No. 9124 
 
 i 
 
 
 ■ 
 

 
 
 
 
 
 > J 
 
 
 ,4^> 
 
 
 
 
 
 ^ ^ *° • * A <> 
 
 * 9 ^ 
 
 
 
 ** v % -. 
 
 
 V v 
 
 
 <* **?Yi* <0 
 
 
 ^ %. -: 
 
 > 
 
 
 
 
 
 
 
 
 '^/ 
 
 
 
 /«* ^> ' • ■ • 
 
 ' %^ I 
 
 
 
 
 
 
 
 ^6* 
 
 \"*^ff-\,/ v^V v*^>^ 
 
 %«♦* • 
 

 
 . ^ ^ s* 
 
 <-^ J* j *^|/ffljii|§=^ o aV^ 
 
 0* _.•!_••. V ^\*« t '-* 
 
 \ .</ *^K* a ' ^ & 
 
 ' ^ AV ♦ 
 
 A V *V o_, 
 
 
 
 ^ V- 
 
 «^<2* 
 
 
 jf " 
 
 IV 
 
 c> * 
 
 ^ a^ *>Wa* «v <£ •fife*- ** a* •>Va° «v <£ 
 
 V ^ " , ^ <%* 
 
 
 •• ^ 
 
 ' * 6 „. % ^ $S A^ 
 
 Vol *.?« ^\ a0 
 
 » cS5\^V^^ . O 
 
 j0 VV 
 
 
 
 4° '%> "'" 
 
 0° .1^1' °o 
 
 %/ *'^K£: V^ .'9Kl "W 
 
 0^ o^^.^O. A> V 
 
 v-o^ 
 
 <". o 
 
 'bK 
 
 
 aV ^ .y^\F/ .V «*. 'J 
 
 >r 
 
 4» 
 
 *.*&&*+ *?>&*'*.-% &*&&*+ <,*>•&'•*+ A> ^ 
 
 
 *iv.»* Ap 
 
 j?-^ 
 
 • «£» 4 „* 
 
 i - ^- ' 
 
 ' o ^ Oft "j 
 
 ^ t £ • fife • ^ ^ •^fA" \ £ • fife** ^ ^ *^Wa« ^. <^ - fc ^K^« ^ 
 
 
 A^ . •■'•,. "^ts 
 
 
 AV -j^ 1 
 
 9 ^. • 
 
 A V .t... <S> 
 
 •0* o " " *^o 
 
 ♦o«o 9 ^ 
 
 * V>» 4 «" 
 
 'by' 
 
 • <1> o * 
 
 .-ft^" o. "^s,!- 1 .,0 
 
IC 9124 
 
 Bureau of Mines Information Circular/1987 
 
 Mined Land Subsidence Impacts on Farmland 
 With Potential Application to Illinois: 
 A Literature Review 
 
 By David L. Veith 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 9124 
 
 
 Mined Land Subsidence Impacts on Farmland 
 With Potential Application to Illinois: 
 A Literature Review 
 
 By David L. Veith 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
jut- q ^ 
 
 Library of Congress Cataloging in Publication Data: 
 
 Veith, David L. 
 
 Mined land subsidence impacts on farmland with potential applica- 
 tion to Illinois. 
 
 (Information circular ; 9124) 
 
 Bibliography: p. 15—16. 
 
 Supt. of Docs, no.: I 28.27: 9124. 
 
 1. Subsidences (Earth movements)— Illinois. 2. Coal mines and mining— Illinois. 
 3. Land use— Illinois. 4, Farms— Illinois. I. Title. II. Series: Information circular (United 
 States. Bureau of Mines) ; 9124. 
 
 TN295:U43 
 
 [QE600.3.U6] 
 
 622 s [333.76'16] 
 
 86-600227 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Geological and land considerations 3 
 
 Geology of the Illinois Basin 3 
 
 Drainage classes of soils 3 
 
 Land use qualifications 4 
 
 Subsidence characteristics 6 
 
 High-extraction mining 6 
 
 Illinois mining 7 
 
 Ground settlements of high-extraction mining 8 
 
 Subsidence effects 9 
 
 Western Pennsylvania ground water 9 
 
 Illinois ground water 10 
 
 Farmlands 10 
 
 Crops 11 
 
 Economic considerations 12 
 
 Bureau of Mines and State of Illinois subsidence research program 13 
 
 Summary and conclusions 14 
 
 References 15 
 
 ILLUSTRATIONS 
 
 1 . Drainage classes of soils 4 
 
 2. Optimized high-extraction underground coal mining plan 7 
 
 3. Typical subsidence from single-panel high-extraction mining in western 
 
 Pennsylvania 10 
 
 TABLES 
 
 1. Crop yields on three Virgin Island soil types with slope and erosion* with 
 
 average to high levels of management 5 
 
 2. Development of underground coal mining techniques in Illinois 7 
 

 UNIT OF MEASURE ABBREVIATIONS USED IN THIS 
 
 REPORT 
 
 ft 
 
 foot pet 
 
 percent 
 
 in 
 
 inch st 
 
 short ton 
 
 m 2 
 
 square meter vol pet 
 
 volume percent 
 
 mi^ 
 
 square mile yr 
 
 year 
 
 mm 
 
 millimeter 
 
 degree 
 
MINED LAND SUBSIDENCE IMPACTS ON FARMLAND 
 
 WITH POTENTIAL APPLICATION TO ILLINOIS: 
 
 A LITERATURE REVIEW 
 
 By David L. Veith 1 
 
 ABSTRACT 
 
 This report summarizes a Bureau of Mines review of selected literature 
 ■on the effects of subsidence due to high-extraction underground coal 
 mining on farmland areas. The data are presented for consideration in 
 evaluating the subsidence effects due to similar mining techniques on 
 the prime farmland areas of Illinois. 
 
 In Illinois the ground water level in the glacial drift is only 2 to 
 15 ft below the nearly flat to gently rolling ground surface. The main 
 subsidence concern is flooding, as caused by the lowering of the ground 
 surface, and the subsequent effects on crop production. Positive drain- 
 age must be maintained in the farmlands, and the need exists for exten- 
 sive regional planning by the mining and agricultural industries to 
 maximize short- and long-term production from both efforts. The Bureau 
 is cooperating with the State of Illinois to develop basic information 
 necessary for such planning. 
 
 1 Mining engineer, Twin Cities Research Center, Bureau of Mines, Minneapolis, MN, 
 
INTRODUCTION 
 
 This report summarizes selected litera- 
 ture dealing with underground mine- 
 related subsidence effects on coal mining 
 lands throughout the United States. Some 
 foreign data are also summarized. The 
 information is presented for consider- 
 ation in the evaluation of subsidence ef- 
 fects on Illinois prime farmland crop 
 production, but in no way is it implied 
 that the information pertains directly to 
 Illinois unless the reference is clearly 
 identified as such. 
 
 As will be illustrated, the effects of 
 underground coal mining subsidence in Il- 
 linois have been investigated for some 
 time, but no formal study of the effects 
 on prime farmland crop production have 
 been conducted. Efforts underway at this 
 time will document such impacts and lead 
 to mitigative measures that should opti- 
 mize production from both the underground 
 coal mining industry and the agricultural 
 industry. 
 
 Much of central and southern Illinois 
 prime farmland overlies high-quality bi- 
 tuminous coal seams. Maximization of 
 underground coal production results in 
 ground movements and subsequent distur- 
 bance of the surface. Illinois ground 
 water lies 2 to 15 ft below the ground 
 surface, and subsidence-induced ground 
 movements can also affect the movement 
 of surface water. The ground water is 
 generally dependent on precipitation 
 to maintain its level and, therefore, 
 its availability for crop production. 
 Any modification of surface water hy- 
 drology could affect the resultant crop 
 production. 
 
 The challenge is to maximize under- 
 ground coal recovery in these Illinois 
 prime farmland areas, and at the same 
 time ensure the productivity levels of 
 crops grown on the overlying soils. The 
 solution lies in the cooperation of these 
 two valuable industries to develop 
 planned mining and agriculture programs 
 to maximize recovery from both natural 
 resources. To acquire the in-depth un- 
 derstanding necessary to achieve this 
 goal, the Bureau of Mines and the 
 State of Illinois are cooperating on a 
 
 coordinated mine subsidence research pro- 
 gram to ultimately develop guidelines for 
 more effective underground mining techni- 
 ques in order to maximize coal extraction 
 while preserving the productivity of 
 prime farmlands. 
 
 Illinois coal mining companies have 
 basically three options for underground 
 operations (1_):2 
 
 1. Mine a low percentage of the coal 
 and leave substantial pillars for total 
 support of the overlying strata (low 
 extraction). 
 
 2. Mine a high percentage of the coal, 
 plan on subsidence, and take the respon- 
 sibility for reclamation of the affected 
 surface (high extraction). 
 
 3. Mine no coal at all (no 
 extraction). 
 
 Obviously there are certain circum- 
 stances under which each of the three 
 options would be the best choice. When 
 considering maximum utilization of both 
 the coal resource and the overlying prime 
 farmland resource, option 2 is the best 
 choice (1_)« High-extraction underground 
 coal mining, planned in advance to mini- 
 mize surface impacts on the overlying 
 agriculture industry, and properly car- 
 ried out, will result in the maximum 
 utilization of both resources. 
 
 In 1982, Peabody Coal Co. reported that 
 193 subsidence events had occurred on its 
 Illinois properties since 1971 (J L )« Less 
 than 2 pet of its mined lands were af- 
 fected. Subsidence regulation proposed 
 at that time would have caused the 
 company to lose about 70 million st 
 of coal reserves (about 8 pet of their 
 total reserves), and would have short- 
 ened their mining life by more than 
 42 yr, or more than 190-mine yr of 
 production. Regulation that reduces 
 mineable reserves because of potential 
 subsidence impacts is, therefore, of 
 great concern to mining companies such 
 as Peabody. Research to improve the 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references at 
 the end of this report. 
 
cohabitation of the mining and agricul- 
 tural industries in the prime farmland 
 areas of Illinois is also of great 
 
 interest to the involved mining compa- 
 nies, the agricultural industry, and both 
 State and Federal governmental agencies. 
 
 GEOLOGICAL AND LAND CONSIDERATIONS 
 
 GEOLOGY OF THE ILLINOIS BASIN (_2) 
 
 Overall, the Illinois Basin is a broad, 
 spoon-shaped trough of sediments con- 
 taining several anticlinal belts. Gen- 
 erally, the folds have gentle slopes with 
 less than 200 ft of relief. Folding and 
 faulting is most prominent in south- 
 eastern Illinois. The topography ranges 
 from flat-lying to rolling, with soils 
 chiefly developed in glacial drift. Till 
 deposits in the northern and central 
 parts of the State reach 600 ft in depth, 
 but the drift is generally less than 
 50-ft deep in southern Illinois. 
 
 Almost all the mapped coal reserves in 
 Illinois are in the middle portion of the 
 Pennsylvanian System, which underlies 
 about 70 pet of the land of the State. 
 Shales and underclays form 65 to 70 pet 
 of the upper portions of the System, 
 limestones form 5 to 10 pet, and coal 1 
 to 2 pet. Shale beds exceed 100 ft in 
 thickness but more commonly are 20-to-40 
 ft thick, and the underclays are commonly 
 2- to 5-ft thick. The Pennsylvanian 
 sequence shows great lateral persist- 
 ence, except for the sandstones, which 
 frequently occur as channel deposits. 
 
 DRAINAGE CLASSES OF SOILS (3) 
 
 It is important in the study of the ef- 
 fects of mine subsidence on prime farm- 
 land to understand the drainage classes 
 of soils and how these affect crop pro- 
 duction. This understanding is par- 
 ticularly important in Illinois where 
 ground water is shallow and essentially 
 contained in glacial overburden, sup- 
 ported by shale overlying the coal seams. 
 
 Figure 1 depicts the five U.S. Depart- 
 ment of Agriculture (USDA) (h) drainage 
 classes of soils and indicates approxi- 
 mate root penetration with respect to the 
 mottled zone in each class. A. mottled 
 zone contains spots of different colors 
 in a uniform soil matrix, indicating 
 
 intermittent wetness with associated 
 oxidized and reduced materials. 
 
 In well-drained soils the moisture is 
 rapidly removed by internal drainage. 
 These soils often are dry because they 
 are close to bedrock, are on very steep 
 slopes, or have coarse textures that 
 limit the moisture holding capacity. 
 
 In moderately well drained soils the 
 water is removed less rapidly than in 
 well-drained soils, so that the profile 
 is occasionally wet for short but signif- 
 icant periods. These soils usually have 
 low-permeability layers in the B or C 
 horizons, and accumulations of seasonal 
 seepage waters. 
 
 Somewhat poorly drained soils are wet 
 for significant periods but not continu- 
 ously, as water is removed slowly. These 
 soils have a low-permeability layer, a 
 high water table, and accumulate water 
 through seepage. 
 
 Poorly drained soils remain wet much of 
 the year because water is removed very 
 slowly. The water table is near the sur- 
 face much of the year; there is a low 
 permeability layer, and seepage is a 
 problem. 
 
 Finally, very poorly drained soils are 
 continuously wet, as the water table is 
 near the surface most of the year. These 
 soils are in depressions and ponding 
 sites where water accumulates. 
 
 According to the USDA, the rooting zone 
 basically stops at the mottled zone, and 
 the depth of this zone determines crop 
 production. Changes in surface elevation 
 with respect to the ground water eleva- 
 tion may change the location of the mot- 
 tled zone, and, therefore, the crop pro- 
 duction capacity of the soil. 
 
 If wet soils are permeable, they can be 
 improved. When wet soils are only 
 slightly permeable, drainage and amelio- 
 ration are often difficult and productiv- 
 ity improvement may only be slight. 
 
 Olson (3) analyzed information from 
 another USDA rating of soils for plant 
 
.Crop root 
 development 
 
 x" 
 
 i- 
 
 0_ 
 LU 
 
 Q 2 
 
 3 L 
 
 MWD 
 
 SPD 
 
 VPD 
 
 Soil profile drainage classification 
 
 Drainage class designation 
 WD - Well drained 
 
 Zone designation 
 A - Rooting zone 
 
 MWD - Moderately well drained B - Mottled zone 
 
 SPD - Somewhat poorly drained C - Gray, brown, or stained zone 
 
 PD - Poorly drained 
 VPD - Very poorly drained 
 
 V - Permanent or fluctuating water table 
 (inferred from zone characteristics) 
 
 FIGURE 1 .—Drainage classes of soils. After Olson (3). 
 
 growth (5). Good plant growth requires 
 well-drained to moderately well drained 
 soil, with very friable to friable, moist 
 consistency. Textures can be very fine 
 sandy loam, fine sandy loam, loam, silt, 
 or silt loam. The thickness of the soil 
 above a hard layer, water table, or bed- 
 rock must be more than 30 in. Finally, 
 the soil slope must be less than 8 pet, 
 and it must contain less than 8 vol pet 
 coarse fragments. Fragments are consid- 
 ered coarse depending on their shape and 
 dimensions. Granular and crumb struc- 
 tures are coarse if their particle diam- 
 eter ranges from 5 to 10 mm, and angular 
 to subangular blocky structures are 
 coarse if their particle diameter ranges 
 from 50 to 100 mm. 
 
 LAND USE QUALIFICATIONS 
 
 Olson (3) describes some physical char- 
 acteristics of Tompkins County, NY, soils 
 related to land use. Some of these char- 
 acteristics can be identified with subsi- 
 dence effects and, therefore, may have 
 some application to Illinois. The county 
 soil map shows that — 
 
 1. More than 75 pet of active pasture 
 and cropland have slopes of less than 
 10 pet. 
 
 2. About 80 pet of abandoned farmland 
 has slopes of more than 10 pet. 
 
 3. About 40 pet of forest land has 
 slopes of 35 to 70 pet. 
 
4. About 75 pet of pasture land has 
 soils with seasonal water tables more 
 than 5 in below the surface. 
 
 5. About 60 pet of the cropland has 
 soils of moderate to rapid permeability. 
 Thus, it appears that the most pro- 
 ductive soils have slopes of less than 
 10 pet, seasonal water tables (pasture 
 land) more than 5 in below the surface, 
 and moderate to rapid permeability 
 drainage. 
 
 Erosion of soils is probably the most 
 destructive process that reduces the pro- 
 ductivity of the land (3). Topsoils and 
 the A horizon generally contain the most 
 nutrients and the best structure for 
 plant growth, and any material eroded 
 from these parts of the soil profile will 
 have a detrimental effect on crop yield 
 and plant growth. 
 
 A common agricultural tool, the Univer- 
 sal Soil Loss Equation, permits planners 
 and farmers to predict the average rate 
 of soil erosion for each feasible alter- 
 native combination of crop management 
 related to a specific soil map unit, the 
 rainfall pattern, and the topography. As 
 described by Olson, (3), the Universal 
 Soil Loss Equation is — 
 
 A - RKLSCP 
 
 where A = the computed soil loss per 
 unit area, 
 
 R = the rainfall and runoff 
 factor, 
 
 K = the soil erodability factor, 
 
 L = the slope length factor, 
 
 S = the slope steepness factor, 
 
 C = the cover and management 
 factor, 
 
 and 
 
 P = the support practice factor. 
 
 Soil is protected from erosion by veg- 
 etation, the design of which is deter- 
 mined by the slope and contour of the 
 land. Since erosion of soils is a nat- 
 ural geomorphic process that can never be 
 eliminated completely, tolerable soil 
 
 losses can be established for each soil 
 type to balance the soil building process 
 and thus to maintain acceptable agricul- 
 tural production over a long period of 
 time. 
 
 Olson (3) describes crop yields in the 
 Virgin Islands for clay and clay-loam 
 soil types of various slopes, with aver- 
 age and high levels of management 
 (table 1). Obviously, slopes greater 
 than 5 pet and erosion are detrimental to 
 crop production, resulting in crop losses 
 ranging from 8 to 42 pet, when compared 
 with production from relatively flat, un- 
 eroded soils. Although probably not ap- 
 plicable to the prime farmlands of Illi- 
 nois, this comparison is included to 
 illustrate the potential impact of slope 
 and erosion on crop production. 
 
 In Illinois prime farmlands, sub- 
 sidence-created slopes are generally 
 less than 1 pet but may reach 4 pet for 
 short distances along their profile. 
 Therefore, it appears that If subsidence 
 from high-extraction underground coal 
 mining creates surface slopes of less 
 than 5 pet, the impact will not be great 
 enough to significantly increase erosion 
 of the soil. Erosion is not the concern 
 in Illinois, but changes in drainage 
 of the flat prime farmlands caused by 
 subsidence are of concern. 
 
 Sarkar (6_) identified 22 independent 
 soil characteristics from which soil 
 scientists attempt to correlate yields. 
 These characteristics are representative 
 of a broad range of soils; many are 
 related to moisture holding capacity and 
 thus are critical to plant growth and 
 crop production. 
 
 TABLE 1. - Crop yields on three Virgin 
 Island soil types with slope and 
 erosion, with average to high 
 levels of management 
 
 Soil type 
 Clay , 
 
 Clay-loam 1. . 
 Clay-loam 2. . 
 1 Eroded. 
 
 Slope, pet 
 
 Yield, pet 
 
 0- 2 
 
 100 
 
 2- 5 
 
 83- 90 
 
 1 5-12 
 
 58- 89 
 
 2-15 
 
 100 
 
 1 5-12 
 
 75- 92 
 
 0- 3 
 
 100 
 
 5-12 
 
 75- 92 
 
Some of Sarkar's characteristics, as 
 described by Olson, which may have ap- 
 plication in Illinois, follow: 
 
 1. Yields on the same field in Mary- 
 land clearly showed the effects of 
 moisture and erosion. 
 
 2. Iowa corn yields related directly 
 to soil variables such as slope, bio- 
 sequence, available water holding capac- 
 ity, erosion, organic carbon, drainage 
 class, clay content, bulk density, pH, 
 available phosphorus, and available 
 potassium. 
 
 3. Soil factors most highly correlated 
 with corn yields in North Carolina were 
 moisture holding capacity, clay and sand 
 combinations, extractable phosphorus, 
 percent base saturation and related 
 properties that control soil acidity, and 
 the charge on the cation-exchange 
 complex. 
 
 Weather and agricultural management are 
 major variables influencing the soils and 
 the resultant yields. Since weather can- 
 not be controlled, agriculture practices 
 and mining activities affecting those 
 practices become the controlling varia- 
 bles. Soils determine the potential for 
 moisture storage, which affects a soil's 
 ability to withstand drought. Soil 
 factors influencing runoff and erosion 
 directly influence crop yields, and 
 
 managing mining activities such that 
 these soil factors are not adversely af- 
 fected will ensure that crop yields can 
 be maximized with proper aricultural 
 practices. 
 
 Olson (3) described a yield measuring 
 procedure called sequential testing, 
 which may be beneficial in measuring the 
 effects of subsidence on crop production. 
 Similar soils exhibit similar character- 
 istics in the same geologic conditions. 
 Sequential testing is the sampling of 
 soils across a landscape in which the 
 soils occupy "sequential" positions along 
 the sampling transect. For example, 
 soils in a humid region commonly have the 
 same drainage sequence in similar geo- 
 logic materials. By sampling the soils 
 along a transect, soil drainage classes 
 can be identified and the growth of 
 moisture-sensitive vegetation can be mea- 
 sured at each sample point. Thus, veg- 
 etative growth can be related to the 
 drainage class and to the soil depth to 
 mottling and seasonal water tables. 
 
 Similar sequences can occur for soil 
 texture, slope, pH, fertility, land use, 
 crop growth, crop yield, and other soil 
 and land characteristics. If experiments 
 are run on contrasting soils, one can 
 evaluate the effects of soil differences 
 on crop production. 
 
 SUBSIDENCE CHARACTERISTICS 
 
 HIGH-EXTRACTION MINING 
 
 Peng (_7) summarized the mechanics of 
 surface subsidence in the Appalachian 
 Coal Basin due to underground coal mining 
 in a 1980 publication. In very general 
 terms, room-and-pillar mining with full 
 pillar extraction can result in subsi- 
 dence similar to that resulting from 
 longwall mining. The author sized the 
 maximum caving dome height at 30 to 50 
 times the mining height with caving 
 angles between 15° and 35° and an average 
 angle of 25°. Ideally, strata overlying 
 the coal seam above the caving zone will 
 remain more or less intact and sag uni- 
 formly, as would a continuous beam, re- 
 sulting in a symmetrical surface sag 
 about the centerline of the single panel. 
 Actually, strata behavior is greatly 
 
 dependent on the characteristics of its 
 components, and the resulting sag may 
 range from uniform to highly irregular. 
 Multiple panels will result in overlap- 
 ping subsidence profiles, skewed toward 
 the previously mined panel. 
 
 Controlling factors of surface subsi- 
 dence discussed by Peng are well known 
 and will not be repeated here. In the 
 discussion on the prevention of subsi- 
 dence impacts the point was made that ad- 
 vance planning is the best method of 
 eliminating or reducing surface ground 
 damage. Regional planning of full- 
 extraction operations, with complete re- 
 gard for maintaining the relative posi- 
 tion of surface contours, appears to be 
 the best method of ensuring positive sur- 
 face drainage. A hypothetical example of 
 such a plan is shown in figure 2. 
 
Surface drainage 
 system 
 
 Surface contour 
 elevation 
 
 Direction of mining 
 advance 
 
 FIGURE 2.— Optimized high-extraction underground coal mining plan. 
 
 ILLINOIS MINING 
 
 Bauer (8_) presented a paper in 1981 
 describing some of the characteristics of 
 subsidence from various coal mining tech- 
 niques in Illinois. Table 2 presents a 
 modified list from Bauer of the progres- 
 sion of mining methods and the related 
 percentages of panel extraction commonly 
 practiced in Illinois. High-extraction 
 retreat and longwall are the methods gen- 
 erally used in Illinois and are probably 
 the methods of the future where subsi- 
 dence is either desired or allowed. 
 Where subsidence is not allowed, blind or 
 checkerboard roora-and-pillar techniques 
 are employed. 
 
 Illinois subsidence takes two basic 
 forms, pit subsidence and sag-trough sub- 
 sidence. Pit subsidence is a sudden drop 
 in the surface such that the hole has 
 
 nearly vertical walls. It is caused by a 
 sudden collapse of the bedrock over a 
 mine void, usually where the mining was 
 close to the surface and the overlaying 
 strata were not competent. 
 
 TABLE 2. - Progression of underground 
 coal raining technique development 
 in Illinois 
 
 Panel extrac- 
 Mining method tion, pet 
 
 Roora-and-pillar: 
 
 Early 1 < 80 
 
 Modified < 80 
 
 Blind 50- 65 
 
 Checkerboard 40- 60 
 
 Longf ace 100 
 
 High-extraction retreat.... 70- 90 
 
 Longwall 100 
 
 1 If pillars pulled. 
 
Sag subsidence refers to a large, near- 
 ly equidimensional subsidence depression 
 over room-and-pillar mines. Trough sub- 
 sidence is similar to sag subsidence, 
 except that the depression is elongated 
 and typically results from high- 
 extraction room-and-pillar and longwall 
 mining techniques. 
 
 Data generated for Illinois by Bauer 
 (jJ) indicate that pit subsidence develops 
 only over shallow mines less than 165-ft 
 deep. Sags or sags and troughs develop 
 over both shallow and deep mines, and 
 pits, sags, or troughs can develop over 
 mines 75-to-165 ft deep. 
 
 Of the possible factors affecting the 
 subsidence profile characteristics with a 
 given mine geometry, the regional geology 
 seems to have the greatest influence (8). 
 Room-and-pillar mining in central Il- 
 linois is in the No. 5 coal seam, which 
 is fairly thin and strong, resulting in 
 strong pillars and, low height-to-width 
 pillar ratios and, therefore, minimal 
 subsidence due to pillar crushing or 
 compression. 
 
 Similar mining techniques are practiced 
 in southwestern Illinois in the Herrin 
 (No. 6) coal seam, which is thicker than 
 the No. 5 seam and has some of the high- 
 est quality mine roof in the State be- 
 cause of well-developed, thick limestone 
 beds overlying the coal (_8). Subsidence 
 in this region is somewhat greater than 
 that in central Illinois. 
 
 Room-and-pillar mining in southern Il- 
 linois, also in the Herrin (No. 6) coal 
 seam, is in an area of major regional 
 geological structures, with little or no 
 limestone in the mine roof (8). Subsi- 
 dence is greater in this region than in 
 the two regions described above. 
 
 In comparing subsidence in Illinois 
 with that in Great Britain, Bauer (8) 
 states that the angle of draw for Il- 
 linois longwall mining is 12° to 25°, 
 which is generally less than that for 
 British operations. Probable causes of 
 this difference are that (1) Illinois 
 overburden rock is stiffer and more 
 resistant to subsurface movements, 
 (2) British rock, unlike the rock in Il- 
 linois, has been subjected to tectonic 
 faulting, and (3) multiple-seam mining 
 is commonplace in Britian and not in 
 
 Illinois. Multiple-seam operations tend 
 to break up the overburden, making it a 
 less stiff rock mass, and thus inducing 
 more widespread subsidence. 
 
 GROUND SETTLEMENTS OF HIGH- 
 EXTRACTION MINING 
 
 Generally, retreat room-and-pillar and 
 longwall mining methods are similar 
 enough to result in similar subsidence 
 patterns where the geology is the same 
 (2^). Longwall mining removes 100 pet of 
 the coal within the panel; retreat room- 
 and-pillar mining usually removes as much 
 of the coal as local conditions allow, 
 and when this removal is a high percent- 
 age of the in-place coal, the resulting 
 caving and ground movement is similar to 
 that for longwall mining of nearly equal 
 dimensions. However, care must be exer- 
 cised in this analogy, as the rock 
 loading sequence differs greatly between 
 the two methods. 
 
 At the Old Ben No. 24 Mine near Benton, 
 IL, a longwall demonstration study was 
 conducted under Bureau contract (2, 9)» 
 Three longwall panels were driven adja- 
 cent to a modified retreat room- 
 and-pillar panel, and comparisons were 
 made of their subsidence profiles. Long- 
 wall panel 1 was first developed adjacent 
 to the narrow room-and-pillar panel; 
 then, in sequence, longwall panels 2 and 
 3 were developed along panel 1. 
 
 Retreat room-and-pillar mining (2_) at 
 Old Ben generally recovered 80 to 90 pet 
 of the coal; however, because of the 
 proximity of the longwall panels, a some- 
 what different retreat room-and-pillar 
 mining method was required for the demon- 
 stration section, which reduced recovery 
 to less than 80 pet. Chain pillars about 
 86 ft wide separated the previously mined 
 retreat room-and-pillar panels from long- 
 wall panel 1. The coal seam was 620-ft 
 deep, and longwall panels 460-ft wide and 
 7-ft thick were mined. Maximum settle- 
 ment observed was 4.3 ft over longwall 
 panel 1 and 2.9 ft over the retreat room- 
 and-pillar panel during the measurement 
 period (9). Retreat room-and-pillar and 
 longwall raining methods are considered 
 high-extraction techniques, but their 
 recovery factors and subsidence profiles 
 
generally are not the same. In this case 
 at Old Ben, with lower than normal re- 
 treat room-and-pillar mining recovery, 
 subsidence over that operation was ex- 
 pected to be less than over the longwall 
 panel. The stumps and fenders of coal 
 left in place in the retreat room- 
 and-pillar mining helped support the roof 
 
 and, although they were readily crushed 
 by the overburden weight, they helped 
 prevent the occurrence of full closure. 
 Additionally, the proximity of the re- 
 treat room-and-pillar panel to the long- 
 wall panel was expected to skew the sub- 
 sidence profile across the longwall 
 panel. Both expectations were realized. 
 
 SUBSIDENCE EFFECTS 
 
 WESTERN PENNSYLVANIA GROUND WATER 
 
 SMC Martin Inc. ( 10 ) studied the ef- 
 fects of coal mine subsidence on ground 
 water aquifers in western Pennsylvania 
 under Bureau contract. Although the 
 structure and hydrological regime are 
 quite different than in Illinois, this 
 study is still of interest in describing 
 the effects of undergound coal mine sub- 
 sidence on the surface and on crop 
 productivity. 
 
 In western Pennsylvania, deep coal min- 
 ing operations often affect regional 
 ground water supplies through subsidence 
 and the resulting fracturing of overlying 
 strata. The existing ground water flow 
 system is then disrupted as it preferen- 
 tially flows toward the mine workings 
 along the newly created or widened frac- 
 ture system. Additionally, more pore 
 space is created in the strata by frac- 
 turing, so the aquifer can store more 
 water. . The water table in the vicinity 
 of the mine becomes depressed or elimi- 
 nated, thus creating a new hydrologic en- 
 vironment. As the rate of subsidence de- 
 creases, the fracture system begins to 
 close due to settlement of the strata. 
 With less direct flow paths to the mine, 
 recharge exceeds discharge and the head 
 increases until a new equilibrium is 
 reached, which may or may not be the same 
 equilibrium point as before mining, 
 depending on the elastic properties of 
 the strata layers. 
 
 According to SMC, longwall mining of 
 coal in western Pennsylvania causes a 
 zone of caving that typically forms a 
 dome 30 to 50 times the height of mining, 
 with the overlying strata remaining in- 
 tact but subject to sagging (fig. 3). As 
 the sag develops, a subsidence trough, or 
 profile, is produced at the surface, 
 
 enclosing an area larger than that of the 
 mined panel. The horizontal limits of 
 the trough depend on the angle of draw, 
 which includes the total area displaying 
 subsidence effects. In western Pennsyl- 
 vania the practical limit of the angle of 
 draw is generally taken as 25°. In Il- 
 linois the subsidence pattern resulting 
 from high-extraction mining tends to 
 exhibit a profile with greater slopes 
 around the inflection point than that 
 shown in figure 3. 
 
 Maximum subsidence over a single panel 
 occurs at the centerline, and the magni- 
 tude depends on the width of the panel, 
 the mined seam thickness, and the verti- 
 cal distance between the seam and the 
 surface. Where the seam is flat with no 
 adjacent panels being mined, the subsi- 
 dence profile generally is symmetrical 
 about the centerline. Multiple panels 
 result in composite subsidence profiles 
 as the effects overlap and are partly 
 additive. 
 
 The response of the overlying aquifer 
 system to longwall mining depends on 
 site-specific variables, including depth 
 to coal, thickness of coal removed, min- 
 ing method, rock mechanics, site stratig- 
 raphy, and aquifer properties. These 
 variables also influence the amount and 
 degree of subsidence. Rock mechanical 
 properties determine both the degree of 
 fracturing in the rock units and the re- 
 compression or healing of the strata that 
 allows water level recovery. Site stra- 
 tigraphy and aquifer properties control 
 the influence of aquitardal layers and 
 types of aquifer systems. 
 
 To determine hydrological changes due 
 to mining operations, it is necessary to 
 analyze data from water level measure- 
 ments, aquifer tests, and borehole 
 geophysics, and to interpret these data 
 
10 
 
 Maximum subsidence 
 
 / \_Subsidence profile 
 (final surface profile) 
 
 Angle of draw 
 
 Seam 
 thickness 
 
 Panel mining width- 
 (Extracted panel) 
 
 FIGURE 3.— Typical subsidence from single-panel high-extraction mining in western Pennsylvania. 
 
 by comparing premining and postmining 
 conditions. The range of ground water 
 fluctuations is a function of the ability 
 of surface infiltration to reach the 
 ground water system and of the degree of 
 hydraulic connection between shallow 
 aquifer zones receiving the surface in- 
 filtration and the deep aquifer zones 
 representing the final repository of 
 ground waters. 
 
 ILLINOIS GROUND WATER 
 
 In some instances, Illinois ground 
 water is mainly contained in glacial 
 overburden supported by shale strata. 
 The shale is highly plastic and, if it is 
 located above the caving zone over a 
 high-extraction mining system, the entire 
 strata should sag and settle without 
 major fracturing. Thus, few channels may 
 open to drain ground water to the lower 
 strata and to the mine, and, except for a 
 temporary depression, the ground water 
 level should return and remain intact. 
 
 In the case of pit subsidence, general- 
 ly associated with roora-and-pillar mining 
 
 close to the surface, the pit walls sink 
 along highly fractured vertical planes. 
 Ground water thus flows more easily into 
 the mine through channels that may take 
 much longer to heal than those formed 
 under sag subsidence conditions. 
 
 Deeper mining and the resulting sag or 
 trough subsidence may have the associated 
 problem of a depressed water table ac- 
 centuated by water draining into the mine 
 and to the clay mine floor. The clay 
 floor absorbs moisture, weakens, and is 
 then heaved by punching pillars. The net 
 results are convergence of the floor and 
 roof, more subsidence, and a greater im- 
 pact on surface topography and the water 
 table. 
 
 The reaction of ground water to subsi- 
 dence in Illinois is being studied under 
 Bureau-sponsored research, and the 
 information will be available upon 
 completion. 
 
 FARMLANDS (1_1) 
 
 The effects of mine subsidence on farm- 
 lands in general depend on the type of 
 
11 
 
 crops, soil character, hydrology, topog- 
 raphy, and other environmental factors. 
 To evaluate such effects requires an ex- 
 tensive data base that does not now 
 exist, although studies are underway. 
 Some potential effects are — 
 
 1. Surface fissures creating paths to 
 drain water from the topsoil, thereby 
 causing drier surface soil conditions and 
 erosion, which widens the cracks. 
 
 2. Changes in ground slope. Steepen- 
 ing slope increases flow velocity, which 
 enhances surface runoff and erodibility. 
 Slope reduction could lead to water- 
 logging and ponding of the soil and 
 eventual crop reduction. 
 
 3. Changes in ground elevation or 
 slope that may disrupt surface drainage 
 and the hydraulic regime, thereby causing 
 flooding or ponding, especially if 
 natural topographical barriers to flow 
 are lowered or the water table is shallow 
 and underlain by an impermeable layer. 
 
 4. Decreases in soil fertility due to 
 modification of the subsurface hydrology 
 that results from downward migration of 
 ground water through cracks. 
 
 5. Changes in ground water quality due 
 to contact with toxic materials. 
 
 6. Occurrences of sinkholes, which may 
 upset the normal drainage system through 
 accumulation or loss of water. 
 
 The USDA (12) related soil erosion po- 
 tential to the Universal Soil Loss 
 Equation. It further identifies slopes 
 ranging from "gently sloping" to "moder- 
 ately sloping" as those most susceptible 
 to water and wind erosion. These slopes 
 are in the range of 5 to 8 pet. Slopes 
 of 6 to 8 pet displayed gradually in- 
 creasing crop losses, but the loss in- 
 creased much more rapidly with steeper 
 slopes. 
 
 Agricultural lands are classified by 
 Guernsey (13) in relation to mine subsi- 
 dence as prime and nonprime farmlands. 
 Prime farmland has "the best combination 
 of physical and chemical characteristics 
 for producing food, feed, forage, fiber 
 and oilseed crops. It is the land that 
 gives the highest agricultural yield with 
 minimum input when managed according to 
 modern farming methods." Generally, 
 prime farmland soils have slopes of less 
 than 8 to 10 pet. 
 
 Basically, subsidence damage to agri- 
 cultural lands may result in the loss of 
 use or reduced productivity, but the ex- 
 tent of this effect is very site specific 
 and, therefore, difficult to quantify in 
 general terms. Ground movement changes 
 the soil environment and the soil build- 
 ing process, and unless the movement is 
 quite severe, it may take many years to 
 detect the changes resulting from subsi- 
 dence. As long as positive drainage is 
 maintained and surface slopes remain gen- 
 tle enough to prevent erosion beyond what 
 is acceptable, the impact of mined land 
 subsidence on prime farmland should be 
 minimal (13). 
 
 CROPS 
 
 In an unpublished preliminary report on 
 the effects of high-extraction coal- 
 mine-induced subsidence on crop produc- 
 tion, Darmody (14) describes the test 
 areas in Illinois selected to compare 
 high-extraction retreat and longwall min- 
 ing methods, and the procedures used to 
 determine the differences in results. 
 Preliminary results indicate that 
 longwall-caused subsidence is much more 
 obvious than that of high-extraction 
 retreat mining; it is more clearly marked 
 on the surface and especially on level 
 divides or in bottoms. 
 
 Although both types of mining make pre- 
 viously wet soils wetter, high-extraction 
 retreat mining wet areas are more random 
 and less well defined than longwall wet 
 areas. The orientation of mining panels 
 tends to affect the severity of subsi- 
 dence effects, in that mine panels run- 
 ning with natural surface drainage seem 
 to cause less impact than those running 
 across the drainage. 
 
 A subsided panel can change the local 
 base of a stream running across it caus- 
 ing ponding. This impact is greatest in 
 areas of subtle topography, where subsi- 
 dence of only a foot or two can change 
 the drainage pattern of the entire 
 watershed. 
 
 Weather significantly affects subsi- 
 dence impacts. In a particularly wet 
 year the subsided area may never dry 
 sufficiently to support crop growth; 
 however, in a dry year the subsided 
 
12 
 
 surface may be able to support vegetation 
 that normally would not survive. 
 
 A general conclusion concerning design 
 criteria for longwall panels is that they 
 should be oriented parallel to natural 
 drainage patterns in areas of subtle to- 
 pography to maintain positive drainage 
 and potentially reduce surface crop dam- 
 age. High-extraction retreat subsidence- 
 induced effects, however, appear too 
 random to generalize this type of conclu- 
 sion, and more investigation is necessary 
 to develop an innovative premine plan- 
 ning system to ensure acceptable drain- 
 age, as was generalized with long- 
 wall orientation. 
 
 ECONOMIC CONSIDERATIONS 
 
 Surveys indicate that the most serious 
 problems resulting from subsidence are 
 depressions or potholes that cause water 
 to stand, and the disruption of drainage 
 patterns to either underground tile or 
 surface drainageways (15). As a result, 
 reduced crop yields and, in some cases, 
 cases, complete crop loss have been 
 reported. 
 
 Restoration of land productivity af- 
 fected by subsidence is accomplished by 
 four main methods: 
 
 1. Restoring surface drainage is the 
 most frequent method; it is most commonly 
 accomplished by digging surface drainage 
 ditches. 
 
 2. Replacing broken underground tile. 
 
 3. Use of mechanical equipment to fill 
 depressions with soil from the surround- 
 ing area. 
 
 4. Hauling in dirt from outside the 
 area to fill depressions. 
 
 The soils in Illinois were formed 
 under varying conditions and, therefore, 
 have differences in structure, texture, 
 and potential agricultural yields. Of 
 those areas where coal mining is 
 practiced, north central, east central, 
 and central Illinois have the high- 
 est potential corn yields under a 
 high level of management, which most 
 successful farm operators now use. 
 West central Illinois has moderately 
 favorable productivity indexes and 
 
 potential corn yields under high level 
 management. Southwestern and southern 
 Illinois soils are less productive, and 
 potential corn yields under a high level 
 of management are, therefore, lower than 
 in the other areas (15). 
 
 Poor drainage, whether natural or sub- 
 sidence induced, will affect the timing 
 and opportunity to perform field tillage 
 and planting operations. Delayed spring 
 planting caused by standing water and wet 
 conditions affects plant growth and crop 
 yield; the extent of such impacts has not 
 yet been determined and will require 
 carefully planned observation and analy- 
 ses. The final evaluation must include 
 both analysis of the effect on annual 
 yields of major crops and the long-term 
 effect on productivity, and the conser- 
 vation of soil for use by future 
 generations. 
 
 Case examples from Illinois described 
 by Guither (15) show crop yields affected 
 by subsidence ranging from 30- to 100-pct 
 reduction in productivity, depending on 
 the location, topography, and rainfall. 
 An interesting note is that in dry years 
 subsided areas may show no impact as lit- 
 tle water collects in the depressions. 
 In fact, in dry areas subsidence-induced 
 depressions may produce more than the 
 surrounding area as they do collect mois- 
 ture. However, in wet years the depres- 
 sion may remain saturated for the entire 
 growing season and totally eliminate crop 
 production. 
 
 The costs of reduced land productivity 
 due to mined land subsidence fall basi- 
 cally into two catagories: (1) loss of 
 crop productivity and (2) restoration of 
 damaged land to full productivity. There 
 are additional costs to the community 
 such as damage to public facilities, loss 
 in land values, and loss in taxes. 
 
 It seems highly probable that, with the 
 advance of high-extraction coal raining in 
 Illinois, the total amount of surface 
 land affected by subsidence will become 
 significant. Detailed analysis now in 
 progress by the State should establish 
 that amount and evaluate crop production 
 loss due to subsidence associated with 
 underground coal raining techniques. 
 
13 
 
 BUREAU OF MINES AND STATE OF ILLINOIS SUBSIDENCE RESEARCH PROGRAM 
 
 Cooperative research between the Bureau 
 and the State of Illinois <16) has been 
 initiated to develop techniques of reli- 
 able subsidence prediction for high- 
 extraction retreat and longwall mining 
 methods. If successful, such prediction 
 techniques will allow the use of high- 
 extraction mining, which will cause 
 planned, immediate subsidence with mini- 
 mal impact on surface crop productivity. 
 The Bureau is currently involved in four 
 areas: (1) analysis of geomechanical and 
 subsidence profile data, (2) prediction 
 and modeling of subsidence, (3) assess- 
 ment of stability problems in mines, and 
 (4) characterization of structural foun- 
 dation response to subsidence. 
 
 The Bureau is cooperating with the 
 State of Illinois in developing data 
 bases for geomechanical properties of the 
 overburden and subsidence profile char- 
 acteristics. The Bureau-sponsored re- 
 search program will increase the data 
 base available in the State for analyzing 
 overburden response to high-extraction 
 mining methods by monitoring the overbur- 
 den and ground surface over an existing 
 high-extraction mine. 
 
 The development of prediction and mod- 
 eling techniques will visually demon- 
 strate what may happen under various min- 
 ing and geological conditions in Illinois 
 coal mines. Models can be excellent 
 guides, and the ability to predict hydro- 
 logical changes caused by surface eleva- 
 tion changes is necessary for the plan- 
 ning of mining operations to minimize 
 impacts on surface drainage patterns. 
 
 A computer program is being developed 
 to model subsidence-related changes in 
 slopes and elevations. Initially sched- 
 uled to be based on previously monitored 
 longwall panels from southern Illinois, 
 the final model will incorporate data 
 from a 10-mi 2 area to ensure that all 
 programs in the model are functional. 
 Ideally, the final model will select a 
 compromise between (1) no raining with no 
 subsidence and (2) full-extraction min- 
 ing with maximum subsidence, such that 
 positive drainage is maintained or 
 reestablished after the surface has been 
 
 stabilized and maximum crop production is 
 assured. 
 
 A research program is underway to mon- 
 itor seven subsidence sags that have de- 
 veloped during the past 20 yr over a 
 room-and-pillar mine. These sags have 
 affected surface drainage. The sags 
 probably resulted from subsidence due to 
 pillar punching and time-related roof and 
 floor squeeze, and depressions gradually 
 developed on the surface. The research 
 is designed to determine why abandoned 
 room-and-pillar mines in Illinois become 
 unstable, collapse, and create subsi- 
 dence-related problems such as impacted 
 surface drainage. 
 
 Another Bureau-sponsored research proj- 
 ect, at Southern Illinois University at 
 Carbondale, is designed to assist in the 
 characterization of pillar strength and 
 stability problems for improvements in 
 the design of planned and unplanned sub- 
 sidence. Combined with State-sponsored 
 work of the physical and mechanical prop- 
 erties of floor materials, this research 
 will aid in pillar stability analysis for 
 mine design. 
 
 Mine planners using high-extraction 
 methods need to know how long subsidence- 
 related movement will continue so that 
 repairs to structures and farmland will 
 not be made until the area is stable. 
 The Bureau is investigating the duration 
 of ground movement from high-extraction 
 mining in Illinois. Generally, when coal 
 is extracted from an area in Illinois, 
 caving and surface movement happen rap- 
 idly. Most existing data indicate that 
 95 pet of movement occurs within 90 days 
 of mining, but because the caved rock 
 continues to settle and compact under its 
 own weight, small movements may occur for 
 years after the raining front has passed. 
 Acceptable limits of residual movement 
 need to be established such that needed 
 restoration can take place as quickly as 
 possible. 
 
 The University of Illinois at Urbana- 
 Champaign ( 17 ) is researching the effects 
 of planned subsidence resulting from 
 high-extraction underground coal raining 
 on subsequent agricultural suitability 
 
14 
 
 and productivity. Mined and unmined 
 lands are being surveyed, and the effects 
 of subsidence on crop growth will be 
 determined. 
 
 Future Bureau and Bureau-sponsored re- 
 search will include developing subsidence 
 prediction methods for the mining and 
 geologic conditions in Illinois. More 
 accurate analytical methods need to be 
 developed, and these must be based on an 
 
 understanding of how geological factors 
 affect the migration of strata movements 
 from the mine itself to the resulting 
 surface profile. Subsidence prediction 
 along with more complete geomechanical 
 data must ultimately form the basis for 
 mine and mining plan guidelines that will 
 minimize the impacts of subsidence on the 
 ability of overlying prime farmlands to 
 sustain maximum crop production. 
 
 SUMMARY AND CONCLUSIONS 
 
 Generally, the Illinois Coal Basin is a 
 broad, spoon-shaped trough of sediments 
 containing anticlinal folds of gentle 
 slope with less than 200 ft of relief. 
 The topography ranges from flat to roll- 
 ing with glacial till soils ranging from 
 600-ft deep in the northern and central 
 parts to less than 50-ft deep in southern 
 Illinois. 
 
 Most of the mapped coal reserves are in 
 the middle portion of the Pennsylvanian 
 System, underlying the southern two- 
 thirds of the State. Overlying shales 
 are generally 20- to 40- ft thick, and 
 underlying clays are only 2- to 5- ft 
 thick. Ground water is contained in the 
 glacial overburden to a level of 2 to 15 
 ft below the surface and is highly 
 dependent on surface recharge. 
 
 Retreat room-and-pillar and longwall 
 are the two high-extraction underground 
 coal mining methods used in Illinois. 
 Both methods are high recovery systems, 
 and their resulting subsidence and sur- 
 face profiles can be similar. 
 
 Subsidence from underground mining in 
 western Pennsylvania disturbs the over- 
 lying ground water by opening fractures 
 in the strata and allowing the water to 
 drain into lower strata and ultimately 
 into the mine. After mining, the over- 
 lying structure generally heals with time 
 due to settling and compression, and the 
 ground water level is restored by re- 
 charge. The water may or may not reach 
 its former level, depending on the new 
 hydrologic balance. 
 
 The potential effects of high-extrac- 
 tion mining subsidence on the ground 
 water in Illinois may be somewhat dif- 
 ferent. The shale layers above the cav- 
 ing zone and the overlying strata are 
 
 flexible and tend to sag over the mined- 
 out area, with only minor fracturing. If 
 the subsided area quickly heals itself, 
 the ground water in the glacial till may 
 be restored to its former level; and, 
 since the normal level is close to the 
 surface, the new water level may exceed 
 the subsided ground level. The results 
 could then be highly saturated soils and 
 ponding conditions that would severely 
 reduce crop production. 
 
 Good plant growth requires well-drained 
 to moderately well-drained soil with good 
 soil moisture consistency and texture. 
 There should be at least 30 in of soil 
 above a hard layer, and the surface slope 
 should be less than 10 pet. Most im- 
 portantly in Illinois, seasonal water 
 tables need to be far enough below the 
 ground surface to allow for good root 
 development. 
 
 Erosion is the single process that is 
 most destructive to a soil, as it reduces 
 the soil's productivity by removing nu- 
 trients and structure that are contained 
 in the upper soil layers. Erosion is 
 mainly dependent on the soil unit, rain- 
 fall, and topography. Of those three 
 factors, only topography (i.e., slope) is 
 controllable and directly affectd by mine 
 subsidence. High-extraction underground 
 coal mining subsidence in Illinois gener- 
 ally results in minor slope changes and, 
 therefore, negligible changes in the 
 erosion potential. The major impact is 
 on drainage, and where the topography is 
 extremely flat, a small change in slope 
 may result in a change from positive to 
 negative drainage. As long as positive 
 drainage is maintained, however, a small 
 change in slope should not severely 
 affect crop production. 
 
The Bureau and the State of Illinois 
 are cooperating on research to develop 
 techniques for reliable subsidence pre- 
 diction for high-extraction retreat room- 
 and-pillar and longwall mining meth- 
 ods in Illinois. Successful prediction 
 techniques will allow the use of 
 
 15 
 
 high-extraction mining methods, resulting 
 in planned, immediate subsidence with 
 minimal impact on surface crop produc- 
 tion. The cooperative program will 
 result in mining plans that maximize both 
 coal production and subsequent crop pro- 
 duction in the prime farmland areas. 
 
 REFERENCES 
 
 1. Guither, H. D. , J. Hines, and 
 R. Bauer. The Economic Effects of Under- 
 ground Mining Upon Land Used for Illi- 
 nois Agriculture (Univ. IL at Urbana- 
 Champaign, Dep. Agric. Econ. , and the IL 
 State Geol. Surv. ) IL Dep. Ener. and Nat. 
 Resour. , Doc. 85/01, Feb. 1985, 185 pp. 
 
 2. O'Rourke, T. D. , and S. M. Turner. 
 Longwall Subsidence Patterns: A Review 
 of Observed Movements, Controlling Param- 
 eters, and Empirical Relationships. Sch. 
 Civil and Environ. Eng. , Cornell Univ. , 
 Ithaca, NY, Geotech. Eng. Rep. 79-6, Nov. 
 1979, 82 pp. 
 
 3. Olson, G. W. Soils and the Envi- 
 ronment, A Guide to Soil Surveys and 
 Their Applications. Dowden & Culver, 
 Inc. , 1981, 178 pp. 
 
 4. U.S. Department of Agriculture. 
 Soil Survey Manual. Agric. Handbook. 18, 
 1962 (reissued), 503 pp. 
 
 5. . Guide for Interpreting En- 
 gineering Uses of Soils. 1971, 87 pp. 
 
 6. Sarkar, P. K. , 0. W. Bidwell, and 
 L. F. Marcus. Selection of Character- 
 istics for Numerical Classification of 
 Soils. Proc. Soil Sci. Soc. America, 
 v. 30, 1966, pp. 269-272. 
 
 7. Peng, S. S., and S. L. Cheng. 
 Prediction of Surface Subsidence Profile 
 Due to Underground Coal Mining. Dep. 
 Min. Eng., Coll. Min. and Ener. Res., WV 
 Univ. , Tech. Rep. TR 80-5, Dec. 1980, 
 46 pp. 
 
 8. Bauer, R. A., and S. R. Hunt. Pro- 
 file, Strain, and Time Characteristics of 
 Subsidence From Coal Mining in Illinois. 
 Paper in Proceedings of Workshop on Sur- 
 face Subsidence Due to Underground Min- 
 ing, ed. by S. S. Peng and M. Harthill 
 
 (Morgantown, WV, 
 Dep. Miner. Eng. 
 Resour. , WV Univ. , Mar. 
 218. 
 
 9. Janes, J. 
 Longwall Mining 
 Ben Coal Co. ). 
 v. 1, 105 pp. ; v 
 
 Nov. 30-Dec. 2, 1981). 
 
 , Coll. Miner, and Ener. 
 
 1982, pp. 207- 
 
 R. A Demonstration of 
 (contract J0333949, Old 
 BuMines OFR 86-85, 1983, 
 2 (appendix), 372 pp. 
 
 10. Pennington, D. , J. G. Hill, G. J. 
 Burgdorf, and D. R. Price. Effects of 
 Longwall Mine Subsidence on Overlying 
 Aquifers in Western Pennsylvania (con- 
 tract J0199063, SMC Martin Inc.). Bu- 
 Mines OFR 142-84, 1984, 149 pp.; NTIS 
 PB 84-236710. 
 
 11. Singh, M. M. , and S. Bhattacharya. 
 Proposed Criteria for Assessing Subsi- 
 dence Damage to Renewable Resource Lands. 
 Soc. Min. Eng. AIME preprint 84-391, 
 1984, 7 pp. 
 
 12. U.S. Department of Agriculture. 
 Land-Capability Classification. Agric. 
 Handbook 210, 1973, 21 pp. 
 
 13. Guernsey, L. , P. Mausel, and 
 J. Oliver. An Overview of the Factors 
 Involved in the Restoration of Mined 
 Prime Farmland. Committee on Interior 
 and Insular Affairs, Subcommittee on 
 Energy and the Environment. 96th Congr. , 
 1st sess., serial 96-4, Mar. 1979, 
 pp. 577-580. 
 
 14. Darmody, R. G. , I. J. Jansen, and 
 N. T. Patterson. Effects on High Extrac- 
 tion Coal Mine-Induced Subsidence on 
 Crop Production. Prelim. Rep. to the 
 Illinois Mine Subsidence Research Program 
 Advisory Committee, Aug. 29, 1985, 3 pp.; 
 available from R. G. Darmody, Dep. Agron- 
 omy, Univ. IL at Urbana-Champaign. 
 
 15087 21' 
 
16 
 
 15. Guither, H. D. The Economic Ef- 
 fects of Subsidence From Underground 
 Coal Mines on Agricultural Land in Il- 
 linois (contract H0222010, Univ. IL at 
 Urbana-Champaign). BuMines OFR 186-84, 
 1984, 60 pp.; NTIS PB 85-109296. 
 
 16. Wade, L. V., and J. J. Olson. 
 Productivity, Safety, and Environment — A 
 Coordinated Approach for Improving Coal 
 Mining Technology. Paper in Proceedings 
 
 of Ninety-Third Annual Meeting of the 
 Illinois Mining Institute (Springfield, 
 IL, Oct. 31-Nov. 1, 1985). IL Min. 
 Inst., 1986, pp. 21-44. 
 
 17. Bauer, R. A. (Illinois State Geo- 
 logical Survey Division). Private com- 
 munication, Nov. 4, 1985; available upon 
 request from David L. Veith, BuMines, 
 Minneapolis, MN. 
 
 US. GOVERNMENT PRINTING OFFICE: 1 987 - 605-01 7/6001 
 
 INT.-BU.OF MINES,PGH.,PA. 28399 
 

 
U.S. Department of the Interior 
 Bureau of Mines— Prod, and Distr. 
 Cochrane Mill Road 
 P.O. Box 18070 
 Pittsburgh, Pa. 15236 
 
 OFFICIAL BUSINESS 
 PENALTY FOR PRIVATE USE. $300 
 
 ^ Do not wish to receive this 
 material, please remove 
 from your mailing list* 
 "2 Address change. Please 
 correct as indicated* 
 
 AN EQUAL OPPORTUNITY EMPLOYER 
 
-v o* +*- * 
 
 
 A 9^ 
 
 ■* *^, • • • » v ' "*^ 
 
 
 k ' *<. 4T * . 
 
 
 
 > v v . 
 
 
 
 
 
 ^^ •«•- v** • ^&- \/ •*»•- %/ 
 

 MAY-JUNE' 
 
 i?. «,."<* 
 
LIBRARY OF CONGRESS 
 
 002 953 939 A 
 
 
 i