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Bureau of Mines Information Circular/1988 
 
 Surface Subsidence Over Longwall Panels 
 in the Western United States— Final 
 Results at the Deer Creek Mine, Utah 
 
 By Frederick K. Allgaier 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 9194 
 
 Surface Subsidence Over Longwall Panels 
 in the Western United States— Final 
 Results at the Deer Creek Mine, Utah 
 
 By Frederick K. Allgaier 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 T S Ary, Director 
 

 Library of Congress Cataloging in Publication Data: 
 
 Allgaier, Frederick K. 
 
 Surface subsidence over longwall panels in the western United States. 
 
 (Information circular; 9194) 
 
 Includes bibliographies. 
 
 Supt. of Docs. no. : I 28.27:9194. 
 
 1. Mine subsidences— Utah. 2. Longwall mining— Utah. I. Title. II. Series: Infor- 
 mation circular (United States. Bureau of Mines); 9194. 
 
 TN295.U4 [TN310] 622 s [622\334] 88-600106 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Acknowledgments 2 
 
 Deer Creek Mine study site 2 
 
 Deer Creek Mine plan 3 
 
 Subsidence monitoring network 6 
 
 Subsidence monitoring surveys 6 
 
 Subsidence profiles • 7 
 
 Angle of draw 10 
 
 Subsidence development 10 
 
 Critical width 12 
 
 Conclusions 15 
 
 Appendix. — Measured subsidence values plotted in figures 5 and 6 17 
 
 ILLUSTRATIONS 
 
 1. Project location map 3 
 
 2. Generalized overburden stratigraphy 4 
 
 3. Deer Creek Mine plan with subsidence monuments shown as dots 5 
 
 4. Face positions and survey dates 6 
 
 5. Subsidence profiles 8 
 
 6. Transverse subsidence profile 8 
 
 7. Surface elevation profile above panel 6E 9 
 
 8. Transverse surface elevation profile 9 
 
 9. Subsidence contours relative to face positions 11 
 
 10. Subsidence development for panel midpoints 12 
 
 11. Critical mining widths from NCB and Deer Creek Mine 14 
 
 12. Deer Creek Mine extraction width and subsidence profile 15 
 

 UNIT OF 
 
 MEASURE 
 
 ABBREVIATIONS 
 
 USED 
 
 IN THIS 
 
 REPORT 
 
 ft 
 
 feet 
 
 
 
 
 pet 
 
 percent 
 
 in 
 
 inch 
 
 
 
 
 yr 
 
 year 
 
SURFACE SUBSIDENCE OVER LONGWALL PANELS IN THE WESTERN 
 UNITED STATES-FINAL RESULTS AT THE DEER CREEK MINE, UTAH 
 
 By Frederick K. Allgaier ' 
 
 ABSTRACT 
 
 This report presents the final data from a 5-yr Bureau of Mines study 
 designed to determine the surface subsidence characteristics resulting 
 from longwall coal mining in a geologic environment common to the West- 
 ern United States. It includes a description of the geologic setting of 
 the study site, the mine plan, measurement techniques, and results of 
 the monitoring program. Measured subsidence values were obtained over 
 four adjacent longwall panels. Major subsidence characteristics such as 
 longitudinal and transverse profiles, angles of draw, time-related sub- 
 sidence development, and critical width are discussed. The maximum sub- 
 sidence value of 5.8 ft was 68 pet of the mining thickness. The average 
 angle of draw was 30°. Subsidence at the center of the first panel con- 
 tinued for 46 months following undermining. The lengths of the longwall 
 panels precluded a definitive determination of the critical width and 
 maximum possible subsidence. 
 
 Supervisory mining engineer, Denver Research Center, Bureau of Miaes, Denver, CO. 
 
INTRODUCTION 
 
 This report is the second and con- 
 cluding part of a Bureau of Mines study 
 of surface subsidence characteristics 
 resulting from longwall coal mining at 
 the Deer Creek Mine in Emery County, UT. 
 The first part was published as Bureau 
 Information Circular (IC) 8896, entitled 
 "Surface Subsidence Over Longwall Panels 
 in the Western United States. Monitoring 
 Program and Preliminary Results at the 
 Deer Creek Mine, Utah." 2 The study in- 
 volved the measurement of surface move- 
 ments above the Deer Creek Mine, owned by 
 Utah Power and Light Co. (UP&L), Salt 
 Lake City, UT. Geologic and mining in- 
 formation was supplied by UP&L. 
 
 An objective of the Bureau's subsidence 
 research program is to provide a means of 
 predicting surface subsidence so as to 
 maximize resource recovery while con- 
 serving surface land values. In order 
 to adequately characterize subsidence in 
 the United States and develop predictive 
 technology, data must first be obtained 
 from a sufficient number of represen- 
 tative sites. The mining and geologic 
 
 conditions at the Deer Creek Mine are 
 representative of many western coal 
 mines; therefore, the results of this 
 study are expected to be applicable to 
 other western mining areas. 
 
 The minimal amount of subsidence data 
 available from the Western United States 
 is due to a lack of research efforts. In 
 many cases, data obtained by mining com- 
 panies may not be available to other 
 researchers. There are very few pub- 
 lished case history subsidence investi- 
 gations from active mining areas in the 
 Western United States. This limited 
 availability and distribution of subsi- 
 dence information and data have hindered 
 both the development of subsidence tech- 
 nology, and the efforts of mining com- 
 panies to comply with the Surface Mining 
 Control and Reclamation Act. The data 
 from this study can be used to develop 
 new prediction methods or to modify ex- 
 isting methods so that more accurate 
 estimates can be made of subsidence under 
 similar conditions in the Western United 
 States. 
 
 ACKNOWLEDGMENTS 
 
 The Utah Power and Light Co. provided 
 valuable assistance in conducting this 
 research. In particular, Don Dewey, Di- 
 rector of Special Projects, Chris Shin- 
 gleton, Director of Technical Services, 
 and Rodger Fry, Director of Exploration, 
 
 made significant contributions to the 
 project. Without the access they pro- 
 vided to company property, mine plans, 
 survey data, drill logs, and other infor- 
 mation relating to the Deer Creek Mine, 
 this study could not have been conducted. 
 
 DEER CREEK MINE STUDY SITE 
 
 The Deer Creek Mine is located on the 
 Wasatch Plateau in central Utah approxi- 
 mately 10 miles west of the town of Hunt- 
 ington (fig. 1). The study site area is 
 located over four adjacent longwall pan- 
 els. The surface elevation of the study 
 area averages 9,100 ft, and the topogra- 
 phy is generally rolling, with a maximum 
 ground slope of 45 pet. 
 
 Two major coal seams are being mined in 
 this area, the Blind Canyon and the 
 Hiawatha. The Deer Creek Mine is located 
 in the Blind Canyon coal seam which is 
 approximately 50 ft above the Wilberg 
 Mine in the Hiawatha coal seam. 
 
 The overburden consists mostly of sand- 
 stones and interbeds of siltstone and 
 sandstone. The total percentage of 
 
 2 Allgaier, F. K. Surface Subsidence 
 Over Longwall Panels in the Western 
 United States. Monitoring Program and 
 
 Preliminary Results at the Deer 
 Mine, Utah. BuMines IC 8896, 
 24 pp. 
 
 Creek 
 1982, 
 
r 
 
 To Price 
 
 Carbon County 
 Emery County 
 
 Huntington 
 
 Orangeville 
 
 Castle Dale 
 
 FIGURE 1. -Project location map. 
 
 sandstone in the overburden is 45 pet, 
 with 35 pet occurring in thick, beds (fig. 
 2). The Deer Creek Fault is located near 
 
 the east end of the study panels; 
 however, there are no faults crossing the 
 panels (fig. 3). 
 
 DEER CREEK MINE PLAN 
 
 The mine plan for the portion of the 
 Deer Creek Mine involved in this study 
 consists of four adjacent longwall panels 
 that were retreat rained from east to west 
 in the sequence 5E through 8E (fig. 4). 
 There were room-and-pillar sections mined 
 to the north (4E) and south (9E) of the 
 longwall panels. To the north of panel 
 5E, section 4E was mined with a total 
 raining height of 10 ft. Section 4E was 
 mined prior to panel 5E. Pillars were 
 not rained in section 4E, and the extrac- 
 tion was 52 pet. North of section 4E was 
 a 200-ft-wide barrier pillar and then 
 another room-and-pillar section, 3E, 
 which had an extraction of 50 pet. South 
 
 of panel 8E, a room-and-pillar section, 
 9E, was mined after completion of the 
 longwall panel 8E. Panel 8E was com- 
 pleted in January 1983, and section 9E 
 was completed in January 1984. The 
 extraction in section 9E was 52 pet. 
 Subsidence over panel 8E stabilized prior 
 to any effect from mining in 9E. The 
 four longwall panels involved in this 
 study were partially undermined by long- 
 wall panels in the Wilberg Mine after 
 subsidence measurements were completed. 
 Undermining began below panel 5E in April 
 1982. The transverse line of subsidence 
 monuments was undermined in November 
 1982. The data presented in this report 
 
DEPTH, 
 " 
 
 50- 
 
 100- 
 
 I50-- 
 
 
 250- 
 
 300- 
 
 350- — 
 
 400- 
 
 450- 
 
 500- 
 
 LITH0L0GY 
 
 .•••.o..«. v* • 
 
 • ■•■■•in 
 
 500- 
 
 550- 
 
 600- 
 
 650-- 
 
 700- 
 
 750- 
 
 800 
 
 850- 
 
 900- 
 
 Castlegate 
 Sandstone 
 
 LEGEND 
 
 Interbeds 
 :'.:>•":] Sandstone 
 5^g Siltstone 
 
 ^f jj Mudstone 
 I Coal 
 
 vl Alluvium 
 
 1,000- it 
 
 1,050- ~ 
 
 goo 
 
 Castlegate 
 Sandstone USO- f-.TTy W 
 
 950- ^^--^rr 
 
 1,300- 
 1350- 
 1.400- 
 
 1,200-=^^= = 
 
 f « . — • ■ . ."T 
 
 1,250 
 
 1450- 
 
 i » _i j — . . 
 
 1,500-1 
 
 Blind Canyon 
 
 coal seam 
 
 1.55 OH 
 
 Hiawatha 
 coal seam 
 
 l.^-v /:•":.' : .- v -"3 Tsi 
 
 Star Point 
 Sandstone 
 
 FIGURE 2.-Generalized overburden stratigraphy. 
 
C50 
 o o 
 
 aDQQan laDaaaananoQQDDcioaaoaaaQai . 
 
 DDQQDDl JQdDDDO section 4eQ d DaaDODa ODDQoaaaDaQai_ 
 
 DDDQa 000000000 DODDDDODaDannDDDODaODDQOODQODaDl 
 
 DaaOOO00OOa ODQ0DQO OODDD0£)£JgiaODOODaO00000QOOOOi 
 
 iX „„„ , , =ai pDDr 
 
 Panel 5E o QQj 
 
 C30 ° pl3 C20 00 CIO 
 
 O O OOOOOOOOOOOOOOOOOOO OOOO 9lP||0 o o 
 
 .JdQoaa 
 [QDaaaa 
 
 ^8888 
 
 PPQaa 
 
 dBDDd 
 
 E50 
 o o 
 
 E40 
 OOOO 
 
 o o o o o o 
 
 E30 
 o o o o o 
 
 o o o o o 
 
 E20 
 o o o 
 
 o o 
 
 r-' 1. 1! 'i innDPaanaiPaaDQ adnaaaaoaaaaaaaQ 
 DQQadK^-l .=»pio 
 
 aaaOOI Panel 6E 
 
 DD00D 
 o]£]<3BE 
 DDOOof^ 
 
 qaonouDB_ 
 
 ddoqod 
 ,naDoaoi F4 o 
 
 Jo^QO^q]! © c 
 
 iPOQo csaczj g=^Q"ca caocaoao CJO~c3 pop 
 
 OOOO 
 
 Panel 7E 
 
 F30 
 o o o o o o 
 
 DaaaDODODI 
 
 aODoonaaoa ^l_ . - — — - - - — 
 
 QDnaaaoaar Panel 8E 
 
 G50 nnaDODDI G40 I 630 
 
 pi 
 
 8 o o o o 
 °PI7 
 
 F20 
 oooo 
 
 5CDc=>C=»C3^»J 
 
 □5oc 
 
 ooolooooooooooo 
 
 620 
 
 cPoooooooooooO 
 
 IDDO0D 
 UDaan 
 
 QDaDD 
 
 Pc3C3t3qoc3gta »=" 
 
 Section 9E < 
 
 Room-ana— 
 
 * a Qoa e=a ea ogg 
 
 o o 
 
 o o o o o 
 
 o o 
 
 o o 
 
 GI0 
 ooooooooo 
 
 lar extraction 
 
 Room-and-plllar extracti 
 
 o 
 
 nsm- 
 
 Scale, ft 
 
 m 
 
 FIGURE 3.-Deer Creek Mine plan with subsidence monuments shown as dots. 
 
 were obtained prior to surface movements 
 caused by mining in the lower seam and do 
 not include any multiseam effects. 
 
 Panel 5E was developed using three 
 entries; the remaining three panels were 
 developed with two entries. Entries 18 
 ft wide were driven on 50-ft centers with 
 crosscuts on 100-ft centers. Dimensions 
 of the mined areas of the four panels are 
 as follows: 5E, 480 by 2,500 ft; 6E, 540 
 by 2,500 ft; 7E, 500 by 2,450 ft; and 8E, 
 
 520 by 2,300 ft. The average depth of 
 cover over the four panels was 1,500 ft. 
 Mining in panel 5E began in December 
 1979, and panel 8E was completed in Jan- 
 uary 1983. Face positions for each month 
 during the mining period are shown in 
 figure 4. The average distance the face 
 moved per month in the four panels was 
 220 ft, including the time it took to 
 move equipment between panels. 
 
Angle of draw 
 
 25' 
 
 Dec 
 79 
 
 
 
 A 
 
 
 A 
 
 
 A 
 
 1 
 
 
 
 Nov 
 
 Oct 
 
 Sep 
 
 
 Aug 
 
 Jul 
 
 1 Jun 
 
 May 
 
 
 79 
 
 79 
 
 79 
 
 
 
 
 79 
 
 79 
 
 I 79 
 
 79 
 
 Panel 
 5E 
 
 Angle of draw 
 28° 
 
 28' 
 
 Jan 
 81 
 
 I 
 
 Dec 
 80 
 
 nn 
 
 Nov 
 80 
 
 Oct 
 80 
 
 Sep 
 80 
 
 u 
 
 Aug 
 80 801 
 
 Jul Jun 
 
 80 
 
 May 
 80 
 
 Apr 
 80 
 
 Mar 
 80 
 
 32° 
 
 35' 
 
 
 
 400 
 
 Scale, ft 
 
 35° 
 Angle of draw 
 
 FIGURE 4.-Face positions and survey dates. 
 
 SUBSIDENCE MONITORING NETWORK 
 
 Feb 
 80 
 
 1 
 
 J) 111 
 
 1 1 
 
 1 
 
 II 
 
 
 Jam Dec 
 83 82 
 
 Nov Oct Sep 
 82 82 82 
 
 1 1 
 
 Aug 
 82 
 
 Jul 
 82 
 
 Jun 
 I 82 
 
 May 
 82 
 
 
 
 
 
 
 aa 
 
 u 
 
 A 
 
 A 
 
 A 
 
 
 Mar 
 
 Feb 
 
 Jan 
 
 Dec 
 
 Nov 
 
 Oct 
 
 Sep 
 
 Aug 
 
 Jul 
 
 Jun 
 
 Mar 
 
 82 
 
 82 
 
 82 
 
 81 
 
 81 
 
 81 
 
 81 
 
 81 
 
 81 
 
 81 
 
 81 
 
 6E 
 
 7E 
 
 Feb 
 81 
 
 8E 
 
 26° 
 
 33 c 
 
 28 
 
 LEGEND 
 Survey dates 
 
 A 
 
 The subsidence monitoring network con- 
 sists of lines of survey monuments lo- 
 cated over the longitudinal axis of each 
 panel and a transverse monument line 
 across the centers of the panels (fig. 
 3). Monument spacing was 100 ft except 
 over panel 8E, where 50-ft spacing was 
 used over the edges of the panel. The 
 purpose of the reduced spacing was to 
 provide a comparison of angle-of-draw 
 calculations for 50- and 100-ft monument 
 spacings. 
 
 Subsidence monuments were constructed 
 of either 1-in-diam steel rods or 1.5-in- 
 diam steel pipes. Monuments were driven 
 
 to a depth of between 3 and 4 ft, 
 depending on the depth of the soil cov- 
 er. Approximately 6 in of the monuments 
 extended above the ground to accommodate 
 the survey target used in the horizontal 
 position surveys. Vertical movement of 
 the monuments due to frost heave or other 
 local soil conditions did not exceed 
 0.03 ft, the accuracy of the elevation 
 surveys. This value is the average stan- 
 dard deviation of the elevations for all 
 nonsubsiding monuments over the duration 
 of the project. Any vertical movement of 
 the monuments not caused by subsidence 
 was less than this value. 
 
 SUBSIDENCE MONITORING SURVEYS 
 
 Initial base line locations were deter- 
 mined following installation of the sub- 
 sidence monuments and prior to any subsi- 
 dence activity. Horizontal coordinates 
 
 for each monument were established by 
 traverse survey procedures from control 
 stations with known coordinates, which 
 were located on stable ground beyond 
 
the subsidence areas. Traverse surveys 
 were used only when horizontal coordi- 
 nates were required in addition to eleva- 
 tions. The majority of the periodic sur- 
 veys conducted during subsidence activity 
 needed only to establish elevations for 
 the subsidence monuments. For these sur- 
 veys, elevations of the monuments were 
 determined using third-order direct level 
 surveying techniques. 3 Closed loops were 
 run from a stable control point into the 
 subsidence area and then back to the 
 control point. 
 
 Periodic monitoring surveys were per- 
 formed on a monthly basis while the site 
 was accessible during the summer months; 
 the site was typically inaccessible from 
 November to June because of snow cover. 
 The lack of data for these time intervals 
 did not adversely affect the overall 
 
 results of the project because adequate 
 data were obtained during the summer 
 months over the 5-yr monitoring period 
 to establish the subsidence profiles. A 
 total of 26 surveys were conducted during 
 the study, including a baseline survey 
 prior to mining (fig. 4). 
 
 Data from each survey were stored as 
 separate computer files, which were com- 
 pared to other surveys to produce numer- 
 ical records of the subsidence, such as 
 coordinate or elevation differences, or 
 were plotted as subsidence profiles, sub- 
 sidence contours, plan plots of the moni- 
 toring network, and horizontal vector 
 plots. Additional details on the sur- 
 veying techniques, equipment, and accura- 
 cy are contained in the preliminary 
 report on this study, published as Bureau 
 IC 8896. 
 
 SUBSIDENCE PROFILES 
 
 The final longitudinal subsidence pro- 
 files for panels 5E , 6E , 7E , and 8E are 
 shown in figure 5, and the final trans- 
 verse subsidence profile across the mid- 
 points of the panel lengths is shown in 
 figure 6. Data for these profiles are 
 contained in the appendix. 
 
 The maximum subsidence measured over 
 the four panels was 5.8 ft, which oc- 
 curred over panel 6E at station P6 on the 
 transverse monument line. This point is 
 approximately 200 ft north of the center 
 of the four panels. The 5.8 ft repre- 
 sents 68 pet of the average extraction 
 height of 8.5 ft over the four panels. 
 
 It is apparent from the transverse sub- 
 sidence profile crossing the four panels 
 (fig. 6) that the chain pillars between 
 panels crushed out to some degree and did 
 not significantly reduce the subsidence 
 above the pillars. There are no charac- 
 teristic undulations or bumps in the sub- 
 sidence profile that would occur above 
 the pillars if they remained stable. 
 
 ■^U.S. Department of Commerce. Classi- 
 fication, Standards of Accuracy, and 
 General Specifications of Geodetic Con- 
 trol Surveys. Rock vi lie, MD, June 1980, 
 12 pp. 
 
 The maximum change in overburden depth 
 due to topography is 175 ft along the 
 panel lengths and 160 ft across the panel 
 widths. Figure 7 shows the surface ele- 
 vations over panel 6E, which is typical 
 of the overburden variations over the 
 four panels; maximum overburden occurs 
 near the center of the panel lengths and 
 decreases toward both ends. Figure 8 
 shows the overburden variation across the 
 panels. The maximum overburden occurs 
 over panel 5E and the minimum over panel 
 8E; the elevation difference is approxi- 
 mately 160 ft. This difference is ap- 
 proximately 11 pet of the average over- 
 burden depth and should have little 
 effect on the magnitude of subsidence or 
 the shape of the subsidence profile. For 
 example, using the National Coal Board 
 (NCB) prediction method, 4 this change in 
 overburden across a 1 , 500-f t-wide opening 
 would change the subsidence factor by 
 only 0.005. 
 
 ^National Coal Board, Production De- 
 partment. Subsidence Engineers' Hand- 
 book. London, 1975, 111 pp. 
 
C50 C45 C40 C35 C30 C25 C20 CI5 CIO C5 CI 
 
 E50 E45 E40 E35 E30 E25 E20 EI5 EIO E5 El 
 
 1,000 
 
 F45 F40 F35 F30 F25 F20 FI5 FIO F5 Fl 
 
 3,000 4,000 
 
 5,000 
 
 1,000 
 
 2.000 
 
 G50 G45 G40 G35 G30 G25 G20 GI5 GIO G5 Gl 
 
 DISTANCE, ft 
 
 FIGURE 5.-Subsidence profiles. A, panel 5E; B, panel 6E; C, panel 7E; D, panel 8E. Shaded areas indicate unmined coal. 
 
 ,000 
 
 2,000 3,000 
 
 DISTANCE,ft 
 
 4,000 
 
 FIGURE 6.-Transverse subsidence profile. Shaded areas indicate coal pillars. 
 
2 
 
 9,180 
 
 9,140 
 
 9,100 
 
 9,060 
 
 9,020 
 
 8,980- 
 
 400 
 
 I i_ 
 
 Scale, ft 
 
 8,94 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I 
 
 E50 E45 E40 E35 E30 E25 E20 El 5 EIO E5 El 
 
 SUBSIDENCE MONUMENTS 
 
 FIGURE 7.-Surface elevation profile above panel 6E. 
 
 9,240 
 
 9,200 
 
 9,160 
 
 9,120 
 
 O 9,080 
 
 9,040- 
 
 9,100 
 
 8,960 
 
 8,920 
 
 400 
 
 Scale, ft 
 
 W-Panel 5E-»| |*-Panel 6E— *| k- Panel 7E— J k Panel 8E— 4 
 1_iJ i i i I i i i i I i i i i I i i i i I i i i i 
 
 J i i !'''■ I i i i i i i 
 
 PI6 
 
 PI2 
 
 P7 
 
 P2 P20 
 
 SUBSIDENCE MONUMENTS 
 
 P25 
 
 P30 
 
 P35 
 
 FIGURE 8.-Transverse surface elevation profile. 
 
10 
 
 ANGLE OF DRAW 
 
 The angle of draw from a vertical ref- 
 erence was calculated for each end of the 
 four panels and for the transverse monu- 
 ment line extending beyond the south edge 
 of panel 8E. The calculated angles of 
 draw are shown on figure 4. 
 
 Angle-of-draw calculations are very 
 sensitive to the accuracy of the surveys 
 used to measure vertical movement. 
 Assuming the overburden depth and the 
 location of the limit of mining are 
 known, the angle of draw is dependent on 
 locating the point of zero subsidence. 
 The more accurate the surveys, the far- 
 ther the point of apparent zero subsi- 
 dence moves away from the mined area, 
 thus resulting in larger calculated 
 angles of draw. Conversely, less accu- 
 rate surveys result in smaller angles of 
 draw. Elevations used to calculate 
 angles of draw were determined by trigo- 
 nometric and differential leveling. The 
 average standard deviation for elevations 
 of nonsubsiding monuments was 0.08 ft for 
 trigonometric leveling and 0.03 ft for 
 differential leveling. 
 
 Another factor that can affect the 
 angle-of-draw calculations is the spacing 
 of the subsidence monuments. Monument 
 spacing was 100 ft over panels 5E, 6E, 
 
 and 7E and 50 ft over panel 8E. The 
 effect of reduced monument spacing is to 
 reduce the distance over which the point 
 of zero subsidence is interpolated. Re- 
 duced monument spacing can improve the 
 accuracy of the angle-of-draw determina- 
 tion, but will not tend to increase or 
 decrease its magnitude. The average of 
 the eight angles of draw beyond the ends 
 of the panels, and the one angle of draw 
 at the end of the P line of monuments 
 south of panel 8E is 30*. 
 
 At the east ends of the panels, the 
 subsidence profiles cross the Deer Creek 
 Fault. The expected effect of the fault 
 would be to reduce the angles of draw. 5 
 A comparison of the angles on either 
 ends of the panels does not support this 
 expectation. On two panels, the angles 
 are smaller on the east ends, and on the 
 other two panels, the angles are smaller 
 on the west ends. Although there is no 
 major effect on the angle-of-draw values, 
 the fault did change the shape of the 
 subsidence profiles. On each of the four 
 longitudinal profiles, there is a dis- 
 tinct step or increase in slope of the 
 profiles between monuments 10 and 13 
 (fig. 5). 
 
 SUBSIDENCE DEVELOPMENT 
 
 Over the first mined panel, 5E, sub- 
 sidence did not occur at the surface un- 
 til the face had retreated between 550 
 and 1,050 ft. Subsidence continued to 
 occur over this panel for approximately 4 
 yr as the three panels to the south were 
 mined. The progression of subsidence 
 over the four panels as a function of 
 face position is shown on a series of 
 subsidence contour plots (fig. 9). Fig- 
 ure 9F represents the final subsidence 
 values. 
 
 The timing, rate, and duration of sub- 
 sidence over the four panels is illus- 
 trated in figure 10. The subsidence 
 values near the midpoint of each panel 
 length (monument 27) are plotted against 
 time. Initial subsidence at the mid- 
 points of the first and second panels 
 
 mined occurred at 3 and 2 months, respec- 
 tively, after the points were undermined. 
 Initial subsidence at the midpoints of 
 the third and fourth panels mined pre- 
 ceded undermining by 3 and 11 months, 
 respectively. Subsidence at the midpoint 
 of panel 8E began as the face passed 
 under the midpoint of the adjacent panel, 
 7E. 
 
 The length of time from undermining to 
 final subsidence became progressively 
 shorter from the first through the last 
 panel. It took 46 months for monument 
 C27 to reach final subsidence after 
 it had been undermined, while monument 
 
 5 Lee, A. J. The Effect of Faulting on 
 Mining Subsidence. Min. Eng., London, 
 v. 125, 1965-66, pp. 735-745. 
 
11 
 
 Panel 
 5E 
 
 6E 
 
 7E 
 
 8E 
 
 A September 1979 
 
 0.4 1.2 2.0 
 
 Panel 
 5E 
 
 1.6 0.8 
 
 6E 
 
 7E 
 
 8E 
 
 C November 1980 
 
 1.0 2.0 
 
 2.0 1.0 
 
 SJuly 1980 
 
 0.5 1.0 1.5 2.0 
 
 8E 
 
 D March 1981 
 
 1 .0 2.0 3.0 
 
 2.0 1.5 1.0 0.5 
 
 3.0 2.0 1.0 
 
 E June 1982 F January 1983 
 
 FIGURE 9.-Subsidence contours relative to face positions. Shaded areas indicate mined portions of the panels. 
 
12 
 
 12 months 
 
 20.5 months 
 
 36 months 
 
 i ' ' i i ' ' 
 
 J_L 
 
 46 months 
 
 i i i i i i i i i i i i i i i i i i i i i i i i i i i i i 
 
 i i i i i 
 
 ' ' ' ' ' ' ' ' 
 
 1979 
 
 1980 1981 1982 
 
 TIME, months 
 
 FIGURE 10.-Subsidence development for panel midpoints. 
 
 1 983 
 
 G27 reached final subsidence in only 
 12 months. Although the elapsed time 
 between undermining and final subsidence 
 varied greatly, the midpoints stabilized 
 
 at the final subsidence values at nearly 
 the same point in time, between July and 
 September 1983. 
 
 CRITICAL WIDTH 
 
 An important parameter to be investi- 
 gated in this study was the critical 
 extraction width. The critical width is 
 the minimum dimension of an extraction 
 area required to cause maximum possible 
 subsidence in the center of the area, and 
 is represented as a function of the seam 
 depth. For instance, in British coal- 
 fields the critical width is 1.4 times 
 
 the depth of the seam. 6 When an ex- 
 traction area increases and the minimum 
 dimension reaches the critical width, the 
 point at the center of subsidence profile 
 will reach maximum possible subsidence. 
 As the minimum dimension of the extrac- 
 tion area exceeds the critical width and 
 
 6 Work cited in footnote 4. 
 
13 
 
 becomes supercritical, the subsidence 
 profile assumes a characteristic flat- 
 bottomed shape, with more than one point 
 reaching maximum possible subsidence. 
 
 The extraction area at the Deer Creek 
 study site is nearly square. The extrac- 
 tion width across the four panels, 2,400 
 ft, is approximately equal to the aver- 
 age panel length of 2,432 ft. The shape 
 of the transverse subsidence profile 
 (fig. 6) indicates that the Deer Creek 
 Mine extraction area is subcritical. 
 There is no indication that the profile 
 is beginning to flatten out near the 
 center; therefore, the critical width is 
 greater than the final extraction width 
 of 2,400 ft. Using the average over- 
 burden depth of 1,500 ft, the critical 
 width is at least 1.6 times the depth. 
 
 Further mining to the south would in- 
 crease the extraction width beyond the 
 panel lengths, and the transverse profile 
 would have a flat bottom; however, the 
 subsidence at the center of the panels 
 would continue to be constrained by the 
 length of the panels and would not be 
 expected to increase beyond the maximum 
 measured value of 5.8 ft. Because the 
 panel lengths are not greater than the 
 extraction width required to cause the 
 transverse profile to flatten out, a 
 determination of the critical width, and 
 thus, the maximum possible subsidence 
 cannot be made. Mining did occur south 
 of the study panels in the 9E room-and- 
 pillar section. During the time 9E was 
 being mined, the center of the transverse 
 profile was affected by longwall mining 
 in the Wilberg Mine below the Deer Creek 
 Mine; thus, it was not possible to dif- 
 ferentiate the subsidence due to each 
 mining operation. 
 
 The relationship between the angle of 
 draw and critical width parameters from 
 this site results in a contradiction when 
 compared to existing definitions. Ac- 
 cording to the NCB, 7 the angle of draw 
 
 7 Work cited in footnote 4. 
 
 can be used to define the critical width; 
 the critical width should be directly 
 proportional to the angle of draw (fig. 
 1L4). At the Deer Creek Mine site, this 
 relationship is not evident (fig. 11B). 
 In the NCB case, the angle of draw over 
 solid, unmined coal can be projected over 
 the caved panel to define the critical 
 width. At the Deer Creek Mine site, the 
 angle of draw over solid coal (30°) is at 
 least 8° less than the angle over the 
 caved panel required to define the criti- 
 cal width (38.6°). 
 
 One explanation for this condition is 
 that the Deer Creek Mine extraction area 
 is critical or supercritical. This pos- 
 sibility is supported by the fact that 
 the angle required to reach the point of 
 maximum subsidence, P6, on the transverse 
 profile from the north edge of the ex- 
 traction area is within 1.5° of the aver- 
 age calculated angle of draw (fig. 12). 
 If this is the case, the points on the 
 profile for a distance of 475 ft south of 
 point P6 toward PI should also reach the 
 maximum subsidence value of 5.8 ft and 
 produce the flat-bottomed profile charac- 
 teristic of a supercritical extraction 
 area. The maximum additional subsidence 
 required for this condition, As, is 0.5 
 ft (fig. 12). This would mean that a 
 condition existed that prevented an area 
 over panels 6E and 7E from reaching maxi- 
 mum subsidence. 
 
 Strata bridging in one of the massive 
 sandstone layers in the overburden, such 
 as the Castlegate Sandstone, is one pos- 
 sible explanation for a delay in subsi- 
 dence at this location. This cannot be 
 confirmed, because there was no instru- 
 mentation in the overburden and because 
 the subsidence from subsequent, adjacent 
 mining was combined with that from mining 
 in a lower seam. A finite-element analy- 
 sis of the Deer Creek Mine conditions and 
 overburden stresses indicated that a 
 strata bridge could support the over- 
 burden load across one panel width. 
 
14 
 
 Ground surface 
 
 A, National Coal Board 
 
 Ground surface 
 
 B, Deer Creek Mine 
 
 FIGURE 11. -Critical mining widths from NCB (A) and Deer Creek Mine (£). 
 
 Another possible cause of incomplete 
 subsidence could be a minimal amount of 
 support from the chain pillars. The 
 location of these chain pillars relative 
 to the transverse subsidence profile 
 (fig. 6) is such that they could be pre- 
 venting the small amount of additional 
 subsidence necessary to produce the 
 
 characteristic flat-bottomed profile of a 
 supercritical extraction area. Again, 
 because no additional panels were mined 
 to the south before the subsidence was 
 influenced by mining in the lower seam in 
 the Wilberg Mine, this possible cause 
 cannot be confirmed. 
 
15 
 
 P25 
 
 FIGURE 12.-Deer Creek Mine extraction width and subsidence profile. 
 
 CONCLUSIONS 
 
 The final maximum subsidence factor was 
 0.68, although it cannot be confirmed 
 that this value represents the maximum 
 possible subsidence because the extrac- 
 tion dimensions precluded determination 
 of the critical width. 
 
 The time required to reach final sub- 
 sidence after undermining can be as much 
 as 4 yr owing to adjacent panel effects. 
 
 The average angle of draw was 30°. 
 This value can be used to define the 
 limit of subsidence beyond the limit of 
 mining, but it cannot be used to deter- 
 mine the critical width. 
 
 A major fault increased the slope of 
 the subsidence profile in the vicinity of 
 the fault, but did not reduce the lateral 
 extent of subsidence. However, the mag- 
 nitude of subsidence beyond the fault was 
 reduced. 
 
 An area of 315 acres was gradually low- 
 ered by mining of the four longwall 
 panels. During the 4 yr that subsidence 
 was monitored at this site, there was no 
 evidence of damage to the land surface, 
 vegetation, or drainage patterns. There 
 was no visual indication of any surface 
 depressions, and no surface cracks that 
 
16 
 
 would adversely affect the foreseeable 
 value or use of this land* The absence 
 of tension cracks can be attributed, in 
 part, to the fact that the chain pillars 
 between panels did not remain stable, 
 which would have caused an uneven subsi- 
 dence profile across the panels. 
 
 Any continuation of this research 
 should begin by making a detailed compar- 
 ison of these results to other case stud- 
 ies in an attempt to isolate the mining 
 or geologic variables controlling specif- 
 ic aspects of the resulting subsidence. 
 Future studies should be designed to re- 
 fine the angle-of-draw estimates obtained 
 
 in this study, define the critical ex- 
 traction width, which is needed to deter- 
 mine the area necessary to cause maximum 
 possible subsidence, and obtain meaning- 
 ful and accurate strain values. These 
 are the parameters that are the most 
 important for predicting the magnitude 
 and extent of possible adverse effects of 
 subsidence from future mining. Once 
 these parameters are known, efforts can 
 be made to eliminate or mitigate these 
 effects through the engineering design of 
 mines and of surface facilities that may 
 be subject to subsidence. 
 
APPENDIX. --MEASURED SUBSIDENCE VALUES PLOTTED IN FIGURES 5 AND 6 
 
 17 
 
 Subsi- 
 
 Subsi- 
 
 Subsi- 
 
 Monument 
 
 dence , 
 ft 
 
 Monument 
 
 dence , 
 ft 
 
 Monument 
 
 dence, 
 ft 
 
 Monument 
 
 dence, 
 
 Monument 
 
 dence, 
 
 
 
 
 ft 
 
 ft 
 
 
 0.1 
 
 
 0.0 
 
 
 0.1 
 
 
 0.0 
 
 
 2.2 
 
 
 .1 
 
 
 .0 
 
 
 • 1 
 
 
 .1 
 
 
 2.6 
 
 
 .2 
 
 
 .0 
 
 
 • X 
 
 
 .1 
 
 
 3.1 
 
 
 .2 
 
 
 .0 
 
 
 • X 
 
 
 .1 
 
 
 3.6 
 
 
 .2 
 
 
 .0 
 
 
 • X 
 
 
 .1 
 
 
 4.7 
 
 
 .2 
 
 
 .0 
 
 
 • X 
 
 
 .1 
 
 
 4.9 
 
 
 .3 
 
 
 .1 
 
 
 .2 
 
 
 .1 
 
 
 5.1 
 
 
 .3 
 
 
 .1 
 
 
 .2 
 
 
 .1 
 
 
 5.3 
 
 
 .4 
 
 
 .1 
 
 
 .2 
 
 
 .1 
 
 
 5.4 
 
 
 .4 
 
 
 .1 
 
 
 .2 
 
 
 .2 
 
 
 5.7 
 
 
 .6 
 
 
 .2 
 
 
 .2 
 
 
 .2 
 
 
 5.8 
 
 
 .9 
 
 
 .5 
 
 
 .3 
 
 
 .4 
 
 
 5.7 
 
 
 2.3 
 
 
 .9 
 
 
 .6 
 
 
 .7 
 
 
 5.6 
 
 
 2.6 
 
 
 2.3 
 
 
 1.8 
 
 
 1.6 
 
 
 5.7 
 
 
 2.9 
 
 
 2.8 
 
 
 2.5 
 
 
 2.0 
 
 
 5.4 
 
 
 3.2 
 
 
 3.1 
 
 
 2.9 
 
 
 2.1 
 
 
 5.1 
 
 
 3.6 
 
 
 3.4 
 
 
 3.5 
 
 
 2.3 
 
 
 4.7 
 
 
 3.8 
 
 
 3.6 
 
 
 4.3 
 
 
 2.6 
 
 
 4.6 
 
 
 4.0 
 
 
 3.9 
 
 
 4.9 
 
 
 3.0 
 
 
 4.4 
 
 
 4.0 
 
 
 4.1 
 
 
 5.2 
 
 
 3.2 
 
 
 4.2 
 
 
 4.1 
 
 
 4.2 
 
 
 5.2 
 
 
 3.4 
 
 
 3.9 
 
 
 4.2 
 
 
 4.4 
 
 
 5.2 
 
 
 3.4 
 
 
 3.4 
 
 
 4.2 
 
 
 4.6 
 
 
 5.2 
 
 
 3.5 
 
 
 2.8 
 
 
 4.3 
 
 
 4.8 
 
 
 5.1 
 
 
 3.5 
 
 
 2.2 
 
 
 4.2 
 
 
 4.9 
 
 
 5.1 
 
 
 3.4 
 
 
 1.9 
 
 
 4.2 
 
 
 5.0 
 
 
 5.0 
 
 
 3.4 
 
 
 1.6 
 
 
 4.2 
 
 
 5.1 
 
 
 5.0 
 
 
 3.3 
 
 
 1.3 
 
 
 4.2 
 
 
 5.2 
 
 
 4.9 
 
 
 3.2 
 
 
 .8 
 
 
 4.1 
 
 
 4.9 
 
 
 4.8 
 
 
 3.0 
 
 
 .5 
 
 
 4.2 
 
 
 4.9 
 
 
 4.8 
 
 
 2.7 
 
 P30 
 
 .3 
 
 
 4.0 
 
 
 4.8 
 
 
 4.7 
 
 
 2.5 
 
 
 .2 
 
 
 3.9 
 
 
 4.7 
 
 
 4.5 
 
 
 2.2 
 
 
 .1 
 
 
 3.6 
 
 E33 
 
 4.4 
 
 
 4.2 
 
 
 2.0 
 
 
 .1 
 
 
 2.9 
 
 
 3.8 
 
 
 3.6 
 
 
 1.6 
 
 
 .1 
 
 
 2.1 
 
 
 3.0 
 
 
 2.6 
 
 G35 
 
 1.2 
 
 
 .0 
 
 
 1.6 
 
 
 2.0 
 
 
 1.8 
 
 
 .8 
 
 
 .0 
 
 
 1.1 
 
 
 1.2 
 
 
 1.2 
 
 
 .6 
 
 
 .0 
 
 
 .8 
 
 
 .8 
 
 
 .8 
 
 
 .4 
 
 
 
 
 .6 
 
 E39 
 
 .6 
 
 
 .7 
 
 
 .2 
 
 
 
 
 .4 
 
 
 .5 
 
 
 .5 
 
 
 .2 
 
 
 
 
 .3 
 
 
 .4 
 
 
 .4 
 
 
 .2 
 
 
 
 
 .2 
 
 
 .4 
 
 
 .4 
 
 
 .2 
 
 
 
 
 .1 
 
 
 .3 
 
 
 .3 
 
 
 .1 
 
 
 
 
 .1 
 
 
 .2 
 
 
 .3 
 
 
 .0 
 
 
 
 
 .0 
 
 
 .2 
 
 
 .2 
 
 
 .1 
 
 
 
 
 .0 
 
 
 .1 
 
 
 .2 
 
 
 .1 
 
 
 
 
 .1 
 
 
 .1 
 
 
 .1 
 
 
 .1 
 
 
 
 
 .1 
 
 
 .1 
 
 
 
 
 .0 
 
 
 
 
 .0 
 
 
 .0 
 
 
 
 
 .0 
 
 
 
 
 .0 
 
 
 .0 
 
 
 
 
 .0 
 
 
 
 Subsi- 
 
 Subsi- 
 
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