^ V '' ** / \* ... *** 1 »°^ v ;• ^ "V i 1 • ^ v -^. : vv so*? 1 - o V * ^ ^ ** ^ l-.^ ^ V ****** : - <, *'~rr«' ,g v "o '••»* a t&"- "^ ^°* ,;• ^/ d> \ <, *'...' ,G V ^o o, 'o , . * A S 1 ' A V ^ ^ ^ V JO y ... °^ • 4.°^ "^ * G u * O.V- O •bv* iP^K V c- ^ /ate-, \/ ■C. *'TT-* «G^ ^5, '».." A ^ *. ... P"*. i "^ " ^0° ^ o_ 4 t - . t> rr.* .6 '/ <^ ** *. ^1> ,v^X l %^*.^% g o^ t .-V_. "*b j?-^ v ;• ^ T i°v /^.-^ ^^^r^/ ^*^ T \^ % •.^r--^ V*--* ,-- .6^ "o, -. . 7 • A ./%. <> ^TT.'^ ..7« A <> *'...' ,G * ^ y ... a ^ 4 o*. ,« -**A ' <> ^ v G° / <» *'T7i' ^6 3 *° «!» °^ :.^.„ o V •^o^ G w * *bv* -^o o V • ct5AW»k . o J£J 8823 Bureau of Mines Information Circular/1980 c-sty Surface Coal Mining Reclamation Equipment and Techniques Proceedings: Bureau of Mines Technology Transfer Seminars, Evansville, Ind., June 3, 1980, and Denver, Colo., June 5, 1980 Compiled by Staff— U.S. Bureau of Mines c This publication has been cataloged as follows: Bureau of Mines Technology Transfer Seminars, Evansville, Ind., and Denver, Colo., 1980 Surface coal mining reclamation equipment and techniques. (Information circular - Bureau of Mines ; 8823) Supt. of Docs, no.: I 28.27:8823. 1. Coal mines and mining — Environmental aspects— Congresses. 2. Strip mining — Environmental aspects— Congresses. 3- Reclamation of land— Congresses. I. United States. Bureau of Mines. II. Title. III. Series' United States. Bureau of Mines. Information circular ; 8823. T-N-23SJJ4 [TD195.C58] 622s [631.6'4] 80-607057 CONTENTS o _ Page ^& - o U X c CO o Z> I) Q. 3 o LU O o o O O o o o o O o ■n. o 1X5 O m CVJ CVJ — — jm/£ p* '3ivcd Nouonaodd WINCH DOZER FIGURE 2. - Winch-drawn blade system. SPECIALIZED BLADES FOR TRACTOR DOZERS As part of the analysis of improving tractor dozer performance, it might be best to first review the requirements of leveling and recontouring area- mined land. Figure 3 shows a typical cross section of a uniform spoil bank. Tractor dozers begin leveling these banks by first pushing the peaks short dis- tances into adjacent valleys. As the work progresses, the spoil bank height decreases and the average push distance increases. For normal spoil banks the maximum distance may never exceed 150 feet. The final work is to grade the land and prepare it for planting. The same process is generally applied for leveling box-cut spoil except that push distances can reach 500 feet or more. These are poor working conditions for conventional tractor dozers. ■Valley centerline to valley center line Note: 0.7X equals the weighted average distance from centerline to repose slope through a vertical cut of Y feet. FIGURE 3. - Typical cross section of a uniform spoil bank. The bank cubic yards (BCY) of material that must be moved depend primar- ily on the type of spoil bank (normal or box cut) , the crest-to-crest distance of the banks, the angle of repose, and the amount of rehandle. Table 1 shows the quantities of spoil material that must be handled in normal spoil as these conditions change. In comparison, it was determined in an extensive field project on leveling spoil banks (discussed later) that an average of 27,901 BCY was handled per acre in leveling 275.9 acres of box-cut spoil. The average for normal 120-foot spoil on this project was 10,073 BCY. Therefore, the average ratio between the material handled in box-cut spoil and that moved in normal spoil was 2.77. TABLE 1. - Theoretical estimate of spoil material handled in normal spoil Bank cubic yards moved per acre Crest-to-crest Angle of repose = = 30° Angle of repose = = 36° distance, ft Rehandle pet Rehandle 25 pet Rehandle 40 pet Rehandle pet Rehandle 25 pet Rehandle 40 pet 90 120 5,239 6,593 6,549 8,241 7,335 9,230 6,986 8,791 8,732 10,989 9,780 12,307 Next, consider an average dozing cycle in leveling spoil. Figure 4 shows the three primary phases, loading the blade, transferring (drifting) the mate- rial, and returning. At an average push distance of about 125 feet, the dozer will spend approximately 20 percent of its time filling the blade, 53 percent drifting the material, and 27 percent returning. Under good working condi- tions the production rate will be approximately 850 cubic yards per hour for a Cutting area Loading 20% of time Drifting area Drifting 53% of time Returning 27% of time FIGURE 4. - Three primary phases of a dozing cycle. tractor dozer with about 400 horsepower and using a U-blade. conditions that affect this production rate follow: The primary job 1. Push distance. 2 . Grade . 3. Type of material. 4. Operator skill. 5. Type of blade. 6. Type of dozing. 7. Job efficiency. 8. Visibility. Each of these has some influence on production. Table 2 shows the range of correction factors applied to the production rate for most of the above job conditions as recommended by a major equipment manufacturer. These factors are multiplied by the production rates for optimum conditions, which are given in manufacturers' handbooks. It is obvious that all are significant if varied from one extreme to the next. The question is, which ones can you change and control to your advantage? Work at the Spokane Research Center has focused on four to date: push distance, type of blades, type of dozing conditions, and operator skills. TABLE 2. - Job conditions and correction factors for tractor dozer Job conditions production rates Correction factors Job conditions Correction factors Type of blade: .50-0. 75 Coal U-blade 1.20 Bowl (stockpiler) 1.30 Type of dozing: Slot 1.20 1 .15-1. 25 Job efficiency: 0.84 0.67 Visibility: Darknes s , ra in , snow, fog, or 0.80 Push distance Refer to manufac- turers' curves. Grade: Uphill (20 pet).. 0.65 Uphill (10 pet).. 0.95 Level (0 pet) 1.00 Downhill (10 pet) 1.15 Downhill (20 pet) 1.22 Type of material: Loose stockpile.. 1.20 Hard to cut 0.60-0.80 Rock 0.60-0.80 Operator skill: Excellent 1.00 Average 0.75 Poor 0.60 Push Distance, Type of Blades and Type of Dozing The first three factors are actually interrelated in our research work and are therefore described together. As seen in figure 1, the shorter the push distance, the higher the production, until the blade becomes full and the operator dumps the load. This is referred to as the blade-full point. If the push distance is less than this, production will drop off because the blade is not full when the tractor dozer reaches the dump point. Consequently, the nearer the tractor dozer works to the blade-full point, the higher production rates will be. There are two techniques that an operator can employ to accom- plish this: 1. Use angle blades that move material short distances laterally towards the outslope under continuous cutting and casting (blade-full) conditions. 2. Use narrow deep blades that fill in short distances and carry large volumes. The first technique is extremely productive in normal 90- to 120-foot crest-to-crest spoil because the blade travels parallel to the spoil bank, moving the material laterally towards the outslope. The average push dis- tances are, therefore, approximately one-half the width of the blade. Also, the blade operates in a continuous cutting and casting action as it moves along the spoil bank, which means that it is always working at the blade-full (optimum) point. High production rates result from this as well as from the fact that the nonproductive backing and positioning time of the dozer is eliminated. The second technique is employed when push distances are short and the blade is not filled when the operator reaches the dump point; such is the case when the push distances are too great for angle dozing but short of the blade- full point. Both of these techniques were researched and evaluated through a joint program between the Pittsburg and Midway Coal Co. (P&M) and the U.S. Bureau of Mines (USBM) . The outcome of the 18-month research effort was a combination of highly productive specialized tools that can be used in combination with conventional tractor dozers and scrapers. The tools are shown in figures 5-8 and include 1. 48-foot angle blade. 2. 24-foot U-blade. 3. 13-foot narrow, deep U-blade. 4. 24- foot grading bar. The 48-foot angle blade proved to be the workhorse of the team and is the result of many months of work designing and field-testing various types and sizes of blades. The angle blade is mounted on two 410-horsepower tractors in an offset configuration, but requires only one operator. The blade is fixed at a 45° angle. The angle blade usually begins its cycle at one end of the spoil bank, where the operator fills the blade and moves forward, casting the spoil material laterally to the outslope. This continuous cutting and casting motion continues the full length of the spoil bank at a speed of approximately 1.5 miles per hour. At the opposite end of the bank, the operator turns the system around and begins cutting and casting material into the opposite valley. The process continues until adjacent spoil banks meet or the lateral reloca- tion distance from the centerline of the spoil bank exceeds approximately 50 feet. The field evaluation of the 48-foot angle blade over a period of 520 oper- ating hours showed an average production rate of approximately 6,000 to 6,500 BCY/hr. When used in conjunction with other specialized tools and conven- tional dozers as support, the system reduced overall work efforts and cost by approximately 50 percent. These reductions were achieved under very controlled field conditions, and it was estimated that the reduction would be 30 to 40 percent under actual mining conditions. This fact was later proven to be the case and will be discussed shortly. The side-by-side offset configuration of the tractors was adopted from an existing system marketed by a major tractor dozer manufacturer which consists of two tractors side-by-side with a large single U-blade. The value of this system was recognized and adopted for the angle blade. In addition, a 24-foot U-blade was purchased for the two tractors, and the system was used as a sup- port tool in normal spoil and as the prime mover in box-cut spoil. The 24-foot U-blade showed an approximate 25 percent increase in production and 25 percent decrease in fuel consumption over two single tractor dozers working separately. In addition, there was an immediate reduction in cost for labor because the system, like the angle blade, requires only one operator. FIGURE 5. - Forty-eight-foot angle blade mounted on two side-by-side tractors in an offset configuration. FIGURE 6. - Twenty-four-foot U-blade mounted on two side-by-side tractors. 10 FIGURE 7. - Thirteen-foot narrow, deep U-blade. FIGURE 8. - Twenty-four-foot grading bar. 11 5,000 O 4,000 tr LlI Q_ CO 3,000 Q < >- ^ 2,000 m O UJ CO o o 1,000 — — V — Angle blade I 50 feet \ 1 — \ \ r Narrow, deep \ reclamation 1 J Dlade f 1 Conventional U bul Idozer i i i 1 1 10 20 30 40 50 60 70 80 HORIZONTAL RELOCATION DISTANCE, feet FIGURE 9. - Effective relocation ranges for specialized and conventional blades. us to the second technique by which an operator using a narrow, deep blade that fills in short d The value of conven- tional bulldozer techniques in land recontouring was not diminished in the success of the 48-foot angle blade and 24-foot U-blade. The field evaluation showed that the angle blade could handle 60 to 80 percent of material that had to be moved ; the remaining 20 to 40 percent had to be handled by conven- tional dozers. It was also observed that these conven- tional dozers required 40 or more feet to get a full blade. As it turns out, this is beyond the effective relocation distance of the 48-foot angle blade as seen in figure 9. If conditions are adverse , such as in rocky material, the blade- full point for dozers could be as much as 70 feet, and yet the required push dis- tance may only be 50 feet. The consequence, of course, is that the operator will dump the load before the blade is full, which brings can increase production: istances . In an effort to study this technique a specialized 13-foot, narrow, deep U-blade was designed and tested under the P&M-USBM contract. A comparison of the blade's specifications with those of a conventional U-blade for a 410-horsepower tractor is shown in table 3. Results of the field test of the deep U-blade show that it could fill in 30 to 40 feet by sidecutting as seen in figure 9 and was very effective in combination with the angle blade in leveling and reshaping spoil banks. The blade design does not represent a major modification in blades; it is an improvement in a tool for a specific job. It is not too specialized to be used for other routine jobs in surface mining, such as long-distance pushes in land leveling, building dragline pads, or even building roads. 12 TABLE 3. - Dimensional comparison of conventional U-blade and narrow, deep U-blade for a 410-horsepower tractor Conventional Narrow, deep U-blade U-blade 15.75 13.0 5.92 5.75 9,280 8,950 37 40.5 25 30 4.21 3.0 26.5 23.0 47.0 54.0 26.5 23.0 Blade length f t . . Blade height f t . . Weight (blade only) lb . . Width (front to back of side plate) in. . Wing angle deg . . Length of each wing f t. . Left wing pet of length. . Center section pet of length.. Right wing pet of length. . The grading bar, as seen in figure 8, was designed to smooth the rough- graded land in preparation for the farming phase of land reclamation. It represents another tool designed to perform a specific job at a cost savings to the mine operator. A number of drag systems, such as I-beams, pipes, and large-diameter wire rope, have been used. However, they all have several basic drawbacks: they will occasionally hang up on large rocks, they require a large turning radius, and they are difficult to operate in limited space areas such as a point of land extending into a water impoundment. The grading bar is based on the idea of pushing the finishing tool rather than dragging it. It is made from 24-foot channel iron, with side wings for carrying live soil, and is mounted under the heel plate of a conventional bull- dozer blade using two 2-inch pins. Mounting time is about 5 minutes. Under operating conditions, the blade support arms rest on top of the channel iron, and the cutting edge of the bulldozer's blade can penetrate the ground about 1 inch. The operator has full control over lift and tilt of the grading bar, since it is attached to the blade. The grading bar was tested under the P&M-USBM contract and smoothed 1,431 acres at rates between 2.5 and 7 acres per hour, depending on ground conditions. It was mounted on a 270-horsepower tractor dozer. The major conclusions drawn from field-testing all of the specialized tools under the P&M-USBM contract follow: 1. The tools designed and tested to work in the short distance reloca- tion range performed satisfactorily and resulted in a 50-percent reduction in cost and tractor time per acre of mined land leveled and reshaped. Propor- tional savings in diesel fuel were also experienced. 2. In leveling and shaping normal 90- to 120-foot crest-to-crest spoil banks, the 48-foot angle blade moved approximately 80 percent of the material while using only 60 percent of the total tractor time. 13 3. Conventional bulldozers are needed in the final stages of the land-shaping process. They will move an estimated 20 percent of the total material but will require approximately 40 percent of the total tractor time. 4. The 24-foot U-blade showed a 25-percent increase in production over two separate tractor dozers of comparable horsepower. 5. The deep U-blade demonstrated higher production rates than conventional U-blades in short-distance relocation range below the blade-full point; above this point, the deep U-blade was comparable to conventional blades. 6. The grading bar demonstrated its efficiency in smoothing rough-graded land at rates between 2.5 and 7 acres per hour depending on ground conditions. 7. No single tool was effective in all situations. It required the combina- tion of tools to effectively and efficiently level and shape the spoil banks. Based on the results of the P&M-USBM contract, a technology transfer project was funded to demonstrate the tools developed and to show that significant reduc- tions in cost and work efforts could be realized by employing the proper combination of specialized and conventional tools. The mine site was in Texas, and the con- tractor selected to contract the demonstration was Russell and Sons Construction Co. The team for the technology transfer demonstration was on location in mid- February 1979; field testing began around March 1 and continued until September. It included the same four specialized tools developed and/or tested under the P&M-USBM contract (figs. 5 through 8) along with conventional dozers. One exception was that a low-ground-pressure (LGP) tractor dozer was brought in as a support tool when the ground conditions were wet and flotation was a problem. The LGP had a ground bear- ing pressure of approximately 6.3 psx as compared to 13 to 15 psi for the other tools. It was used primarily in unstable soil conditions as well as in finish grading. The demonstration was conducted in five test areas located throughout the mine. The five areas, totaling 312 acres, included 120-foot crest-to-crest spoil areas and box-cut spoil. The field results are shown in table 4 and equate to a 32-percent decrease in cost and fuel for normal spoil and a 27-percent decrease in cost and fuel for box-cut spoil, compared with costs using conventional equipment. TABLE 4 . - Results of technology transfer demonstration in Texas Location and type of spoil Area 1 , Area 2 , Area 3 , Area 4, Area 5 , Total or box-cut and box-cut and box-cut and irregular irregular average irregular irregular irregular Approximate number of working days.. 26 26 43 34 25 154 Acres reclaimed... 38 49 83 68 74 312 Acres reclaimed per working day.. 1.46 1.88 1.93 2.00 2.96 2.03 Total horsepower- hours per acre... 6,904 7,912 9,049 5,363 4,717 6,778 As a result of the excellent performance of the specialized equipment, the man- ager of the mine adopted the equipment as his primary land-leveling and recontouring tools. 14 Operator Skills This is the fourth job condition mentioned earlier which the USBM is researching for possible reduction in mined-land recontouring costs and work effort. This also leads us to the following, second major topic of this paper, as discussed in the following section. BULLDOZER WORK RATE INDICATOR The work rate indicator is actually a draft power sensor system designed to help the bulldozer operator to maintain high production rates without first acquiring extensive operator skill . This system continuously measures both the push of the blade against the spoil and the true ground velocity of the bulldozer. It multiplies those quantities to determine the real work rate of the machine. The system consists of a velocity sensor, a blade load sensor, processing circuits, and a work rate indicator. The processing circuits include an analog multiplier which has an output signal representing the draft power (velocity X load = power) . The draft power, or pushing power, is a measurement of the work rate at that moment. The velocity sensor consists of an ultrasonic continuous wave transmitter and receiver operating at a fixed transmission frequency. This sensor is housed in a metal container located behind the operator's cab (fig. 10). FIGURE 10. • Velocity sensor mounted behind operator's cab. 15 The signal from the velocity sensor transmitter strikes the ground behind the bulldozer and is partially reflected back to the receiver. When the bull- dozer is moving forward, there is a reduction in the frequency at which the signal is received. The load sensor is a strain gage installed on the neck of one of the push- beam trunnion's balls (fig. 11). The neck is highly stressed when the resist- ance of the load is transmitted through the blade and the push-beams. An audible beeper was the indication preferred by the operators. The number of beeps per second increases as the work rate increases. Each beep is about 1/10 second long and consists of a tone burst of low sonic frequency, approximately 400 Hz. A blinking light display and meter are also available. These displays, the beeper, and the processing circuitry, are contained in a rugged metal box mounted in the cab area. As the bulldozer moves forward with the blade up and away from the ground, the work rate will be zero. Because the product of the velocity (say 1.5 mph) multipled by the zero load against the blade is zero, the beep rate produced is essentially zero. As the blade is lowered and digs into the ground, a load is put on the blade and beeping begins. As the blade pushes more material, the load increases and so does the beep rate until the maximum work rate is reached. Depending on the resistance of the material being moved, the horsepower available at the tracks, and the traction conditions, the bulldozer can reach the combination of velocity and blade load that produces the maximum work rate possible for those conditions. Once the beeping reaches the fastest rate attainable for those conditions, the operator attempts to maintain that rate. This is usually done by raising or lowering the blade. Electronic circuit box True ground speed sensor Draft force sensor FIGURE 11. - Location of draft force sensor and electronic circuit box. 16 For example, if the blade is allowed to penetrate too deeply and the load against it becomes too large, the bulldozer will lose speed, either because the tracks slip or because the engine slows down. As the bulldozer work rate decreases, the beep rate will decrease proportionally. The operator must par- tially raise the blade to again achieve an optimum combination of velocity and blade load. Moving into an area of reduced traction would normally cause a similar indication and a lower work rate due to slippage. The correction would be similar. On the other hand, if the beep rate dropped while the bulldozer velocity increased, this could indicate to the operator that the load against the blade had decreased. The work rate might increase if the blade were lowered. The system works regardless of the change in dozing conditions. The prototype system, which was developed by the Southwest Research Institute under a Bureau of Mines contract, was field-tested early in 1978 at a large lignite mine in Texas. Two 410-horsepower bulldozers were fitted with this system and used for leveling and recontouring spoil banks. A test area of 105 acres was divided into smaller areas to accommodate various tests. Several operators ran the bulldozers both with and without the use of the work rate indicator. Logs were kept showing machine time, identity of the operator, weather conditions, fuel consumption, and other pertinent data. Tests were run for approximately 3 months. The data showed that when the work rate indicator was used, the land was recontoured faster, providing a potential for reduced labor and capital costs. Furthermore, less fuel was used per acre. The volume of material moved per hour increased between 20 and 25 percent in the various test areas. Although the hourly rate at which the bulldozers consumed fuel increased, this effect was more than offset because fewer hours were required to level and recontour an area. The approximate results follow: fuel consumption per hour, up 7 percent; hours of bulldozing required per acre, down 25 percent; fuel consumption per acre, down 20 to 25 percent. The prototype design is being production-engineered as a rugged product, readily installed and used on existing reclamation bulldozers. A series of field tests of this improved system will be conducted on bulldozers of several different manufacturers and sizes. Results should be available in late 1980. BACKFILLING FINAL HIGHWALLS WITH DRAGLINES Public Law 95-87 mandates that all mined land be returned to approximately the original contour with all highwalls eliminated. The regulations actually specify that the backfilled slopes covering the highwall cannot exceed the approximate premining slopes. 17 The major problem confronting the mine operator in complying with the regulations is moving large volumes of material over long distances under con- ditions that will vary depending on the original ground contour (flat, rolling, etc.)> overburden thickness, and the orientation of the coal seam(s) (flat or dipping) . At present, the industry is relying primarily on tractor dozers, drag- lines, scrapers, and trucks to move the required material; this is logical since such equipment is usually available at the mine site or at least the operator is familiar with it. A number of studies have been, and are continuing to be, conducted by the mining industry and the Government on various methods for eliminating high- walls. Most of the methods include the utilization of the above-mentioned equipment with varying modification as to size, deployment, combinations, etc. This section of this paper will address an evaluation of several types and combinations of equipment for backfilling highwalls in modified area mining. The mine site selected for the evaluation is in eastern Ohio and involves three different pit configurations: 1. Pit A, which was excavated by a medium-size shovel (less than 60 yd ) . See figure 12. 2. Pit B, which was excavated by a small dragline (less than 40 yd ) . See figure 13. 3. Pit C, which was excavated by a large dragline (greater than 100 yd ) . See figure 14. Three basic approaches were selected for backfilling the highwalls in each of the three pits. The three approaches include 1. Conventional tractor dozers. 4 2. Conventional dragline working on the spoil side of the pit. 3. Conventional dragline working on the highwall side of the pit. The specific equipment for each approach for pits A and B included 1. Conventional tractor dozers — 410-horsepower units. 2. Conventional dragline — 11-cubic-yard diesel with 170-foot operating radius. 410-horsepower tractor dozers were used for support work as required. 3. Conventional dragline — same as above except had a 20-cubic-yard crescent-shaped bucket and 600 feet of hoist and drag rope. 410-horsepower tractor dozers were also used for support work. 18 FIGURE 12. - Typical cross section of pit A. FIGURE 13. - Typical cross section of pit B. y rvininol gro» n _j. FIGURE 14. - Typical cross section of pit C. For pit C, the specific equipment included 1. Conventional tractor dozers — 410-horsepower units. 2. Conventional dragline — 35-cubic-yard electric dragline with 201-foot operating radius. 410-horsepower tractor dozers were used for support work. 3. Conventional dragline — same as above except had a 60-cubic-yard crescent-shaped bucket and 800 feet of hoist and drag rope. 410-horsepower tractor dozers were used for support work. The procedure for moving the spoil in each of the three approaches was the same for all pits. In the first approach, the tractor dozers moved the 19 material from the spoil side to the pit in a series of cuts in three primary lifts. The first lifts involved pushing approximately 25 percent of the required spoil material down a slope of 9.6 percent (5.5°) at a rehandle of 25 percent. The second lift involved pushing approximately 50 percent of the material over a zero percent slope (±2.0 pet) at a rehandle of 40 percent. The third lift involved pushing the remaining 25 percent up a slope of approxi- mately 17.6 percent (10°) at a rehandle of 25 percent. There was sufficient material in the spoil banks to backfill the highwall and attain the final slopes, as seen in figures 12-14; consequently, material from other locations, such as the box-cut spoil, was not required. In the second approach, the dragline is placed on a bench prepared by a dozer on the spoil side of the pit as seen in figure 15. The dragline was positioned to obtain the maximum dumping range. The dozers assisted the drag- line by pushing spoil to the loading zone if some spoil material could not be reached. The tractor dozers also did the final grading in the pit spoil area and filled in any areas that the dragline could not reach. In the third approach, the dragline was placed on top of the highwall (fig. 16) and equipped with additional hoist and drag rope along with a nrnvofmuJIU" ' Ui FIGURE 15. - Dragline backfilling from spoil side of pit. s s s FIGURE 16. - Dragline backfilling from highwall side of pit. 20 crescent-shaped bucket for dragging the material into the pit similar to a tower excavator. A 300-horsepower track- type pipelayer was used for the tail- block assembly. The dragline-tower system was able to reach all required spoil material. The final leveling and grading work was done with 410-horsepower tractor dozers. Specifics about each pit follow. Pit A Because the pit (fig. 12) contained several inside and outside curves, its length of 2,636 feet was divided into six sections; each was evaluated separately and the results were compiled for each of the three combinations of equipment. The average highwall height was approximately 88 feet, and the average pit width was 70 feet. Each linear foot of highwall required an aver- age of 273 BCY of spoil to backfill to the top. For this study it was assumed that no blasting would occur to facilitate backfilling. The average spoil relocation distance from the centroid of the cut area (required spoil) to the centroid of the fill area was 203 feet. Results of the analysis are shown in table 5. TABLE 5 . - Summary of results for pits A, B, and C Conventional Dragline Dragline Pit and primary dozers on si )oil on highwall recontouring equipment Cost/ft Change, Cost/ft Change , Cost/ft Change , highwall pet highwall pet highwall pet Pit A: Small dragline with conventional 11-yd bucket and 20-yd 3 cres- cent bucket; conventional $144 $108 -25 $100 -31 Pit B: Small dragline with conventional 11-yd 3 bucket and 20-yd 3 cres- cent bucket; conventional 144 -120 -17 104 -28 Pit C: Dragline with conventional 35-yd 3 bucket and 60-yd 3 cres- cent bucket; conventional 299 151 -49 108 -64 NOTE. — Change percent is the difference from operation with conventional dozers , Pit B Figure 13 shows a typical cross section of pit B. Like pit A, this pit was divided into sections which were evaluated separately and the results com- pleted. The average highwall height is approximately 84 feet, the average pit width is approximately 90 feet, and the pit length is approximately 7 ,690 feet. 21 Each linear foot of highwall averaged approximately 264 BCY of spoil to back- fill to the top. As in pit A, it was assumed no blasting of the highwall would take place. The average spoil relocation distance was 236 feet. Results are shown in table 5. Pit C Figure 14 shows a typical cross section of pit C. In comparison to pits A and B, this pit necessitated a major deviation in some equipment because of its size and required spoil material for backfilling of the highwall; however, deployment of equipment and movement of material was essentially the same. The average overall highwall height is approximately 138 feet; the average pit width is approximately 140 feet with an average bench width of approximately 30 feet. The pit length is approximately 800 feet. Each linear foot of high- wall required approximately 352 cubic yards of spoil material to backfill to the top of the bench. As in pits A and B, it was assumed no blasting of the highwall would take place. The average spoil relocation distance was 292 feet. Results are shown in table 5. Summary It is apparent, from at least this study, that the potential exists for gaining some significant cost savings in backfilling highwalls by using drag- lines either sidecasting or dragging material from atop the highwall. The next step is to conduct a comparative field evaluation study of the three sys- tems at an active mine site. This should provide reliable data for mine oper- ators to assess their backfilling requirements in modified area mining employing these combinations. CONCLUSION The primary approach Bureau research has taken to date in its efforts to reduce costs for recontouring mined land is to develop relatively inexpensive attachments for existing machines that will convert them to high-volume, low- cost tools. Emphasis is on the development of specialized tools to assist the operator until such time as (1) the industry develops systems that do not pile the spoil, or (2) enough surface coal mines increase production and their mined acreage to warrant using large expensive land-leveling equipment solely for recontouring mined land. BIBLIOGRAPHY 1. Caterpillar Performance Handbook. Caterpillar Tractor Co., Peoria, 111., 9th ed., October 1978, pp. 4-17 through 4-26. 2. Goris, J. M. , and H. S. Benson. Maximizing Dozer Work Rate With Draft Power Sensing Systems. Pres. at Earthmoving Industry Conference, Peoria, 111., Apr. 23-25, 1979, SAE Paper 790510, 11 pp. 3. Howland, J. W. Application of High Volume Earthmoving Methods to the Reclamation of Area Mined Spoil Banks. Final Report to U.S. Bureau of Mines, Contract No. HO252012, February 1978. 22 DESIGN CONSIDERATIONS OF TERRACE-PIT MINING by Gregory G. Miller 1 INTRODUCTION A dragline is the least expensive method to strip overburden where simple digging and casting are used. However, deep overburden, dipping seams, faulted seams, multiple seams, thin interburden, and toxic materials make dragline min- ing procedures very complex, and in any of these situations it is questionable whether dragline stripping is the best mining method. Other mining equipment such as shovels, bucket wheel excavators, scrapers, and backhoes may be better. Such equipment is best used where benches or terraces must be constructed to reach a deep coal seam. Figure 1 shows a typical shovel-truck equipment system terrace-pit-mining a single coal seam. Here four terraces are used to mine the overburden and one terrace to dig the coal. The benches are level and trucks haul the spoil around the pit to be back-dumped. In this way, the pit is continuously backfilled and reclaimed as the mine progresses. RECTANGULAR PROPERTY SHAPE If the terrain is flat and the coal seam has practically no dip, a long and narrow, rectangular property can be mined in two panels with one turn- around. The turnaround allows a better face length and places the second panel's final void close to the first panel's box-cut stockpile. The final void can then be completely backfilled with the box-cut material. In a rectangular mine, the faces should be advanced in parallel. If the mine needs to produce 20 million tons of coal per year for 40 years, a 15-square-mile property is needed with a 50-foot coal thickness. If the property is two sections wide and eight long, the above two-panel technique can be used. But if it is four sections square, four panels may be necessary to keep an optimal face length and still place the final void near the original box-cut stockpile. CIRCULAR PROPERTY SHAPE In the Western United States, it is rare that mine property be other than rectangular. However, surface terrain and the coal itself may make the actual mine property shape circular. Here the optimum pit shape may be circular and instead of advancing the faces in parallel, the faces are rotated around the center of the circle, with the face length equal to its radius. Sectorial panels are used again, depending on how the terrain rises and falls, and concentric panels may also be used and advanced to or retreated from the center. Mechanical engineer, Spokane Research Center, Bureau of Mines, Spokane, Wash. FIGURE 1. - Single-seam shovel-truck terrace-pit system. DIRECTION OF ADVANCE If the coal seam is lying horizontally or dips slightly (up to 3°), advance can be essentially in any direction as long as the terrain is flat. This condition is preferred in terrace-pit mining because coal production will remain uniform. However, geotechnical factors, ground water, or location of toxic zones in the overburden may dictate the direction of advance. In the case of slightly dipping seams such as those found in the Powder River Basin, if the coal does not cropout within the mine property boundary, an area should be chosen with the least amount of box-cut spoil to initiate mining. In cases of rising terrain and horizontal coal seams, it is usually preferred to advance perpendicular to the rising terrain if stability of the material permits, because of the reduced strip ratio in the first panel. If the mine property is rectangular but the seam dips about 3°, it is generally recommended that the mine advance along the strike. However, the mine can also proceed along the dip. The decision partly depends on how the property lies to the dip, and if it is long and narrow or nearly square. However, economics play a major role in deciding whether to advance downdip or along the strike. For 24 < or Q_ Q_ 20 MINE LIFE, years KEY Mining along strike with two panels and open slot Mining along dip with four panels and open slot Mining with no slot left open a mine situation where the length of the mine property occurs along the strike, advancing the first panel along the strike is very economic for the first half of the mine life because of its low stripping ratio. However , there is a great danger that the coal will not be mined on the second panel because of its higher stripping ratio. Figure 2 shows the relation between the stripping ratio and a mine life of 40 years. Dur- ing the first 20 years the first panel's stripping ratio average remains uni- form; then as the mine turns to mine the second panel, the stripping ratio jumps up dramatically to a level to be maintained for the last 20 years. If a slot is not left between the two panels, a portion of the first panel must be rehandled in mining the second panel. This raises the second panel's average stripping ratio. FIGURE 2. - Change inthe stripping ratio overthe life of a rectangular mine property with a dipping coal seam subcropping along its long side. If this same property is mined along the dip, four panels will be necessary. Figure 2 shows how the stripping ratio will fluctuate over the life of the mine. At a 40-year site, the first panel will proceed downdip, the second panel updip, the third downdip, and the fourth updip. If slots are not left between adjacent panels, the average stripping ratio will be the same as for the first panel. If slots are left, the last three panels will have a reduced stripping ratio. When mining downdip, problems result because there is less room to spoil the overburden into the previous cut. When retreating updip, the trucks may encounter haulage problems, but the waste is more stable, the ground water is drained from coal and overburden, and there is more space available for spoil. Generally, a terrace mine can operate on a 3° to 9° dip either along the strike or along the dip. However, when the coal dips more than 9°, the pit floor becomes too steep for truck haulage. Terrace-pit mining can still pro- ceed by two methods. One method is to mine neither along the strike nor along the dip, but at an angle to them. This tends to reduce the dip to a somewhat smaller angle. In the other method, the terraces are kept horizontal, and the coal is mined selectively with hydraulic shovels as the coal crops out in the bench. 25 NUMBER OF SEAMS The efficiency of coal mining depends on the thickness of the overburden, interburden, and coal seams. Thick coal seams and thin waste are preferred in all mining situations because of the low stripping ratio. However, multiple thin seams may be economic to mine even down to several hundred feet if the cumulative strip ratio is low and the mine is properly designed. GROUND WATER A small flow of ground water from interrupted aquifers can be allowed to drain into sumps cut into the pit floor and into the benches. The water can then be pumped out for uses such as dust control. If an aquifer of significant size will be interrupted, the mine must be properly designed to handle problems associated with wet overburden. Although this is not particularly a problem in the Powder River Basin or the Four Corners region, the Texas lignite region has areas of high flow rates and in some cases artesian pressures. Because artesian pressure in the underburden can cause floor heave and flood the pit, pumping wells should be placed in and around the pit to lower the water level. GEOTECHNICAL DATA Considerable premine research should be conducted to supply to the mine- design engineers critical geotechnical data on the properties of the site. This data will be used to determine the excavation equipment necessary and the layout of the mine that will prevent slope stability problems. Several oper- ators have had to redesign their mines at a considerable financial loss because the excavator was unable to dig the overburden. There are cases where the excavator became spoilbound because the swell factor was not properly determined and cases where the stability of the waste and overburden was not considered important, resulting in slope failures. TERRACE HEIGHTS Terrace heights will vary in a multiple-seam mine because the interburden, overburden, and coal seam thicknesses change. The slope of the land or the pitch of the coal seam causes the terrace height to change as the mine pro- gresses. Significant changes will require the addition or deletion of terraces and their side-pit haulroads. Generally, the height should be designed to be as near optimal for the loading equipment as possible. TERRACE WIDTH Any unnecessary bench width will increase haulage distance and costs. Therefore, all terraces, including the exposed coal seam, should be kept to a minimum width. The benches should be around 100 to 150 feet wide to permit equipment passing and turnaround, and to minimize congestion in the loading area. Generally, their width and haulroad width should be at least three times the maximum vehicle width, thereby enabling two haulage vehicles to pass maintenance equipment without interrupting production. However, the produc- tion rate or the excavator size may also be the determining factor of the final bench width. 26 SPECIAL TERRACES The geological and physical characteristics of the various overburden strata encountered may require different equipment combinations or separate terraces. For example, unconsolidated overburden and easily fragmented rock, like certain shales, may be most economically excavated by scrapers, while other material, like sandstone, might be best excavated by a shovel-truck team. In addition, if a toxic layer of overburden exists in sufficient quantity, a special terrace should be included in order that the material can be exca- vated and deposited in the most beneficial location. SPOIL TERRACES Spoil terraces should be kept on the same level as the excavation terrace so that negative grades will not be encountered. If special toxic material terraces are used in excavation, a counterpart spoil terrace will be needed. This may be at a different level than its excavation terrace, thereby encoun- tering adverse grades and reduced production. This toxic spoil terrace should be located at a level in the spoil profile to sufficiently isolate the mate- rial from contact with the environment. FACE LENGTH Determining the optimum face length is difficult because it depends on many variables. It is usually done in the detailed planning stage of an actual mine. Often property boundaries do not allow the use of the optimum face length, so a compromise is necessary. A whole number of panels must be planned to fit into the property, and an even number of panels is preferred because it positions the final voids near the original box-cut stockpile. In a case of an irregular property boundary that intersects the faces, a variable face length could be used to uncover all the coal. However, once mining is initiated, a significant deviation from the planned face length could require an extensive redesign of the mine. Long face lengths are not desirable because of the numerous excavators required. In addition, Federal and State regulations may prohibit long faces because they represent an extensive source of interruption of the environment. The rate of face advance also may be less than backfilling requirements call for. However, a large production rate from a single pit may dictate the use of a long face. In such cases, coal and overburden haulage through the middle of the pit may be desirable. On the other hand, a short face would dictate a series of narrow panels. This is not desirable because the length of coal haulage roads would be continually fluctuating. Short faces require wide benches and a longer pit to maintain production levels. METHODS OF TURNING When a panel has advanced to the end of the property, the mine must execute a 180° turn into the next panel. This can be done three ways. First, the turn can be performed with two 90° turns. In this method, the technique of advancing the faces in parallel is maintained. When the mine has advanced 27 to the end of the panel, the shovels are turned 90° and begin excavating the next panel. This short turning panel is advanced to the full width of the new panel while backfilling the void in the first panel; then the excavators are turned 90° again and begin retreating that panel, normally to its full length. Second, a 180° turn can be executed by rotating the pit around a point common to both panels with the radius of the swing equal to the face length. This method is similar to that used in mining properties that are nearly circular. Sectorial panels are used, and some corner coal may be lost. Third, another turn may be performed if new equipment will be purchased at the end of 20 years. Here a box-cut can be developed in the next panel before the first panel is complete. When the first panel finishes, it can backfill its void with the second panel's box-cut material. These three turning methods are quite complicated to execute and will require constant pit monitoring. SPOIL SLOTS When two or more panels are required for the mine property, it is bene- ficial not to backfill a wedge-shaped portion of the pit immediately adjacent to the next panel. This creates an open area, called a slot. By not back- filling this slotted area, rehandling of the previous panel's spoil to expose all coal is not required upon turning and retreating along the next panel. Generally, there will be spoil room available for constructing slots every panel. This results in each panel's waste being shifted over the width of the slot when backfilling takes place. The creation of a slot in the first panel may require overdeepening of its backfill area or stockpiling to dispose of the excess material caused by leaving the slot open. Savings in rehandling in subsequent panels should offset these costs. Two-panel property requires one slot whereas four-panel property requires three slots. In two-panel property with a 40-year life, portions of the slot could be open up to 40 years. Certain regulatory permits may be required for slots because of this long-term exposure. Slope reduction and revegetation of the slot highwalls may be necessary, or slots may be banned in favor of complete backfilling to the original contour. COAL HAULAGE The coal haulage road can be through the middle of the pit or along the edge of the pit where the panels meet. The overburden and coal haulage costs will dictate its location. For a shovel-truck terrace-pit mine, if the face is shorter than 4,700 feet, a side panel coal haulroad is preferred because this layout allows higher average truck speeds and lower costs per ton-mile. In this situation the slot between panels can be used for coal haulage, or the coal can be taken directly in-pit to the surface and hauled to the tipple. If the slot is used, it can also become the coal haulroad in the next retreating panel. When the face length for a shovel-truck mine exceeds 4,700 feet, it is preferable to have the coal haulroad through the middle of the pit because overburden and coal haulage distance become excessive. A coal haulroad slot can be left in the middle of the panel, but the use of two slots, the slot between adjacent panels and a coal haulage slot, may not be feasible. 28 FIGURE 3. - Multiseam scraper terrace-pit system. Figure 3 shows coal being hauled directly to the surface. Generally coal haulage through the side slot is preferred, because coal can be hauled up a shallow incline to the surface, rather than up steep in-pit haulroads. The spoil slot or wedge should be wide enough to permit two coal haulage trucks and a road grader to pass simultaneously. Because of this required road width, the advantages of reduced rehandle and the low grade of the haulroad may not be fully realized, because the slot must be either partially backfilled or increased in overall size to obtain a wide haulroad. This increases spoil rehandling. In addition, the slot slope angles may need to be reduced for long-term stability. OVERBURDEN HAULAGE Overburden is hauled to one side of the pit only to avoid interference with the coal haulroad; for example, when a side-pit coal haulage slot is used. Overburden haulage on the same side as coal haulage would require steep ramps down into the pit and back up to the spoil terraces. These roads are hard to maintain, lower production because of adverse grades, and are had on equipment. Overburden haulage from one side of the pit, opposite coal haulage, 29 is preferred because level roads can be maintained. If midpanel coal haulage is used and no slot is left, coal haulage can be along both pit sides and through the middle. Terrace-pit mining requires constant overburden haulroad construction and backfilling as the mine progresses. EXCAVATING EQUIPMENT Bucket-wheel excavators (BWE's) appear to have potential in the Texas lignite region and possibly in North Dakota where the overburden is uncon- solidated. They cannot be used effectively to dig material that needs to be blasted. They can follow the lignite on dips up to 3°, but for steeper dips, horizontal benches should be maintained. In this latter case, the lignite is selectively mined where the dipping coal crosses the highwall. In fact,\ a BWE can be quite effective where selective mining is necessary. A BWE can be very efficient in rebuilding the original stratigraphic sequence of the overburden. Generally, however, BWE's are relatively inflexible. They are designed for specific uses, and no significant deviation from planned mining techniques is possible. Therefore, if a BWE is to be used where flexibility may be required, the machine must be specially designed and set up. Competent overburden should be mined with shovels. Truck haulage can permit very selective rebuilding of the spoil and produce high spoil compac- tion. Trucks can operate economically in a one-way-haul distance of several miles within the range needed in terrace-pit mining. Scrapers can be used to terrace-mine unconsolidated overburden. 30 TOPSOIL ROCK REMOVAL by T. M. Brady, 1 W. W. Kaufman, 2 and D. N. Reynolds 3 INTRODUCTION An important element of surface mining reclamation is topsoil since its quality is critical for obtaining successful revegetation of reclaimed land. In most surface mines, scrapers are used for topsoil removal, stockpiling, and redistribution. After topsoil redistribution, the soil must be prepared for revegetation or use as farmland. If the disturbed soil contains too many large rocks, farmland will not be as productive as originally. Farming in areas where no care has been taken to remove large rocks may result in damaged farm equipment and less water permeability, and in smaller, less desirable harvests. To ensure that the soil maintains its productivity and permeability, many States have enacted laws and policies to control the size and quantity of rock in the topsoil. On the Federal level, the Office of Surface Mining (OSM) has established strict regulations governing revegetation of the reclaimed areas. Removing rocks from the topsoil is a fairly easy task; however, maintaining productivity levels is much more complex, requiring years of monitoring. After topsoil redistribution, the soil must be prepared for revegetation. If there are too many large rocks in the topsoil, graders may be used to eliminate them prior to revegetation. Since this method does not penetrate the soil, it is often inadequate and does not comply with many regulations. When deeper penetration is desired, rock rakes attached to dozers are employed. Rakes can eliminate large rocks to depths of 18 inches and deeper, but do not remove the smaller rocks less than 6 inches in size. While the spacing of tines on rock rakes is easily adjustable, if the tines are spaced too close, the soil will be pushed in front of the dozer and rocks will not be eliminated. Since graders and rock rakes are not totally effective for rock removal, some mining companies have elected to use rock pickers. These pickers, which are not classified as mining equipment, are generally sold as farming equip- ment, and to date their use by the mining industry has been limited. Why aren't rock pickers popular within the mining industry? Often the topsoil is so plentiful and free of large rocks that there is simply no need for them. Also, since rock pickers are generally associated with the farming industry, mining companies simply may not have explored their potential for rock removal. iGeneral engineer, Spokane Research Center, Bureau of Mines, Spokane, Wash. 2 Mining engineer, Energy Division, Skelly & Loy, Harrisburg, Pa. 3 Geologist, Energy Division, Skelly & Loy, Harrisburg, Pa. 31 The following discussion outlines the extent of the rock problem through- out the United States, discusses in detail the legal requirements that affect the reclamation process, analyzes the state of the art of current rock pickers including their physical limitations, presents an analysis of rock pickers applied to mine reclamation, surveys environmental effects that may take place, and details the benefits that can result from introducing rock pickers into the mining industry. REGULATORY ROCK REMOVAL REQUIREMENTS For years surface mining was conducted without concern for future land uses. Consequently, the overburden strata were overturned, burying the origi- nal topsoil, and abundant rock fragments were introduced into the soils. The resultant deterioration of land utility has prompted the promulgation of regu- lations to insure every effort is made to restore mined areas to their original conditions. State Requirements As States became increasingly concerned with the adverse effects of sur- face mining, they began enacting and enforcing more stringent regulations governing mine operations. Among the adverse effects of surface mining that were identified was "rock pollution. " The contamination of the soils with an unnaturally high percentage of rocks and the prevalence of large rocks, at or near the surface, hindered revegetation efforts, especially where farming was attempted as a postmining land use. The current tendency of regulatory legis- lation is to aim toward requiring mine operators to return affected land to its original condition. Thus, the States having the most rock-free soil would need the most specific regulations on rock content limitations for the topsoil layer. However, with proper handling these regulations should not impose a hardship on the reclamation efforts. Table 1 provides a comparison of existing specific restrictions, implied regulations, and pending surface mine amendments. The States that are shown as having specified regulations are those defining limitations of rock size and/or percent in the topsoil layers of surface coal mine reclamation. Implied regulations are indefinite limitations pertaining to rock content in the topsoil layer. Such limitations are worded to the effect that "large rocks" will not hinder postmining land uses. The strictness of pending legis- lation was not discernible; however, almost all pending legislation was expected to reflect the intent of the new regulations promulgated by OSM. Among the States that are monitoring topsoil rock content, the most strict regulations are found in Illinois, Indiana, Kansas, Oklahoma, and Virginia. 32 TABLE 1 STATE REGULATIONS ON TOPSOIL ROCK CONTENT STATE SPECIFIED STATE REGULATIONS IMPLIED STATE REGULATIONS z o o z K 111 — a U 111 _l CURRENT POLICY Alabama O • o Replace as was Alaska O O o None Arizona O o •* None Arkansas O o • * None California O o •* None Colorado O o • * None Connecticut O o o None Delaware O o o None Florida O o o None Georgia o o o None Hawaii o o o None Idaho o • o Replace as was Illinois • o •* No 1 0" rocks in top 4 feet Indiana • o o Bury 6" rock at least 6" deep Iowa • • o Implemented interim OSM regulations 8/78 Kansas • o • Bury 6" rocks at least 6" deep Kentucky o o • * Replace as was Louisiana o o •* Replace as was Maine o o o None Maryland o • •* Replace as was Massachusetts o o o None Michigan o o •* Replace as was Minnesota o o • Requires removal of 6" rocks from surface Mississippi o o •* None Missouri o o •* Requires removal of excess rock LEGEND: • Yes O No Will Conform to Office of Surface Mining (OSM) Regulations. 33 TABLE 1 (Cont'd.) STATE REGULATIONS ON TOPSOIL ROCK CONTENT STATE SPECIFIED STATE REGULATIONS IMPLIED STATE REGULATIONS z e> o z f= z 5 mph 1350ft 3' 4" 12' 0" 3' 6" $ 1,625 No 45 to 8 mph 2800# 7' 0" 20' 6" 7' 7" $ 6,082 No >40 2 to 4 mph 2510# 6' 8" 14' 3" 8' 0" $ 3,459 No 60 1 to 4 mph 4850# 8'-0" 15' 0" 5' 3" $ 6,200 37 The digging head can take two forms. It is normally either a fixed blade or a rotating rake. The fixed-blade pickup method uses a steel blade to lift £ layer of soil and rocks from the surface. Forward motion of the rock picker forces this material into the separation mechanism. The cutting depth is hydraulically variable on some models to permit adjustment while in operation. Soil conditions and operating speed affect the depth of penetration. In general, the deeper the cut, the slower the rock picker must travel to avoid overloading the separating mechanism. The fixed-blade pickup method is used by many models in conjunction with potato-chain, rotating-cage, or passive- rake separation modes. Rotating-Rake Rock Picker The rotating rake is generally best suited to surface and shallow rock picking. The rocks must be loose and free, or else the spring-loaded rake teeth will ride over them. As the rake turns, it lifts rocks up onto a screen which allows the soil to drop out while the rock is directed into a collection box. These machines require dry, vegetation-free soil since vegetation and damp soil bind the separation mechanism and make it inoperative. Rotating-rake rock pickers operate on the principle of a rotating, spring- loaded picking reel passing over a heavy grill-bar-type apron (fig. 2). The depth at which the leading edge bar of the apron runs through the soil is con- trolled hydraulically, on most models, from the tractor. The action of the reel teeth loosens the rock, helps to break up clods, and rapidly moves the rock back into the hopper. Manufacturers claim that continuous picking r Stone box Rotating rake ction ravel FIGURE 2. - Rotating-rake separation mode. (Adapted from Degelman Product literature.) 38 operation even during tight turns is possible. They also claim a speed range from 1 to 5 mph, depending on soil conditions. Self-cleaning action and very little jamming should be attained using rake rock pickers. The design of the aprons is generally such that, when used for surface work on pasture or sod, the machine will take all the surface rock with little tearing of the sod. Rotating-Cage Rock Picker The rotating-cage rock picker (fig. 3) does not penetrate the soil; rocks must be windrowed before this machine is employed. A rotating shaft pushes the rocks onto a conveyor belt that transfers them into the rotating cage. As the cage turns, tumbling rocks break up dirt clods, liberating soil particles that can fall through the cage openings and return to the ground. The inclined cage directs the rocks through the length of the cage to the rear conveyor, which deposits them into a storage hopper or following trucks. For best performance by this type of rock picker, the rocks should not be mixed with excessive amounts of soil and vegetation. The separation area of this machine is the smallest of the four types. If plant material is encoun- tered, it tends to clog the cage openings and reduce the available separation area even more. Passive-Rake Rock Picker Passive-rake rock pickers (fig. 4) are the least complicated of all the available rock pickers. Most passive-rake rock pickers have a fixed rake with adjustable tines. They are not designed to penetrate the soil more than a few inches. As the passive rake is towed behind a tractor, the rocks are maintained on the L-shaped tines, while the fine particles fall through. When the tines are full of rocks, the collecting head is hydraulically lifted and dumped into the rear storage hopper. For effective operation, the soil must be loose and dry. Rotating cage FIGURE 3. - Rotating-cage separation mode. (Adapted from Hurley Product literature.) 39 Direction of travel FIGURE 4. - Passive-rake separation mode. (Adapted from Leon Product literature.) Rock Rakes Another form of rock removal device is the rock rake. Table 3 lists the general specifications of some popular models. Rock rakes can be either dragged behind a tractor or pushed by a dozer. The dragged varieties are used for light-duty application and will not penetrate the surface. Dragged rakes only windrow surface rock and debris. Other methods must be used to pick up the windrowed material. 40 TABLE 3 ROCK RAKE SPECIFICATION COMPARISON TABLE COMPANY MODEL HORSE POWER REQUIRED OPERATING SPEED (MPH) TINE SPAC (IN) PENETRATION (INCHES) WEIGHT (LBS) HEIGHT WIDTH PRICE ( 1979 FOB FACTORY ) DRAG TYPE AUSTIN PRODUCTS INC. LITTLE RHINO 55 HP 0-6 2 DRAGGED ON TOP OF EARTH 370 3'-4" 8'-0" $825 BRILLION IRON WORKS LR-8 30 HP 0-5 2 455 4'-6" 8'-0" $854 DEGELMAN INDUSTRIES LTD. ROCK RAKE W/BRUSH KIT 50 HP 3-5 2 3200 3'-8" 14-0" $4,860 YORK MODERN CORPORATION R.E. 25 HP 2-6 2 425 3'-2" 8'-0" $1,550 PUSH TYPE FLECO CORPORATION 9-S USE WITH D-9 DOZER VARIES WITH EQUIPMENT 12 21 10.520 5'-4" 13'-8" $18,100 ROCKLAND FF-3 FOR FIAT ALLIS USE WITH FIAT- ALLIS DOZER 12 20 5,800 5-8" 11 '-6" $8,710 ROCKLAND RF-3 FOR CAT FOR D-9H DOZER 11 20 7,500 5'— 11" 11'-11" $8,710 The push-type rock rakes are attached to the front of a dozer. They can be effectively used to remove large rocks and vegetation from the soil. Again, since the rocks are not picked up, they must be pushed into a pile or burial pit. The tines on the rake are generally about 12 inches long. TOPSOIL ROCK CONTENT INVESTIGATIONS To explore the feasibility of transferring topsoil rock removal technol- ogy in its present state from its agricultural origin into surface mine recla- mation, nine representative mine sites were visited. Figure 5 shows the location of the sites visited. By sampling rock contents of soils before and after they were affected by mining, an indication of the need for incorporat- ing rock removal into the reclamation plans could be ascertained. In addition, the capability of current rock-picker technology to function in mining environ- ments was assessed. Each site chosen provided a unique combination of topsoil quality, topography, climate, and method of mining. Further considerations were made of the States that had rock limitation regulations. In addition, mines using rock removal devices to improve reclamation were sought to assess successes and problems. Each mine visit consisted of a discussion with mine operators of mining methods, availability of topsoil, overburden characteristics, reclamation equipment, amount of land reclaimed annually, average amount of time spent on 41 IDAHO WYOMING OHIO CH-5. VA,/\W CH-61 H-3 JJ^CH- TENN •CH-J ALA DEL. LEGEND 200 400 600 CH-I CASE HISTORY • MINE SCALE IN MILES FIGURE 5. - Location map— mine visitation sites. reclamation each year, and any particular reclamation problems experienced at the mine. The operator would then provide a tour of the operation for a first- hand view of mining practices and rock content evaluation of the soils. Rock content was evaluated by digging small test holes and then separat- ing and weighing the rock and soil components. Assuming a maximum mechanical picking depth (for optimum rock removal operation) of 12 inches, the samples were examined in two stages. The percent by volume of rock to soil was calculated at to 6 inches and for 6 to 12 inches. Segregation of rocks from soil was made by considering all material that passes through a 1-inch sieve to be soil and all that is retained to be rock. Those rocks in excess of 3 inches in their smallest dimension were weighed separately; however, in most cases this size fraction was a small portion of the total rock content. Test results for each mine are summarized in table 4. 42 TABLE 4 TEST HOLE RESULTS MINE SITE ORIGINAL ROCK CONTENT (%) RECLAIMED ROCK CONTENT (%) HOLE DEPTH HOLE AVG. HOLE DEPTH HOLE AVG. 0-6" 6-12" (i) 0-6" 6- 12" (i) CH-1* CH-2* CH-3* CH-4 5 10 7.5 5 6 5.5 CH-5 10(2) 10(2) 10(2) CH-6 7 13 10 9 14 11.5 CH-7 7 12.5 9.75 9 14 11.5 CH-8* CH-9 7 10 8.5 5 7 6 * DENOTES MINE SITES IN PRIME FARMLANDS (,) HOLE DEPTHS VARIED BETWEEN 8-12" DUE TO DIGGING DIFFICULTIES AND TOPSOIL THICKNESS (2) PRIOR TO ROCK PICKING STEP; AFTER PICKING IT IS RETURNED TO FOR ALL CATEGORIES 43 Sensitivity Analysis To determine the effects of incorporating a rock picker into the reclama- tion plans, a sensitivity analysis was performed on two of the mines visited. While keeping certain criteria constant and varying those items that would most likely fluctuate, sensitivity graphs were constructed. Criteria held constant throughout this analysis were 1. 6-inch effective penetration depth of rock picker. 2. 8-foot effective picking width. 3. 5-mile-per-hour ground speed during dumping cycle. 4. 60-second dump cycle. 5. $30,000 cost for rock picker and tractor. 6. 7-1/4-hour shifts. 7. UMW operator for tractor (Grade 1). 8. 90-percent availability of rock picker and tractor. Items considered as variable were 1. Operating speed — 1 to 5 miles per hour. 2. Hopper capacity — 4 to 16 cubic yards. 3. Haul distance to dump — to 5,000 feet. 4. Hopper versus direct loading. Each of the four variable items was graphed as a function of the percent of rock contained in the topsoil. These analyses of the relationship between the rock content of the topsoil and the horsepower required to remove that rock (expressed in horsepower-hours per acre) provide a visual display of the sensitivity of the reclamation effort to these variables. Horsepower-hour per acre units were chosen to portray the incremental increases in the rock removal effort as the rock content increased in order to provide a relationship of universal and timeless application. These units reveal the physical energy required to accomplish given tasks by summing the products of the total available potential flywheel horsepower outputs of all contributing pieces of equipment multiplied by the total hours over which they were applied. This figure is, in turn, divided by the number of acres reclaimed. These units can be converted to cost per acre in a single step, at any future point in time, by simply multiplying times a conversion factor. 44 Projected Rock Picker Efforts Table 5 presents the topsoil removal and reclamation efforts with proj- ected rock picker effort for all nine mine sites visited. Effort data obtained from the sensitivity analysis were used to compute the projected rock picker efforts at the other seven sites visited. Also included in table 5 are topsoil removal and reclamation efforts per ton of coal with and without the addition of a rock picker. Table 6 translates effort into costs based on 35 cents per horsepower-hour . TABLE 5 TOPSOIL REMOVAL AND RECLAMATION EFFORTS WITH PROJECTED ROCK PICKER EFFORTS MINE SITE EFFORT WITHOUT ROCK PICKER PR0JECTEI WITH R0CI ) EFFORT ( PICKER H.R-HRS/ACRE H.R-HRS/TON H.R-HRS/ACRE H.R-HRS/TON CH-1 44X00 5.0652 46.462 5.0668 CH-2 72.700 15.9942 74.262 15.9958 CH-3 35.100 9.3535 36X62 9.3558 CH-4 123.100 11.3315 124X62 11.3363 CH-5 7.500 3X608 9X62 3.6761 CH-6 217.100 15.5063 218X62 15.5175 CH-7 25.700 11.4131 27.262 11.4247 CH-8 113.900 16.0300 115.462 16.0312 CH-9 148.300 30.2588 149X62 30.2695 AVERAGE 87.600 13.1793 89.151 13.1860 45 TABLE 6 TOPSOIL REMOVAL AND RECLAMATION EFFORTS WITH PROJECTED ROCK PICKER EFFORTS MINE SITE EFFORT WITHOUT ROCK PICKER EFFORT WITH ROCK PICKER PERCENT INCREASE CH-1 1.77/ TON 1.77/ TON CH-2 5.60/TON 5.60/TON CH-3 3. 27/ TON 3. 27 /TON CH- 4 3. 97/ TON 3. 97/ TON CH-5 1.28/ TON 1.29/ TON .78 CH-6 5. 43/ TON 5. 43/ TON CH-7 3. 99/ TON 4. 00/ TON .25 CH-8 5.61/TON 5.61/TON CH-9 10. 59/ TON 10 59/ TON AVERAGE 4.61/TON 4. 62/ TON .22 CONCLUSIONS AND ENVIRONMENTAL IMPACT Rocks are a natural component of soil, yet at times they can be detri- mental to revegetation efforts. Large rocks hinder attempts to seed an area. A prevalence of rock on or near the surface retards the establishment of vegetative cover by restricting root growth and limiting moisture distribution, As a side effect of this impedance to vegetation, there will be an increase in the amount of sedimentation. Erosion, transportation, and deposi- tion of soil particles impair environmental quality. The source area is robbed of nutrient-providing soil, the transporting water becomes turbid and affects the aquatic life of the receiving stream, and the deposition can result in a clogged stream channel, lake, or pond, or in suffocation of produc- tive land. There can also be harmful effects on the wildlife from erosion and sedimention in the form of destruction of their refuge areas. These are often damaged or destroyed without being noticed, since they are remote from the "affected area." 46 Past mining practices led to mixing of consolidated and unconsolidated strata within the same spoil pile. In the process, the strata were inverted, making it impossible to replace the topsoil in its original condition. To alleviate the destruction of the natural soil conditions, States began requir- ing separate handling of the topsoil. The segregated removal, storage, and replacement of soil horizons during coal mining virtually eliminate the introduction of bedrock fragments into the reclaimed topsoil layer; thus the rock content should be unchanged and reclaimed areas should be of equal quality to their premining conditions. Recently, implementation of the Federal surface mine law forced the segrega- tion of soil horizons to be implemented nationwide. This practice has had a noticeable effect in States without previous rock content restrictions, where an extreme decrease in the contamination of topsoils by rocks is apparent. Although national implementation of rock pickers by the mining industry is neither necessary nor probable, for those instances when land use improve- ment is desired, a rock removal system may prove to be surprisingly cost effective. Of the currently available designs, the direct-acting rock pickers (figs. 1-3) — those that continuously loosen and sieve a layer of soil — perform better and more efficiently than cyclic-acting machines (fig. 4). Passive rakes often bounce off large rocks or force them deeper into the soil, and are thus less effective for rock removal. In addition, they are slower owing to the required stops for emptying the rake into the storage hopper and for dumping the storage hopper. These two nonproductive cycles of a three-cycle operation greatly limit productivity rates as compared to the continuous direct-acting types of rock pickers. For the operator who plans to improve the land use from its premining status, the employment of a rock removal system is effective and relatively inexpensive. The economic impact on both the small and large operators is slight, as shown by the previous sensitivity graphs and unit cost estimates. In terms of the cost versus benefit, any area whose land use has been improved will be more valuable than it was. The cost of utilizing a rock removal system that is properly sized for the volume of rock removal necessary can be more than offset by the increased land value. Surface mine operators with a vested interest in the properties they mine could be shown that, for a nominal investment of capital and effort, a sizable valuation increase could be derived. In areas where the former optimum land use was woodlands owing to an inherently excessive rock content, the use could conceivably be upgraded to grasslands. Likewise, in areas where cropland is scarce, a suitable substitute might be produced from previous grasslands or even woodlands. The most impressive cost-benefit results, however, would be in upgrading rocky waste- land into developable property. There are many minable areas with rocky or no topsoil and abundant bedrock outcrops. When these areas are mined, an increased amount of soil materials is produced. The utilization of a rock picker to decrease rock content would manufacture land of a quality that surpasses that of its surroundings for developmental purposes. 47 The financial advantage of a rock removal system begins even before the reclamation is completed on a severely rocky site. The removal of boulders and/or the reduction of the rock content can decrease the planting cost by permitting the mechanical preparation of a proper seedbed, mechanical tree planting, and improved revegetation success. Thus, the initial cost of plant- ing, as well as the probability of partial or total replanting (to meet the bond release requirements), will be reduced. In areas like the semiarid Southwest, where topsoil is of limited quan- tity and poor quality and is underlain by decomposed sandstones, the probabil- ity of successful establishment of vegetative cover may be improved by special rock reduction methods. The productivity of a reclaimed area might be improved by employing a machine that crushes the rock it engulfs and returns the reduced rock particles to the ground. If this type of rock reduction was applied to the upper subsoil layers, it would increase the amount of soil material, improve the availability of soluble minerals for plant nutrients, increase the moisture-retention capabilities of the root medium, and accelerate the development of soil horizons. A possible disadvantage of using rock pickers in the reclamation of surface mines would occur when the removal of rocks accelerates the erosion of restored slopes. Removal of the resistance to erosion that rocks provide may allow excessive gullying to occur. This disadvantage of rock removal could be eliminated by frequent terraces, or contour plowing, raking, or disking. These practices retard surface flow velocities, reducing the water's erosive power. Areas that are reclaimed for farming uses will experience the reoccurrence of rocks periodically, due to the combined effects of repetitive plowing patterns, siltation, and frost action. Plowing overturns the topsoil, and if the same plowing pattern is repeated year after year, the result is a lateral shift of soil, which is most pronounced on sloping ground. Siltation can carry away thin layers of topsoils, which decreases the rock cover. Finally, the frost action physically pushes rocks toward the surface. Separately these are minor factors, yet collectively they will allow rocks below the cleared level to migrate up into the tillage zone. This return of rocks will take varying amounts of time, depending on the depth of rock removal and the depth of frost penetration. Overall, the infiltration of rocks into the tillage area is extremely slow and is not a formidable problem; current restoration practices will provide a reoccurrence rate similar to that of adjacent, unmined lands of similar strata. 48 TRANSPLANTING NATIVE VEGETATION by Earl M. Frizzell, l James L. Smith, 2 and Kent A. Crofts 3 INTRODUCTION Transplanting native vegetation (trees, shrubs, and other species) is a viable alternative for reclamation of surface-coal-mined lands. Transplanted native vegetation both provides mature growing plants immediately to the reclaimed area and creates a nucleus from which seeds and other organisms can reinvade the area. Transplanting also provides immediate cover for wildlife, can be used for erosion control, and improves landscape aesthetics of recontoured areas. The transplant system described in this paper, consisting of a front-end loader and a transporter, is intended to provide equipment with which transplanting can be accomplished effectively and efficiently with minimal costs since current mechanized transplanting systems are expensive as compared with reseeding or planting of nursery stock. Most of the current transplanting equipment has evolved from nursery and landscape applications and is not sufficiently durable for the operating environment and steep slopes encountered in surface mines. Further, with this equipment, it may be possible to move only one moderately sized plant at a time, and the removal operation generally destroys virtually all the vegetation around the plant. Other specialized pieces of equipment, although suitable for reclamation, have high acquisition costs, and since the reclamation period may be of short duration, restricted usage may make their purchase difficult to justify. However, if the reclamation equipment can serve as a backup to regular mine production equipment when not in reclamation service, economic analysis may show the investment justifiable. Examples of such equipment are tree spades and mechanical transplanters. FRONT-END LOADER STUDY / The front-end loader (FEL) is a piece of mine production equipment that has been used, on a limited basis, for transplanting native vegetation in surface mine reclamation. However, the FEL is expensive, in terms of both capital and operating costs. Therefore, if an FEL is used in reclamation, its functions and capabilities should be optimized to achieve maximum productivity during the time it is available. Conventional FEL buckets are designed to maximize the volume of material that can be loaded from piles or embankments. However, for transplanting, the ^General engineer, Spokane Research Center, Bureau of Mines, Spokane, Wash. 2 Professor of agricultural engineering, Colorado State University, Fort Collins, Colo. 3 Manager of reclamation and environment, Energy Fuels Corp., Steamboat Springs, Colo. 49 FEL bucket should be designed to maximize the area of material Csoil plus vegetation) that can be removed. Further, because of operating costs and production efficiency, the FEL should be used only for removing clumps of vegetation from undisturbed soil and transporting them short distances to the transplanting area. Many mine reclamation operations require moving native vegetation several miles. Also, to maximize use of available vegetation, it may be necessary to remove clumps of vegetation and store them in a holding area for several weeks before they are moved to the transplant site. In these situations, the transplant system requires a transport capability in addition to the removal capability of the FEL bucket. The transporter should be capable of picking up several clumps of vegetation, moving them several miles rapidly, and plac- ing them on the ground at the transplant site. Transplant Bucket Operating Procedure Conventional FEL buckets are designed to load from piles or embankments. Therefore, they are deep and have relatively high sides, and the horizontal distance that the bottom extends beyond the bucket top is relatively small. When this type of bucket is filled with clumps of vegetation, this configura- tion disturbs taller plants such as trees, and after transplanting they may be crooked. The general design of the transplant bucket requires understanding the operating procedure used for transplanting. This procedure, which is markedly different from typical FEL operation, follows: 1. A vertical bank or step, approximately 2 feet high, is cut around the source of trees and shrubs. This must be done with the front-end loader and transplant bucket. 2. With the bucket bottom parallel to the ground surface and between 12 and 24 inches below the top of the vertical bank, the bucket is pushed into the bank. 3. When the bucket is full or driven to refusal, it is lifted vertically, thereby removing a clump of vegetation and soil. 4. The bucket is tilted back (towards the loader) about 10° to 15°, and the clump is transported by the loader to the transplant or storage area. 5. At the transplant area, the bucket is tilted forward (30° to 45° or more) and the loader is reversed, leaving the clump on the ground. 6. The loader is returned to the source of vegetation, and the cycle is repeated. Any access roads that may be required for transplanting are constructed prior to picking up the next clump, and any necessary surface leveling is done. All roadbuilding and leveling operations must be done with the reclamation bucket. 50 Bucket Design Criteria The reclamation bucket design criteria follow logically from the above operating procedure. The criteria developed for the reclamation bucket are 1. The force required to push the reclamation bucket into the soil bank was determined. To accomplish this, a series of "plate penetration tests" was conducted. The plate penetration apparatus consisted of a flat plate and a cutting edge, representative of a segment of the bottom of the reclamation bucket. The force required to push the plate into the soil bank was deter- mined as a function of the distance the plate was pushed into the bank. 2. The tractive capability of a Terex 1 * model 72-71A FEL was obtained from the loader manufacturer and standard construction equipment resource information. A similar procedure could be used for any size or make of FEL. 3. The size of the reclamation bucket was determined by matching the tractive capability of the FEL to the force required to push the bucket into the soil bank. 4. The force required to lift the clump of vegetation vertically from the soil bank was determined and compared with the lift capability of the FEL as given in the manufacturer's specifications. 5. The safe transport load for the reclamation bucket was determined from the manufacturer's specifications and standard construction equipment resource information. 6. Soil must be held on the plant roots with minimal disturbance during loading and unloading. In this regard, a suitable liner or coating should be provided on the surface of the reclamation bucket to reduce friction and decrease the tendency for soil to stick. The latter problem becomes particularly serious in cold weather because of the tendency of soil to freeze to the surface of the bucket. Once a soil clod sticks to the surface of the reclamation bucket, it disturbs the clump of vegetation until it is physically removed. 7. The force required to push a bucket into a soil bank can be reduced by mounting teeth on the cutting edge of the bucket. This was confirmed during the plate penetration tests. However, it is also necessary to confine soil in the clump of vegetation, particularly if the clump includes trees. Confin- ing soil in the clump is a problem if the clump is transported in the bucket. Teeth allow soil to fall out of the clump and were, therefore, not included on the initial bucket. Reclamation Bucket Specifications 1. Size will be 15 feet wide, 5 feet deep, and 3 feet high. This size is within the operating capability of the Terex model 72-71A loader. Reference to specific equipment or trade names does not imply endorsement by the Bureau of Mines. 51 2. Lucite will be used to line the inside bottom of the reclamation bucket. This material proved superior in field tests and will significantly reduce the sticking problem and problems of soil freezing to the bucket. 3. The front cutting edge of the reclamation bucket will be straight and balanced (the cutting edge will have an equal angle and length bevel on top and bottom) . This will aid in controlling the depth of cutting and help con- fine soil in the clump. TREE CLUMP TRANSPORTER Analysis of the FEL vegetation clump transplanting operation indicated two factors as limiting the operation. The first was that the FEL was very efficient in removing clumps and planting them, but was relatively inefficient as a means of transportation, particularly if the distance was more than 300 yards. The second limitation was that some mines may not have an FEL available when needed for the transplanting operation. The FEL is a very common piece of production equipment in surface mines, but the total time an FEL was available for transplanting might be relatively small. These problems can be solved by including a separate transporter in the transplant system. The vegetation clump transporter must pick up clumps of vegetation removed from undisturbed premined land by an FEL, transport the clumps, and place them in a transplant area. Proposed design criteria for the transporter are 1. Capable of picking up clumps of vegetation, each having an area of 75 square feet, and including small trees. 2. Capable of transporting approximately 200 to 300 square feet of vegetation clumps per load at speeds up to 20 miles per hour. 3. Capable of placing the vegetation clumps in the transplant area either as individual clumps or as groups of clumps up to the total area on the transport. A used Hesston stack mover is presently being modified and tested to evaluate the functions required for the transporter. The machine was origin- ally manufactured to load, transport, and unload haystacks. It consists of the follwoing mechanical elements: 1. A tilt-bed trailer having a surface area of approximately 170 square feet. 2. A chain conveying system capable of sliding the stack across the top of the trailer. 3. A pickup roller for separating the stack from the ground. 4. A set of tracks located at the rear of the trailer to pull the trailer under the stacks. 52 The rear tracks are synchronized with the conveyer so the stack is pulled up into the trailer at the same rate the tracks pull the trailer under the stack. When unloading, the stack is moved off the trailer at the same rate the rear tracks push the trailer forward. The maximum tilt angle of the trailer is approximately 15° (about 20 percent of the angle used between the FEL transplant bucket and the ground surface when unloading) . When the clumps of vegetation are handled by the transporter, they are subjected to minimal bending, and the plant survival rate should be satisfactory. The stack mover was converted to a vegetation transporter by the following modifications: 1. The subframe and tilt bed were strengthened for increased load- carrying capability. 2. The pickup roller was removed, and a short incline was located on the tail of the trailer to slide the vegetation clumps up on the conveyor chain. 3. The tilt-bed trailer was covered with Lucite to reduce friction and facilitate moving vegetation clumps across the top of the trailer. 4. A self-contained hydraulic system was mounted on the trailer, so only a prime mover (truck or farm tractor) will be required for operation of the transporter. It should be noted that although the converted stack mover is narrower than the transplant bucket (9 feet compared to 15 feet) , it will be possible to move clumps having the full 5-foot lateral dimension of the transplant bucket. This is the critical dimension, since it represents the length over which the clumps are subjected to bending as they are moved on and off the transporter. In the final design concept, the vegetation clump transport system would be operated as follows: 1. An FEL would be used for a short time to remove a large number of clumps of vegetation from the undisturbed premined land and store them conveniently nearby. The FEL would then be free to return to mine production activities. 2. The transporter would pick up the stored clumps of vegetation, move them to the transplant area, and place them on the ground. FIELD DEVELOPMENT TEST During the growing season of 1980, a developmental test of the vegetation clump transplant system will be conducted to study its effectiveness. Field test studies will be conducted in the following areas : 1. Survival rate by species. 53 2. Growth rate by species. 3. Survival of species as affected by the time of year transplanted. 4. Equipment operating efficiency and costs. 5. Provision for wildlife cover in transplant areas. 6. Buildup of moisture in transplant areas due to retention and buildup of snowpack. 7. Provision of ground cover and/or erosion control in the transplant areas. 8. Cold weather transplanting procedures. 9. Method analysis to reduce number and/or complexity of operations. The prime contractor for the field test is Colorado State University, Fort Collins, Colo. The cost-sharing cooperator is Energy Fuels Corp. , which will provide senior staff, machinery, equipment, and facilities for evaluation of the tree transplant system. Field test development will be conducted at the Energy Fuels Corp. mine, near Steamboat Springs, Colo. SUMMARY Advantages of the complete transplanting system, including the transplant bucket and transporter, are 1. Native vegetation can be moved efficiently and economically over longer distances, perhaps several miles, than is possible with the FEL alone. 2. An FEL, a piece of conventional mine production equipment, would be readily available but would be used only on a limited basis so as not to impede production activities. 3. The transporter could be used continuously without interfering with mine production. Larger areas could be thus transplanted in the same time period. 4. Native vegetation could be removed from an unmined area, placed in a holding area by the FEL, and moved by the transporter to the transplant area when convenient. This will allow maximum productivity with the FEL when it is available and provide increased flexibility in scheduling the FEL. 5. The transporter would be lower in initial cost than an FEL and less expensive to operate. Transplanting costs would therefore be reduced. 6. A truck, large farm tractor, scraper tractor, or other piece of reclama- tion equipment, not directly required for mine production, could be used to pull the transporter. All power for the transporter operation other than mobility is self-contained, so the prime mover could be changed easily. 54 SELECTIVE OVERBURDEN PLACEMENT by Gregory G. Miller 1 INTRODUCTION The Bureau of Mines sponsored a study of selective overburden handling at a coal mine in Colstrip, southeastern Montana. The Montana Agricultural Experi- ment Station in Bozeman, Mont., performed the work. They determined a recom- mended drilling intensity needed to accurately identify salt and trace metal materials that would be inhibitory to plant growth and performed a selective handling demonstration. DRILLING INTENSITY Current practice of identifying toxic ions of salts and trace metals involves drilling on a 1-mile grid in unfaulted areas and on a 1/2-mile grid in faulted areas. This guideline is based on a commonly accepted assumption that if inhibitory materials are present, they will be located in a physio- chemically uniform geologic strata. Consequently, if an inhibitory zone is found, selective overburden handling of this single strata is necessary. To evaluate this guideline, 300 boreholes were drilled on an approximate 150-foot grid over a 100-acre premine site. Samples were taken on 5-foot intervals, and approximately 100,000 separate physiochemical laboratory tests were per- formed at a mobile laboratory at the mine site. Data on the physiochemical properties at the site were graphed showing a three-dimensional distribution of each parameter. Figure 1 is a three- dimensional view of the distribution of clay at the site where the first four dragline passes would occur. This diagram and other diagrams of soluble salts, lead, and nickel show that inhibitory physiochemical parameters are distrib- uted in overburden zones independent of the geologic strata and generally independent of each other. It was also determined that the horizontal extent of the toxic zones was considerably less than 1 mile, indicating that the cur- rent guideline is not effective. To detect each parameter at a 90-percent accuracy level required an overburden drilling grid of 100 to 200 feet, con- siderably less than the guidelines suggest. Therefore, to properly identify inhibitory material, a two-step drilling program is proposed. First, the overburden should be drilled on a 1/2-mile grid. This would identify which physiochemical parameters exist in inhibitory concentrations. Then the site should be drilled on a 100- to 200-foot grid to identify the vertical and horizontal extent of those parameters determined to be present in inhibitory concentrations. This two-step procedure will reduce the costs of laboratory analysis by eliminating repeated analysis of parameters Mechanical engineer, Spokane Research Center, Bureau of Mines, Spokane, Wash, 55 100 Scale, meters FIGURE 1. - Three-dimensional view of clay distribution. found in step 1 to be insignificant. Another conclusion is that, generally speaking, mines that selectively bury a certain strata based on a drilling grid identification in the thousands of feet are likely to entirely miss considerable zones of inhibitory material. INHIBITORY MATERIALS In the Western States, inhibitory materials contain concentrations of salts and trace elements. Salts of calcium, magnesium, and sodium associated with sulfates (SO^) and carbonates (HCO3) are present. Trace metal ions of nickel, cadmium, zinc, molybdenum, and lead were a problem at the study site, and levels of copper, manganese, mercury, selenium, and boron should be checked. Suspect levels of pH, ammonium, sand, and clay were found at the site. High concentrations of salts adversely affect plant-water relationships by upsetting the plants' osmotic pressure. High concentrations of trace metals cause metabolic interference in plant cell physiology. Spoils contain- ing more than 40 percent clay prevent plant root penetration and water infil- tration. Clays are usually associated with high levels of positive trace metals ions which cling to negatively charged clay. Spoil containing more than 70 percent sand retains little water or nutrients essential to plant life. Drinking water contaminated with salts and trace metals causes metabolic prob- lems in animal life. 56 THE LEACHING PROCESS Leaching takes place if the spoil water begins to flow by gravity, carry- ing with it soluble constituents of the spoil. The water content must be above the field capacity for leaching to be significant. The field capacity is the amount of water held in the spoil after excess water has drained away and the rate of downward movement has substantially decreased. Leaching is most significant as the water content approaches saturation. It is desirable to suppress the leaching process in the presence of spoil containing inhibitory concentrations of trace metals or salts. This may be done in four ways: (1) The inhibitory material can be sealed with an imper- meable layer; (2) the inhibitory material can be diluted through mixing; (3) a topographic dome can be made above the inhibitory material to divert surface water away; and (4) subsurface water can be consumed by plantlife. Clay seals and dilution were investigated in this project. CLAY CAPPING Figure 2 shows selectively handled inhibitory material that was buried and capped with clay. It is desirable to use spoil located at the mine as a source of clay to reduce haulage costs. A clay cap intended to divert water is constructed with spoil dominated by a smectite clay. Smectite clay has a 2:1 lattice structure of a tetrahedral-octahedral-tetrahedral arrangement. Two-to-one lattice clays do not have a hydrogen bonding effect, so the units can readily expand and contract with wetting and drying, creating a formation that tends to be impermeable when wet. If the clay source is dry, it must be irrigated to achieve an optimal moisture content of 14.6 percent by weight. The clay should be laid over the inhibitory zone with scrapers. The scrapers should also attempt to compact the clay to a standard Proctor density of 112 pounds per cubic foot. The cap should be formed with a 5:1 grade in all directions to create an umbrella effect to shed percolating water. The clay cap should be thick enough so that it will not rupture when the dragline spoils overburden on it. A 60-cubic-yard dragline was able to build the foundation material and selectively place saline inhibitory material for capping. This was performed on approximately two-thirds of an acre and 14,000 cubic yards of a saline material were buried. The saline material was originally located in the top 15 feet of the overburden. The stripping ratio was 3:1. The cost of the operation was 50 percent more than normal dragline operations. The cost and complexity of selective overburden handling rest on whether the inhibitory materials are at the top, middle, or bottom of the overburden profile, and on the availability of clay. More efficient selective over- burden handling procedures could significantly reduce costs. The inhibitory overburden material should be buried deep enough to pre- vent future contact with the surface environment caused by man or nature. If the mine has interrupted an aquifer, the material should be buried above the predicted reestablished aquifer. The new aquifer capillary fringe must not 57 \ \ 0? f RFVEGETATED SLOPED SURFACF I *'*0, IT? / ^SATURATED FLOW SPOIL MPERVIOUS CLAY CAP WATER TABLE I I I I I I I I I I I I I ■U.LUJJJJJJ.J.J.mU.mL.Um.i. /CAPILLARY FRINGE ■ I..L.U...U I .L.L.U..I .SATURATED ZONE OF RE-ESTABLISHED AQUIFER CONFINING STRATA FIGURE 2. - Infiltrating water is diverted by clay cap away from the inhibitory material. intercept the buried inhibitory material. (The capillary fringe is a zone above the new aquifer into which unsaturated water enters due to capillary rise.) If the capillary fringe intercepts the inhibitory material, fluctua- tion of the water table level causes a corresponding fluctuation in the capil- lary fringe. When the aquifer level drops, the fringe drops. When it later rises, the chemical constituents are now in the aquifer zone. The fringe can then carry dissolved chemical constituents with it. Because of the semiarid climate at the site after 2 years, unsaturated flow of water through the spoil has not been enough to evaluate the effective- ness of the clay cap. However, a small (50-foot-diameter) experimental cap was also built which could be flooded with water to determine its effective- ness in shedding the downward flow. Over a period of 2-1/2 months, about 9-1/2 feet of water was applied in a diked area above the cap. This water application rate was extremely intense in comparison to the amount of water normally expected from precipitation. The change in the water content above and below the clay cap was monitored. The wetted front mushroomed out 58 laterally over the cap. Although the cap Itself became quite wet, the inhibi- tory material beneath it never reached saturation. The cap was determined to be an effective barrier to saturated flow. DILUTION OF INHIBITORY MATERIALS Mixing of inhibitory spoil material with other "clean" spoil tends to dilute the concentration of inhibitory material to acceptable levels. Mixing can be performed three ways with a dragline through digging and spoiling. First, when an inhibitory zone intersects the digging face, the dragline can drag the bucket at an incline, mixing clean and inhibitory material. Second, the dragline can dump the spoil as it swings, spreading and thus mixing the material. Third, the dragline can dump on spoil peaks, causing mixing as spoil rolls down. Three types of dragline spoiling techniques were investigated: normal, dump, and scatter. Normal spoiling with a 60-cubic-yard dragline with a 325-foot boom generally results in a bucket load of material being cast over an area 65 feet long by 35 feet wide. This was found to be true for several dragline operators, although their styles differed. Dump spoiling is used for initial spoiling on the pit floor. This involves stopping the dragline swing before dumping the load. It is used to avoid entrapments of pit water in the spoil because entrapped water causes subsidence and slope failure. Dump spoil- ing covers an area 35 feet square. Scatter spoiling involves dumping the load on the swing. The material is cast over a large area about 130 to 200 feet long. Scatter and dump spoiling increase cycle time. Three volumes of spoil were created with each method. Dump spoiling generally results in less mixing of inhibitory zones, and the technique should be used only when necessary. Scatter spoiling seemed to produce the best degree of mixing; however, normal spoiling could not be judged to be significantly different. Analysis of the resultant spoil yielded the following conclusions. When the inhibitory material constitutes less than 5 percent of the total overburden volume, the inhibitory zone was diluted to acceptable levels. When the inhibi- tory zone constitutes 5 to 15 percent of the overburden volume, only partial dilution occurs. When the inhibitory material exceeds 15 percent, only a small portion is diluted. In this case, selective overburden placement is necessary. No mixing occurs if the inhibitory material is spread throughout the entire overburden. Additionally, surficial overburden material may not be mixed as well as subsurface material. This may be due to a tendency to spoil surface materials onto the pit base in a dumping fashion, whereas deeper overburden materials are often cast normally or scattered over a larger area and slide down an existing spoil pile. It is always preferable to mix clays and sands . Although mixing of inhib- itory concentrations of trace metals and salts will increase the surface area available for deep leaching, mixing reduces the amount of inhibitory material in the plant root zone and the amount of inhibitory material available for leaching in the reestablished aquifer zone. 59 GROUND WATER Because of the limited depth of surface strip mining, only the shallow ground-water system was studied. Three aquifers were present in this system. The first is located in the permeable sandstone portion of the overburden, and the other two in the two coal seams. The second coal seam was not mined. Its aquifer was confined, and research found that surface strip mining has little effect on it. The top two aquifers were disturbed by mining, significantly affecting their level and direction of flow. A fourth aquifer now exists in the shallow ground-water system located in the spoils. How and where this new aquifer forms will impact water supplies down gradient. Water availability in this semiarid region is critical to local agricultural activities. The spoils aquifer should be constructed of pervious , uncontaminated material so that leaching of soluble salts and trace metals will not take place. Wells placed in the spoil confirm that the new spoils aquifer is form- ing and is exibiting confinement characteristics similar to those that exist in the unmined coal seams . A network of monitoring wells were placed in the overburden and spoil. Water levels and water quality measurements were taken. Data suggest that mining activities have had little effect on the overburden water levels at distances greater than 2,000 feet from the mine pit. This may be due, in part, to variations in lateral hydraulic conductivity, lack of sufficient time for adjustment to new conditions created by continued mining, and greater amounts of precipitation during the monitoring period. The top coal seam water level was reduced up to 1 mile from the mine pit. The water level tended to drop more in the coal seam aquifer than in the overburden aquifer. This seems to be due to the relatively continuous and homogeneous nature of the coal seam and the highly discontinuous and heterogeneous nature of the overburden. Con- sequently, dewatering of the coal seam is evident at a greater distance from the mine pit than is dewatering of the overburden aquifer. Surface water from streams, ponds, impounded water, and the mine settling ponds can be expected to be a source of recharge of the aquifers. The mine hydrologist must gather enough data to estimate the aquifer level in the spoil. This estimate is used in specifying the depth an inhibitory material can be safely placed. A comparison of 1923 water quality data with 1973 analyses indicates that no major changes in water quality have occurred owing to commercial mining at the site. Our analyses of water quality coming from the new spoil squifer indicate the water is generally more mineralized and of higher salinity. Mining altered the ground-water flow pattern in the overburden and coal towards the pit. However, this change in flow direction will cease once mining in the area has been completed and the spoil recharge is complete. 60 PREMINING HYDROLOGIC CONDITIONS OF FIVE SOUTHEASTERN OHIO WATERSHEDS by Gary E. Mcintosh 1 INTRODUCTION The Bureau of Mines is currently sponsoring a research project in east- central Ohio to study the effects of surface mining of coal on ground and surface water. In Appalachia, land is being disturbed by surface mining at an accelerating rate to obtain coal for electric power production and other uses. Such mining may have profound effects on runoff, erosion, and water quality in a watershed. Strip mining may bring changes in the hydrology of surface-mined areas in two interrelated phenomena: flooding and sediment transport. Barren spoil areas and decreased infiltration rates tend to increase peak flow rates of runoff from mined areas. Such increased runoff erodes the spoil areas and carries spoil particles that cause sedimentation of waterways and reservoirs. Until spoil areas become stabilized with vegetation, significant quantities of sediment will continue to be transported. In addition, Federal and State governments have passed laws that require minimizing the disturbance to an area being mined and reestablishing the hydrologic integrity of a mined area. The Surface Mining Control and Reclamation Act of 1977 also requires that the mining company shall make a "determination of the probable hydrologic consequences of the mining and reclamation operations, both on and off the mine site, with respect to the hydrologic regime." The law states that if there is not enough information to make this determination, no mining permit will be granted. Because of the need for more knowledge on how a surface mine affects its surroundings, the Bureau of Mines has established a study with the U.S. Depart- ment of Agriculture - Science and Education Administration - Agricultural Research (USDA-SEA-AR) and the Ohio Agricultural Research and Development Center (OARDC) to 1. Obtain and analyze hydrologic and water quality data from four treat- ment watersheds, 30 to 60 acres in size, scheduled for mining of different coal seams. Obtain and analyze hydrologic and water quality data from erosion and treatment plots and a control watershed. 2. Characterize the study watershed and plots, and obtain physical and chemical data for the soils and overburden materials prior to surface mining and for the replaced topsoil and underlying spoil material following surface mining. Geologist, Denver Research Center, Bureau of Mines, Denver, Colo, 61 3. Describe the hydrogeology of the watersheds and the water quality characteristics of the aquifer systems before and after surface mining, and develop or adapt a ground-water model for simulations of the ground-water flow conditions and movement of solutes before and after surface mining. This research program was started in January 1976, and completion is planned for January 1983. This paper deals with the premining hydrologic conditions of the watersheds. MONITORING PROGRAM Five watersheds, ranging in size from 29 to 52 acres, were selected to study the effects of mining and reclamation on hydrology and water quality. Four of these watersheds will be mined, and one will be left in its natural state and used as a control watershed. All the watersheds are located in east-central Ohio (fig. 1), and are numbered in accordance with surface- minable coal seams. The study watersheds in Coshocton County (C06 and A06) and the one in Muskingum County (M09) are located in the Muskingum River basin. The two Jefferson County Sites (Jll and J08) drain into small tribu- taries of the Ohio River. On each watershed soil and vegetation surveys were run, and geologic cores were obtained in order to determine baseline physical conditions. Weather stations were set up to monitor precipitation (quantity and quality) , temperature, relative humidity, wind speed, and solar radiation. Infiltration tests are being run throughout the project , on all watersheds, to determine how infiltration capacity changes from premining to postmining conditions. Surface water quantity and quality measurements are being taken by the use of H-flumes, drop-box weirs, a broad-crested V-notch weir, a Parshall flume, a cashocton vane, and check ash samplers. Composite sediment samples are also being collected from runoff and base flow events. Ground-water conditions are being determined with gologic coring, an observation well network, and pump and slug tests. Ground-water quality samples are collected quarterly. In addition to the monitoring of the watersheds, erosion and treatment plots have been set up at three of the mine sites. The erosion plots were installed on four different slopes, and with four different lengths on the slopes. The treatment plots (10 at each mine) consist of standard plots on a 9-percent slope, with treatments of different depths of topsoil and different mulching rates. The information from these plots will be useful for develop- ing criteria for diversion spacing and for establishing erodibility factors for soil loss prediction equations. 62 H Jefferson Co. A. Appalachian Exp. Ws. -> Coshocton Co. >1 A06 Muskingum Co. Columbus Zaneville -"' V C06 M09 *\^ c '^-- V <~\ j N / 10 20 30 40 I I I L__J Scale, miles FIGURE 1. - Location of study sites. RESULTS FOR PREMINING INVESTIGATIONS The periods of premining record for each watershed, and for each parameter for a watershed, varied as instruments were installed and mining progressed. The premining records for C06 and M09 cover less than 1 year. The end of the premining phase occurred when the watershed hydrology was changed by tree 63 removal and roadbuilding prior to mining. The Jll site has not yet been mined, and the A06 control site will not be mined, but an aribtrary cutoff date of December 31, 1977, was made for all the premining data included in this report. Because J08 has not been completely instrumented, its premining period has not begun except for collection of some ground-water data. Data on air temperature, relative humidity, wind, and solar and net radiation collected at the Jll site, however, can be extrapolated to J08, since the sites are only about 5 miles apart and variations over short distances are expected to be minimal for these parameters. The parameters which were analyzed from the surface water, precipitation, and ground-water samples are listed on page 64. Watershed C06 The premining condition of watershed C06 (fig. 2) is characterized by an ephemeral stream 2,000 feet long. The maximum elevation is 1,075 feet, and the minimum elevation is 930 feet. The watershed has an area of 52 acres, with a southeast aspect. Eight soil types, constituting 26 soil delineations, were mapped in the watershed. Five of the most extensive and representative soils - Johnsburg, Gilpin, Dekalb, Coshocton, and Monogahela - were sampled, and complete descriptions and characterization data were obtained. In general, these soils have favorable rooting depths and medium to high water-holding capacities. Most of the soils analyzed, except the Dekalb, would provide good material for topsoiling. LEGEND Natural spring Instrument plot Spring development Buried pipeline Core site Well monitoring the 2nd aquifer Sediment pond Gaging standard Watershed boundary Contour line Coal outcrop Access tube FIGURE 2. - Premining topographic map of watershed C06 showing instrumentation sites. 64 Parameters for Which Samples Were Analyzed Parameters for Sediment Fraction for Surface Water Parameters for Surface Water Parameters for Ground Water Aluminum Cadmium Calcium Copper Iron, total Lead Magnesium Manganese Mercury Nickel pH Phosphorus , total Sodium Strontium Sulfate Total organic carbon Zinc Parameters for Precipitation Aluminum Antimony Barium Bicarbonate Cadmium Calcium Copper Hydrogen sulfide Iron Lead Magnesium Manganese Nickel Nitrate (N) pH (laboratory) Phosphorus Silver Sodium Specific conductance Strontium Sulfate Zinc Acidity Alkalinity Aluminum Ammonia (N) Antimony Arsenic Barium Bicarbonate Cadmium Calcium Carbon dioxide Chloride Chromium Color Copper Cyanide Flow rate Fluoride Hardness Hydrogen sulfide Iron Lead Magnesium Manganese Mercury Nickel Nitrate (N) pH (field) Phenols Phosphorus Selenium Silver Sodium Solids, suspended Solids, dissolved Strontium Sulfate Temperature Zinc Alkalinity, as CaC0 3 Aluminum, total Antimony, total Arsenic, total Barium, total Bicarbonate Cadmium, total Calcium, dissolved Carbon dioxide Carbon, total organic Carbonate Chloride, dissolved Chromium, total Color Copper, total Cyanide Fluoride, dissolved Hardness , noncarbonate Hardness, total Hydrogen sulfide Iron, dissolved Iron, total Lead, total Magnesium, dissolved Manganese, dissolved Manganese, suspended Manganese, total Mercury, total Nickel, total Nitrogen, NH^ as N total N0 2 + N0 3 as N pH (field) Phenols Phosphorus, total as P Phosphorus, total Potassium, dissolved Residue, dissolved (calculated sum) Residue, dissolved Sodium absorption ratio Selenium, total Silica, dissolved Silver, total Sodium, dissolved Sodium (percent) Specific conductance (field) Strontium, total Sulfate, dissolved Water temperature (° C) Zinc, total 65 The vegetation on the watershed consisted mainly of deciduous trees. The site had poor species composition and growing conditions. Major species are aspen, dogwood, black cherry, maple, red oak, and musclewood. Ground cover was also quite variable. Average ground cover values for herbs, woody vegetation, duff, and bare soil and/or rock are 32, 14, 38, and 16 percent, respectively. The precipitation record spanning the C06 watershed premining period was from December 6, 1975 through November 3, 1976. The total precipitation for the period of record was 40.37 inches, with snowfall accounting for 2.79 inches. The most extreme event during the premining phase occurred on July 8, 1976, when the rainfall totaled 1.65 inches. The peak intensity of this event was 5.16 in/hr for 5 minutes — totaling 0.43 inch. The highest 2-hour intensity during this event was 1.60 in/hr, approximately a 5-year precipitation event. Infiltration tests were run on the watershed on the Coshocton, Gilpin, and Dekalb soils. At application rates of 2.0 and 2.5 inches per hour, equilibrium rates of 0.56 and 1.25 inches per hour were reached in about 3 and 4 hours for the Coshocton and Gilpin soils, respectively. The data for the Dekalb are considered questionable. A spring was developed on the watershed at the coal outcrop. The minimum flow was 0.003 cubic foot per second (cfs) , and the maximum was 0.012 cfs. The spring's range of average daily flow was 0.003 to 0.052 cfs. Mining commenced on watershed C06 before a full year's water quantity and quality data were obtained (data for the fall are missing) . The total surface flow for the period of record (1-1-76 to 11-3-76) was 33.54 inches. The peak event of 5.86 cfs occurred on July 7-8, 1976, with the causative precipitation totaling 2.39 inches. Base flow water had average concentrations of 183 yg/1 iron, 102 yg/1 manganese, and 247 mg/1 suspended solids, and an average flow rate of 0.44 cfs. The runoff water had average concentrations of 209 yg/1 iron, 97 yg/1 manganese, and 870 mg/1 suspended solids, and an average flow rate of 2.13 cfs. Ground-water levels indicate that the ground-water divide for both the top and middle aquifers at C06 coincides with the surface drainage divide. The top aquifer is above the clay that underlies the No. 6 coal. The middle aquifer is above the clay that underlies the No. 4 coal. Water in the deep aquifer moves northward; the top of this saturated zone is 30 to 100 feet below the middle aquifer. Water in the top aquifer is mostly of the calcium bicarbonate type. Specif ic-conductance values indicate that dissolved-solids concentration in parts of the middle and deep aquifers exceed the Environmental Protection Agency's recommended limit of 500 mg/1. Concentrations of dissolved iron and manganese commonly exceeded the recommended limits of 0.3 and 0.05 mg/1, respectively. Concentration of dissolved cyanide exceeded the recommended limit (0.01 mg/1) in one sample. 66 Watershed M09 The premining condition of watershed M09 (fig. 3) is characterized by a continuously flowing stream 1,800 feet long. The maximum elevation of the watershed is 1,165 feet, and the minimum elevation is 933 feet. The watershed has an area of 43.5 acres, with a south-southeast aspect. Fourteen soil types, constituting 33 soil delineations, were mapped in the watershed. Five of the most extensive and representative soils — Lowell, 200 J Scale.feet LEGEND Instrument plot Spring development Core site Well monitoring the 2nd aquifer Sediment pond Gaging standard Watershed boundary Intermittent streams Contour line Coal outcrop • Access tube FIGURE 3. - Premining topographic map of watershed M09 showing instrumentation sites 67 Upshure, Wellston, Tilsit, and Brookside — were sampled, and complete descrip- tion and characterization data were obtained. In general, these soils have a high available-moisture-holding capacity. The texture, cation exchange capacity, and base status make these soils well suited for plant growth, except where there is a high clay content near the surface. With the excep- tion of the Upshur mapping unit and other areas where high clay contents are found near the surface, the soils of the watershed would be very good for topsoiling. The vegetation on the watershed consisted mainly of pasture species. Woody species occurring on the site included sycamore, tulip poplar, elm, red maple, red oak, white oak, and dogwood. Approximately 77 percent of the ground area was covered with a mixture of grasses and broadleaf herbs, and 8 percent with woody vegetation; the remaining 15 percent was bare and/or covered with organic matter. The precipitation record spanning the M09 watershed premining period was from May 1, 1976, through January 19, 1977. The total precipitation for the period was 24.02 inches, with snowfall accounting for 2.93 inches. The most extreme event occurred on July 11, 1976, when rainfall amounted to 3.02 inches. The peak intensity of this event was 3.60 in/hr for 3 minutes — totaling 0.18 inch. The frequency associated with the event was a 25-year, 3-hour event of 2.73 inches. A spring was developed on the watershed at the outcrop of the No. 9 coal seam. The minimum flow rate of the spring was 0.0 cfs, and the maximum was 0.214 cfs. The average daily springflow ranged from 0.0 to 0.0444 cfs. Mining commenced on the watershed before a full year's water quantity and quality data were obtained (data for the winter and early spring are missing) . The total flow for the period of record (6-8-76 to 1-19-77) was 12.44 inches, while the total precipitation for the same period was 20.21 inches. The peak runoff event occurred on July 11, 1976. The peak flow for the event was 81.95 cfs with the causative precipitation being 3.02 inches. Base flow water had average concentrations of 46 yg/1 iron, 24 yg/1 manganese, and 157 mg/1 suspended solids, and an average flow rate of 0.024 cfs. Runoff water had average concentrations of 228 yg/1 iron, 92 yg/1 manganese, and 1,110 mg/1 suspended solids, and an average flow rate of 2.711 cfs. Three aquifer systems were measured in watershed M09. The ground-water divide for the top aquifer (above the clay that underlies the No. 9 coal) coincides with the surface drainage divide. Flow in the middle aquifer (above the clay that underlies the No. 8 coal) involves an unmeasured west-to-east underflow across the northern part of the watershed. This aquifer is part of a more extensive flow system which is away from the influence of the stream and is recharged and discharged mostly outside of the watershed. Potentiom- etric head in the northwest part of the middle aquifer is above the overlying clay, at least during part of the year, so that confined conditions exist. In the deep aquifer, water movement is northerly; the top of this saturated zone is about 70 feet below the middle aquifer. 68 Dissolved solids concentration of much of the water in the middle and deep aquifers exceeds the recommended 500 mg/1 limit. Chloride concentration in excessive (greater than 250 mg/1) in the eastern part of the middle aquifer and in the deep aquifer. Water in the top aquifer is very hard (greater than 180 mg/1 hardness as CaC0 3 ). It is softer in parts of the deeper aquifers where sodium is the dominant cation. Dissolved iron exceeded the recommended limit (0.3 mg/1) in one sample, and dissolved manganese was excessive (greater than 0.05 mg/1) in several samples. The recommended limit for dissolved cyanide concentration (0.01 mg/1) was exceeded in two samples from the middle aquifer and two from the deep aquifer. Watershed Jll The premining condition of watershed Jll (fig. 4) is characterized by an ephemeral stream 1,400 feet long. The maximum elevation is 1,280 feet, and the minimum elevation is 1,135 feet. The watershed has an area of 29.1 acres, with a western aspect. 200 200 i Scale, feet .EGEND istrument plot Core site /ell monitoring the 2nd aquifer Sediment pond Gaging standard /atershed boundary Intermittent streams Contour line Coal outcrop Access tube FIGURE 4. - Premining topographic map of watershed Jll showing instrumentation sites. 69 Four soil types, constituting 10 soil delineations, were mapped in the watershed. The soil mapping units are the Berks, Coshocton, Culleka, and Gilpin. Soil sampling has not been completed for this watershed. Much of the area is in pasture, both open and wooded. Only 4 of 11 sample points are wooded, and average timber volumes are low. The dominant species are black cherry, ash, and ailanthus. Ground cover for the area is quite variable, including herbaceous vegetation ranging from 40 to 100 percent, woody vegetation to 9 percent, duff to 55 percent, and bare soil and/or rock to 14 percent. Average ground cover values for herbs, woody vegetation, duff, and bare soil are 87, 2, 10 and 1 percent, respectively. The precipitation record for the Jll watershed began on May 1, 1977. Since the watershed has not yet been mined, the report was arbitrarily cut off at December 31, 1977. The total precipitation for the period was 28.64 inches. The most extreme event during the period occurred on July 21, 1976, when rainfall amounted to 1.93 inches. The peak intensity of this storm was 7.5 in/hr for 2 minutes, totaling 0.25 inch. The frequency associated with the event was a 2-year, 3-hour event of 1.66 inches. The total surface flow for the period of record was 2.07 inches, while the total precipitation was 27.14 inches. The peak event occurred on July 21, 1977. The peak flow for the event was 6.31 cfs, with the causative precipitation being 1.93 inches. Base flow water had average concentrations of <3 yg/1 iron, 25 yg/1 manganese, and 44 mg/1 suspended solids, and an average flow rate of 0.042 cfs. The runoff water had average concentrations of 14 yg/1 iron, 54 yg/1 manganese, and 118 mg/1 suspended solids, and an average flow rate of 0.89 cfs. The top aquifer at the Jll site is above the shaly clay that underlies the No. 11 coal; the middle aquifer occurs above the shaly clay that underlies the No. 9 coal. Underflow does not appear significant in either aquifer. The top aquifer discharges to the surface as evapotranspiration and at one ungaged spring; the middle aquifer discharges as evapotranspiration and base flow. The two deepest wells penetrate mined-out openings in No. 8 coal and are dry; much of the No. 8 coal has been removed. More detailed description of the' Jll ground-water system will be undertaken as premining data collection continues. The top aquifer at Jll contains water of the calcium bicarbonate and calcium sulfate types. Samples collected from the middle aquifer were bicarbonate waters, and sodium and calcium were the dominant cations. The predominance of one major ion over another is not as extreme at Jll as at other study watersheds. Watershed J08 The premining condition of watershed J08 Cfig- 5) is characterized by a continuously flowing stream 1,200 feet long. The maximum elevation of the watershed is 1,200 feet, and the minimum elevation is 880 feet. The watershed has an area of 51.8 acres, with a southern aspect. 70 6 -200 LEGEND Well monitoring the 2nd aquifer Gaging standard Watershed boundary Intermittent streams Contour line Coal outcrop Access tube -N- 200 _l Scale, feet FIGURE 5. - Premining topographic map of watershed J08 showing proposed and existing instrumentation sites. Four soil types, constituting 13 soil delineations, were mapped on the watershed. The soil mapping units are the Elba, Gilpin, Guernsey, and surface mine spoil. Soil sampling has not been completed for the watershed. On this watershed herbaceous vegetation cover ranges from 6 to 63 percent, woody cover from to 5 percent, duff from to 77 percent, and bare soil and rock from to 82 percent. The average cover values for herbs, woody vegeta- tion, duff, and bare soil and/or rock are 35, 4, 42, and 19 percent, respec- tively. The gross sawtimber volume is 389 board feet per acre, and the major species are black locust, black cherry, American elm, osage orange, and black walnut. Major poletimber species, representing a gross of 7.8 cords per acre, are black cherry, osage orange, black locust, and white ash. Woody 71 reproduction species include white ash, cherry, black locust, oak, osage orange, and elm. Weather data collected for the Jll site are being used for this site also. No surface water quality or quantity data are available, since measuring and sampling equipment is yet to be installed. Definition of the flow systems is not possible because only one well was completed in each aquifer. Analyses of ground water from J08 indicate calcium sulfate water in the top aquifer, sodium bicarbonate water in the middle aquifer, and sodium chlo- ride water in the deep aquifer. Water in the top aquifer is very hard and has dissolved-solids concentration exceeding the recommended limit of 500 mg/1 and sulfate concentration exceeding the recommended limit of 250 mg/1. Water in the middle aquifer is much softer, but slightly brackish and contains chlo- ride concentrations exceeding the recommended limit of 250 mg/1. Water in the deep aquifer is highly brackish. Watershed A06 Watershed A06 (fig. 6) is the control site and will not be mined. The watershed is characterized by a continuously flowing stream 1,750 feet long. The maximum elevation is 1,290 feet, and the minimum elevation is 1,008 feet. The watershed has an area of 43.6 acres, with a southern aspect. Four soil types, constituting 10 soil delineations, were mapped in the watershed. The soil mapping units are the Berks, Coshocton-Rayne complex, Dekalb, and Rayne. Vegetation is quite diverse, ranging from upland oak-hickory types to planted stands of white and red pine. Vegetation within the area is of a discontinuous cover form. Small areas within the watershed show recent interruptions. Ground cover is quite variable, including herbaceous vegeta- tion ranging from 2 to 56 percent, woody vegetation from 1 to 42 percent, and duff from 38 to 86 percent. The average cover values for herbs, wcody vegetation, duff, and bare soil and/or rock are 3, 16, 68, and 3 percent, respectively. The gross sawtimber volume is about 18,000 board feet per acre, and the major species are tulip poplar, red oak, white oak, red pine, and white pine. Poletimber gross volume is 27.0 cords per acre, and the major species include red pine, tulip poplar, and black locust. The precipitation record considered for this report covers the period from July 1, 1976, through December 31, 1977. The total precipitation for the period of record was 95.32 inches. The most extreme event occurred on July 11, 1976, when the rainfall amounted to 1.75 inches. The frequency associated with the event was a 5-year, 1-hour event of 1.61 inches. Springflow was measured from an existing developed spring on the Clarion clay, which comprises the second highest impermeable layer in the watershed. The minimum flow rate of the spring was 0.0003 cf s , and the maximum was 0.0712 cfs. The average daily springflow ranged from 0.0003 to 0.444 cfs. 72 ■1200 -N- 200 I Scale.feet LEGEND Well monitoring the 2nd aquifer Gaging standard — Watershed boundary Contour line Coal outcrop Intermittent streams Access tube FIGURE 6. - Premining topographic map of watershed A06 showing instrumentation sites. The total surface water flow for the period was 33.95 inches. The peak runoff event occurred on July 11, 1976. The flow for the event was 13.80 cfs, with the causative precipitation being 1.75 inches. Base flow water had average concentrations of <22 yg/1 iron, 344 yg/1 manganese, and 45 mg/1 suspended solids, and an average flow of 0.0098 cfs. The runoff water had average concentrations of 52 yg/1 iron, 64 yg/1 manganese, and 147 mg/1 sus- pended solids, and an average flow rate of 0.84 cfs. The top aquifer at the A06 site occurs above the clay that underlies the No. 6 coal, and the middle aquifer occurs above the clay that underlies the No. 4 coal. Surface loss from the top aquifer is mainly as evapotranspiration; that from the middle aquifer is evapotranspiration, base flow to the stream, and spring flow at spring gage. Underflow out of the watershed to the north- west occurs in both aquifers, although the top aquifer flow is from the divide toward the coal outcrop at times. In the deep aquifer water moves southward; the top of this saturated zone is about 20 feet below the middle aquifer. 73 Ground water in the top aquifer of the control watershed is of the calcium bicarbonate type. As in the other watersheds, water types in deeper aquifers are more diverse. In the middle aquifer, calcium, sodium, sulfate, or bicarbonate may each predominate. The deep aquifer contains sodium bicarbon- ate and sodium sulfate waters. Dissolved-solids concentration exceeded 500 mg/1 in two samples from the middle aquifer and from both wells in the deep aquifer. Most water is hard to very hard. Recommended limits of concentra- tion for dissolved iron and manganese (0.3 and 0.05 mg/1, respectively) were commonly exceeded in all aquifers. Cyanide concentration exceeded 0.01 mg/1 in one sample. SUMMARY Demand for coal will increase in the future. Demands for environmental safeguards will also grow, as evidenced by the passage of the Federal surface mining law and by various State enactments. Mines will be required to monitor ground water and to determine the hydrologic effects of mining, and regulatory agencies are required by law to determine the effects of mining by incorporating all of the hydrologic information gathered by mining companies. It is felt that this research program will be a first step in helping companies comply with the laws by establishing patterns for developing this information. 74 DRAGLINE CABLE REMOVAL PROJECT by G. Ken Derby 1 INTRODUCTION During a routine visit by a Bureau of Mines representative to a surface coal mine using draglines for overburden removal, a drag cable broke. When inquiries were made about how repairs would be accomplished, the cannon method of socket and wedge separation was explained. During the discussion, the service personnel stated that they considered removing the cable in this way to be efficient but hazardous, and that they felt relieved when the task was completed without an accident or an injury. This concern was reiterated at other mines and in discussions with industry representatives. Upon further investigation, it was discovered that although socket and wedge separation is the predominant method of performing the task in the United States, it has been outlawed in Canada owing to its inherent hazards. The objectives of the project reported herein included gathering data to determine the level of force required to separate wedge and socket cable terminations of various sizes and makes of draglines, establishing the level of forces generated by the cannon method, and using the data compiled to improve or create new methods and equipment for cable removal. PRESENT SEPARATION METHODS Cable removal, specifically socket and wedge separation, is usually performed by one of three methods when the cable is attached to the drag bucket. In brief they are 1. Explosive Impact. -Commonly referred to as the cannon method, this is the predominant method used in the United States. The main body of the device (fig. 1) used to hold and direct the charge and impeller is generally fabrica- ted from whatever type of steel material is available, in diameters ranging from 14 to 16 inches by 32 to 36 inches long. The bore is governed by the width of the wedge being removed, which is generally in the range of 4 to 6 inches. The impeller is made of steel with a diameter 1/8 inch smaller than the bore and a length ranging from 12 to 20 inches. Explosive force is generated by either 40- or 50-grain primer cord. The length of charge is determined by trial-and-f ail method. A starting length of charge is decided upon and tried. If separation is not achieved, the length is increased in increments until separation is accomplished. Thereafter, the successful amount of charge is used unless a failure to affect separation occurs. In this event, the length of charge is again increased until separation occurs. This method, although considered hazardous, is highly effective. ^Mechanical engineering technician, Spokane Research Center, Bureau of Mines, Spokane, Wash. 75 FIGURE 1. - Cable wedge removal cannon and impeller. In this version, the cannon is bored to 4-1/8 inches with a 4-inch-diameter impeller, 14 inches long. 2. Manual Impact . -This method is now in general use in Canada and by some operators in the United States. Impact force is applied by use of a hand-held sledge hammer, or a pendulum ram suspended from a mobile crane. Because the degree of force required to effect separation increases in relation to the size of the dragline, use of hand-held sledge hammers is restricted to draglines under 40 yards in capacity. 3. Burn Out. -This method is no longer in general use. It is accomplished by use of an extended oxyacetylene nozzle to flame-cut the cable wedged inside of the socket to relieve the pressure fit. PROJECT RESEARCH TO DATE Fabrication and Trials of Pendulum Impact Rams Present and past users of this type of device were surveyed to ascertain problems experienced and optimum weight needed to generate the required force. The largest ram we uncovered weighed 1,600 pounds and was used for removing the cables on 110-cubic-yard bucket draglines. We also learned that users had 76 experienced difficulty in holding the ram level for proper impact and problems with reverberation in the crane cable. Our present ram design (fig. 2) offsets the known problems. A chain, two-point connecting harness with a 15- foot leader was used. Chain material was chosen for flexibility and strength. The 15-foot leader enables cinching of the crane hook to the boom to reduce reverberation. The two-point hookup eliminates the effort required to main- tain the device on a level keel, permitting an even and maximum impact. To date, four rams have been fabricated in weights of 400, 800, 1,000, and 1,400 pounds to accommodate the various sizes of draglines. Separation has been attempted on four separate occasions with two positive and two negative results. On each attempt, the two drag links were worked. The two successful attempts were on 60-cubic-yard machines using the 800-pound ram. One of the unsuccessful attempts was on a 60-cubic-yard machine that had previously yielded positive results, and the second was on a 78-cubic-yard machine. The 800- and 1,000-pound rams were tried on both occasions. Investi- gation to determine why separation was not attained produced the following results: 1. On the 60-cubic-yard machine, a new type wedge and socket made from a softer material had been installed. This allowed the cable to cut deeper into both the wedge and socket, producing a tighter fit. Laboratory separation of the newer design units proved that a much higher force was required to effect separation than for the older design. The manufacturer confirmed that this aspect was not taken into consideration when the design change was made. 2. The second negative attempt is believed to be our fault in not recog- nizing the need for firmly anchoring the socket during impact. Force was absorbed by movement of the unit. The operators of the second unit have agreed to supply us with joined units for laboratory separation testing. When we have determined the separation forces required, they will allow further attempts with the ram. Controlled Wedge and Socket Separation — Eight units have been separated to date using a Tinius Olsen, 400,000-psi testing machine (fig. 3). Six of the wedge and sockets were from the 60-cubic-yard machine with which we experi- enced the failure on the second ram attempt. We found that a wide range of force was required to effect separation. The first two units separated were of the older design and required 59,300 and 76,900 pounds of force. The force required for the four units of the newer design ranged from 93,000 to 132,200 pounds. The remaining two units separated were from a different make of machine, but of the same size. Separation force required was much lower at 31,250 and 45,250 pounds. Cannon Method Force Generation Determination — The Spokane Research Center fabricated a cannon to determine the degree of force generated using a typical cannon design with 40- and 50-grain primer cord as the explosive force. Instrumentation was a mix of specially designed and fabricated items with commercial products. Testing was designed to measure the force generated at detonation and the velocity of the impeller, which in turn can be converted 77 FIGURE 2. - Fourteen-thousand-pound pendulum impact ram. 78 FIGURE 3. - Wedge-and-socket controlled separation. Wedge-and-socket unit from a 60-cubic- yard machine mounted in a locally fabricated holder. The testing machine is a 400,000-psi Tinius Olsen. 79 f FIGURE 4. - Cannon device instrumented for testing. to impact force (fig. 4). Preliminary testing was started but was halted before conclusive data could be compiled owing to failure of a commercial transducer used to measure the internal force. Testing will continue when the failure has been corrected. FUTURE PROJECT PLANS Research will continue to follow different avenues of approach to deter- mine (1) magnitude of forces required to effect separation of the socket and wedges of the various sizes and manufacture of dragline cable terminations, (2) magnitude of forces produced by the cannon and impact rams, and (3) improved methods and equipment for cable removal. Arrangements have been completed to obtain four more joined sockets from a 60-cubic-yard dragline and four from a 78-cubic-yard dragline. Preliminary discussions have also been conducted to obtain joined units from 110-cubic- yard draglines. When the complete range of data is compiled and analyzed, 80 it will provide a better, but not complete, understanding of the forces required for cable separation. Tests to date indicate that a wide range of forces may be needed within each size of dragline. Variations in design and strength of material of the socket and wedges, as well as length of time in use, affect the amount of force needed for removal. A complete understanding of the subject could be obtained only by controlled separation testing of all models of the various manufacturers of dragline equipment over the working life of the units. This is not possible under the limited time and funding allotted for this project. However, it is believed that sufficient data will be obtained to produce significant improvements in removal equipment design and procedural techniques. When complete data have been compiled as to the forces now generated by the cannon method, they will be presented to ballistic experts to determine the extent of present hazard, and if a less hazardous explosive charge and procedure can be devised. The data will also be used to help determine the forces needed to effect separation of various sizes and makes of draglines, and correlated with the forces generated by the different weights of impact rams to determine their capabilities. Other areas of equipment design will also be explored, such as portable hydraulic equipment designed for on-site use and improved cannon design. ■frU.S. GOVERNMENT PRINTING OFFICE: 1980-603-102/38 int.-bu.of mines,pgh.,pa. 24621 **%> ■& •- ^** :1ft' ^^ v^' o°*.^>A .Av^-X .c *.-^:.^ „/// * ^ ^cr 'bV ' ^>. 4 ."„ '• A V ^ * A* "** 4> . % *bV" •5 .' ^ ^°^ .0' ^••- , <» v :. ^. 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