Clay Veins: Their Occurrence, Characteristics, and Support

Home , Slickenside, Vein (geology)

Bureau of Mines Report of Investigations/ 1987

By Frank E. Chase and James P. Ulery

UNITED STATES DEPARTMENT OF THE INTERIOR Report of Investigations 9060

Clay Veins: Their Occurrence, Characteristics, and Support

By Frank E. Chase and James P. Ulery

UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary

BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data :

Chase, Frank E. Clay veins : their occurrence, characteristics, and support.

(Report of investigations/United States Department of the Interior, Bureau of Mines ; 9060)

Bibliography: p. 18-19.

Supt. of Docs. no.: I 28.23: 9060.

1. Ground control (Mining) 2. Clay veins. 3. Coal mines and mining-Safety measures. I. Ulery, J. P. (James P.) 11. Title. 111. Series: Report of investigations (United States. Bureau of Mines) ; 9060.

TN23.U43 86-600245 CONTENTS Page Abstract ...... Introduction...... Clay vein origins ...... Clay vein occurrences...... Depositional setting and interpretations ...... Clay vein composition...... Coalbed and roof rock characteristics ...... Roof support...... Prediction and mine plan modifications ...... Conclusions and recommendations...... References...... ILLUSTRATIONS Clay vein occurrence map for the Eastern United States ...... Single-feeder clay vein ...... Multiple-feeder clay vein ...... Coalbed bedding plane warping in proximity to a clay vein ...... Clay-vein-associated fracture plane ...... Clay-vein-related fault plane ...... Major and minor slickenside plane sets associated with a large clay vein .. Clay-vein-associated slickenside plane sets displaying a "V-up" pattern ... Steel mats effectively controlling fragmented clay vein roof with slickensides...... Rib-line clay vein ...... Clay-vein-associated fracture and fault plane bolting diagrams ...... Roof trusses effectively controlling clay-vein-disturbed roof ...... Histogram of bimodal clay vein distribution...... Rose diagram of multidirectional clay vein distribution ...... Distribution of clay veins on a synclinal flank ...... Schematic drawing illustrating up-dip shifting of clay-vein-disturbed rock ...... Distribution of clay veins and paleochannels in mine workings ...... TABLE 1 . Roof instability associated with different clay vein strikes...... UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

feet m meter

inch Pet percent

inch per day CLAY VEINS: THEIR OCCURRENCE, CHARACTERISTICS, AND SUPPORT

By Frank E. Chase1and James P. Uleryl

ABSTRACT

Clay veins found in coal mines have caused numerous injuries and fatalities. These structures plague all phases of mining, including entry development, pillar recovery, and panel extraction. Clay veins also in- crease production costs and may disrupt or halt mining. These detri- mental aspects have prompted the Bureau of Mines to investigate the physical characteristics of and roof instability problems associated with clay veins. This was accomplished by observing and mapping clay veins in surface and underground mi-nes. The occurrence and origins of clay veins were also investigated to determine predictive capabilities. The investigators found that clay veins normally occur in more stable, less rapidly subsiding coal basins. Clay veins result when tensile stresses develop fissures which are later infilled. These fissures can be propagated by compactional processes and/or tectonic stresses active during and subsequent to coalification. The Bureau also found that associated faults, fractures, and slickenside planes commonly parallel clay veins and disrupt the lateral continuity of the immediate and, sometimes, main roof. When clay veins parallel or subparallel the direction of face advance, the roof is segmented into cantilever beams, causing unstable conditions. Consequent- ly, the strata on either side of the clay veins should be bolted and strapped together to form a beam.

'~eolo~i4t,Pittsh~~rgh Research Center, Rurenu of Mines, Pittshrrrqh, PA. INTRODUCTION

Accidental roof falls continue to be Previous studies have indicated that a major cause of injuries and fatal- clay veins (also referred to as clay ities in underground coal mines (26).- dikes, horsebacks, or mudslips) were The Bureau of Mines, in keeping with formed by either compactional processes its goal of promoting a safer work envi- or tectonic stresses. Occurrence infor- ronment, has conducted several in-mine mation collected during this investi- investigations to determine the geo- gation seems to confirm both theories. logic structures and conditions respon- Furthermore, since clay veins are ac- sible for accidental roof falls. These tually infilled fissures, the authors studies have confirmed that many roof contend that any compactional process or falls can be correlated with specific ground stress capable of developing a geologic features. Moreover, the Bu- fissure, or fracture that can later reau's investigations have enabled lim- widen, can result in the Eormation of a ited prediction of occurrences of these clay vein. hazardous geologic features in [lnlni i~ed portions of the coalbed.

CLAY VEIN ORIGINS

Clay veins are infilled f issllres. Gresley (z), and Oldham (E), have These fissures developed when tensile attributed fissures to earthquake dis- stresses ruptured the coa,l and adjacent turbances, which are often related to sediments during or after the coalifica- tectonic activity. tion process. Previous studies have in- Fissures may be infilled as a result of dicated that the fissures responsible for gravity, downward-percolating ground wa- clay vein formation can be propagated by ters, or compactional pressures which compactional processes and/or tectonic cause unconsolidated clays or thixotropic (regional or mountain-building) stresses sands to flow into the fissures. This active during and subsequent to coalifi- latter (plastic-f low) nethod of infilling cation. Theories advocating cornpaction occurred in the Upper Freeport Coalbed in suggest that the fissures resulted from Garrett County, MD, where high compres- the unequal shrinkage of peat (24) or sive st rc?.;l;cs have pressure-injected un- from differential compaction (iy 30). consolidated underclays into fissures Proponents for a tectonic origin inchl-de associated with floor heave. Some of ?kCulloch (14), Price (221, and Smith the fissures intersect coal ribs, forming (25). other investigators , including mining-induced clay veins.

CLAY VEIN OCCURRENCES

Clay veins occur in the United States, mine observations. Other clay vein oc- the United Kingdom, Czechoslovakia, New currence information uas obtained from Zealand, and elsewhere. This investi- the Mine Safety and 'riealtl~Administration gation was limited to the eastern United (MSHA), State enforcement agencies, State States (fig. 1) and includes portions of the Arkoma, Illinois, Northern and South- 3~lthough sedimentary dike or clastic ern Appalachian, and Warrior Coal Basins. dike is the more exact geologic term for The information shown in figure 1 was an approximately vertical, tabular, sed- compiled by Bureau personnel based on imentary infilled discontinuity, the term "clay vein" is used here because it is 2~nderlinednumbers in parentheses re- firmly es tahlished in the coalfields that fer to items in the list of references at have the greatest incidence of related the end of this report. injuries and fatalities. FIGURE 1.-Clay vein occurrence map for the Eastern United States, after McNeal (75). geological surveys, and mine personnel containing clay veins were deposited in throughout the eastern and central United various marine and nonmarine environ- States. ments. Individual roof rock types con- Distribution data indicate that clay taining clay veins incllide thin, massive, veins commonly occur with varying Ere- or interbedded limestnnes, mudstones, quency in the Illinois and Northern sandstones, shales, and siltstones; how- Appalachian Coal Basins fig 1 The ever, clay veins occur less frequently immediate and main roofs above co:ilheds under massive sandstone units.

DEPOSITIONAL SETTING AND INTEKPRE'rATIONS

Depositional conditions in the investi- widespread presccvat ion of fossilized gated portions of the Illinois and North- trees 1cettl.ehottoms). This is consis- ern Appalachian Basins were similar in tnt with information the Bureau has col- that both basins were deposited on more lected in the Southern Appalachian and stable (less rapidly subsiding) platforms i-Jarrior Basins. with correspondingly slower rates of sed- Depositional conditions in less stable iment influx (9, 27). Clay veins are basins dere also responsible Eor similar rarely encountered in the Arkoma, South- roof rock types being stacked one above ern Appalachian, and Warrior Basins. 1.1- the other, as is the case in southern vestigated areas in these basins were de- Vest Virginia where facies prograde slow- posited on less stable (nore rapidly ly (5). Overall, less differential com- subsiding) platforms with correspondingly paction or deformation occurs when the faster rates of sediment influx (2, 13, same type of roof rock is stacked verti- -28). From a depositional point of view, cally (2). Conversely, rock types pro- these conditions are optimal for the grade rapidly in northern Vest Virginia where the basin is more stable (8). as readily sheared and/or distorted as These conditions are conducive to offset are muds (29),- which cornpac~Lnto shale. rather than vertical stacking, and con- Increased soft sediment deformation, sequently, more differential compaction faulting, and fracturing associated with occurs (3). differential compaction during lithifica- The type of sediments involved also tion may explain why clay vefns occur determines how much differential compac- more frequently in a more stable basin, tion occurs during lithification (10). such as northern West Virginia. In the In southern West Virginia, where clay Illinois Basin, differential compact ion veins are rare, sandstone is more abun- may also be responsible for clay veins dant than shale (5). The opposite is tenrl i 115 to parallel boundaries between true in northern West Virginia (21). different roof rock types (17).- During lithification, sands are not

CLAY VEIN COMPOSITION

Sediments that infill clay veins may be Water from continuous miner spraying derived from above and/or below the coal- systems someE irnes softens and weathers bed. Sediments may enter the coalbed the claystone matrix of clay veins, caus- fissure via one conduit or feeder (fig. ing roof spalling, which continues until 2) or through smaller, multiple, inter- adequate support is employed. Mining secting (branch-like) feeders (f ig. 3). through structures composed of hard sand- Clay veins are predorni~lni~[:l.y cqmposed of stone or siltstone is more troublesome. claystone; however, structures inf illed Typically, roof vibration is severe, and with sandstorle, siltstone, and/or lime- miner bits shear constantly. Friction- stone do occur. Frequently, large (1 to al heat and/or sparks generated while 8 in), angalar to sub-rounded fragments mining through these harder structtires oE the wall rock (limestone, coal, sand- have caused numerous face ignitions. Ab- stone, etc.) are encompassed in the clay normally high methane emissions often vein :natrix. Pyrite nodules are common occur when mining through clay veins (c),and occasionally, secondary calcite because these stc:ictures act as nat- and quartz mineralization occurs within ural barriers or dams to free gas flow clay veins. (23) The type of sediments which infills a clay vein may affect mining conditions.

COALBED AND ROOF ROCK CHARACTERISTICS

Most clay veins have a zigzag appear- noted where clay veins penetrate the ance, as if the coalb2d were pulled apart floor. (fig. 2); others have V- or U-shaped con- Upward and/or downward warping of coal- figurations. A clay vein's geometry and bed and roof rock bedding planes commonl-y cross-sect iorlal. width often change along occurs on either side of a clay vein. its trend or strike. Marked variations This warping is illustrated in Eigure 4, in shape and size are commonly observed which shows normally horizontal bedding 011 adjacent ribs. Clay veins observed planes approaching 30" dips. Bedding underground ranged from less than 0.1 to plane warping das measured as far away as 16 Et in width where they entered the 8 ft from the cJfly vein. Normally ver- coalbed. The lengths of clay veins vary tical coal cleat within this warped zone from tens of feet to over 1.5 miles (16). are also inclined. The degree and lat- Approximately one-third of the exnmKe(1 c:r.al extent of the zone of inclination clay veins terminated in the co;il.i~t?cI, appeared to be governed by the severity while the remainder penetrated throt~gh of deformation associated with the clay the coalbed into the floor. A convex up- vein. Bedding plane and cleat distur- ward bulge in the underclay is sometimes bances were readily observable at the face and on adjacent ribs as clay veins were approached. Where present, bedding plane warping and cleat rotation indicate that the clay vein formed after cleat development. From a support point of view, clay veins can be broken down into two cate- gories: those with associated fracture (fig. 5), fault (fig. 6), and slickenside planes (fig. 7) in the roof, and those without these features (fig. 2). Clay veins without associated planes are normally composed of claystone or shale. These clay veins are sometimes moisture sensitive and weather rapidly. Fault, fracture, and slickenside planes associated with clay veins had dips ranging from 30' to 90° (vertical). Clay vein faults may displace adjacent portions of the coalbed up to 18 f t vertically (11).- However, displacements are more common- FIGURE 2.-Slngle-feeder clay vein (wlth veln outllned in ly less than 3 ft. Fault planes are black).

FIGURE 3.-Multiple-feeder clay vein. FIGURE 4.-Coalbed bedding plane warping in proximity to a clay vein. distinguished from fracture planes, along are actually warped and striated bedding which no detectable movement has oc- planes. When clay veins become larger, curred. Fault and fracture planes ex- the associated slickenside planes in- tending as high as 20 ft into the main crease in frequency and magnitude (fig- roof were noted in the Springfield (also ures 7 and 9), expanding the distur5ed referred to as No. 5 or Harrisburg) Coal- zone laterally. Figures 7 and 9 were bed near Springfield, IL. taken 10 ft away From clay veins and only Slickensides are highly polished and show the set of parallel slickenside striated planes of weakness. Slicken- planes on the left sides of two different sides associated with clay veins may be "V-down" clay veins. In addition to the oriented in parallel sets or randomly. gajor planes mentioned above, minor or Parallel sets of intersecting slickenside secondary sets of intersecting fracture planes are oriented in one of two ways, and slickenside planes are associated "V up" (fig. 8) or "V down." The clay with some clay veins (fig. 7). The cumu- vein generally occurs in the middle of lative effect of all fracture sets is a the intersecting sets, as shown in fig- loose and fragmented roof. ure 8. Some major slickenside planes

ROOF SUPPORT

Clay veins with associated fault, frac- vein's strike is parallel or subparal- ture, and slickenside planes disrupt the lel to the face, the clay vein divides lateral continuity of the immediate and, the roof slab into parallel beams. sometimes, main roof. Where the clay However, where the stri-ke parallels or FtOURE 5.-Clay-vein.asrocfst& fracture plane. FIGURE 7.-Major and minor slickenside plane sets associatad with a large ~fayv&n. FIGURE 8.-Clay-veln-associated slickenside plane sets dlsplaylng a "V-up" pattern.

FIGURE 9.-Steel mats effectively controlling fragmented clay vein roof wlth slickensides. subparallels the direction of face ad- major fault or fracture planes in the vance, the roof slab is divided into one roof. or two cantilever beams. One cantilever Whether or not a beam can be built in beam occurs if the clay vein coincides highly fractured rock with multiple in- with or runs along the rib line, as shown tersecting major and minor slickenside in figure 10. Two cantilever beams are planes is debatable. Some operators and formed when the clay vein occurs within roof control specialists believe that the the entry or crosscut as in figures 5 and fragmented rock mass must be suspended llA. To determine if there is a corre- or keyed to insure stability. Under con- lation between roof stability and a clay trolled laboratory conditions, highly vein's strike with respect to the direc- fractured rock can be stabilized, pro- tion of face advance, 471 clay vein seg- vided the fragments are compacted by vi- ments were analyzed in a mine operating bration and confined laterally in boxes in the Upper Kittanning Coalbed in south- until bolted (12). Unfortunately, under- western Pennsylvania. Observations were ground conditGns do not afford these categorized as follows: (1) clay veins amenities, and quite commonly, the frag- striking parallel to subparallel to the mented roof sometimes associated with direction of face advance (0" to 30°), clay veins sags and unravels (spalls) (2) clay veins striking subperpendicular prior to and subsequent to bolting. to perpendicular to face advance (61" to Rates of convergence beneath clay veins 90°), and (3) clay veins striking inter- can sometimes be useful in predicting mediately (31" to 60"). An analysis of roof stability. For example, ground con- the data in table 1 indicates a direct trol personnel in a central Illinois mine correlation between roof stability and monitor convergence beneath potentially a clay vein's strike, corroborating the hazardous clay veins located along the above mentioned beam theories. track, belt, and other critical areas. The cantilever effect often associated When sag rates exceed 0.2 in/d, past ex- with clay veins can sometimes be cor- perience suggests an impending fall, and rected by bolting and strapping the roof additional supplemental support is imme- on each side of the major fault or frac- diately installed. Rates equaling 1.1 ture plane together to construct a beam. in/d have been recorded beneath clay Mine personnel should be aware of the veins prior to roof failure in this mine. plane's orientation (strike and dip) so Tensioned bolts help compress a loose they can determine the proper bolt length fragmented roof with slickensides into and angle of installation (fig. 11). The a somewhat competent unit (6). Mech- orientation of major fracture or fault anical bolts can be used, provided they planes may be hidden in the roof prior to are anchored out of the disturbed clay spalling. However, in certain cases, ex- vein zone in competent strata. However, amination of the clay vein material in delimiting the disturbed zone both ver- the coalbed reveals one or more smaller tically and horizontally immediately parallel fault or shear planes (fig. 6). after mining is often difficult. Where Observations indicate that these smaller mechanical bolts are anchored into clay coalbed fault or shear planes can be used veins composed of incompetent claystones to approximate the orientation of the or highly fractured shales with internal

TABLE 1. - Roof instability associated with different clay vein strikes

Strike of clay vein with respect to Total Roof falls requiring cleanup direction of face advance observations Number Pct of total observations Parallel to subparallel (0"-30°).....,... 141 63 47 Intermediate (31"-60") ...... bb.. 173 15 9 Subperpendicular to perpendicular

(61'-90') ...... b..b...b....b..b..bbb.. 157 12 8 FIGURE 10.-Rlb-llne clay veln. A Ineffective bolting B Roof behaves as independent Minor cantilever beams Maior slickensides

C Beam built by using longer roof D Beam built by using angled roof bolt and mat bolt and mat

KEY Cool pillar 1- Floor ~oof Clay vein with I1Entry associated fault or fracture plane

FIGURE 11.-Clay.veln-associated fracture and fault plane bolting diagrams. planes of weakness, stress concentrations planes by infilling fractures and voids, at the anchor may crush or break already essentially gluing adjacent fragmented weak or fractured rock (1). Under these blocks. Therefore, in workings where conditions, excessive bleedoff or an in- clay veins frequently occur, the routine ability to attain or maintain required installation of resin grouted bolts torque values may be a signal that longer should be considered. Since many north- bolts or resin anchorage is needed. Con- ern West Virginia mines have converted to versely, resin-grouted bolts insure bet- resin grouted bolts, the West Virginia ter stability in weak rock with a low an- State Department of Mines has reported chorage capacity (2). Based on the fewer clay-vein-related ground control above, tensioned point-anchor resin bolts problems. should insure better stability in clay- Bolts should be installed in conjunc- vein-disturbed rock. Underground obser- tion with crossbars or steel mats im- vat ions confirm this. mediately after undermining to help sta- Full-column resin bolts are also ef- bilize slickensides and prevent spalling. fective in controlling some clay veins. Crossbars and mats should be installed Although nontensioned, fully grouted perpendicular to the clay vein's strike bolts eliminate problems associated with for maximum effectiveness. Mats should moisture along the length of the bolthole be flexible enough to conform to ir- (1)and help to prevent slippage along regular top. Fiber-reinforced concrete also controls clay vein spalling, and controlling large or hazardous clay veins roof sealants prevent moisture-sensitive (fig. 12). When a clay vein is coinci- clay veins from deteriorating. Pressure dent with and runs along the rib line, grouting with polyurethane binders also cutter-type roof failure sometimes oc- helps to consolidate broken strata with curs. Rib-line clay veins are particu- randomly oriented slickensides. For sup- larly hazardous and warraqt cribbing. porting large or hazardous clay veins Where equipment maneuverability is a con- like those shown in figures 10 and 12, cern, operators- have effectively angle even the best bolts prove ineffec- bolted rib-line clay veins into the com- tive. Physical support in the form of pression zone over pillars. If a clay steel sets and/or cribbing is required. vein occurs where a crosscut is being In critical entries where equipment turned, turn posts should be employed un- maneuverability is a concern, roof til the cut is permanently supported. trusses have proven very successful in

PREDICTION AND MINE PLAN MODIFICATIONS

Short- and long-range predictions of next. This is because fissures or frac- clay vein occurrences can be made, de- tures resulting from tectonic stresses pending on their origin. Clay veins re- can form parallel (22,- 31), perpendicular sulting from tectonic stresses should (22, g), and/or at oblique angles (22, display the same or a similar preferred 25) to the maximum compressive principal orientation from one mine property to the stress, which is referred to as sigma

FIGURE 12.-Roof trusses effectively controlling clay-veln-disturbed roof. one (01). Therefore, clay vein distributions observed underground may be uni- directional, bidirectional, or multidirectional. To determine if the clay veins in a particular mine resulted from tectonic stresses, it is necessary to plot on a mine map the trend of every roo clay vein encountered. Clay veins are 0 easily distinguished prior to rock dust- 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 ing, and minimal time is required for the ORIENTATION, deg face boss to plot the structure's trend FIGURE 13.-Histogram of bimodal clay vein distribution. (orientation or strike) on a mine map. Analysis of clay vein distribution can be achieved by dividing the clay vein trends into straight-line segments and plotting Knowledge of preferred clay vein ori- the length of these segments versus their entations enables mine operators to plan spatial orientation. main entries perpendicular to or at Figure 13 represents the bidirectional oblique angles to the maximum number of clay vein distribution of a particular clay veins in order to achieve optimum mine site. More complicated multidirec- roof conditions. Barring other mining tional distributions are more easily vis- factors, longwall panels should be ori- ualized and interpreted using a 360' rose ented so that the face obliquely inter- diagram (fig. 14) rather than a histo- sects preferred clay vein orientations. gram, although some distortion does re- The longwall face should never parallel a sult. The 6 miles of clay vein data preferred clay vein orientation. shown on figure 15 were mapped along the Clay veins associated with compactional northwestern flank of the Johnstown Syn- processes may or may not be predictable. cline in Somerset County, PA. The aver- If clay veins are coincident with paleo- age dip encountered was 11". Analysis of topographic (ancient topographic) highs figure 14 indicates a clustering of clay or lows as defined by coalbed structure veins approximately at right angles to contour maps, then clay veins can be the northeast-southwest-directed maximum anticipated under similar conditions in compressive stress (18). This suggests advance of mining. Patterns associated that these clay veinsoriginaced as re- with topographic irregularities may be lease fractures that were both formed and linear or radial. Some clay veins also later widened during stress release or appear to be byproducts of slumped and/or unloading. The clustering of clay veins faulted sediments that have been dif- at 45O to a1 may have originated as shear ferentially compacted adjacent to coarser fractures which later widened during un- paleochannel (ancient stream channel) de- loading. Although a certain amount of posits. The paleochannels and clay veins scatter about the idealized peaks is ap- shown in figure 17 were mapped in south- parent in figure 14, this may be attrib- western Pennsylvania in the Pittsburgh uted to the fact that the rock mass was Coalbed. Figure 17 indicates that all 16 subjected to and fractured by at least of the clay veins over 50 ft in length two distinct stress fields (18).- Roof occur within 50 ft of the paleochannel control problems associated with clay system. Thirteen of the 16 clay veins veins are compounded in tectonically dis- occur along the margins of the two turbed areas. As figure 16 illustrates, largest channels. Pesek (20)- has also up-dip lateral shifting due to flexural noted the occurrence of clay veins in slip folding often masks zones of clay- proximity to paleochannel deposits. vein-dis turbed roof. LEGEND -Release fractures ...... Shear fractures Direction of maxi mum 4 fll - principal stress

FIGURE 14.-Rose diagram of multidirectional clay vein distribution. ? Inaccessible F ---iJ-L':--

_----1,300' -k"------lnaccer- - I-- - 1,200' LEGEND .Structure contour lines on base of Upper Kittanning Coalbed, _---- contour interval = 100 ft a /-I, lu" Clay vein -. -- L ROO~fall +synclinal axis ----lgOO'-f? ~3,200 0 400 800 1,200 Scale, ft

FIGURE 15.-Dlstrlbutlon of clay velns on a synclinal flank.

Scale, ft

FIGURE 16.-Schematic drawing illustrating up-dip shifting of clay-vein-disturbed rock. Clay veins generally have a linear to curvilinear strike. Therefore, once mapped, clay veins can be projected for varying distances into unmined portions of the coalbed. Anticipating clay veins in advance of mining sometimes allows minor mine plan modifications that can minimize or eliminate associated roof hazards. For example, some mines shift entry locations so that rib-line clay veins are contained within a pillar. Other mines avoid turning crosscuts that coincide with clay veins. Crosscuts are turned slightly before or after the disturbed zone is encountered. Similar short-term mine plan modifications can be made to avoid hazardous intersections of two or more clay veins. Seven underground observations of three clay veins intersecting were made. In every case, FIGURE 17.-Distribution of clay veins and paieochanneis falls up to or above the anchorage hor- in mine workings. izon were noted by Bureau personnel.

CONCLUSIONS AND RECOMMENDATIONS

1. Clay veins are infilled fissures. veins with intersecting slickenside Fissures develop when tensile stresses planes. Bolts should be installed in rupture the coal and adjacent sediments. conjunction with wire mesh and/or steel These fissures can be propagated by com- mats immediately after undermining to pactional processes and/or tectonic help stabilize slickensides and prevent stresses active during or subsequent to spalling. Crossbars and mats should be the coalification process. installed perpendicular to the clay 2. Distribution data indicate that vein's strike. clay veins frequently occur in more 5. Preferred clay vein orientations stable coal basins where more differ- can only be determined if clay veins ential compaction took place. are mapped and analyzed. Preferred clay 3. When clay-vein-related fault or vein orientations should be considered fracture planes parallel or subparallel in the planning of main entries and the direction of face advance, the roof longwalls. is segmented into cantilever beams. The 6. Clay veins generally have linear strata on either side of the clay vein to curvilinear strikes. Therefore, once should be bolted and strapped together mapped, clay veins can be projected to form a beam. Mine personnel should for varying distances in advance of be aware of the fault or fracture mining. Anticipating clay veins in plane's orientation so they can determine advance of mining sometimes enables the proper bolt length and angle of slight mine plan modifications that installation. can minimize or eliminate associated 4. A fragmented, sagging, and spalling roof hazards. roof is sometimes characteristic of clay REFERENCES

1. Caverson, Be, and J. Parker. Roof 11. Krausse, He F., He He Damberger, Bolts Hold Best With Resin. Min. Eng. We J. Nelson, S. Re Hunt, C. T. Ledvina,. (N.Y.), V. 23, NO* 5, 1971, pp. 54-57. C. G. Treworgy, and We A. White. Engi- 2. Coates, D. F., and T. S. Cochrane. neering Study of Structural Geologic Fea- Development of Design Specifications for tures of the Herrin (No. 6) Coal and Rock Bolting From Research in Canadian Associated Rock in Illinois. Volume Mines. Can. Mines Branch, Res. Rep. 2--Detailed Report (contract H0242017, IL R-224, 1970, pp. 1-12. State Geol. Surv.). BuMines OFR 96(2)- 3. Donaldson, A. C. Pennsylvanian 80, 1979, 218 pp.; NTIS PB 80-219462. Sedimentation of Central Appalachians. 12. Lang, T. A. Theory and Practice Paper in Carboniferous of the South- of Rock Bolting. Trans. Soc. Min. Eng. eastern United States, ed. by G. Briggs. AIME, V* 220, 1961, pp* 333-348. Geol. Soc. America Spec. Paper 148, 1974, 13. Matteo, A. P. Depositional His- pp. 47-95. tory of the Hartshorne Formation, Arkoma 4 . . Origin of Coal Seam Dis- Basin, East-Central Oklahoma. M.S. The- continuities. Sec. in Carboniferous Coal sis, Univ. MO, Columbia, MO, 1981, Guidebook, ed. by A. Donaldson, M. Pres- 80 PP* ley, and J. Renton. WV Geol. and Econ. 14. McCulloch, C. M., We P. Diamond, Surv. Bull. B-37-1, 1979, pp. 102-132. B. Me Bench, and M. Duel. Selected Geo- 5. Donaldson, A. C., J. Jo Renton, logic Factors Affecting Mining of the and M. We Presley. Pennsylvanian De- Pittsburgh Coalbed. BuMines RI 8093, posystems and Paleoclimates of the Ap- 1975, 72 pp* palachians. Int. J. Coal Geol., v. 5, 15. McNeal, W. He 1975 Keystone Coal 1985, pp* 167-193. Industry Manual. McGraw-Hill, 1975, 6. Gerdeen, J. C., V. We Snyder, 996 ppe G. L. Viegelahn, and J. Parker. Design 16. Moebs, N. N., and J. L. Ellenber- Criteria for Roof Bolting Plans Using ger. Geologic Structures in Coal Mine Fully Resin-Grouted Nontensioned Bolts To Roof. BuMines RI 8620, 1982, 16 pp. Reinforce Bedded Mine Roof . Volume 17. Nelson, W. J. Geologic Disturb- I Executive Summary and Literature Re- ances in Illinois Coal Seams. IL State view (contract 50366004, MI Technol. Geol. Surv. Circ. 530, 1983, 47 pp. ~niv.). BuMines OFR 46(1)-80, 1977, 208 18. Nickelsen, Re P., and V. D. Hough. pp.; NTIS PB 80-180052. Jointing in the Appalachian Plateau Pro- 7. Gresley, W. S. Clay Veins Ver- vince of Pennsylvania. Geol. Soc. Amer- t ically Intersecting Coal Measures. ica Bull., v. 78, 1967, pp. 609-629. Geol. Soc. America Bull., v. 9, 1897, 19. Oldham, D., and Re Mallet. Notice pp* 35-58. of Some of the Secondary Effects of the 8. Horne, J. C., and J. C. Ferm. Earthquake of 10th January 1869 in Carboniferous Depositional Environments: Cachar. Q. J. Geol. Soc. London, v. 28, Eastern Kentucky and Southern West Vir- 1872, pp* 255-270. ginia. A Field Guide. Dep. Geol., Univ. 20. Pesek, J. Erosion and Clastic of SC, Columbia, SC, 1978, 151 pp. Dikes in Coal Seams of the Central Bo- 9. Horne, J. C., Jo C. Ferm, F. T. hemian Basins and Their Significance for Caruccio, and Be P. Baganz. Depositional the Determination of Plant Substance Models in Coal Exploration and Mine Plan- Coalification. Fol. Mus. Rer. Natur. Bo- ning in Appalachian Region. Am. Assoc. hem. Occid., Plzen, Czechoslovakia, Geol. Pet. Geol. Bull., v. 62, 1978, pp. 2379- 12, 1978, pp* 3-34. 2411. 21. Presley, Me W. Facies and Deposi- 10. Kent, Be Geologic Causes and Pos- tional Systems of Upper Mississippian sible Preventions of Roof Fall in Room- and Pennsylvanian Strata in the Central and-Pillar Mines. Pa. Geol. Surv. , Appalachians. Sec. in Carboniferous Coal IC 75, 1974, 17 ppe Guidebook, ed. by A. Donaldson, M. Pres- 27. Wanless, H. R. Studies of Field ley and J. Renton. WV Geol. and Econ. Relations of Coalbeds. Paper in Proceed- Surv. Bull. B-37-1, 1979, pp. 1-50. ings of the Second Conference on the 22. Price, P. H. Clay Dikes in Red- Origin and Constitution of Coal. Nova stone Coal, West Virginia and Pennsyl- Scotia Dep. Mines, Crystal Cliffs, 1952, vania. Bull. Am. Assoc. Pet. Geol., v. pp. 148-1800 17, 1933, pp. 1527-1533. 28. Wanless, H. R., J. K. Baroffio, 23. Prosser, L. J., G. L. Finfinger, and P. C. Trescott. Conditions of Dep- and J. Cervik. Methane Drainage Study osition of Pennsylvanian Coalbeds. Using an Underground Pipeline, Marianna Geol. Soc. America Spec. Paper 114, 1969, Mine 58. BuMines RI 8093, 1981, 29 pp. pp. 105-1420 24. Savage, T. E. Clay Seams or So- 29. Weller, J. M. Compaction of Sed- Called Horsebacks Near Springfield, Illi- iments. Bull Am. Assoc. Pet. Geol., v. nois. Econ. Geol., v. 5, 1910, pp. 178- 43, 1959, pp* 273-3090 187. 30. Wilson, W. B. The Origin of Clay 25. Smith, K. G. Structure Plan of Slips. Econ. Geol., v. 11, 1916, Clastic Dikes. Trans. Am. Geophys. pp* 381-3890 Union, v. 33, 1952, pp. 889-892. 31. Winslow, M. A. Clastic Dike 26. U.S. Mine Safety and Health Ad- Swarms and the Structural Evolution of ministration (Dep. Labor). Coal Ac- the Foreland Fold and Thrust Belt of the cident, Fatality, and Injury Reports, Southern Andes. Geol. Soc. America Bull, 1972-84. V. 94, 1983, pp* 1073-1088.

U.S. GOVERNMENT PRINTING OFFICE: 1 987 - 605-017160009