test site, seven ties were randomly selected 
 within a 200 ft test zone, well away from the ends of the concrete tie section 
 to avoid any effects of the transition zones. Each of the selected ties was 
 then instrumented on one rail seat and at the tie center. The tie instrumen- 
 tation was calibrated in place using a fixture which was proven in the lab to 
 closely approximate the responses recommended by the AREA specification. 
 
 Analysis of data collected on both consolidated and freshly surfaced track 
 shows that rail seat bending responses tended to be greatest when track was 
 freshly surfaced, while tie center responses tended to increase with accumu- 
 lated traffic. These trends however, did not appear to be strong for the 
 combinations of conditions observed at these test sites. 
 
 Although it was originally assumed that a 300 Hz data bandwidth was sufficient 
 to characterize bending moments, a detailed examination of the dynamic re- 
 sponse of the ties at Aberdeen (at the maximum recorded bandwidth of 2000 Hz) 
 showed that data must be analyzed to bandwidths near 1200 Hz to achieve 95 
 percent of "true" strain amplitudes experienced in ties excited by wheel im- 
 pacts. The resulting rail seat bending moment distributions from each of the 
 sites are shown in Figure 21. They are generally similar in nature to the 
 load distributions shown previously in Figure 19. Of the five sites measured, 
 only Aberdeen and Roanoke exhibited very large bending moments**. These large 
 moments at the lower probability levels easily exceeded the cracking strength 
 of the ties. The nominal cracking strength of most ties is between 350 and 
 375 kip-in. in the rail seat region, which is well above the current 300 kip 
 in. AREA specification for ties installed on 30 in. centers (the highest tie 
 strength specified). 
 
 The summary curves shown in Figure 21 are the responses that would be experi- 
 enced by an average tie in each test section. These were determined by com- 
 puting the mean response of the seven instrumented ties at each level of 
 exceedance. Variations in support conditions under each tie can be assumed to 
 
 * The term "consolidation" is used here in the normal railroad context of 
 compaction by normal traffic because the more proper, technical term 
 "compaction" is often interpreted as a process performed by a special 
 machine (which can actually reduce the degree of compaction). 
 
 **Note however, that the Roanoke tie bending data are qreater than that at 
 Aberdeen at the higher levels while the converse is true for the wheel load 
 data. This may be a result of a non-linear response of the cracked ties at 
 Roanoke where all (including the instrumented ties) had advanced cracks. 
 This could not be verified by the in-site calibration which could not apply 
 bending moments above the pre-stress limit. 
 
 51 
 
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 RAIL SERT BENDING, klp-ln 
 
 FIGURE 21. SUMMARY OF TIE BENDING AT ALL SITES 
 
 52 
 
be the primary cause for deviations from the mean bending moment response. As 
 an example of the range of variability seen at different test sections, Figure 
 22 shows that at Streator, the plus-one-standard-deviation curve fits within 
 about 10 percent of the mean curve at the 0.1 percent level of exceedance, 
 thus indicating uniform loading and/or support conditions for the recently 
 surfaced track. On the other hand, Roanoke data in Figure 23 show a plus- 
 one-standard-deviation curve about 25 percent higher than the mean curve at 
 the 0.1 percent level of exceedance and proportionally larger values than that 
 in the upper part of the curve for track which is thoroughly consolidated. 
 This observation is contrasted by the results of the static stiffness tests, 
 discussed in Section G, where freshly tamped track shows considerably more 
 variation in static stiffness than consolidated track. Unfortunately, no 
 subsurface investigations were performed at Roanoke to provide a possible 
 explanation for this variability, but it is assumed that the main effect is 
 the support condition at the tie/ballast interface. 
 
 Another possible cause for the large variations in tie responses encountered 
 at Aberdeen and at Roanoke may be experimental error. As discussed in Section 
 8.1, a high percentage of the ties at Aberdeen were found to have small -to- 
 medium rail seat flexural cracks at the time that data were collected. At 
 Roanoke, it was determined that 100 percent of ties were cracked prior to in- 
 stumenting these same ties. Previous lab tests have shown that when a strain 
 gage coupon is installed adjacent to or over a flexural crack on a prestressed 
 concrete tie, the response will be similar to that of an uncracked tie up to 
 the point that the prestress limit has been exceeded. Above that, a new 
 coupon sensitivity may occur. 
 
 Generally, if the coupon's active area bridges the crack, the apparent sensi- 
 tivity of the coupon will increase slightly. On the other hand, if the crack 
 lies outside the sensitive region of the coupon, there will be a reduction in 
 sensitivity caused by the stresses being concentrated near the top of the 
 cracked region. Because the calibration fixture was not capable of loading 
 the ties to levels above the prestress limit, it was not possible to verify 
 the high level strain sensitivities. It can be assumed that at very high 
 levels of strain the coupon slightly overestimates the magnitude of the bend- 
 ing moment. In general , however, levels of bending moment up to the cracking 
 threshold are of primary interest. 
 
 The cracking threshold bending moments were shown in Figure 21 to be exceeded 
 frequently at Aberdeen and Roanoke. At Aberdeen this occurrence happens about 
 once every 1 to 2 days at an average tie location, while at Roanoke it occurs 
 as often as 5 time per day. If the plots for Streator and Richmond were 
 extended to the lower probability, higher bending moments (which would require 
 more data to accurately characterize), they would also show levels exceeding 
 the cracking limit as is evidenced by the observed cracked ties. Wheel inspec- 
 tion techniques in maintenance programs on each railroad will determine at which 
 point on this otherwise ever expanding scale that the curve truncates. At 
 FAST where every wheel is frequently inspected and well maintained, the curve 
 can be seen to truncate at or below the 0.1 percent level. Although similar 
 heavy haul traffic exists on Chessie and N&W, the data indicate a relative 
 difference in wheel conditions on these two railroads. Some of this differ- 
 ence may be attributed to the curved track at the Chessie site which may 
 
 53 
 
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 AVERAGE PLUS ONE STD 
 
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 50 100 150 200 250 300 350 400 450 500 550 600 
 
 RRIL SERT BENDING, klp-ln 
 
 FIGURE 22. STATISTICAL RAIL SEAT BENDING RESPONSE AT STREATOR-CONCRETE 
 
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 55 
 
tend to reduce the severity of the wheel impacts by causing a shift in lateral 
 position of the wheels away from the regions of maximum irregularity. 
 
 5.3 Tie Center Bending 
 
 Figure 24 shows a summary of the tie center bending moments measured at the 
 five test sites. At three of the five sites, the center bending moments are 
 quite small, being limited to a range of + 50 kip-in. These ties were de- 
 signed to a specification of 200 kip-in., of negative center bending moment, 
 and typically test to levels above 250 kip-in. before crack initiation. As 
 before, the two sites where significant levels are achieved were Aberdeen and 
 Roanoke. The Aberdeen data show that tie center impacts occur at about the 
 same level of exceedance as the rail seat bending impacts (about 3 percent) 
 and cause bending moments that approach the cracking limit of the tie center. 
 Roanoke data demonstrate that center-bound conditions exist along with the 
 impact problem. This results in relatively large loads being exerted by 
 all the 100-ton equipment, along with the contribution from the bad 
 wheel population. 
 
 Because of the low center bending load levels encountered at FAST, Streator, 
 and Richmond, there was little variability in the tie center data acquired. 
 As shown in Figure 25, however, at Roanoke, where the center bound condition was 
 developing, there were large variations observed. There were in fact, two 
 groups of three ties, one group which showed no appreciable center binding 
 while the other showed a significant degree of center binding, producing 
 center bending moments between 100 and 150 kip in. under the loaded, 100-ton 
 cars. Several tie centers were cracked at Roanoke; unfortunately extensive 
 ballast cover prevented a valid estimate of total center cracking. An exami- 
 nation of the data from all sites would indicate that for the center-bound 
 condition to develop, may require a combination of large tonnage accumu- 
 lations without surfacing (perhaps in excess of 100 MGT), combined with a 
 thoroughly fouled ballast that restricts the flow of ballast under the 
 tie center necessary to relieve the stress concentration. 
 
 5.4 Ancillary Dynamic Measurements 
 
 A variety of dynamic measurements were performed to support characterization 
 of the test sites as well as to explore some phenomena not previously understood. 
 Of particular interest is an analysis of the dynamic response of the ties due 
 to the impacts from the flat wheels. In addition, tie pad isolation of impact 
 loads and fastener performance characteristics were considered. However, 
 these data have been examined more thoroughly in other programs. [5, 7] 
 
 5.4.1 Tie Bending Modes 
 
 Initial examination of dynamic data acquired showed a prolonged vibratory 
 response of the ties under the randomly occurrinq impacts. This phenomenon had 
 been seen earlier [8], and it was shown to be primarily associated with the 
 first bending mode of the tie. To more accurately characterize this response, 
 a modal analysis was performed on a concrete tie in the laboratory. The 
 results of these analyses were compared with acceleration responses measured 
 
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 EACH TIE 
 
under field conditions. The tests showed that there are three primary bending 
 modes which are consistently excited by an impact. As shown in Figure 26A, 
 the first bending mode has its nodes at the rail seat regions and the maximum 
 strains occur at the tie center. Because this is the lowest natural fre- 
 quency, it is the easiest to excite and can be seen even under relatively 
 smooth wheels, such as those at FAST. Under laboratory conditions this first 
 mode frequency is around 108 Hz, while in the field the variability of nominal 
 wheel loading and support conditions will cause this frequency to vary between 
 about 110 and 130 Hz on the CC244C tie. 
 
 The second bending mode shown in Figure 26B, is the asymmetric mode which 
 occurs at about 330 Hz and causes maximum strains to occur in the rail seat 
 region. As discussed in Section 5.1.2, examination of simultaneous samples of 
 data taken on each rail circuit shows that the probability of occurrence of 
 the high magnitude impact loads is rarely coincident on both rails. This 
 implies that an asymmetric impact (only one wheel causing an impact) has a 
 very high probability of occurrence and this will excite the asymmetric second 
 mode. It also indicates that an impact on one rail seat may cause a crack to 
 occur on the opposite rail seat. This has been shown to occur in laboratory 
 tests. [9] It also implies that reverse bending cracks can occur. While 
 reverse cracks have been observed in the field, no direct proof of the cause 
 has been demonstrated. 
 
 The third bending mode seen in Figure 26C is similar to the static deflection 
 curve normally assumed for a tie supported on a uniform foundation with 
 vertical loads at the two rail seats. This mode occurs at about 630 Hz and 
 would be excited by either symmetric or asymmetric impacts. From spectral and 
 time domain analyses of acceleration data from ties in the field it was 
 determined that most large impacts induce combined, second and third mode 
 responses. 
 
 Examination of rail seat bending moment time histories show that a typical 
 impact will cause a strain pulse duration of about 1.5 milliseconds at 
 Aberdeen, while large impacts at Roanoke occurred over durations up to 3 to 4 
 milliseconds. The 1.5 millisecond duration is characteristic for a 330 Hz, 
 half-sine pulse, while the longer durations seen at Roanoke typically exhibit 
 a more complex wave form which indicates more response at the first mode. 
 This may be in part caused by tie center binding at Roanoke. 
 
 5.4.2 Rail and Tie Accelerations 
 
 The primary purpose in measuring accelerations was to characterize the influ- 
 ence of the fastener and pad assembly on tie response. Transfer function 
 analysis of accelerometer pairs (one mounted on the rail base and one next to 
 the fastener shoulder on the tie) shows an almost rigid coupling of the rail 
 to the tie out to 400 Hz., thus transmitting almost all impact energy into the 
 tie. Results shown in Figure 27 indicate that flexible pads can significant- 
 ly reduce the energy transmitted to the tie, particularly in the second and 
 third mode regions which were shown to cause larger strains in the railseat 
 region. The softer pads do tend to transmit more at the first mode frequency. 
 However, this does not contribute significantly to rail seat cracking. 
 
(A) FIRST BENDING MODE RESPONSE 
 
 (B) SECOND BENDING MODE RESPONSE 
 
 
 
 
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 FIGURE 26. SAMPLES OF FIRST THREE BENDING MODES FOR CC-244-C CONCRETE TIE 
 
 60 
 
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6.0 TRACK SYSTEM CHARACTERISTICS AND PERFORMANCE 
 
 The overall track structure's mechanical performance is dependent on the 
 properties and performance of the individual elements within the track 
 structure as well as the interaction of these elements under the combined 
 effects of traffic loading and weather. Because of this complex relationship 
 and its affect on track stiffness and strength, vertical track stiffness and 
 permanent settlement were both measured to characterize each site and provide 
 inputs for verification of analytical models. 
 
 6. 1 Track Stiffness/Modulus 
 
 Vertical track modulus has long been considered an important means of charac- 
 terizing track condition. Because of the interaction between stiffness and 
 strength in ballast and subgrade materials, it has been generally considered 
 desirable to have a track with high stiffness because that same track will 
 probably have higher strength. Track modulus is usually calculated from 
 force-deflection measurements applied to the rail head using the equation 
 
 u = 0.25 [1/EI(P/6) 4 ] 1/3 UnitS: lb/l '" /1n (1) 
 
 where P = wheel /rail load 
 
 <S = rail vertical deflection 
 
 EI = flexural rigidity of the rail 
 
 and P/6 = rail head or track stiffness. 
 
 Vertical track stiffness measurements were made both before and after surfac- 
 ing operations at Streator and Richmond;while at the other locations, measure- 
 ments were made with whatever degree of consolidation existed. The method 
 used to measure vertical track stiffness was to load both rails at one tie 
 location with a hydraulic jack system suspended beneath a loaded hopper car. 
 Load cells attached to the jacks monitored 6-kip load increments from to 30 
 kip. Resulting deflections were measured with a surveyor's theodolite sight- 
 ing a machinist's scale calibrated in 0.01 in. increments. The scale was 
 attached to the rail directly beneath the applied load. The jacks were typi- 
 cally 10 ft. from the nearest wheel on the hopper car. Where possible an 
 initial, zero deflection reading was established prior to moving the work 
 train over the test position. This allowed for verification of any distur- 
 bance of the rail position from the adjacent wheels while in the test loca- 
 tion. Peak deflections under the hopper car wheels were also noted as a cross 
 check on the measurement scheme. Deflection resolution was approximately 
 0.003 in. by interpolation. Typical initial offsets due to the influence of 
 adjacent wheels were less than + 0.01 in. for the concrete tie track, while 
 the wood tie track at Streator approached 0.10 in. downward. All readings 
 were rezeroed prior to starting the load cycle. 
 
 Figure 28 is a summary of the mean track vertical response to the point load 
 application, as determined by averaging 7 to 10 locations at each revenue test 
 
 62 
 

 
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 63 
 
site and by periodic measurements at one location at each test zone in Section 
 22 of FAST. Note that the consolidated stiffness of the four revenue, con- 
 crete tie sites all fall within a small range to the left of the plot. The 
 stiffness of the freshly resurfaced, concrete tie track at Streator as well as 
 the wood tie section at streator both show more "slack" at the lower load 
 levels resulting in overall, lower secant stiffnesses, about half that for 
 the consolidated concrete tie sections. 
 
 Stiffness data acquired from FAST were measured at 50 MGT intervals at only 
 one tie position in each of the two test sections. Four sets of data were 
 acquired for 50 thru 200 MGT. The values acquired at the first 3 intervals 
 indicate a significant amount of "slack" while the fourth and final values 
 acquired are much more consistent with the results acquired at the revenue 
 sites. This large variability would indicate that the technique of selecting 
 single ties for stiffness measurements will not assure average values for the 
 track as a whole. 
 
 Note that the Richmond data and the Streator wood tie data indicate no signi- 
 ficant change in mean stiffness as a result of the surfacing operation. The 
 data from the concrete tie test section at Streator show that there is a sig- 
 nificant loss of stiffness at the lower load levels as a result of surfacing, 
 while the tangent stiffnesses at maximum, nominal wheel load levels are essen- 
 tially identical before and after surfacing. 
 
 A surprising result of comparing data acquired before and after surfacing is 
 that the surfacing operation pr..1uces a significant increase in the variabil- 
 ity of the support under the ties. Figures 29 through 31 show pairs of curves 
 for before-and-after-surfacing data. The cross-hatched areas indicate the ± 
 one standard deviation values before maintanance and the shaded areas indicate 
 the effect of surfacing. Note that the variability nearly doubles in each 
 case. Also note that the slight increase in average stiffness seen in Figure 
 28 as a result of surfacing the Streator wood tie test section is of minimal 
 significance when compared to the degree of variability indicated at that 
 section. Results of stiffness tests at Aberdeen and at Roanoke show minimal 
 variability: comparable to the pre-maintenance data from Streator concrete. 
 
 If the tangent stiffness at the nominal maximum wheel load is not significant- 
 ly altered by the surfacing operation, then this would indicate that the top 
 layer of ballast directly beneath the tie-, which is disturbed in the surfacing 
 operation, does not contribute significantly to the loaded track stiffness. 
 Results from the plate load tests discussed in Section 7. 2.2, however, show 
 that there is a substantial reduction in the load-deflection characteristics 
 in that layer resulting from surfacing. This would indicate that there must 
 be a significant change in the contact area between the bottom of the tie and 
 top of the ballast, such that the net reduction in plate load stiffness is 
 offset by a change in the effective bearing area under the tie, under full 
 load conditions. Fffective stiffness at low load levels must be strongly 
 affected by a combination of tamping technique and ballast physical states 
 such that Streator-concrete showed a significant reduction resulting from 
 surfacing while Richmond showed no appreciable change. 
 
 Table 3 summarizes the track modulus values derived from the track stiffness 
 data. Stiffness and modulus values are shown for three ranges of incremental 
 
 64 
 
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 DEFLECTION, INCHES 
 
 FIGURE 29. TRACK VERTICAL RESPONSE TO POINT LOAD APPLICATION AT STREATOR-WOOD 
 
 65 
 
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 30. TRACK VERTICAL RESPONSE TO A POINT LOAD APPLICATION AT STREATOR- 
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load. The values for the 18-ki p to 30-kip loading increment best describes 
 the response of the track to nominal wheel loads. 
 
 During the first field tests (at Streator) there was a concern as to whether 
 the technique used to calibrate the concrete ties would have an affect on the 
 track stiffness due to minor disturbances to the ballast. Therefore, during 
 the Richmond tests, two groups of ties were tested for stiffness values, the 
 seven instrumented CC244's and seven randomly selected uninstrumented 
 RT-7S's. Table 4 compares these two sets of data. Note that the secant 
 stiffness values (0 to 30 kip) are increased by the surfacing operation for 
 the undisturbed ties and decreased for the instrumented ties. In con- 
 trast, the 18-to-30-kip values are both increased slightly by the surfacing 
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 explained by a greater loss of compaction associated with the tamping opera- 
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 about 2 in. wide by 1 in. deep across the base of the tie 15 in. on either 
 side of the railseat, to allow insertion of a nylon strap. During the sur- 
 facing operation, this position is approximately adjacent to the two outer 
 tamping forks for that rail. If the tamper operator squeezes the tamping 
 forks the same number of strokes on that instrumented tie as he does on the 
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 the excavation. This would tend to reduce the support for that tie at the 
 railseat because overall, less material is available for support. As a result 
 of this finding, stiffness data acquired at Aberdeen and Roanoke were acquired 
 only in undisturbed locations. In fact, dynamic data at Roanoke were acquired 
 with instrumented ties not calibrated until after data collection was com- 
 pleted to avoid any disturbance to the support. This was particularly impor- 
 tant at Roanoke because of the thoroughly consolidated ballast section. 
 
 6.2 Track Settlement/Roughness 
 
 Survey-to-benchmark measurements were taken at all revenue sites, except 
 Roanoke, then continued at 6-month intervals. Three benchmarks were installed 
 at each test zone, one at each end and one at the center. The test zones were 
 between 450 and 600 ft long. Because the original test plan called for rough- 
 ness measurements acquired from geometry cars and only mean settlement values 
 acquired from survey-to-benchmark measurements, the Streator and Richmond 
 sites were initially laid out with approximately 20 randomly located points 
 along the test zone. After the initial site surveys at Streator and Richmond, 
 it was concluded that track geometry car data would not be sufficiently con- 
 sistent to provide the desired roughness data. Therefore, all sites were laid 
 out with uniform 10-foot intervals, so that both roughness and settlement 
 could be derived from the survey data. The surface of each rail, the corres- 
 ponding cross level, and the alignment of one rail were measured. The abso- 
 lute elevation and offset data were then curve fitted and detrended to elimi- 
 nate overall curvature and grade effects, so that the nominal roughness and 
 settlement could be seen more easily in graphical plots as well as provide 
 more useful statistics. Ten-foot intervals were considered sufficient to de- 
 velop characteristic roughness, considering that these sites did not have any 
 anomalies in running surface caused by bolted joints or special track work. 
 Comparing the data taken on each visit allowed for evaluation of settlement 
 
 69 
 
TABLE 4. EFFECT OF DISTURBANCE OF BALLAST SUPPORT 
 ON TRACK STIFFNESS AND MODULUS 
 
 
 Richmond 
 
 Uninstrumented RT-7S 
 
 (Undisturbed) 
 
 Richmond 
 Instrumented CC-244 
 (Disturbed) 
 
 
 Pre- 
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 Post- 
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 417 
 
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 7470 
 
 4580 
 
 3460 
 
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 7610 
 
 8860 
 
 70 
 
performance, both qualitatively and quantitatively. Of particular interest, 
 was the absolute settlement of the track and whether or not there was an 
 underlying relationship between increased track roughness as a function of 
 absolute settlement or accumulated tonnage. 
 
 Figure 32 shows the characteristic roughness and settlement at FAST, Section 
 22, for the concrete tie zone after the maintenance at 93 MGT. Note that most 
 of the apparent roughness that develops shows up at one or two distinct loca- 
 tions such as stations +100 and -120. The upper family of curves are the 
 actual detrended elevations while the lower set of curves show the relative 
 amounts of settlement referenced to the original surface. The rapid settle- 
 ment after only 1.4 MGT is equivalent to the subsequent settlement after an 
 additional 50 MGT. 
 
 The survey results shown in Figure 33 for the Streator Concrete tie section 
 reveal almost no change in apparent roughness after 36 MGT in spite of initial 
 roughness indicated, particularly on the left end of the plot. Notice the 
 dramatic difference in settlement between the second and third measurement 
 sets, compared to almost no perceptable settlement for the first and last 
 intervals. 
 
 At Richmond, there was also little change in roughness, as seen in Figure 34, 
 in spite of having the greatest total settlement of all sites surveyed. The 
 upper trace is from the original, random interval survey discussed previously. 
 The zero elevation reference mark refers to the average elevation of both the 
 high and low rails from the first survey. Only the high rail data are shown. 
 
 The Aberdeen data in Figure 35 clearly show the smoothest track surveyed. 
 Although the last survey indicated one or two locations approaching the lower 
 limits of Class 6 track, it was difficult to see any surface or line errors 
 with the naked eye. Unfortunately, the test section was resurfaced just prior 
 to a fourth survey attempt. 
 
 Figure 36 i s a summary plot of mean settlement at each test site, beginning 
 with a survey made as close as practical to the moment that the site was 
 freshly surfaced. It has been generally known that track settles rapidly upon 
 the first few load cycles and then begins to asymptotically approach a low, 
 uniform settlement rate controlled primarily by the load spectrum and the 
 performance of the ballast and subgrade materials. In fact, ballast strain 
 data at Aberdeen indicated that essentially all permanent settlement was 
 occurring within the upper 13 in. of the ballast layer. Instances when it was 
 not possible to survey immediately upon completion of surfacing required an 
 estimation of the initial settlement occurring under the first trains passing 
 the test site. However, the resulting characteristic settlement rates of each 
 site once the initial reconsolidation of the upper ballast layer has occurred, 
 still reveal some interesting results. As Figure 36 shows, all sites tend to 
 follow one of two general ranges of settlement rates. A very low settlement 
 rate on the order of 0.002 in. /MGT (500 MGT/in.) is seen at the one extreme, 
 and as high as 0.025 in. /MGT (40 MGT/in.) at the other. At three of the sections 
 surveyed--Streator concrete, Streator wood, and Aberdeen, --some form of seasonal 
 effect seemed to be causing accelerated settlements during the winter and 
 early spring. Moisture levels measured at the base of the ballast section and 
 
 71 
 
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rainfall statistics (discussed in Section 7.3) do not seem to correlate with 
 the seasonal settlement effect. Therefore, it has been assumed that this 
 effect may be associated with either freeze-thaw cycles or perhaps an in- 
 creased track modulus when the ballast is frozen, causing higher impact loads 
 from wheel irregularities resulting in higher stresses in the ballast and sub- 
 grade. There is no indication of a similar trend at Richmond which does not 
 have heavy frost or Pueblo where moisture levels are quite low and no signif- 
 cant impact loads occur. 
 
 Survey data derived to characterize track roughness show only a weak correla- 
 tion between average track roughness and either absolute settlement or accumu- 
 lated track tonnage. This can be seen qualitatively in Figures 32 thru 35 and 
 is discussed in more detail in Section 9. It must be emphasized, however, 
 that these data were collected over deliberately chosen homogeneous sections 
 of track containing no obvious anomalies such as joints, engine burns, grade 
 crossings, or culverts. Overall, track geometry was also sufficiently smooth 
 to minimize any vehicle dynamics which otherwise might cause fluctuating 
 loads. The lack of correlation with settlement or traffic tends to confirm 
 the assumption that relative track roughness is driven primarily by discrete 
 anomalies within the track structure; either in terms of local imperfections 
 in the running surface or abrupt changes in stiffness or strength in the track 
 structure. None of these anomalies was observed within the surveyed portion 
 of the test sites. However, some transients did develop in the running sur- 
 face at the ends of the concrete sections where track stiffness changes 
 occurred. This further emphasizes the importance of track uniformity. 
 
 Wood tie test sections at FAST and Streator were studied along with the con- 
 crete tie sections to compare the relative peformance of wood and concrete 
 ties. In Section 22 at FAST, wood and concrete ties were built with new 
 components upon similar subgrades and ballast beds, built and maintained at 
 the same times with common procedures. By contrast, the Streator test sites 
 had different histories. The concrete tie test site was newly built track 
 (1974) with 14-in. of fresh Georgia granite, while the wood-tie control sec- 
 tion represented mature mainline track. This original wood-tie track had the 
 expected mix of new and old ties with random lengths and support conditions 
 built on an old 9-in. ballast bed of small, thoroughly fouled slag material. The 
 results of these site comparisons show that when constructed under identical 
 conditions wood ties at the traditional 19-1/2 in. spacings and concrete ties 
 at the currently accepted 24-in. spacing produce almost identical settlement 
 rates and comparable degrees of track roughness. By contrast, there was a 
 slight advantage in quality of surface and line of the concrete test section 
 over adjacent wood-tie section at Streator. This may be attributed primarily 
 to differences in the ballast sections and to tie condition. One clear advan- 
 tage that the concrete ties have over the wood ties is their ability to main- 
 tain a very precise and consistent gauge as seen in Figure 37. Note also that 
 the surface roughness seen in Figure 37 has little resemblance to the surveyed 
 data in Figure 33. This can be explained by the short chord length of the 
 geometry car system which is best suited for spotting dipped joints and other 
 short wave length errors, while the survey-to-benchmark work could not justify 
 a higher density survey than the 10 ft interval. In addition, the geometry 
 car is measuring "loaded" geometry while the survey was taken "unloaded," 
 which would have some influence particularly in the wood tie section due to 
 the cut spike fasteners. 
 
 11 
 
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 78 
 
7.0 BALLAST AND SUBGRADE CHARACTERISTICS 
 
 A variety of field tests were conducted at the sites to assess the physical 
 states of the ballast materials as they existed prior to a track maintenance 
 operation. These physical state tests were repeated after surfacing to deter- 
 mine the changes in ballast properties that occurred due to the maintenance. 
 In addition to these tests, standard and Dutch cone penetration tests, and 
 undisturbed tube sampling for laboratory testing were used to investigate the 
 subgrade support characteristics. 
 
 The ballast and subgrade materials recovered from the field sites were sub- 
 jected to a series of index and classification tests. The results were used 
 to develop subsurface profiles describing the composition of the track founda- 
 tions. Laboratory triaxial tests, both static and repeated load, were also 
 performed on samples of these materials to characterize their stress-strain- 
 strength properties. The results of these triaxial tests were used in the 
 prediction of the vertical track modulus and permanent settlement at each of 
 the field sites. Details of these test results are given in Volume II. 
 
 7.1 Ballast Descriptions 
 
 During the revenue site investigations, it was necessary to remove some of the 
 ties and excavate through the ballast materials in order to position subgrade 
 instrumentation. During the excavations, the descriptions and characteristics 
 of the track formation were logged. The excavation descriptions were combined 
 with the laboratory classification results, ballast and subballast moisture 
 contents, and shallow subgrade auger samples to determine the general ballast 
 profiles for the revenue field sites. These profiles are shown in Figures 38 
 through 41 for the Streator wood, Streator concrete, Richmond, and Aberdeen 
 test sections, respectively. 
 
 At the request of the N&W engineering department, no comparable evaluations 
 were performed at Roanoke on the the ballast and subgrade, because of the pos- 
 sible disruptive effects on its long-term evaluations of track performance 
 However, clearing of cribs for the tie inspections and installation of strain 
 gages revealed a fouled condition somewhat similar to Richmond. This fouling 
 is caused by the cumulative affects of 270 MGT of loaded, coal trains 
 depositing coal dust into the ballast layer. The resulting mixture of coal 
 fines and granite were sufficiently "cemented" to require extensive use of a 
 pick to break loose the ballast material enough that a ballast fork could be 
 used for removing material from the crib. 
 
 A detailed examination of the other sites showed that the crib areas were less 
 fouled than the material below the tie. The water content of the crib materi- 
 als was very low, generally less than 1 percent, as would be expected. Water 
 content increased as degree of fouling increased. In all of the excavation 
 profiles shown, the first stratum corresponded roughly to the crib materials, 
 and the bottom of the ties are located within a few inches of this first pro- 
 file boundary shown in Figures 38 through 41. Particle sizes decrease with 
 depth for the field sites. Visible evidence of distinct particle crushing was 
 
 79 
 
Site: Streator (Leeds), Illinois 
 Wood Tie Section 
 
 DESCRIPTION OF SOIL 
 
 WATER 
 CONTENT (%) 
 
 5 10 
 
 Slag ballast, clean and loose at 
 surface, becoming fouled with sandy 
 black fines. Largest particle 
 size 2". 
 
 USCS: GP AASHTO: A-l-4 AREA: 4 
 
 Bottom of Tie 
 
 Fouled ballast. Fouling material 
 is black, sandy. Very compact. 
 
 Ballast particle size: l-l/2"-l/2" 
 
 USCS: GW AASHTO: A-l-a 
 
 Brown, sandy subballast-type 
 material. Slightly moist but 
 not wet. 
 
 USCS: GW AASHTO: A-l-a 
 
 3- 
 
 FIGURE 38. BALLAST PROFILE FOR STREATOR WOOD TIE SECTION 
 
 80 
 
Site: Streator (Leeds), Illinois 
 Concrete Tie Section 
 
 DESCRIPTION OF SOIL 
 
 Clean granite ballast, No 
 noticeable crushing in cribs. 
 Particle size 2-1/2" - 1-1/2" 
 USCS: GP AASHTO: A-l-a AREA: 4 
 
 Bottom of Tie 
 
 Ballast is quite clean, but has 
 some sandy, black moist fines. 
 Noticeable particle crushing, 
 particularly below rail seats. 
 Size: 2" - 3/4" 
 USCS: GP AASHTO: A-l-a 
 AREA: 4 
 
 Very compact, fouled ballast, 
 with moist sandy fines. Par- 
 ticle size: 1-1/2" - 1" 
 
 Brown, sandy subballast-rtype 
 material. Very few ballast 
 particles. Moist but not wet. 
 
 USCS: SW AASHTO: A-l-a 
 
 3- 
 
 WATER 
 CONTENT (%) 
 
 i 5 10 
 _ I i_ 
 
 FIGURE 39. BALLAST PROFILE FOR STREATOR CONCRETE TIE SECTION 
 
 81 
 
Site: 'Richmond, Virignia 
 Concrete Tie Section 
 
 DESCRIPTION OF SOIL 
 
 WATER 
 CONTENT (%) 
 
 Predominantly limestone ballast 
 with some coarse to fine sand, 
 trace silt. 
 
 USCS: GP 
 AREA: 4 
 
 AASHTO: A-l-a 
 
 Bottom of Tie 
 
 Clean Ballast 
 
 size l"-2' 
 
 Heavily fouled ballast with 
 black, sticky fines. Very com- 
 pact and moist. Some fine gra- 
 vel. USCS: GP, AASHTO: A-2-4 
 
 Black, wet, gravel size parti- 
 cles, some ballast particles. 
 
 USCS: GW AASHTO: A-2-4 
 
 Dark brown to black coarse to 
 fine gravel (Ballast) 
 
 Some c-*f sand, trace c+£ Silt. 
 
 Largest particle 1-3/8" 
 
 FIGURE 40. BALLAST PROFILE FOR RICHMOND CONCRETE TIE SECTION 
 
 82 
 
Site: Aberdeen, Maryland 
 Concrete Tie Section 
 
 DESCRIPTION OF SOIL 
 
 WATER 
 CONTENT (%) 
 
 Clean, compact traprock ballast. 
 Largest particle size 3-l/2"-l-l/2" 
 USCS: GP AASHTO: A-l-a AREA: 24 
 
 Bottom of Tie 
 
 Slightly fouled, very compact 
 ballast, becoming very fouled with 
 depth. Fouling material is black, 
 moist, oily. Particle size: ""T 
 2-1/2" - 1-1/2" with some smal- C 
 ler sizes. w * 
 
 USCS: GP 
 AREA: 4 
 
 AASHTO: A-l-a 
 
 Mostly cinders with some black 
 fines and ballast particles. 2, 
 Largest particle size 2-1/2" 
 
 USCS: GP AASHTO: A-l-a 
 
 Black medium to fine gravel (slag) , 
 and coarse to fine Sand, some Silt 
 
 FIGURE 41. BALLAST PROFILE FOR ABERDEEN CONCRETE TIE SECTION 
 
 83 
 
present at the Streator concrete site, particularly near the rail seat areas 
 under the ties. However, gradation comparisons of materials taken from the 
 crib and under-tie areas showed that the crib ballasts were always coarser 
 than the under-tie materials. Thus, breakage undoubtedly occurred at the 
 other sites as wel 1 . 
 
 A comparison of the gradation curves for the under-tie material in the revenue 
 service sites in Figure 42 shows that the Streator wood tie section ballast 
 was much finer than the other ballasts. The Richmond under-tie material is 
 basically similar to the Streator concrete and Aberdeen material for the 
 coarser particles, say greater than 3/4 in., but contains more particles less 
 than the 3/4-in. size. Aberdeen crib material was classified as AREA 24 mate- 
 rial. The crib materials at all other sites, and the under-tie materials at 
 the Streator concrete and Aberdeen sites, were classified as AREA 4. The 
 under-tie materials at the Streator wood tie section and the Richmond site die 
 not fall within any standard AREA classification. 
 
 The most appropriate index tests for the specification of acceptable ballast 
 materials are still being debated, although Gaskin and Raymond [10] have 
 attempted to relate certain index properties to track performance. The most 
 commonly used index tests were therefore performed on the ballast materials. 
 There were: (1) specific gravity and absorption according to ASTM standards 
 E-12, C125, C127-73 and C128-73, (2) Los Angeles abrasion according to ASTM 
 C131-69 standards, (3) magnesium sulfate soundess according to ASTM C88 
 standards, (4) scratch hardness according to ASTM C235-68 standards, (5) 
 petrographic analysis for mineral mode data, Moh's hardness, degree of 
 cleavage and mineral alteration, and (6) particle SDhericity, angularity 
 (roundness) and flakiness. The results of these tests are given in Table 5. 
 
 It should be noted here that although differences in ballast materials were 
 observed, ballast compaction was a much more important factor in overall trad 
 performance. 
 
 7.2 Physical State Tests 
 
 In order to characterize the physical state or structure of the ballast at 
 field test sites, a series of special field tests were performed. Prior to a 
 scheduled maintenance operation, physical state measurements were made at the 
 revenue sites by the University of Massachusetts geotechnical staff. These 
 tests included the ballast density test (BDT), the plate load test (PLT), and 
 the lateral tie pus;i test (LTPT). These physical state tests were repeated 
 after the track was raised and tamped so that quantitative assessments of the 
 change in ballast physical state could be made. 
 
 The locations for the ballast density tests were under the tie at the rail 
 seats and in the cribs near the rail seats. A few ballast density tests were 
 also done under the center of the tie. Plate load tests were done in the 
 cribs near the rail seats, and under the ties at the rail seats and tie cen- 
 ters. Measurements of plate bearing index and lateral tie push resistance, 
 both pre- and post-maintenance, were also available for FAST Section 3 and 
 the wood and concrete portions of FAST, Section 22. Ballast density test 
 results for FAST Sections 3 and 22 were not available. The determination of 
 
 84 
 
CO 
 
 UJ 
 
 o 
 
 s 
 
 Ui 
 
 PARTICLE DIAMETER (mm.) 
 
 FIGURE 42. COMPOSITE GRADATION CURVES FOR UNDER-TIE BALLASTS 
 FROM REVENUE SITES 
 
 85 
 
the in-situ ballast physical states will be used to provide basic information 
 needed for the correlation of track performance between the revenue sites and 
 FAST. 
 
 One month prior to the site visit to Streator, a track gang came through the 
 concrete tie section and performed a track surfacing operation, unaware of the 
 scheduled ballast testing. Thus, the pre-maintenance test series measurements 
 could not be obtained for this site. The amount of track disturbance and 
 amount of raise given to the Streator concrete tie section due to this unsche- 
 duled maintenance is unknown. 
 
 TABLE 5. SUMMARY OF BALLAST INDEX TEST RESULTS 
 FROM FIELD SITES 
 
 Test 
 
 
 Streator 
 
 Wood 
 Under-Tie 
 
 Streator 
 Concrete 
 Under-Tie 
 
 Richmond 
 Concrete 
 Under-Tie 
 
 Aberdeen 
 Concrete 
 Under-Tie 
 
 Specific Gravity 
 Bulk 
 
 2.34 
 
 2.78 
 
 2.70 
 
 2.87 
 
 Apparent 
 
 
 2.50 
 
 2.81 
 
 2.68 
 
 2.90 
 
 Absorption (%) 
 
 
 2.25 
 
 0.36 
 
 0.33 
 
 0.32 
 
 Los Angeles 
 Abrasion 
 
 (%) 
 
 29.22 
 
 39.94 
 
 19.25 
 
 17.79 
 
 0.37 
 
 0.05 
 
 0.73 
 
 0.00 
 
 9.00 
 
 16.00 
 
 11.00 
 
 17.00 
 
 0.67 
 
 0.63 
 
 0.61 
 
 0.62 
 
 0.28 
 
 0.25 
 
 0.22 
 
 0.26 
 
 Magnesium Sulfate 
 Soundness, 5 
 Cycles (%) 
 
 Flakiness Index [%) 
 
 Sphericity 
 
 Roundness 
 
 Scratch Hardness, 
 
 (%) Soft by Weight NA 0.00 0.00 0.00 
 
 7.2.1 Ballast Density Tests 
 
 The ballast density test determines the in-situ density of the ballast mate- 
 rials. This test, described more thoroughly in References 11 and 12, uses a 
 water replacement technique to determine the volume of a membrane-lined, hand- 
 excavated hole in the ballast. The volume of the hole along with the weight 
 and moisture content of the excavated material is used to calculate the 
 
 86 
 
in-situ dry density, Y<jf. The field density measurements are used along 
 with a laboratory reference density test [12] to determine the relative 
 compaction state in the field. The maximum density that can be achieved using 
 the reference density apparatus is referred to as the ultimate reference dry 
 density, Y u if The ratio of the field density to the ultimate reference 
 density is the relative compaction, R c , expressed in percent. The smooth 
 steel walls of the mold used to determine reference density in the laboratory 
 result in systematically lower ultimate reference densities than the 
 
 field measurements, although the actual densities may be similar. Relative 
 compaction is more useful for studying changes in ballast density due to 
 traffic histories and maintenance effects than the actual density values, 
 because it tends to compensate for differences in gradation and particle 
 specific gravity. 
 
 The results from the ballast field density tests and the laboratory ultimate 
 reference density tests are shown in Figure 43. For reasons previously ex- 
 plained, the lab ultimate reference densities were all lower than the field 
 measurements. The pre- and post-maintenance densities for the Aberdeen site 
 were very close. The amount of track raise at Aberdeen was only 0.1 in., 
 which could result in less disturbance to the material under the tie than a 
 large raise. The relative compaction of the ballast under the tie at Aberdeen 
 was therefore not affected by the maintenance operation. In contrast to this, 
 the Richmond site exhibited the largest changes in both pre-and post- 
 maintenance densities and relative compaction under the ties. The Richmond 
 site also had the largest raise, about 2 in., which would significantly 
 disturb the ballast structure. A large change in relative compaction was also 
 observed for the Streator wood tie section, which was raised about 1.5 in. 
 
 The pre- and post-maintenance densities and lab ultimate densities for the 
 crib locations are shown in Figure 44. The crib densities and relative 
 compactions, both pre- and post-maintenance, were lower than the under-tie 
 values for all of the field sites. The ultimate lab reference densities for 
 the crib ballasts were also lower than the ultimate reference densities for 
 the under-tie material. This may be due to differences in the crib and 
 under-tie gradations. It was previously shown that the crib materials were 
 consistently coarser than the under-tie materials. Also, the crib materials 
 were less fouled and would be expected to have higher void ratios and lower 
 dry densities, since fewer fine particles would be present to fill the 
 interstices between the larger ballast particles. 
 
 The changes in relative compaction of the crib ballasts as a result of mainte- 
 nance are shown in Figure 44. The largest change in crib relative compaction 
 due to the maintenance operation occurred at Aberdeen. Even though the lift 
 height was small for the Aberdeen site, the crib area would be disturbed by 
 the insertion of the tamping tools, independent of the amount of raise. How- 
 ever, the Richmond site contained crib ballast which was very fouled. Thus it 
 would not be expected to density as much as the clean crib ballasts as a re- 
 sult of traffic vibrations. This may be the reason that the relative com- 
 paction change due to maintenance at Richmond was negligible. The ballast in 
 the cribs at the Streator wood tie section was also quite fouled and showed 
 changes in relative compaction about half as large as the changes measured at 
 Aberdeen . 
 
 87 
 
LL 
 
 Z w 
 < 
 
 Ulfe 
 
 fe 2 
 
 8! 
 
 l S 
 CD O 
 < -J 
 
 140-1 
 
 130- 
 
 120- 
 
 110- 
 
 100- 
 
 90- 
 
 80 
 
 PRE-MAINT. 
 
 \ 
 
 i 
 
 i 
 
 POST-MAINT. 
 •LAB ULTIMATE 
 
 55 
 
 1 
 
 O 
 
 o 
 
 UJ 
 
 > 
 
 -J 
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 120 -J 
 
 110- 
 
 100 
 
 PRE-MAINT. 
 
 POST-MAINT. 
 
 i^ i^ i^ 
 
 STREAT0R STREAT0R RICHMOND 
 
 WOOD CONCRETE 
 
 Qi 
 
 ABERDEEN 
 
 FIGURE 43. BALLAST DENSITIES - UNDER TIE AT RAIL SEAT 
 
 88 
 
u 
 
 111 != 
 
 5 UJ 
 P 5 
 
 a. ° 
 
 So 
 
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 130-1 
 
 120- 
 
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 STREATOR 
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 PRE- MAINT. 
 
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 A' 
 
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 RICHMOND ABERDEEN 
 
 FIGURE 44. BALLAST DENSITIES - CRIB NEAR RAIL SEAT 
 
 89 
 
7.2.2 Plate Load Tests 
 
 The plate load tests were conducted in the cribs near the rail seats and under 
 the ties, near the rail seats and tie centers. Descriptions of the plate load 
 test procedure and apparatus can be found in Refs. 12, 13 and 14. The test 
 consists of imposing a vertical load on 5-in. diameter steel plate which is 
 seated on the ballast using gypsum gauging plaster. The plate contact pres- 
 sure per unit deflection is the ballast bearing index, B^. This is a 
 measure of vertical ballast stiffness. The B|< values are calculated as 
 fol lows : 
 
 Bk «-P- , 
 A • 6 
 
 where P = applied vertical load, 
 A = plate area , and 
 6 = vertical deformation. 
 
 A deformation level of 0.1 in. was chosen as the reference, although relative 
 comparisons could be made at any deformation value. 
 
 The ballast bearing indices, B^, at 0.1-in. deformation as measured under 
 the ties at the rail seats are shown in Figure 45 for the revenue sites and 
 FAST. The pre-maintenance values at Richmond were the highest, possibly 
 because of the high degree of fouling. The largest decrease in plate bearing 
 index due to maintenance was also at the Richmond site. This site had the 
 largest raise, about 2 in., which would significantly disturb the ballast 
 structure, particularly when the ballast is fouled. This is consistent with 
 the observation that the Richmond site also showed the largest decrease in 
 relative compaction at the under-tie location. The Aberdeen site showed the 
 smallest change in plate bearing index at the under-tie location as a result 
 of the small raise, only 0.1 in. 
 
 The post-maintenance values of plate bearing index were very similar for all 
 of the sites, with the exception of Aberdeen. The maintenance raises for the 
 Streator and Richmond revenue sites were on the order of 1.5 to 2 in. The 
 raises at the FAST s-ite were also about 2 in. For all of the sites where 
 significant trackbed disturbance under the ties resulted from raising and 
 tamping, the plate load tests showed no significant difference in ballast 
 stiffness, independent of ballast type. 
 
 Values of the plate bearing index were also measured under the center of the 
 tie. The results of these measurements for the revenue sites are shown in 
 Figure 46. Again, the Richmond site had the highest average B|< value before 
 the maintenance. The Aberdeen values at this location showed no change 
 resulting from maintenance, but do show that the B^ values under the center 
 of the ties prior to maintenance were only 1/3 of the value measured under the 
 tie at the rail seat. The plate load tests for all of the revenue sites 
 showed that the ballast stiffnesses were always greater under the tie at the 
 rail seat than under the tie center, prior to maintenance. After the mainte- 
 nance operations, the ballast stiffnesses under the tie were about the same at 
 both locations, although still slightly greater near the rail seat areas. 
 
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7.2.3 Lateral Tie Push Tests 
 
 -he lateral tie push test is a common field measurement of track conditions 
 ,sed by the railroad industry. The lateral tie push test measures the 
 distance of a single tie to lateral displacement under un oaded rail 
 :o d It o s. For the test, the tie is separated from the rail an r 
 ; asteners and then pushed from one end after removing the shoulder ballast, 
 rhe resistance of the tie to lateral loads is an indirect measure of the 
 
 alias? physical state and degree of compaction. A common variation on the 
 ■inile tie push test involves the use of a track panel containing a number of 
 !l2. A compilation of past research and test results of lateral track 
 
 esi stance tests can be found in Ref. 15. 
 
 rhe lateral tie push test results for the test sites are shown in Figure 47. 
 [he lateral displacement level at which the results were taken was 2 mm. 
 
 rhP lateral tie resistance for the Aberdeen site again showed the smallest 
 hange f om maintenance. The Streator concrete tie section P°st-maintenance 
 
 Results were quite high relative to the FAST, Streator wood, and Richmond 
 
 ;ec ons Unfortunately, pre-maintenance values for the Streator concrete tie 
 ect on were not available for comparison. With the exceptions of the 
 
 Aberdeen and Streator concrete results, as noted, the post-maintenance t le 
 
 )ush resistances were all very similar. The low values were due to mainte- 
 
 ce d tu b an e and reduction of crib confinement Visua observations of 
 he ballast in the cribs at the Richmond site showed unusually depleted cribs 
 
 iner maintenance, with a ballast depth of only a few inches above the bottom 
 
 >f the tie. 
 
 7.3 Subgrade Description 
 
 The subgrade conditions at the revenue field sites wer % ^P 1 ?^"^^^ ^^ 
 tandard penetration tests (SPT) and Dutch cone penetration tests (CPT). The 
 SPT was selected to aid in the subsurface investigation for two purposes. 
 Mrst it was an efficient means to obtain samples for visual identification. 
 Second, it provided values of blow count which are commonly use a rough 
 index of soil properties. The SPT's were done in accordance with ASTM 
 procedure D1586. The CPT was used because it was rapid was not expected to 
 iisturb the roadbed significantly, and was the simplest test thought to have 
 Potential for soil property correlations. The CRT's were one in accor dance 
 vith ASTM procedure D3441, using a mechanical Begemann-type tip with friction 
 eeve For all test borings, a truck-mounted drilling rig equipped with rail 
 vheels was used, and borings were taken along the track centerline. A 
 jetailed description of the SPT and CPT results from the revenue sites is 
 :jiven in Ref. 16. 
 
 7.3.1 Standard Penetration Tests 
 
 The standard penetration resistances for the field sites are shown ^Figure 
 IS as a function of depth. The consistencies of the subgrade soils for the 
 Streator sites could be described as stiff for depths from about 5 to 13 ft. 
 telow these depths, the material was very soft. 
 
 93 
 

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 94 
 
STANDARD PENETRATION RESISTANCE, N 
 ( blows / ft ) 
 
 TOP OF 
 
 5-J 
 
 10- 
 
 Q- 
 U 
 
 O 
 
 15- 
 
 20— 
 
 STREATOR, 
 WOOD 
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 T I I r 
 
 STREATOR, 
 CONCRETE 
 20 40 
 
 i I i r 
 
 RICHMOND 
 
 20 40 
 
 i I I r 
 
 ABERDEEN 
 
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 FIGURE 48. STANDARD PENETRATION RESISTANCE VERSUS DEPTH FOR FIELD SITES 
 
 95 
 
The granular material located at depths of 3 to 5 ft at the Richmond site had 
 relative states ranging from dense to medium. From depths of 5 to 16 ft, the 
 consistency of the subgrade increased from stiff to very stiff. Below 16 ft 
 to the end of the exploration depth, the soils were hard. 
 
 The materials at the Aberdeen site were primarily granular, with some zones 
 containing varying amounts of silt. From 2 to 7 ft, the relative states of 
 the soil decreased from medium-dense to loose. A uniformly loose zone was 
 located from depths of 7 to 13 ft. The sandy material below 13 ft and extend- 
 ing to the end of the boring depth could be classified as medium. 
 
 7.3.2 Cone Penetration Tests 
 
 The cone penetration resistances for the four field sites are shown in Figure 
 49 as a function of depth. The values given represent the average cone 
 resistances from 8 to 11 tests per site. Cone penetration through the upper 
 few feet of the track foundations was not possible due to the very dense 
 nature of the ballast and granular materials. Thus it was necessary to auger 
 through these materials before cone soundings could begin. 
 
 The CPT values for the Streator wood and concrete sections were again similar, 
 although shifted vertically due to the bubsurface stratifications. The trends 
 shown for the SPT tests at Streator can be clearly correlated to the changes 
 in cone resistance measured at these site. 
 
 The cone resistances at the Richmond site also followed the trends identified 
 by the SPT. The cone resistances tended to increase with depth. The cone 
 tests identified a zone of stiffer materials at a depth of about 15 ft, fol- 
 lowed by a reduction in tip resistance that was not detected using the SPT. 
 However, both the SPT and CPT detected a hard zone at a depth of about 18 ft. 
 
 The depth at which SPT tests were initiated at the Aberdeen site was approxi- 
 mately 2.5 ft below the top of the cross ties. As previously stated, cone 
 penetration through the upper 5 ft of the Aberdeen foundation was not possible 
 because of the dense nature of the upper zone of soil. The CPT identified a more 
 gradually increasing resistance to penetration than did the SPT, although the 
 general subsurface profiles explored by each method showed similar results. 
 
 At present, there are no well-defined general correlations between cone resis- 
 tances, q c , and soil consistencies or relative states, although considerable 
 effort is being made to develop these relationships [17]. 
 
 7.3.3 Water Content and Atterberg Limits 
 
 The variations in natural water content and the Atterberg liquid and plastic 
 limits for the four field sites evaluated are shown in Figure 50. The mois- 
 ture content in the upper few feet of the formations were very low, even 
 though all the ballast sections were fouled. 
 
 96 
 
CONE RESISTANCE, q c 
 (kg/sq cm) 
 
 TOP OF 
 TIE 
 
 1 
 
 5- 
 
 Z io- 
 
 X 
 Q 
 
 15- 
 
 STREATOR, 
 
 WOOD 
 20 40 
 
 1—1 — i — r 
 
 20- 
 
 STREATOR, 
 
 CONCRETE 
 20 40 
 
 RICHMOND 
 20 40 
 
 FIGURE 49. CONE RESISTANCE VERSUS DEPTH FOR FIELD SITES 
 
 97 
 
WATER CONTENT (%) 
 
 (jj £ = liquid limit 
 
 oip= plastic limit 
 
 o = natural water 
 content 
 
 FIGURE 50. WATER CONTENT AND ATTERBERG LIMITS VERSUS DEPTH FOR FIELD SITES 
 
 98 
 
Moisture content and Atterberg limits alone are not sufficient to define spe- 
 cific engineering properties, since soil behavior is a function of moisture 
 content, soil type, and density or void ratio. However, some general trends at 
 the field sites could be identified. The first was the similarity between the 
 adjacent track sections at Streator, as previously noted. Also, the natural 
 moisture content for all of the soils containing significant amounts of 
 plastic fines were at or very close to the plastic limits. This would 
 indicate a low potential for the development of continued excessive subgrade 
 deformations. 
 
 7.4 Moisture Instrumentation and Weather Data 
 
 Six electronic moisture sensors, patterned after the prototypes developed by 
 Selig and Wobschall [18] [19], were installed at each field site to monitor 
 the variations in moisture that occurred at the top of subgrade. The depths 
 of installation for the sensors below the top of the ties were 18, 25, 20 and 
 29 in. for the Streator wood, Streator concrete, Richmond, and Aberdeen sites, 
 respectively. 
 
 The field measurements with the embedded sensors were taken at weekly inter- 
 vals by persons residing near each field site using a remote readout device. 
 Weather data in the form of monthly cl imatol ogical reports from the National 
 Oceanic and Atmospheric Administration (NOAA) were used to supplement the 
 moisture sensor readings. 
 
 The reduced data from the moisture sensors implanted at the Streator wood and 
 concrete tie sections, along with the rainfall data for those sites, are shown 
 in Figure 51. These data cover the period from November 1979 to December 
 1981. This figure shows that the subgrade moisture content at the Streator 
 concrete tie section was consistently greater than that in the Streator wood 
 tie section. This could be due to the greater depth of burial (25 vs. 18 in. 
 below top of tie) of the sensors in the concrete tie section. Reference to 
 Figure 50 shows that the moisture content at a depth of about 2 ft in the 
 Streator concrete section initially was greater than the moisture content at 
 1.5 ft in the wood tie section. 
 
 The moisture content in the Streator wood tie section appeared to fluctuate 
 over a larger range than in the concrete tie section. This could also have 
 been caused by the differences in burial depths of the sensors. During the 
 first year of the measurements, the trends in moisture content between the 
 wood and concrete sections were almost identical , except for an offset of 
 about 4 percent. The readings in the wood tie section became more variable 
 from about February 1981 until December 1981, although they were still 
 consistently lower than the subgrade moisture contents in the concrete tie 
 section. 
 
 The subgrade moisture contents and rainfall for the Richmond and Aberdeen 
 sites are shown in Figure 52. The moisture content in the trackbed at a depth 
 of 20 in. at the Richmond site remained constant at 8.1 percent for the dura- 
 tion of the monitoring period, despite the significant amounts of rainfall 
 shown. There were virtually no variations in the moisture contents monitored 
 
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over this 2-year period. A possible explanation of this is that the very 
 compact, heavily fouled ballast conditions effectively served as a seal for 
 the upper subgrade zone, permitting no downward migration of the water enter- 
 ing the bal last. 
 
 The moisture content at a depth of 29 in. at the Aberdeen site also showed only 
 slight variations from the period of June 1980 to December 1981. The average 
 moisture content was about 4.5 percent and independent of rainfall with a 
 range of only about ±0.5 percent. This may be attributed to both the depth 
 of burial and the degree of fouling evident in the trackbed. 
 
 The cumulative amounts of precipitation recorded at the field sites were also 
 recorded. The seasonal trends for the field sites were in very close agree- 
 ment. A conclusion drawn from the cumulative rainfall data was that there 
 appeared to be no significant differences in the amounts of precipitation, on 
 a seasonal and long-term basis, between any of the sites. The rates of preci- 
 pitation accumulation over periods from January to October were the same for 
 each of the sites. The decreases in precipitation accumulation rates from 
 October to January were also similar. 
 
 7.5 Laboratory Stress-Strain and Strength Testing 
 
 Ballast and subgrade samples recovered from the field sites were tested to 
 determine elastic properties and deformation behavior. The results of these 
 tests were used in the prediction of the sites' vertical track moduli and 
 permanent settlement. Resilient moduli values for the ballast materials were 
 determined based upon repeated load tri axial tests. These tests were 
 performed using constant-amplitude and variable-amplitude repeated load 
 conditions, as well as loadings incorporating shear stress reversal. The 
 resilient moduli measurements along with the resulting inelastic behaviors are 
 discussed in detail in Volume II. 
 
 A new laboratory testing technique was developed that was intended to simulate 
 field behavior of the ballast. This ballast box apparatus, shown in Figure 
 53, was used to investigate both the permanent deformation behavior of the 
 ballast and to measure the residual, horizontal stresses that build up due to 
 repeated loadings. The results of these tests indicated that large residual, 
 horizontal compressive stresses build up in ballast within the first few 
 cycles of loading. These residual stresses can have a large effect on the 
 resilient modulus of the ballast. 
 
 The residual, horizontal stresses also appear to play an important role in tie 
 migration and may explain the mechanism of tie skewing. For example, during a 
 related study near the test zone at Aberdeen, sixty consecutive ties were 
 replaced with new ties to study tie cracking. On six-week intervals or more, 
 alternate cribs were opened at both railseats to allow for inspection for 
 flexural cracks. They were then refilled with ballast immediately after 
 inspection. After the third inspection (the same alternate cribs were opened 
 each time), the ties had migrated toward each other about two inches in the 
 direction of the opened cribs. This would indicate that the unopened cribs 
 had built up sufficient residual stress prior to each inspection to cause the 
 
 102 
 
END 
 PANELS 
 
 I LOAD 
 
 ZZZZJ 
 
 F 
 
 TIE 
 SEGMENT 
 
 c 
 
 24 in. 
 
 T 
 
 H 
 
 A 
 
 |< 9 in. 
 
 »n 
 
 1 
 
 |< — 8 in. 
 
 A 
 
 FIGURE 53. BALLAST BOX TEST APPARATUS 
 
 103 
 
ties to move toward the uncompacted cribs after inspection, until equilibrium 
 was achieved. 
 
 Similar tie movements were observed at Streator-concrete after the damaged 
 ties were replaced, with some ties being up to six inches from their original 
 positions, along with some skewing. A variety of other causes may, however, 
 have contributed to this case, including unintentional movement caused by the 
 
 tamper. 
 
 Another phenomenon which may be affected by the build-up of residual, hori- 
 zontal compressive stresses is the relationship between ballast shoulder width 
 and track roughness. Studies at FAST showed the surprising result that wider 
 ballast shoulders help maintain smoother track surface [20]. This may indi- 
 cate that the residual stresses in the ballast layer are inherently stabiliz- 
 ing and that wider shoulders help sustain higher residual stresses. 
 
 There are also indications that the loss in lateral tie resistance after main- 
 tenance, shown previously in Figure 47, may be affected by the loss of confine- 
 ment provided by the crib ballast. Detailed descriptions of the ballast box 
 test results and the implications on the predicted track settlements are given 
 in Volume II. 
 
 104 
 
8.0 COMPONENT PERFORMANCE 
 
 The long-term response of the ties and fasteners to the combined effects of 
 traffic and environment were evaluated by visual inspections. "Top inspec- 
 tions," which are fairly easy to perform and do not disturb the test sections 
 have been performed routinely by the railroads and other interested groups 
 since these sites were built. To maintain continuity, Mr. John Weber, 
 Consultant and a recognized expert in concrete ties, performed most of these 
 inspections in this project. The corresponding summaries of these top inspec- 
 tions are primarily intended to aid in qualifying the relative condition of 
 the components at each site. A rigorous correlation with FAST components was 
 not possible because of the relatively short time interval, short test zones, 
 and small populations of components available and the random and mostly un- 
 known degree of maintenance which was performed at each revenue site. 
 Component tests at FAST, as well as extensive inspections on the Northeast 
 Corridor, have shown that performance indices are often defined by only one or 
 two percent failures. Test sections on the order of one-quarter-mile long 
 would be more appropriate for these failure levels. In addition, some indices 
 require higher degrees of curvature than were available for the tests. 
 
 On the other hand, open crib inspections, when combined with newly developed 
 techniques to identify very small flexural cracks under the rail seats, are 
 fundamental to this correlation study, particularly because of the correspond- 
 ing measurement of dynamic loads. 
 
 8.1 Rail Seat Flexural Cracks 
 
 Visual inspection for 
 condition of concrete 
 as in the tie center 
 design loads. Other 
 factum" ng defects, ma 
 impacts. Of particul 
 seat cracks which gen 
 bottom surface of the 
 can have cracks exten 
 fastener shoulders on 
 
 cracks has been a standard procedure for determining the 
 
 ties. Flexural cracks in the rail seat region as well 
 are generally an indication of tie loading greater than 
 types of cracks may be related to factors such as manu- 
 intenance equipment (procedures) or dragging equipment 
 ar interest in this discussion are the transverse rail 
 erally range from 1 to 6 in. long extending from the 
 
 tie as shown in Figure 54. In more advanced cases, ties 
 ding up to the top surface after branching out toward the 
 
 either side of the rail seat. 
 
 Transverse Rail Seat Cracks 
 
 , r^l .(5b 
 
 
 171 ■ i ■ t . i . ■ i ■ ; . i . ■ . 
 
 i ■ i i 
 
 FIGURE 54. CONCRETE TIE TRANSVERSE RAIL SEAT CRACKS 
 
 105 
 
In June 1980 while data were being acquired at the Aberdeen test site, an 
 improved technique was used for the first time to aid in visually inspecting 
 for cracks in the concrete ties. After experimenting with a variety of 
 liquids with different vapor pressures, three were adopted for use, depending 
 on the temperatures of the ambient air and the tie surface being inspected. 
 At the colder temperatures, up to about 50 to 60 degrees F, Freon TF in 
 aerosol cans was used. For moderate to warm conditions, ethyl alcohol was 
 used;and at higher temperatures, i sopropyl alcohol or even water provided the 
 best evaporation rate. 
 
 The technique for enhacing the crack visability first required cleaning 
 the area using a rag wet with the inspecting liquid. Then after the sur- 
 face is clean and dry an initial "unaided" check can be performed, or the 
 enhancing liquid can be applied by spraying (via squeeze bottle or aerosol 
 can) the entire region to be inspected. This is typically no larger than 
 a 6 in. by 8 in. area at one time. It is important to determine an 
 optimum amount of fluid to be applied such that the fluid has an opportunity 
 to soak into any cracks that may exist. Excess fluid can be wiped off the 
 surface with a clean, dry rag. If the proper fluid has been used, it will 
 quickly evaporate off the surface of the concrete leaving the crack enhanced 
 by the dark line generated by the fluid migrating back to the surface. Too 
 slow an evaporation rate seems to draw out the fluid in the crack at almost 
 the same rate as the surface material, while too rapid a rate will make it 
 difficult to spot the crack. If any cracks are observed, the process can be 
 repeated many times if necessary to verify their locations and lengths. 
 
 As discussed earlier, once a crack travels up beyond the neutral axis of the 
 tie it will tend to branch out. It is often very difficult to trace exactly 
 the crack in the "branch," but occasionally the crack can be located on the 
 upper corner of the tie and followed back toward the base of the branch. The 
 upper crack may have been generated independently from a reverse bending load, 
 however, and should not necessarily be assumed as "growing" from the lower 
 branch. 
 
 Variations of this inspection technique include the use of a minute amount of 
 dye in the fluid to leave a more permanent trace of the crack. The success of 
 this is in part affected by the quality of the surface of the concrete. If 
 minute surface cracks and pits are too numerous, then the flexural crack may 
 be partially obscured. 
 
 Certainly, cracks were made visible using this technique which would not 
 previously have been detected. The original visual inspection at Aberdeen 
 showed that over 70 percent of the rail seats were cracked after only 35 MGT 
 of total traffic. Using this technique at the other sites allowed for a 
 consistent set of statistics which revealed considerably more cracked ties 
 than was previously anticipated considering that the results from FAST had 
 shown no rail seat cracks after 450 MGT. A summary of the most recent inspec- 
 tions at each site is shown in Table 6. Note that at Aberdeen, the percentage 
 of cracked rail seats increased to over 90 percent after an additional year of 
 traffic increased the total tonnage to 60 MGT. 
 
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While no crack on any tie inspected had progressed to the point where the tie 
 was no longer functional, the history of concrete tie performance in this 
 country indicates that these types of cracks may considerably shorten the 
 50-year life expectancy of the tie. As can be seen by the brief description 
 of the traffic loads in Table 6, and the more detailed description in Section 
 5.1, severe flats and wheel irregularities on high-speed passenger trains 
 correlate well with the occurrence of cracked ties. At FAST, where wheels are 
 maintained in very good condition, no flexural cracks were observed in any of 
 600 ties inspected even though the nominal wheel loads are higher at FAST than 
 at any other location. 
 
 8.2 Top-of-Tie Inspections and Fastener Performance 
 
 The following paragraphs summarize the tie surface and fastener inspections 
 for each of the field sites. 
 
 Streator . The test section at Streator (Leeds) provided a unique opportunity 
 to evaluate the consequences of a derailment-like incident on concrete ties 
 while also negating several of the original plans for this site. Table 7 
 summarizes the top of tie and fastener conditions prior to the damage caused 
 by the dragging side frame. Although a variety of minor surface cracks and 
 spalls are noted, the track was generally in excellent condition. The note at 
 the bottom of the table indicates that the non-sloping ends of the CC244C ties 
 suffered considerably more chipping problems than the sloped ends of the 
 RT-7S. These chips and spalls appear to be primarily cosmetic and are not 
 likely to develop into a structural problem. 
 
 Table 8 is a partial description of the track condition a year after mainte- 
 nance for the derailment damage was completed. However, some general observa- 
 tions may be more enlightening than are the statistics. Santa Fe chose to 
 leave in all damaged ties which could still provide proper fastener support 
 and most damage noted in Table 8 reflects this. All damaged ties were moder- 
 ately to severely spalled on the east, field side of the north rail seat. As 
 W. Autrey summarized in his address to the AREA [21], the CS-5 fastener in 
 particular suffered the most damage due to the vulnerable position and rela- 
 tively small cross section of the cast-in-sti rrup shaped shoulder. Therefore, 
 proportionately more of the ties with CS-5 fasteners were replaced. 
 
 After a year of weathering, a few ties which sustained impacts from the side 
 frame showed additional degradation. Most of this appeared to be a freeze- 
 thaw type of spalling beneath the original spalled areas. One or two ties 
 were developing cracks that were initiated near the original spalls. 
 
 Several consequences of the maintenance performed were also noted. The track 
 crew ignored the differences in types of ties and fastener systems within the 
 test section as well as the variety available for replacement. There was no 
 attempt made to match tie types when replacements were made, which left the 
 site looking rather haphazard (much to the chagrin of the engineering depart- 
 ment!). However, of more importance to this study, the subtle variations of 
 fastener hardware within one generic type (Pandrol) were mixed between older 
 and newer ties, resulting in possible overstressed clips or reduced toe loads 
 
 108 
 
TABLE ' 
 
 7. SUMMARY OF THE TIE SURFACE AND FASTENER 
 INSPECTION AT STREATOR, 11/2/79 
 
 TOTAL NO. OF TIES INSPECTED = 400 
 
 
 
 South Rail 
 
 North Rail 
 
 onqitudinal Tie 
 jrface Cracks 
 
 40 
 
 51 
 
 urface Spalls 
 r Chips 
 
 Tie Rail Tie Rail Tie 
 End Seat Center Seat End 
 
 103 94 7 96 69 
 
 ads - Dislocated 
 
 
 
 2 
 
 Damaged 
 
 
 
 2 
 
 astener CI ips 
 
 Field Side 
 
 Gauge Side 
 
 Field Side 
 
 Gauge Side 
 
 Dislocated 
 
 
 
 
 
 
 
 1 
 
 Shoulders Worn 
 by Clips 
 
 8 
 
 6 
 
 10 
 
 6 
 
 nsulators 
 
 
 
 
 
 Cracked 
 
 1 
 
 7 
 
 1 
 
 1 
 
 Broken 
 
 
 
 13 
 
 
 
 11 
 
 Upside Down 
 
 
 
 
 
 1 
 
 
 
 Plastic Part 
 Broken 
 
 1 
 
 2 
 
 
 
 1 
 
 ote: 
 
 64 CC244C tie; 
 5 RT-7S ties h 
 10 RT-7S ties 
 93 CC244C tie 
 
 5 have damaged 
 ave damaged en 
 lave damaged e 
 5 have damaged 
 
 ends near nor 
 ds near north 
 nds near south 
 
 ends near sou 
 
 109 
 
 th rail . 
 ra i 1 . 
 
 rail . 
 th rail . 
 
 
TABLE 8. SUMMARY OF TIE SURFACE AND FASTENER 
 INSPECTION AT STREATOR, 4/22/81 
 
 TOTAL NO. OF T! r S INSPECTED = 210 
 
 
 
 North Rail 
 
 South Rail 
 
 Longitudinal Tie 
 Surface Cracks 
 
 1 
 
 
 
 Surface Spalls 
 or Chips 
 
 107 
 
 Pads - Dislocated 
 
 3 
 
 1 
 
 Fastener Clips 
 
 
 
 Broken 
 
 1 
 
 
 
 Dislocated 
 
 3 
 
 3 
 
 Shoulders Worn 
 by Clips 
 
 12 
 
 1 
 
 Insulators 
 
 
 
 Broken 
 
 32 
 
 4 
 
 Dislocated 
 
 13 
 
 4 
 
 Plastic Part 
 Broken 
 
 6 
 
 
 
 Note: 
 
 A good portion of the damage was due to a derailment, 
 
 110 
 
and premature insulator failures. This emphasizes the difficulty for even 
 "production" track such as that on the NEC to keep from inadvertently mixing 
 hardware that long-term changes in hardware design will ultimately allow. 
 
 Tie skewing appeared at Streator only as a result of tie replacements. As 
 discussed in Section 7.5, there is a tendency for a tie to migrate toward a 
 recently opened crib, such that the replacement of a tie will generally cause 
 the ties on either side to move toward it. Any differential movement will 
 result in skewing. The final site inspection showed up to six-inch tie move- 
 ments in the vicinity of several replaced ties. Note however, that some tie 
 movement will occur during the surfacing operation, and this was not measured 
 separately to distinguish it from in-service movement. 
 
 Richmond . Table 9 summarizes the top inspection performed at Richmond. Al- 
 though this track had accumulated 150 MGT, it was generally in good to excel- 
 lent condition. The CS-5 fasteners exhibited significantly more dislocated 
 pads in the 0-1 inch range than the Pandrol , while no pads were considered 
 damaged under the CS-5's compared to about seven percent under the Pandrol 
 clips. 
 
 The most noticeable problem on this curved site is the rail wear. Chessie has 
 had some difficulty with the performance of this rail resulting in more exten- 
 sive gauge face wear and some corrugation. The corrugation appeared strongest, 
 although barely perceptible, within the concrete tie section compared to the 
 adjacent wood-tie section of the same 3 degree curve. 
 
 A more thorough physical inspection of tie tops and fasteners was performed by 
 Chessie and reported to FRA.[22] 
 
 Aberdeen . The top inspections at Aberdeen summarized in Table 10 were per- 
 formed on the 300 ties arbitrarily selected as the "test zone" for the survey- 
 to-benchmark measurements. Within this zone were adjacent "buffer" rail seg- 
 ments attached with field welds into strings of continuous welded rail (CWR) 
 on each rail. Amtrak installs safety straps across these welds and the bolts 
 typically interfere with at least one of the fastener clips on the supporting 
 ties. Normal field practice was to install the clip backwards if the bolt 
 shank caused interference. These backwards clips have reduced toe loads and 
 are more likely to fall out. 
 
 Frequent maintenance precludes any conclusions about trends in fastener per- 
 formance which may otherwise be determined from these inspections. There is 
 currently insufficient knowledge to explain the random occurrence of a single 
 clip missing or broken or a dislocated insulator. Anomalies in the running 
 surface correlate well with a high probability of one or more missing clips 
 and recent walking inspections indicate an average of 0.8 percent missing 
 clips in that region of the NEC. 
 
 Roanoke . There was no formal top inspection performed at Roanoke. However, a 
 walking inspection of the site provided several observations. 
 
 Ill 
 
TABLE 9. SUMMARY OF TIE SURFACE AND FASTENER INSPECTIONS 
 AT RICHMOND, 12/18/79 
 
 TIE SURFACE CONDITION 
 
 RT-7S TIES 
 
 CC244 TIES 
 
 
 NUMBER INSPECTED 
 
 106 
 
 119 
 
 
 NO. WITH SURFACE SPALLS 
 
 20 
 
 3 
 
 
 (No other conditions recorded.) 
 
 
 
 
 CS-5 FASTENERS (On 106 Ti 
 
 es) HIGH (SOUTH) RAIL 
 
 LOW (NORTH) RAIL 
 
 
 PADS - DISLOCATED 
 
 - 1": 41 
 Over 1": 6 
 
 - 1": 43 
 Over 1": 3 
 
 
 DAMAGED 
 
 
 
 
 
 
 FASTENER CLIPS 
 
 FIELD SIDE 
 
 GAUGE SIDE 
 
 FIELD SIDE 
 
 GAUGE SIDE 
 
 
 BROKEN 
 
 
 
 
 
 
 
 
 
 
 DISLOCATED 
 
 9 
 
 22 
 
 7 
 
 9 
 
 
 INSULATORS 
 
 
 
 
 
 
 CRACKED 
 
 1 
 
 1 
 
 1 
 
 
 
 
 BROKEN 
 
 7 
 
 2 
 
 
 
 6 
 
 
 DISLOCATED 
 
 
 
 
 
 
 
 
 
 
 UPSIDE DOWN 
 
 
 
 
 
 
 
 
 
 
 PANDROL FASTENERS WITH INTERNAL INSULATION (On 18 Ties) 
 
 
 (No damage or dislocation of clips or pads.) 
 
 
 PANDROL FASTENERS WITH EXTERNAL INSULATORS (On 101 Ties) 
 
 
 
 HIGH (SOUTH) RAIL 
 
 LOW (NORTH) RAIL 
 
 
 PADS - DISLOCATED 
 
 - 1": 1 
 OVER 1": 3 
 
 0-1": 6 
 
 Over 1": 2 
 
 
 
 
 DAMAGED 
 
 5 
 
 9 
 
 
 FASTENER CLIPS 
 
 FIELD SIDE 
 
 GAUGE SIDE 
 
 FIELD SIDE 
 
 GAUGE SIDE 
 
 
 
 (No clip dislocation or damage.) 
 
 
 INSULATORS 
 
 
 
 
 
 i 
 
 CRACKED 
 
 1 
 
 4 
 
 6 
 
 
 
 
 BROKEN 
 
 1 
 
 7 
 
 3 
 
 1 
 
 
 DISLOCATED 
 
 
 
 
 
 
 
 1 
 
 
 UPSIDE DOWN 
 
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 1 
 
 
 
 1 
 
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 113 
 
The constant, downhill direction of traffic appears to cause pads to migrate 
 with traffic, at least relative to tie motion. Average pad dislocation was on 
 the order of 0.5 to 1.0 in. 
 
 The composite (two piece) Pandrol insulators tended to work downhill on the 
 north side and uphill on the south side of each rail (downhill is east). 
 Perhaps by coincidence, this orientation is consistent with the direction the 
 clip moves when being installed. Many of the metal "ears" on the composite 
 insulators had begun to move past their respective corners of the fastener 
 shoulders. 
 
 Tie condition on the top surface was about average. A few ties had chips and 
 spalls which were apparently caused by freeze-thaw action. Of the ties which 
 had no ballast covering the top, center area (mostly CC244C's) many had 
 readily visible flexural cracks. Some had two or three parallel cracks within 
 the center region. Roughly 10 percent of the ties had center cracks based on 
 the limited number of ties with exposed tops. 
 
 One CC244C tie was in an advanced stage of disintegration. The top layers of 
 concrete had spalled away exposing the upper pre-stress wires in the center 
 portion of the tie, although there was no loss of fastener integrity yet. 
 There was no obvious cause for this tie failure such as signs of impact from 
 dragging equipment or advanced center bending cracks. This tie was located 
 however, in the general vicinity of the "rough spot" discussed in Section 3.5. 
 
 114 
 
9.0 CORRELATIONS 
 
 The following section covers several areas where separate sources of informa- 
 tion are compared to show either newly identified relationships such as the 
 cracking of concrete ties versus the measured dynamic traffic loads, or pre- 
 dicted versus measured performance of the track structure such as vertical 
 track settlement. 
 
 9.1 Tie Loads vs. Tie Cracking 
 
 As discussed in Section 8, a selection of concrete ties were inspected at all 
 sites for cracks under the rail seats. For this correlation, however, the 
 initial inspection at Streator and Richmond are excluded because the visual 
 enhancement techniques were not used and would therefore bias the results. 
 Additional data are incl uded from another program [5] which was performed about 
 one-half mile from the Aberdeen site on the same track. Thesedata provide 
 important information about the performance of newly installed ties with low 
 accumulated tonnage. 
 
 The percentage of cracked rail seats versus accumulated tonnage are tabulated 
 in Table 11 and plotted in Figure 55. Also tabulated and plotted are the 
 percentages of rail seat bending moments above the cracking strength of the 
 concrete ties, which were obtained in the dynamic measurements. 
 
 An empirical equation can be established to correlate the percentage of 
 cracked rail seat regions and the percentage of rail seat bending moments 
 above the cracking strength of the ties. Let 
 
 C = percentage of cracked rail seats; 
 
 N = total number of axles passing over ties; 
 
 B = percentage of rail seat bending moments above the cracking 
 strength of concrete. 
 
 The increase in the percentage of cracked rail seats should be proportional to 
 the increase in the percentage of the number of axles producing rail seat 
 [ bending moments above the cracking strength of concrete. Hence: 
 
 dCa d(NB)/NB 
 
 Furthermore, the increase in the percentage of cracked rail seats should be 
 proportional to the percentage of uncracked rail seats i.e., 
 
 dCa (100-C) 
 
 115 
 
tn 
 
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 FIGURE 55. RESULTS OF FINAL INSPECTIONS 
 FOR CONCRETE TIE CRACKS 
 
 116 
 
Therefore, dC = K ^ d(NB) ( 10 o-C)/NB 
 
 /dC/(100-C) = K ] /d(NB)/NB 
 -ln(lOO-C) = K ] ln(NB) + K 2 (Eq * 9 '^ 
 
 where Ki and K2 are constants. A log-log plot of (100-C) versus (NB) at 
 Aberdeen is shown in Figure 56. 
 
 In computing the percentage of cracked rail seat regions, we should be able to 
 use any arbitrary crack length to define a crack as long as the same criterion 
 is used consistently, i.e., 
 
 -In (100-C ) = K. 1n(NB) + K (Eq. 9.2) 
 
 1 n ^n 
 
 where the subscript n denotes crack length criterion. The criterion used in 
 Figure 56 is about one inch, the lower limit of detection. Plots with other 
 criteria such as 4 or 6 inches should be straight lines parallel to the line 
 in Figure 56. However, there are insufficient data to validate this. 
 
 The computation of the total number of axles (N) is based on the 
 tonnage data (T) and the mean static vertical wheel load (V) from load data 
 (Table 11): 
 
 N - T x 10 6 /V x 2 kips/ton 
 
 IN (axles) ' (MGT) A /v (kips/wheel ) x 2 wheels/axle 
 
 In two inspections at Aberdeen (MP 68.8), only about 50% of the 30 concrete 
 ties were inspected. As shown in Table 11, the percentages of cracked rail 
 seat regions are inconsistent with those obtained in the other two more 
 complete inspections. Consequently, the two incomplete inspections are not 
 included in Figure 56. 
 
 The test data (Table 11) show that at Roanoke the rail seat regions were 100% 
 cracked when (NB) was 6300. According to figure 56, 99% of the rail seat 
 regions at Aberdeen will be cracked when (NB) is 3000, which corresponds to 
 280 MGT. Table 11 also shows that at Streator and Richmond an extremely 
 small percentage of large bending moments were measured. Although values 
 were identified for inclusion in the table, there is limited statistical 
 confidence in these data. Much larger populations of axle loads would be 
 required to accurately characterize these low probability bending moments. 
 
 Conceptually, given the kind of load and crack data acquired at Aberdeen, the 
 trends indicate the ability to estimate the tonnage at which all ties will be 
 cracked. With additional data on the incidence of long cracks and ultimate 
 strength, it may also be possible to predict the useful life of the ties, 
 assuming no change in the population of impact loads seen by the ties. 
 
 117 
 
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 118 
 
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Assume that a series of dynamic measurements at several sites *was made for a 
 sufficient time to produce the family of tie bending moments depicted in 
 Figure 57a. Correlation of these load populations with crack lengths might 
 produce a distribution of equal probability curves such as shown in Figure 
 57b. Or looking at it another way, population "e" could produce the family of 
 curves in Figure 57b at successive accumulations of tonnage. In fact, the 
 horizontal line along the minimum level of detection is the threshold from 
 which the actual data plotted in Figure 56 were referenced. 
 
 9.2 Predicted vs. Measured Track Vertical 
 Load-Deflection Response 
 
 Using procedures discussed in detail in Volume II, track vertical load- 
 deflection response was predicted for Streator (Leeds) concrete and wood tie 
 sites, Richmond, Aberdeen, and FAST, Section 22. The approach used was to 
 combine the results of laboratory tests and physical states measured in the 
 field to provide appropriate parametric values for running the computer model, 
 GEOTRACK. Figure 58 summarizes the dimensions and material properties used to 
 make the prediction. The specific load-deflection increment used for the 
 prediction was the 6-to-30-kip interval previously shown in Table 3. 
 
 Figure 59 shows the results of the comparison of measured and predicted track 
 deflection for the 6-to-30-kip load increment. The corresponding calculated 
 values for track moduli, both predicted and measured, are shown in Figure 60. 
 The success of the prediction is excellent for Aberdeen and Richmond and 
 reasonable for Streator wood and concrete sections. However, both of the 
 Streator site predictions underestimate the deflections, resulting in corres- 
 ponding overestimation of the moduli. This is, however, a remarkable achieve- 
 ment considering the complexities of modeling soils behavior. 
 
 The measured and predicted values of track modulus are dependent on several 
 factors, one of which is the support condition of the tie. These support 
 conditions are a function of track settlement and maintenance effects. The 
 support conditions would affect concrete and wood ties in a different fashion. 
 
 The GEOTRACK model used uniform properties throughout each layer, including 
 the support and contact under all ties. The field plate load tests [2] showed 
 that the ballast stiffness was not uniform under the ties, but was greater 
 near the rail seat areas than under the tie centers. Furthermore, after the 
 maintenance, the ballast physical state was more uniform than before mainte- 
 nance. However, even uniform physical state or modulus does not result in 
 uniform support conditions along the tie. 
 
 After the maintenance operation in which a high raise was given to the track, 
 the ballast physical properties would be more uniform. However, the tamping 
 and raise during the maintenance is done only near the rail seats, which could 
 cause a gap near the center of the ties. This causes the actual load bearing 
 areas to be near the rail seats because of the lack of contact near the centers 
 This increased load bearing near the rail seats would cause higher rail de- 
 flections directly under the applied load than would result from a continuous- 
 ly supported condition. The GEOTRACK model uses continuous contact between 
 
 120 
 
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 Minimum Detectable 
 
 
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 Equal Probability Curves for 
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 (b) Percent Cracked Ties 
 
 FIGURE 57. CONCEPT FOR ESTIMATION OF TONNAGE 
 AT WHICH ALL TIES WILL BE CRACKED 
 
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STREATOH Wood 
 
 0.02 0.04 0.06 0.08 
 Predicted Differential Rail Deflection (in.) 
 
 0.10 
 
 FIGURE 59. MEASURED VERSUS PREDICTED DIFFERENTIAL 
 RAIL DEFLECTIONS FOR 6- TO 30-KIP LOAD RANGE 
 
 123 
 
the tie directly under the applied vertical load and the ballast surface, 
 leading to a lower rail deflection and higher track modulus than measured in 
 the field after maintenance. 
 
 As traffic accumulates over the track, the ballast beneath the rail seats is 
 recompacted and becomes stiffer, but the tie contact becomes continuous (at 
 least above some initial load level). The more uniform support across the tie 
 leads to a lower rail deflection and hence a higher track modulus. In the 
 case of a small maintenance raise, the initial ballast physical states may be 
 less uniform under the tie than after a large raise; however, the contact 
 along the tie may be more continuous. This would result in a higher track 
 modulus after a small raise than after a large raise, or at least not much 
 change in the pre- and post-maintenance values. 
 
 In the case of centerbound track, a greater portion of the rail loads would be 
 carried by the central portion of the ties. In this situation, as the applied 
 loads increase, the wood ties would have a greater bending deflection prior to 
 achieving contact with the ballast surface beneath the rails than the concrete 
 ties, because the bending stiffness of concrete ties is about 4.5 to 6 times 
 greater than that of wood ties. 
 
 The interactions between the variable ballast physical states, tie support 
 conditions, and structural factors such as tie stiffness and rail size make 
 generalizations about track modulus uncertain. This is particularly true 
 since the degree and type of maintenance disturbance and traffic history of a 
 site can change the ballast physical states in varying amounts. The scatter 
 of the field measurements were such that there were no clear trends distin- 
 guishing the pre-maintenance track moduli values from the post-maintenance 
 values. The predictions of track modulus using the GEOTRACK program are some- 
 what limited by the uniform layer property and full contact representations, 
 and the inability to represent the maintenance factors for the field sites. 
 For these reasons, variations between the measured and predicted track moduli 
 values for the sites can be expected because of the variation in ballast proper- 
 ties and support conditions which were affected by the maintenance operations. 
 
 The possible effects of centerbinding and uniformity of support conditions 
 beneath the tie bottom are not fully understood. However, these effects may 
 not be a significant contributing factor to the track modulus values. Differ- 
 ences between the bending stiffnesses of the wood and concrete ties would also 
 not result in large differences in track moduli. Since only 10% to 20% of the 
 total track deformation occurs because of ballast compression (not include .j the 
 above mentioned tie/ballast interface effects), the subgrade deflections 
 appear to be much more important. Parametric studies indicate the subgrade 
 contribution to track modulus should be about the same for wood and concrete 
 ties. The FAST dynamic measurenents of resilient subgrade deflection also 
 showed no significant difference between the deflections in wood and concrete 
 sections. 
 
 124 
 
9.3 Correlation of Track Modulus With Ballast Depth 
 
 The track modulus values shown previously in Figure 60 were also evaluated to 
 determine causes for the differences in absolute magnitude between the four 
 sites. Part of the differences in absolute magnitude of the average field 
 track modulus measurements can be explained in terms of the differences in the 
 track substructures. The parametric study using the GEOTRACK model indicated 
 that track modulus increased as ballast depth increased. The ballast profiles 
 and the simplified layer characterizations used in the GEOTRACK analyses shown 
 in Figure 58 show that the Streator wood section had only about 9 in. of 
 ballast beneath the tie, whereas the Streator concrete section contained about 
 14 in. The Aberdeen site had 20 in. of ballast, and the ballast depth at 
 Richmond was estimated to be 28 in. below the tie. This trend of increasing 
 track modulus with increasing ballast depth for the field sites is clearly 
 confirmed by the field measurements in Figure 61. 
 
 The track modulus is also influenced by the subgrade characteristics. As men- 
 tioned earlier, the GEOTRACK model indicates that the compression of the bal- 
 last layer accounts for about 10 to 20% of the total vertical elastic deflec- 
 tion of the track structure. The remainder of the total deflection is due to 
 the compression of the subgrade materials. Furthermore, 25 to 40% of the sub- 
 grade elastic deformation indicated by GEOTRACK occurs below a depth of about 
 10 ft., even though the stresses below this depth are low [23], This is in 
 contrast to the inelastic (permanent) deformation which occurs mostly in the 
 ballast and is responsible for track settlement. 
 
 9.4 Predicted vs. Measured Track Settlement 
 
 An important goal established at the beginning of this program was to attempt 
 a prediction of vertical track settlement and compare that prediction to 
 actual settlement at each of four revenue sites (excepting Roanoke) and at 
 FAST, Section 22. The procedures for these predictions are discussed in 
 detail in Volume II. 
 
 The goal was to follow the settlement process from the initial condition of 
 freshly surfaced track to an advanced, traffic-consolidated state. As 
 discussed in Volume II, permanent deformations or settlement resulting from 
 maintenance (surfacing) are almost entirely restricted to the ballast layer. 
 (This is assuming an old, established roadbed.) 
 
 The stress states were estimated using GEOTRACK. The layer profiles and divi- 
 sions and subgrade moduli for the revenue sites were the same as used for the 
 track modulus predictions shown previously in Figure 58. The layer divisions 
 used for the FAST predictions consisted of two 7.5 in. ballast layers under- 
 lain by the silty sand subgrade material. 
 
 The resilient strain-shear stress ballast formulation, as described in Volume 
 II, was used to characterize the ballast at all of the sites, and multiple-axle 
 loading configurations were used to accommodate the synergistic influence of 
 adjacent wheel loads. Because it was not practical to directly utilize the 
 detailed descriptions of dynamic wheel loads discussed in Section 5 and shown 
 
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 FIGURE 61 . BALLAST DEPTH VERSUS TRACK MODULUS FOR REVENUE FIELD SITES 
 
 127 
 
in Figure 19, representative loads at the 50, 10, 1, and 0.1 percent load 
 exceeded levels were selected to characterize the traffic at each site. These 
 were shown previously in Table 2. The number of associated load cyles at each 
 load level were determined for each MGT of traffic by estimating the average 
 number of axles per MGT. Ballast and subgrade dynamic data have previously 
 shown [24] that the effective load cycle for the ballast includes both axles 
 on one truck. At greater depths, the stress distributions overlap sufficient- 
 ly that all four axles at adjacent ends of two cars represent one load cycle. 
 This effect was included in the prediction process. 
 
 Variations in the assumed stress paths along with the consideration of shear 
 stress reversals discussed briefly in Section 7 and thoroughly in Volume II 
 provided four separate stress paths for consideration in the prediction 
 process. Once the stress paths had been established for the various com- 
 binations of dynamic wheel loadings, the next operation was to determine the 
 strains that would be expected to develop due to repeated applications of the 
 prescribed stresses. This was done using the laboratory results from the 
 various test series described in Section 7 and Volume II. 
 
 The permanent deformations that accumulate in ballast due to repeated applica- 
 tion of vertical stresses were shown to be related, in general, to the perma- 
 nent strain or deformation that occurred in the first cycle of load. Thus, 
 the first step in predicting the track deformations was to determine the 
 strains that are expected to develop from the first load cycle. Since the 
 stress paths for the ballast layers involve shear stress reversals, the 
 accurate determination of these first cycle strains is difficult. 
 
 For each of the field site predictions, the first cycle strains were estimated 
 from the curves shown in Figure 62 for four stress ratios. These are: 
 
 Strain Curve 
 One-Way Uncompacted 
 One-Way Uncompacted 
 Uncompacted Stress Reversal 
 Uncompacted Stress Reversal 
 
 The rates of strain accumulation with repeated load cycles were determined 
 with further laboratory tests along with pertinent ballast constants as 
 discussed in Volume II. These soil constants along with the first cycle 
 strains were used in the equation 
 
 e N = ej (1 + Clog N) (Eq. 9.3) 
 
 where £ m is the permanent axial strain at the N tn cycle 
 
 £j is the permanent axial strain developed due to the first 
 
 28 
 
 Ratio 
 
 St 
 
 ress Path 
 
 Pmax/qf 
 
 
 CB 
 
 qmax/Qf 
 
 
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 Aq/qf 
 
 
 CB 
 
 Aq/qf 
 
 
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i.4r 
 
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 a 
 
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 0.4 
 
 0.2 
 
 Uncompacted 
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 One-Way Loading 
 Uncompacted 
 
 Compacted 
 
 Compacted 
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 0.4 0.6 
 Stress Ratio, 
 
 1.4 
 
 q max /q f ° r Aq/q f 
 
 FIGURE 62 . NORMALIZED FIRST CYCLE STRAINS AS A FUNCTION OF STRESS RATIOS 
 
 129 
 
cycle of load, N = 1 which is also the intercept of the 
 Ejyj vs. log N relationship 
 
 C is the soil constant, and 
 
 N is the number of applied load cycles, to determine the permanent 
 strain after N cycles of a constant cyclic load. 
 
 Because wheel loads are not constant, a valid superposition of the representa- 
 tive loads was necessary. Therefore, a series of staged tri axial tests were 
 performed on ballast materials to justify the use of a cumulative damage rule 
 (see Volume II). Briefly, this rule states that the sequence of loading is 
 not important so long as the total number of cycles at each load level remains 
 fixed. 
 
 The resulting calculated strains in each layer must then be multiplied by the 
 corresponding layer thickness to get the total settlement contributed by that 
 layer. 
 
 As discussed earlier, for settlement predictions related to maintenance, only 
 the disturbed ballast layers were included. The depths influenced by the 
 revenue site maintenance operations were estimated to be *rom 6 to 8 inches 
 below the ties. The representative points for these ballast depths were thus 
 taken as the midpoint depths for these disturbed ballast zones. 
 
 Since the survey data from FAST indicated only slight differences between the 
 wood and concrete track settlement, only predictions for the concrete tie 
 section of FAST, Section 22, were made. However, these were subdivided into 
 two sets. The first set was for the to 93 MGT (after rebuild) period and 
 considered the entire 15-in. ballast depth. The second was for FAST, Section 
 22, after the maintenance operations at 93 MGT. For this set, a 7.5-in.-deep 
 disturbed ballast layer was assumed. 
 
 Streator Settlement 
 
 The predicted track settlements for the Streator wood tie section are shown in 
 Figure 63. The predictions made using stress path DE gave the largest defor- 
 mation and were close to the uncorrected survey measurements. The settlement 
 rates appeared to level off for the second field measurement interval and was 
 about parallel to the predictions. However, the predictions all underesti- 
 mated the track vertical settlement, particularly when any adjustments were 
 made to correct for the intial settlement. 
 
 The measurements and predictions for the Streator concrete tie track section 
 are shown in Figure 64. The field survey measurements showed a very large 
 change in track settlement from the 10 to 24 MGT measurements, which was much 
 larger than the initial change from the to 10 MGT readings. This occurred 
 over the winter months and may have been associated with frozen ballast. The 
 two final survey measurements appear to indicate that the track settlement 
 rate was leveling off, as was expected and predicted, but additional data are 
 required to substantiate this conclusion. The predicted values are all much 
 
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lower than the measured values after 20 MGT and show a slower rate of increase 
 with MGT. 
 
 Richmond Settlement 
 
 Figure 65 shows the measured survey track settlement and the predicted track 
 settlement for the Richmond site. The field measurements indicated a contin- 
 uous settlement of the track, with no indication that the deformations were 
 leveling off with increased MGT. The predictions always showed a lower set- 
 tlement rate after about 10 MGT traffic. All predictions for the Richmond 
 site overestimated both the initial settlement and the cumulative settlement. 
 
 Aberdeen Settlement 
 
 The results from the strain coil measurements and corrected survey measure- 
 ments, along with the predictions of track settlement for the Aberdeen site, 
 are shown in Figure 66. As previously indicated, the track settlement at 
 Aberdeen apparently was due primarily to the upper ballast permanent deforma- 
 tions. The linear format of Figure 66 shows that following a high initial 
 deformation rate in the first 3 MGT, the ballast deformations continued to 
 increase at a lower constant rate, showing no tendency to level off with 
 increased traffic accumulation. Again, further survey data or strain coil 
 measurements would have been useful to help interpret longer term trends past 
 the 30 MGT level. Although the measured values lie within the range of 
 predicted values, the shapes of the predicted curves after about 5 MGT were 
 quite different from the observed settlements. These data are discussed 
 further in a subsequent section. 
 
 FAST Settlement 
 
 Two sets of predictions were made for FAST, Section 22. Both sets were done 
 for the concrete tie section track parameters. The first set of predictions 
 considered the to 93 MGT period directly after the 1979 rebuild. For these 
 predictions, the full 15-in. depth of newly placed ballast was considered. 
 The second set of predictions assumed that only the top half of the ballast 
 was disturbed because of the maintenance operation that took place after 93 
 MGT traffic. 
 
 The measured and predicted vertical track settlement at FAST are shown in 
 Figure 67. The to 93 MGT track settlements and ballast deformations both 
 showed an irregular increase from about the 30 to 50 MGT interval, followed by 
 a reduced settlement rate up to the time of the surfacing operations. The 
 shapes of both measured and predicted ballast deformations were similar. How- 
 ever, the predictions for to 93 MGT were all greater than the measured bal- 
 last deformations obtained from the strain coils. This could be due to the 
 compaction sequences used during the rebuild operation, which would have 
 resulted in lower ballast strain under subsequent traffic loading. 
 
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The difference between the to 93 MGT survey measurements and the ballast 
 deformations from the strain coil readings appeared consistent with the 
 measured subgrade deformations, even though the subgrade deformation data are 
 questioned. This could have resulted from compensating errors. 
 
 Instrumentation measurements of the ballast and subgrade cumulative deforma- 
 tions were not available after the 93 MGT maintenance at FAST. However, the 
 survey measurements and predictions after the surfacing are shown in Figure 
 67. Both the shapes of the initial and longer term predicted settlement were 
 similar to the survey measurements. The magnitudes were also in general 
 agreement for the CB stress paths. 
 
 The measured track settlement from to 93 MGT after rebuild for the stain 
 coils and from the surveys after the maintenance showed a similar amount of 
 initial track settlement. However, these data, as well as the predictions, 
 showed larger deformations from traffic after rebuild than were observed after 
 subsequent maintenance. This was primarily due to the differences in the 
 initial ballast physical state in the lower portion of the ballast layers, 
 even though there was some initial compaction of the ballast during the 
 rebuild. This appears to confirm the previous assumptions that only the upper 
 6 to 8 in. of the ballast layer should be considered as disturbed by mainte- 
 nance. Overall, the agreements between measured and predicted track 
 settlements were good. 
 
 Discussion of Settlement Predictions 
 
 There are a variety of factors which influence the accuracy of the predic- 
 tions. Generally, these factors can be divided into two broad areas: those 
 associated with the complexities of the loading environment, and those 
 associated with the necessary abstraction of measuring soil performance in 
 practical, laboratory tests. 
 
 The best example of the first area is the comparison of the load environment 
 at FAST with those at the revenue sites. The FAST loads, as discussed in 
 Section 5, are very consistent. There are no extraordinarily large loads as 
 seen at most revenue sites. There are only minimal track vibrations because 
 these vibrations are usually induced by the same wheel tread irregularities 
 causing the large loads. As a result (perhaps by coincidence) the FAST 
 settlement predictions are very qood. They not only predict about the right 
 settlements, but also the shape of the settlement curves are wery close. 
 Other factors may influence the loading environment or cause ballast degrad- 
 ation such as the seasonal effects (or other unique influences) that resulted 
 in non-uniform settlement at Streator during the winter-early spring interval 
 between surveys. Pursuing these anomalous effects was beyond the scope of 
 this project 
 
 The second area of measuring soil performance was based on the invariant 
 transformations of the three-dimensional stress tensors, elements of which are 
 assumed and/or measured in the field, into axisymmetric, constant-confining- 
 pressure triaxial test conditions. The roadbed stresses were then approxi- 
 mated by the assumed equivalent stress paths labeled CB and DE in the settle- 
 ment prediction plots since paths similar to the one defined by the actual I 
 
 137 
 
moving load under field conditions could not be reproduced using the present 
 laboratory equipment. 
 
 The predictions showed varying amounts of agreement with the measurements that 
 were not clearly attributable to any of the particular stress paths. The main 
 difference between the results obtained using the two stress paths, CB or DE, 
 was in the first cycle strains associated with these stress paths. The choice 
 of ballast constant, C, from either the one-way repeated loading tests or from 
 the box test results was of minor consequence compared to the value of first 
 cycle strain used for the predictions. 
 
 In addition to the ballast deformations that resulted from cyclic loadings 
 and/or vibration, there are numerous factors that have not been accounted for 
 in the prediction methodology. These include ballast recompaction , ballast 
 degradation, and subgrade effects, as well as the previously mentioned sea- 
 sonal effects. The consequences of all these factors are discussed thoroughly 
 in Volume II. 
 
 Considering the complex nature of the problem and the material behavior in- 
 volved, and considering the large field variability, the magnitude of the 
 predicted settlements for the revenue sites was in reasonable agreement with 
 that of the field measurements. Certainly the agreement was within the range 
 normally experienced in geotechnical predictions. 
 
 Logrithmic Settlement Rates 
 
 Since most laboratory soils testing tends to show a logrithmic permanent 
 strain rate for constant amplitude cyclic loads and since that logrithmic 
 trend is part of the basis for the prediction process (see Equation 9.3), the 
 field settlement data were evaluated to determine whether comparable trends 
 were apparent. 
 
 Survey-to-benchmark data from FAST, Section 22, were analyzed to derive the 
 average settlement for each interval of accumulated traffic. Both concrete 
 and wood tie sections were included. The planned measurement intervals were 
 in themselves approximately logrithmic to the accumulated tonnage (1, 2.5, 5, 
 10, 25, 50 MGT) , which allowed for an accurate estimate of this settlement 
 trend if it did exist. 
 
 Figure 68 shows the mean settlement values calculated for data collected after 
 the surfacing at 93 MGT, and the corresponding logrithmic curves fitted to 
 that data. As indicated by the term r2, the coefficient of determination, 
 the logrithmic approximation is nearly perfect for the concrete section while 
 the wood tie data suffer from a "jump" or offset in the trend line in Figure 
 68, which if not adjusted for, reduces r2 to 0.80. Curve fitting the four 
 points from 2.4 to 24.5 MGT results in r2 = .996, again nearly a perfect 
 fit. One explanation for the wood tie track "jumping" up by 0.18 in. is that 
 this interval occurred during January and February of 1981 when several days 
 of below freezing temperatures occurred. This may have induced a slight frost 
 heave condition. However, no comparable effect was seen in the adjacent con- 
 crete section. A detailed examination of the elevation plots for the wood tie 
 
 138 
 
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section indicate most of the "heave" occurred toward the end of the test zone 
 away from the concrete section. Cross-checking of maintenance data did not 
 reveal any spot maintenance in that area. 
 
 With the availability of the strain coil data from Aberdeen, a similar attempt 
 was made to identify a logrithmic settlement rate. These data were also taken 
 frequently at the early part of the monitoring period with progressively 
 longer intervals after the first six months. The surprising results of plot- 
 ting these data on a logrithmic scale are shown in Figure 69. For some reason 
 there is a very distinct break in the settlement rate at about 10 MGT. This 
 happened to occur, like Streator, in the late fall/early winter period, so a 
 seasonal effect may be present. 
 
 The log curve fit happens to be nearly perfect for each of the two curve 
 segments and, as indicated, most data points fall directly on the curves. 
 Currently, the only explanation for this shift in rates is the increase in 
 impact loading resulting from the track structure hardening from extended 
 consolidation from traffic with a possible "trigger" caused by either frozen 
 ballast or cold temperature set on the tie pads. Neither effect can be 
 substantiated at this time. 
 
 9.5 Track Roughness vs. Absolute Settlement 
 
 Differential settlement, or roughness, is one of the principle criteria which 
 determines the need for track maintenance. In general , one would expect 
 differential settlement to increase with some proportionality to the increase 
 in absolute settlement which results from cumulative traffic tonnage. As 
 discussed in Section 6, however, the survey data did not show any qualitative 
 indication of this relationship. In an effort to establish the relationship 
 within the limits of the available data, a variety of analyses were performed. 
 
 As discussed in Section 6, the surveys were performed at 10-ft intervals over 
 600 ft of track, thus providing up to 122 elevation readings (both rails) per 
 survey. Unfortunately, in the context of roughness, 10-ft intervals do not 
 reveal the same types of roughness that would normally be identified by track 
 geometry cars. Nevertheless, to approximate this effective roughness, the 
 survey data were "string-1 ined" by a computer program with lengths of string- 
 lines between 20 and 60 feet long. The string-lined data were then evaluated 
 for roughness by computing the standard deviation of all readings. Because of 
 the commonly used 62-ft chord, the roughly comparable 60-ft chord data were 
 then evaluated for a trend of increased roughness with settlement. 
 
 FAST Section-22 data were used because of the number of surveys performed and 
 because of the opportunity to compare wood and concrete tie construction under 
 ideal conditions. Figure 70 is a plot of the roughness values for both test 
 sections against MGT. Because settlement was shown to be related to Log MGT 
 in the previous discussion, this should show any comparable trends for rough- 
 ness. Both the wood tie and the concrete tie results are inconclusive. For 
 the concrete tie data, if the "wild point" at 53 MGT is included, then there 
 is a slight dependency on settlement, while excluding the 53 MGT value would 
 leave a constant value for roughness. A similar effect can be seen for the 
 wood tie data, if the 100 MGT point is considered. 
 
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 142 
 
Realizing that roughness is often an accumulation of discrete anomalies, it 
 seemed appropriate to take the process one step further by developing histo- 
 grams of roughness. This was accomplished by sorting the individual 60-ft. 
 
 mid-chord offset values into bins of 0.05 in. width. Subsequently, the 95 
 percentiles for each histogram were plotted and are shown in Figure 71. 
 
 Differences between wood and concrete tie sections may be attributed primarily 
 to the unloaded rails in the wood tie section smoothing out some of the rough- 
 ness because of the freeplay under the cut spikes. 
 
 143 
 

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 144 
 
10.0 CONCLUSIONS 
 
 10.1 Wheel Loads vs. Tie Cracking 
 
 • Flexural cracks at the rail seats of concrete ties were found at 
 all revenue service test sites. The cracks are produced by impact 
 loading from wheel tread defects on a small percentage (less than 
 
 1 in 1000) of freight and passenger car wheels. These cracks are 
 of the same type that have led to failure of earlier ties 
 designed to lower bending strength requirements. Without detec- 
 tion and removal of the worst wheel tread conditions or otherwise 
 attenuating the impact loads, the cracks could lead to major 
 reductions in the useful service lives of the ties. 
 
 • Rail anomalies such as battered welds, engine burns, and bad joints 
 can produce impact loads comparable to those produced by wheel 
 defects. Where ties are installed with rigid pads, these rail 
 anomalies can result in structural failure of the ties. 
 
 • No flexural cracks were found on concrete ties at FAST. Although 
 FAST has the highest mean axle loads of any site examined, crack- 
 producing impact loads do not occur at FAST because the wheel 
 treads and the rail surfaces are maintained in excellent 
 condition. 
 
 10.2 Ballast/Subgrade Support and Track Settlement/Roughness 
 
 • Track surface maintenance (raising and tamping) loosens the 
 ballast structure, reducing the uniformity of support offered by 
 the ballast. 
 
 • Average track modulus does not change appreciably after surfacing 
 but the variability in modulus increases considerably. 
 
 • Residual, horizontal compressive stresses build up early in the 
 ballast even in the crib regions. These residual stresses affect 
 the performance of ballast materials and the manner of simulating 
 loading in laboratory tests. Variations in the residual stresses 
 may be associated with tie migration and skewing. The improved 
 performance of track with wide shoulders (determined at FAST) may 
 be related to the residual stresses. 
 
 • The results of the ballast physical state tests (plate bearing, 
 lateral tie push resistance) varied widely before maintenance but 
 were very uniform, at much lower levels, after maintenance. This 
 indicates that these mechanical properties are principally depen- 
 dent on the state of ballast compaction, rather than on ballast 
 material properties. 
 
 145 
 
• No correlations were determined between the long-term maintenance 
 of track geometry and any of the following potential indicators: 
 ballast geotechnical properties, ballast fouling, and ballast 
 physical state tests. 
 
 No direct correlation was found between settlement and roughness 
 for periods beginning with newly surfaced track and extending up 
 to 64 MGT. However, all sections examined contained uniform 
 support without major track anomalies. The lack of correlation 
 supports the assumption that relative roughness is driven largely 
 by discrete track structure anomalies, such as rail defects or 
 changes in support stiffness. 
 
 • Permanent settlement of the track is proportional to the log of 
 traffic loading cycles. This trend has been well known in labora- 
 tory testing but not previously verified in track because of poor- 
 ly defined traffic loads. Uniformity of loads at FAST allowed this 
 logrithmic trend to be verified. 
 
 10.3 Wood vs. Concrete Tie Track 
 
 • There were no significant differences in the development of 
 settlement or roughness for wood and concrete tie track built on 
 identical ballast beds and subgrades at FAST, although differences 
 were seen at Streator because of the varied length and condition 
 of the wood ties and the deteriorated condition of the ballast 
 compared with the more recently constructed concrete tie test 
 section. 
 
 • The major performance improvement offered by concrete tie track is 
 its ability to hold gauge more consistently. 
 
 146 
 
REFERENCES 
 
 [1] Dean, F.E., Harrison, H.D., Prause, R.H., Selig, E.T., McMahon, D., 
 Measurement and Correlation Analysis Plan for Concrete Tie and 
 Fastener Performance Evaluation , U.S. Department of Transportation, 
 Federal Railroad Administration, 1979, Report No. FRA/ORD-79-51 , 
 (PB 80-183-882). 
 
 [2] Stewart, H.E., and Selig, E.T., Correlation of Concrete Tie Track 
 Performance in Revenue Service and at the- Facility for Accelerated 
 Service Testing , Volume II, Predictions and Evaluations of Track 
 Settlement , U.S. Department of Transportation, Federal Railroad 
 Administration, 1984, Report No. DOT/FRA/84/02.2. 
 
 [3] Dean, F.E., Harrison, H.D., Stewart, H.E., McMahon, D., Correlation 
 of Concrete Tie Track Performance in Revenue Service and at the 
 Facility for Accelerated Service Testing , Volume III, Field 
 Measurements and Data Analysis , Progress Report, July 1982. 
 
 [4] Prause, R.H., Kennedy, J.C., Arnlund, R.C., An Evaluation of 
 
 Performance Requirements for Cross Ties and Fasteners , U.S. Department 
 of Transportation, Federal Railroad Administration, 1978, Report No. 
 FRA/ORD-78/37. 
 
 [5] Dean, F.E., Harrison, H.D., Prause, R.H., Tuten, J.M., Investigation 
 of the Effects of Tie Pad Stiffness of the Impact Loading of Concrete 
 Ties in the Northeast Corridor , U.S. Department of Transportation, 
 Federal Railroad Administration, 1982, Report No. FRA/ORD-82/18. 
 
 [6] Ahlbeck, D.R., "An Investigation of Impact Loads Due to Wheel Flats 
 
 and Rail Joints," Paper No. 80-WA/RT-l , American Society of Mechanical 
 Engineers Winter Annual Meeting , November 1980. 
 
 [7] Dean, F.E., Investigation of Rail Fastener Performance Requirements , 
 U.S. Department of Transportation, Federal Railroad Administration, 
 1982, Report No. FRA/ORD-82/10. 
 
 [8] Prause, R.H., Harrison, H.D., Kennedy, J.C., Arnlund, R.C., An 
 Analytical and Experimental Evaluation of Concrete Crosstie and 
 Fastener Loads , U.S. Department of Transportation, Federal Railroad 
 Administration, 1977, Report No. FRA/0RD-77/71 . 
 
 [9] Dean, F.E., and Harrison, H.D., Laboratory Study to Determine the 
 Effects of Tie Pad Stiffness on the Attenuation of Impact Strain in 
 Concrete Railway Ties , U.S. Department of Transportation, Federal 
 Railroad Administration, 1982, Report No. FRA/ORD-82/19. 
 
 [10] Gaskin, P.N., and Raymond, G.P., "Contributions to Selection of 
 
 Railroad Ballast," Journal of the Transportation Engineering Division , 
 American Society of Civil Engineers , Vol. 102, No. TE5, May 1976. 
 
 [11] Yoo, T.S., Chen, H.M., and Selig, E.T., "Railroad Ballast Density 
 Measurement," Geotechnical Testing Journal , American Society for 
 Testing and Materials, Vol. 1, No. 1, pp 41-54, March 1978. 
 
 147 
 
[12] Selig, E.T., Yoo, T.S., and Panuccio, CM., Mechanics of Ballast 
 
 Compaction, Vol. I, Field Methods for Ballast Physical State 
 
 Measurements, U.S. Department of Transportation, Federal Railroad 
 Administration, 1982, Report No. FRA/ORD-81/16.1 . 
 
 [13] Panuccio, CM., Wayne, R.C, and Selig, E.T., "Investigation of a 
 
 Plate Index Test for Railroad Ballast," Geotechnical Testing Journal , 
 ASTM, Vol. 1, No. 4, pp 213-222, December 1978. 
 
 [14] Panuccio, CM., Dorwatt, B.D., and Selig, E.T., "Apparatus and 
 Procedures for Railroad Ballast Plate Index Test," Geotechnical 
 Testing Journal , ASTM, Vol. 1, No. 4, pp 223-227, December 1978. 
 
 [15] Selig, E.T., Yoo, T.S., and Panuccio, C.W., Mechanics of Ballast 
 
 Compaction, Vol. 5, Summary Report, U. S. DeDartment of TransDortation, 
 Federal Railroad Administration, 1984, Report No. FRA/ORD-81/16.5. 
 
 [16] Bukoski, R.F., "Railroad Subgrade Soil Characterization for Track 
 Performance," M.S. Project Report, Department of Civil Engineering, 
 University of Massachusetts at Amherst, No. FRA-81-2, February 1981. 
 
 [17] Schmertmann, J.H., "Guidelines for Cone Penetration Test Performance 
 and Design," U.S. Department of Transportation, Federal Highway 
 Administration, Report No. FHWA-TS-78-209, Washington, D.C, 1978. 
 
 [18] Selig, E.T., Wobschall, D.C, Mansukhani , S., and Motiwala, A., 
 
 "Capacitance Instrumentation for Measurement of Moisture in Bases, 
 Subgrades and Earth Materials," SUNYAB, Final Report No. 21-2(2) to 
 Highway Research Board, National Cooperative Highway Research Program, 
 Washington, D.C, July 1974. 
 
 [19] Selig, E.T., Wobschall, D.C, Mansukhani, S., and Motiwala, S., 
 
 "Capacitance Sensor for Soil Moisture Measurement," Transportation 
 Research Board, Record No. 532, Washington, D.C, pp 64-76, 1975. 
 
 [20] Bosserman, B., and Sluz, A., Ballast Shoulder Width Experiment , 
 
 Facility for Accelerated Service Testing Report, FAST/TTC/TN-81/03, 
 June 1981 . 
 
 [21] Autry, W.S., "Incident at Leeds - Emergency on Concrete Tie Track," 
 
 American Railway Engineering Association Bulletin 683 , June-July 1981. 
 
 [22] Reiner, I. A., Concrete Tie In-Track Performance Test , Report No. 
 FRA/0RD-20015-L-8F, September 1981. 
 
 [23] Stewart, H.E. and Selig, E.T., "Predicted and Measured Resilient 
 Response of Track," Accepted for Publication in Journal of th e 
 Geotechnical Engineering Division , ASCE, April 1982. 
 
 [24] Selig, E.T., Yoo, T.S., Adegoke, C.W., and Stewart, H.E., "Status 
 
 Report - Ballast Experiments, Intermediate (175 MGT) Substructure 
 
 Stress and Strain Data," Interim Report No. FRA/TTC/Dr-10 (IR), 
 1979. 
 
 148 
 
 •U.S. GOVERNMENT PRINTING OFFICE : 1984 0-461-816/10115