By Alan A. Campoli, Carla A. Kertis, and Claude A. Goode 

UNITED STATES DEPARTMENT OF THE INTERIOR 
Information Circular 91 49 

Coal Mine Bumps: Five Case 

Studies in the Eastern 

United States 

By Alan A. Campoli, Carla A. Kertis, and Claude A. Goode 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Donald Paul Hodel, Secretary 

BUREAU OF MINES 

David S. Brown, Acting Director 
Library of Congress Cataloging-in-Publication Data 

Campoli, A. A. (Alan A.) 

Coal mine bumps. 

(Information circular ; 9149) 

Bibliography: p. 34. 

Supt. of Docs nu : I 'LS 27:9149. 

1. Coal mines and rn~n~ng-United States-Accidents. 2. Rock bursts. I. Kertis, Carla 

A. 11. Goode, Claude A. 111. Title. IV. Series: Information circular (United States. Bureau 

of Mines) ; 9149. 
Page 

Abstract .................................... 1 

Introduction ................................ 2 

Acknowledgments ........................... 2 

Pillar loading and bump mechanisms ........... 2 

Case studies ................................ 5 

Mine1 ................................... 5 

Stratigraphic relationships ................. 5 

Structural setting and overburden thickness . . 5 

Bump occurrence ......................... 5 

Mine2 ................................... 13 

Stratigraphic relationships ................. 13 

Structural setting and overburden thickness . . 14 

Bump occurrence ......................... 17 

Mine3 ................................... 19 

Stratigraphic relationships ................. 19 

Structural setting and overburden thickness . . 

Bump occurrence ......................... Longwall mining ........................ Room-and-pillar mining ............ : ..... Mine4 ................................... Stratigraphic relationships ................. Structural setting and overburden thickness . . 

Bump occurrence ......................... Mine5 ................................... Stratigraphic relationships ................. Structural setting and overburden thickness . . Bump occurrence ......................... Conclusions and recommendations .............. References .................................. 

Page 

20 

22 

22 

23 

24 

24 

24 

28 

29 

29 

30 

30 

34 

34 

ILLUSTRATIONS 

1 . Adjustment of stress around a single entry ...................................................... 3 

2 . Adjustment of stress around a wide pillar ....................................................... 3 

3 . Adjustment of stress around a narrow pillar ..................................................... 4 

4 . Adjustment of stress due to the yielding of a narrow pillar ......................................... 4 

5 . Idealized diagram of core confinement loading of a critical size pillar ................................ 4 

6 . Generalized stratigraphic column for mine 1 ..................................................... 5 

7 . Sandstone thickness map of Eckman Sandstone, which immediately overlies Pocahontas No . 4 Coalbed, 

mine1 .................................................................................. 6 

8 . Structure contour map for mine 1, drawn from elevation of top of Pocahontas No . 4 Coalbed ............ 7 

9 . Overburden map for mine 1 ................................................................... 8 

10 . Plan view of area of bump accident on October 18, 1983, mine 1 .................................... 9 

11 . Plan view of mining sequence prior to bump accident, mine 1 ...................................... 10 

12 . Idealized diagram of abutment force transfer in area of bump accident, mine 1 ........................ 10 

13 . Location of hydraulic load cells in relation to area of bump accident, mine 1 .......................... 11 

14 . Progress of mining maps, for mining periods 1 through 6, of hydraulic load cell readings, mine 1 ........ 12 

15 . Graphical display of hydraulic load cell readings, for mining periods 1 through 6, mine 1 ............... 13 

16 . Generalized stratigraphic column for mine 2 ..................................................... 13 

17 . Sandstone thickness map of Eckman Sandstone, which immediately overlies Pocahontas No . 4 Coalbed, 

mine2 .................................................................................... 14 

18 . Structure contour map for mine 2, drawn from elevation of top of Pocahontas No . 4 Coalbed ............ 15 

19 . Overburden map for mine 2 ................................................................... 16 

20 . Thin-pillar mining method diagram, mine 2 ..................................................... 17 

21 . Results of auger drilling of bump block left by thin-pillar mining method, mine 2 ..................... 18 

22 . Thin-pillar mining method as used to retreat old mains located between two gobs, mine 2 .............. 19 

23 . Generalized stratigraphic column for mine 3 ...................................................... 20 

24 . Structure contour map for mine 3, drawn from elevation of top of Pocahonatas No . 3 Coalbed ........... 20 

25 . Overburden map for mine 3 .................................................................... 21 

26 . Locations of retreating longwall bump events and overburden thicknesses, mine 3 ..................... 22 

27 . Plan view of longwall gate road entries and location of bump event, mine 3 .......................... 22 

28 . Plan view of shot-fire softening technique, used on tail entry of longwall gate roads for bump control, 

mine 3 ..................................................................................... 22 

29 . Plan view of modified bump control gate road design, mine 3 ....................................... 23 

30 . Convergence contour map for room-and-pillar retreat mining, mine 3 ................................ 23 

31 . Graph of convergence effects of water infusion of pillar C, mine 3 ................................... 23 

32 . Generalized stratigraphic column for mine 4 ..................................................... 24 

33 . Sandstone thickness map of Lower Winifrede Sandstone, which immediately overlies Chilton Coalbed, 

mine4 ..................................................................................... 25 

34 . Structure contour map for mine 4, drawn from elevation of top of Chilton Coalbed ..................... 26 

35 . Overburdenmap for mine 4 .................................................................... 27 

36 . Pocket-and-wing method mining sequence, mine 4 ................................................. 28 

37 . Overview of bump accident area, mine 4 ......................................................... 28 

38 . Plan view of immediate area of bump accident, mine 4 ............................................ 29 
Page 

39. Generalized stratigraphic column for mine 5 ..................................................... 30 

40. Structure contour map for mine 5, drawn from elevation of top of No. 2 Gas Coalbed. .................. 31 

41. Overburden map for mine 5 ................................................................... 32 

42. Plan view of area of bump accident, mine 5. ..................................................... 33 

I 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

ft foot ~ct percent 

ft3/st cubic foot per short ton psi pound (force) per square inch 

gallmin gallon per minute ~sig pound (force) per square inch, 

h hour gauge 

in inch st short ton 

Yr year 

s 
COAL MINE BUMPS: FIVE CASE STUDIES 

IN THE EASTERN UNITED STATES 

By Alan A. Campoli,l Carla A. Kertis,* and Claude A. Goode3 

ABSTRACT 

This Bureau of Mines study was conducted to obtain a better understanding of the 

coal mine bump problem and its effect on underground coal mining in the Eastern United 

States. To accomplish this, information was collected on the geologic conditions, mining 

techniques, and engineering parameters at five bump-prone mines. Two geologic conditions have been found to cause the occurrence of bumps in the Eastern United States: 

(1) relatively thick overburden and (2) extremely rigid strata occurring immediately 

above and below the mine coalbed. Additionally, the probability of bump occurrence 

is increased by certain mining practices that concentrate stresses during retreat mining, in areas where geologic conditions are conducive to bumps. Mining plans that permit 

the development of pillar line points or long roof spans that project over gob areas should 

be avoided because these features may contribute to the occurrence of bumps. 

'Mining engineer. 

'Geologist. 

'Manager of Test Facilities. Pittsburgh Research Center. Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

A review of literature and accident reports on violent 

failures in coal mines reveals confusion as to the definition 

of the type of failure involved. Violent failures in coal mines 

may be classified as bounces, bursts, and outbursts. A 

bounce is the sudden forceful impact or vibration of a coal 

pillar, which may be accompanied by rib or face sloughage. 

A burst is the instantaneous explosive failure of coal or 

associated strata. An outburst is the spontaneous ejection 

of coal and gas from the solid face. The coal is pulverized 

in the process. The gas released is a mixture of predominantly methane and carbon dioxide. Outbursts result in a 

cavity ahead of or to one side of the entry. During an outburst, large quantities of gas are emitted. Subsequently, 

there is a rapid reduction in the gas emission rate with time. 

This paper deals with bursts encountered during retreat 

coal mining. Because "bump" is the term applied to this 

type of failure in the Eastern United States, the term will 

be used throughout this paper. Retreat coal mining concentrates stresses on the pillars directly outby gob areas. This 

stress situation is made worse when mining is conducted 

in areas encased in rigid associated strata. Overlying strata 

form cantilever beams over adjoining gob areas that 

transfer pressure onto adjacent outby pillars. Available data 

show bumps have caused 49 accidents from 1978 to 1984 

and resulted in 14 fatalities from 1959 to 1984 in the eastern 

States of Kentucky, West Virginia, Pennsylvania, and 

Virginia. 

ACKNOWLEDGMENTS 

This work could not have been accomplished without 

the help of many people well acquainted with coal mine 

bumps. Cloyde Blankenship, mining engineer, MSHA, 

Princeton, WV; Anthony Zona, chief, roof control division, 

MSHA, Bruceton Safety Technology Center, Pittsburgh, 

PA; Harry Harmon, district engineer, Frank Bacho, senior 

engineer, and Robert Pawlowski, geologist, U.S. Steel Co., 

Gary District Office, Gary, WV; A. R. Christian, administrative manager, Charles Couch, superintendent, Rick 

Bonham, chief engineer, and Gerald Lucas, safety director, 

Milburn Colliery Co., Burnwell, WV; Kenneth Cooper, 

general manager, John T. Clark, chief engineer, and Francis Oliver, safety director, W-P Coal Co., Omar, WV; James 

R. Vilsek, general manager, Leonard P. Mokwa, manager 

of engineering, Island Creek Coal Co., Virginia Pocahontas Div., Oakwood, VA; Dan Ashcraft, director of coal mines, 

K. V. Rao, chief mining engineer, LTV Steel Co., Pittsburgh, 

PA; Martin Valeri, general superintendent, Dwight Strong, 

superintendent, Don Winstone, chief engineer, Chandra 

Sharma, senior mining engineer, Olga Coal Co., Coalwood, 

WV; and Martin Hayduk, mining consultant, Peterstown, 

WV, provided the valued information, insight, and advice 

that made this publication possible. 

Coal and adjoining rock, when subjected to an increasing load, such as is imposed by an approaching pillar line, 

adjust by deformation and fracturing of the roof, floor, and 

coal pillars. Occasionally the ground failure is catastrophic. 

When this occurs, coal may be expelled violently from the 

pillar. In some areas the floor may heave suddenly. The 

failure is usually accompanied by a very loud report, and 

tremors or vibrations that can be detected some distance 

away are set up in the surrounding earth and in the mine 

atmosphere. 

A failure of this kind may involve only a single pillar, 

part of a pillar, or several pillars, with varying degrees of 

violence. Such failures usually occur in the vicinity of a 

pillar line in a room-and-pillar mining panel, or at or near 

the face in an advance or retreat longwall mining panel. 

Several geological conditions are believed to cause 

bumps in the eastern U.S. coalfields. The overburden is 500 

ft or more thick. A strong, overlying stratum, usually a 

massive sandstone or a conglomerate, occurs immediately 

above or close to the coalbed. The floor is strong and does 

not heave readily. These assumptions were drawn from an 

examination of 117 bump incidents during the period from 

1925 to 1950, performed by Holland and Thomas (1 The 

case studies that follow reaffirm many aspects of their work. 

The size and configuration of coal mine pillars are determined by the function they are to fulfill. They may be required to support the overburden to minimize surface subsidence or to prevent the ingress of water from adjoining 

workings. In these cases the pillars are usually wide and 

exceed the width required to support the overburden. Oversized pillars may also be required to provide a barrier to 

shield important main underground roadways from structural damage. Ventilation or haulage requirements on advance may force the pillar geometry away from the optimum 

design for retreat mining. Mining under heavy cover with 

strong, competent adjacent strata that may cause coal 

bumps to occur is better accomplished using a yield pillar 

design to prevent dangerous accumulations of stress (2). 

When an opening is developed in a coalbed, a portion 

of the natural ground support is removed, and the load of 

the roof over the mined out area must be carried by the coal 

41talic numbers in parentheses refer to items in the list of references at 

the end of this report. 
that remains. The floor also reacts to that added load 

through the coal. The natural tendency of the roof, floor, 

and coal pillars is to close this opening. In actuality, coal 

pillars bearing substantial load will deteriorate, resulting 

in perimeter yielding and sloughing. This widens the 

unsupported span and transmits an additional load onto the 

remaining structurally competent coal. Figure 1 is an 

idealized illustration of the adjustment of the stress field 

to the loss of equilibrium and the creation of high loading 

at the edge of the coal pillar because of stress concentration. 

The load transferred to a pillar is determined by the percent of extraction and the thickness of the overburden. The 

stress distribution in the pillar, however, is governed by 

the physical properties of the roof, floor, and coalbed, along 

with pillar design geometry. The probable stress distribution on a wide pillar is idealized in figure 2. Idealistically, the pillar has enough roof contact area to carry the 

load without failure and sufficient floor bearing area to 

resist the load. It is further postulated that the roof and floor 

are very resistant to yielding. Since coal generally is a 

friable material, the edges of the pillar yield. Thus, the 

stresses are low at the yielding edges of the pillar and increase rapidly over a short distance into the core of the 

pillar. The state of stress in the core zone of the pillar is 

a function of its width and the length of time it has been 

supporting the roof. In a wide pillar it is postulated that 

the stress level is substantially lower in the pillar core than 

near the edges (3). 

Figure 3 indicates the idealized stress pattern over a 

narrow pillar. As a narrow pillar takes load, the pillar yields 

and the roof and floor tend to converge. Under this 

condition, the yield pillar is incapable of carrying subsequent loadings. As a result, solid coal bears the additional 

weight. The formation of a secondary arch as shown in 

figure 4 is time dependent, being a function of the nature 

of the strata (3). 

The pillar loading hypotheses just presented for development of a pillar section are similar for retreat mining, with 

the addition of abutment zone forces. While the stress 

distribl-' . n in the gob is difficult to measure, the effect of 

the associated abutment pressures on the active pillar section is indicated by convergence directly outby the pillar 

line. Roof-to-floor convergence, brought on by the nearing 

pillar line, represents the total movement of the roof, floor, 

and pillar system. Depending on the physical properties of 

the coalbed, adjacent strata, and the depth of cover, the 

lateral extent of the zone of convergence may vary from a 

few tens of feet to hundreds of feet. In the Pocahontas No. 

4 Coalbed, to be discussed in two of the case studies that 

follow, massive sandstone roof, combined with a friable 

coalbed,leads to cantilever loading and zones of convergence 

300 ft outby the pillar line. 

Coal pillars exposed to high abutment zone pressures 

will yield or support the load, depending on their size and 

strength. A bump hazard may develop in a pillar of intermediate size, especially when the pillar is surrounded by 

smaller yielding pillars. The intermediate-sized pillar in the 

Pocahontas No. 4 Coalbed is generally 160 by 160 ft square 

(2). A pillar of this size may yield around its periphery. The 

yielded coal around the perimeter confines the pillar core. 

Figure 5 is an idealized plan view of the conditions in such 

a pillar. The lateral forces exerted by the pressurized core 

are counterbalanced by the lateral confinement provided 

by the yielded perimeter. 

Figure 1 .-Adjustment of stress around a single entry. 

Figure 2.-Adjustment of stress around a wide pillar. 
Figure 4.-Adjustment of stress due to the yielding of a narrow pillar. 

LEGEND 

- Yield zone 

Figure 5.-Idealized diagram of core confinement loading of a critical size pillar. 
y g

() 

Hard, micaceous, brown 

sandstone 

Medium-gray hard shale 

with laminations, slip plane 

and plant fossils 

Very bright, banded coal 

Shale binder 

Soft bright coal with some 

prominent cleat faces 

Shale binder 

Soft, medium-bright coal 

Medium- to dark-gray 

hard shale floor 

Figure 6.-Generalized stratigraphic column for mine 1. - 

northwestern area of the mine where the coalbed drops in 

elevation under several topographic highs (fig. 9). with the 

exce~tion of a limited area in the southeast corner. mine 

1 lies beneath more than 500 ft of cover. 

Bump Occurrence 

On October 18,1983, two miners were killed by a bump 

accident on a continous miner section, located as marked 

on figures 7 through 9. No deviations from the general structural trend were evident in the area (fig. 7). Therefore, 

unusual structural conditions did not lead to the occurrence 

of the bump. Overburden thickness was in excess of 900 R 

(fig. 9). Additionally, data from a Mine Safety and Health 

Administration (MSHA) accident report (5) and in-mine 

observations indicated that a hard sandstone approximately 

60 ft thick was present immediately above the coalbed (fig. 

7). The bump occurred during the mining of the 140- by 

350-ft No. 3 barrier pillar. Figure 10 illustrates the conditions directly after the accident. Eight entries on 39-ft 

centers were planned to divide the pillar. Forces from the 

bump moved the continuous miner against the right rib and 

the shuttle car into the crosscut between entries 5 and 6 

(fig. 10). The left rib in the No. 5 entry was displaced 

approximately 8 ft and coal filled the rest of the entry to 

a depth of 42 in for a distance of approximately 86 ft. The 

displaced coal is indicated by a dashed line on figure 10. 

The roof bolting machine was not moved by the forces; 

however, coal was expelled, filling the No. 2 entry with coal 

from 3.5 to 5 ft deep, for a distance of 60 R (5). 

According to mine management, the narrow-room 

~ethod had been used for several years. However, the 
Corehoie data point 

0 Data from accident reports 

Location of bump 

Outline of mine workings 

Figure 7.-Sandstone thlckness map of Eckman Sandstone, which immediately overlies Pocahontas No. 4 Coalbed, mine 1. 
LEGEND 

,,, Structure contour line 

(Contour interval = 20 ft) 

e Location of bump 

Figure 8.-Structure contour map for mine 1, drawn from elevation of top of Pocahontas No. 4 Coalbed. 
\ - - 

LEGEND 

 burden ,@/herburden tMckness contwr li~ 

500 to 1,000 fi Contour Interval = 100 ft 

Owburden thickness * Location of bump 

1m to '$00 ft - outline of mine ~ings 

Overburden thickmas 

a ap toemn . . 

Flgurs 9.arbrrrdm map lor mine 1. 
18, 1983, mine 1. 

specific approach to mining was determined on block-byblock evaluation, based on the knowledge of the miners and 

mine management (5). Two pillars of similar size and shape 

(directly inby) were mined prior to the fatal bump pillar (fig. 

11). The No. 2 barrier pillar was also developed using the 

narrow-room method. It bumped during an idle shift, 

expelling several tons of coal and moving the continuous 

miner. The No. 1 barrier pillar was split into blocks similar 

in size to the adjacent chain pillars and was retreated 

without incident. 

The change in the projected development of the No. 3 

barrier pillar was due to the bump that had occurred in the 

No. 2 barrier pillar. It was determined by mine management that the No. 2 entry (fig. 10) should be developed first 

to create a chain pillar the same size as the inby pillar, 

which was developed in the 1930's. Entries 8, 7, 6, 5, and 

4 were driven in sequence to form a right-to-left stepped 

pattern of working faces. It was hoped that this plan would 

allow a gradual release of any stored energy. A cut-by-cut 

mining plan was formulated and followed by mine management. The No. 3 barrier pillar had been mined down to a 

gpgpy y g

the load cell pressure readings plotted against a time scale 

in weeks. A scale is included on each graph relating it to 

the mining period maps. 

During mining period 1, the general pattern of the 

advance retreat method is demonstrated. The area of pillars 

directly outby the pillar line is split and the second row of 

pillars outby contain bump cuts. Bump cuts are single cuts 

taken from the center of solid pillars. This procedure reduces 

the structural capacity of the pillars in the abutment zone 

to bear load, allowing the pillars to crush gradually. With 

the lateral expansion of the pillars adjacent to the pillar 

line, load is transferred to the outby pillars. This is 

demonstrated by cell 2 in pillar A (fig. 15A). An increase 

in load occurred with the splitting of the pillars directly 

inby, even though the pillar line is approximately 350 ft 

inby. Cell 2 malfunctioned at the end of week 3; cell 3 was 

installed nearby directly afterward. Note, the load cells 

indicate differential pressure only, in that they measure the 

increase in load because of mining. 

While the cells were not placed uniformly with respect 

to the pillar geometry, they do demonstrate three trends. 

Pillars A and D did not load significantly until the nearby 

inby pillars were split (fig. 15). An increase in cell readings 
LEGEND 0 100 200 300 

a Gob 

I I I 1 

Scale, ft 

Figure I1 .-Plan view of mining sequence prior to bump accident, mine 1. 

did not take place in pillar D until mining period 5 (fig. 14). 

At that time pillar C was split halfway and bump cuts were 

made in a pillar adjacent to pillar A. Second, the cells load 

evenly up to the point of periphery yield and confined core 

loading. This phenomenon is verified by all cells except for 

the data from pillar B. Finally, all four pillars demonstrated 

an increase in core loadings upon periphery yield. 

The reduction in pillar load-bearing capacity must be 

carefully controlled or a squeeze may result. Roof-to-floor 

convergence of as much as 3 ft has occurred, which forces 

the taking of the floor. The pillar splitting for stress relief 

illustrated by figure 14 requires a significant increase in 

equipment travel distance as opposed to conventional roomand-pillar retreat. Mining must be conducted simultaneously in locations as much as 400 ft apart. At this mine, 

the mining sequence is determined on a case-by-case basis. 

Direction 

of 

I load transfer 

LEGEND 

2 Entry 

Figure 12.-Idealized diagram of abutment force transfer in area of bump accident, mine 1. 
0 - 600 

Scale, ft 

Fatal bump 

(10-1 8-83) 

LEGEND 

@ Hydraulic coal cell 

Scale, ft 

Figure 13.-Location of hydraulic load cells, in pillars A: B, C, and D, in relation to area of bump accident, mine 1. 
Mining period 2 Mining period 5 

Mining period 3 Mining period 6 

Scale, ft 

LEGEND 

EZBl Mining prior to period / 

D Mining during period 

l!B%B Mining in prior periods 

Figure 14.-Progress of mining maps, for mining periods 1 through 6, of hydraulic load cell readings, mine 1. 
MINE 2 

Stratigraphic Relationships 

Mine 2 operates in the Pocahontas No. 4 Coalbed near 

Gary, McDowell County, WV. Mine 2 lies immediately to 

the east of mine 1, and the two are separated by a barrier 

pillar. Conditions in the two mines are similar. Both are 

retreat mining old workings consisting of chain pillars and 

barrier blocks that were developed as long ago as the early 

1900's. The Pocahontas No. 4 Coalbed is very soft and 

friable and crushes easily. The coalbed is about 6 ft thick 

on the average, and locally may attain thicknesses in excess 

of 8 ft. The coal occurs in several benches, each separated 

by a clay binder (fig. 16). 

Underlying the coalbed is a firm gray shale. As with 

the floor shale in mine 1, the bottom often cracks and heaves 

in areas where stresses are applied. Two distinct roof 

lithologies lie above the Pocahontas No. 4 Coalbed. One is 

a variable sequence of laminated shale and coal, and sandy 

shale, ranging from 0 to 10 ft thick. Above the shale 

sequence, or immediately above the coalbed where the shale 

is absent, lies the second distinct roof lithology, the hard, 

medium-gray Eckman Sandstone (7). The distribution of this 

sandstone over mine 2 is similar to that over mine 1 in that 

the sandstone displays variable thicknesses (fig. 17). 

However, the overall thickness of the overlying sandstone 

is much greater at mine 2 than at mine 1. A thinner band Figure 16.-Generalized stra 

Medium- to darkgray sandstone 

Laminated shale, coal, 

and sandy shale 

Bright, banded coal 

Clay binder 

Bright coal 

Clay binder 

Bright coal 

Firm,gray shale floor 

 tig graphic column for mine 2. 
\\\\ LEGEND 

Figure 17.-Sandstone thickness map of Eckman Sandstone, which immediately overlies Pocahontas No. 4 Coalbed, mine 2. 

of sandstone (<90 ft) occurs in the north-central to east- No. 3 Coalbed varies from 4 to 7 ft thick and is overlain 

central portion of mine 2. Other areas of the mine property by up to 3 ft of weak shale (2). The coal is fragile and friable 

contain thicker total sandstone accumulations, some in and breaks apart easily. No bumps have been reported in 

excess of 170 ft. This sandstone is difficult to break on the mines working the Pocahontas No. 3 Coalbed in the area 

line of pillar extraction. As at mine 1, numerous straight, of mine 2, and this may be attributed to the buffering efdigitate coal washouts, many with associated rolls, are fect of the overlying weak shale (2). 

found throughout mine 2. The hard shale and sandstone 

units create very stable roof conditions; however, bumps 

tend to occur where the thick sandstone directly overlies Structural Setting and Overburden Thickness 

the coalbed. Where any of the various shale lithoiogies are 

present, bumps are generally not experienced. The structure at mine 2 is straightforward and 

In the area of mine 2, the Pocahontas No. 3 Coalbed, uncomplicated. The Pocahontas No. 4 Coalbed falls in elevalying approximately 60 ft below the Pocahontas No. 4 Coal- tion from the axis of the Dry Fork anticline, which lies to 

bed, also occurs in minable thicknesses. The Pocahontas the southeast, and dips gently to the northwest (fig. 18). 
Figure 18.-Structure contour map for mine 2, drawn from elevation of top of Pocahontas No. 4 Coalbed. 

Major faults are absent; however, a few minor faults have 

been recognized by mine personnel. No clastic dikes have 

been observed. Numerous kettlebottoms, which are 

sometimes concealed, have been noted in roof rock of both 

the Pocahontas No. 4 and No. 3 Coalbeds. 

Overburden thicknesses at mine 2 are less extreme than 

those at mine 1. The Pocahontas No. 4 Coalbed crops out 

along Tug Fork where several portals lead into mine 2 

toward the west. Highest overburden thicknesses are 

attained in the west-central portion of the mine (fig. 19). 

Two major bumps have been documented from this area; 

both occurred in areas with greater than 1,000 ft of cover. 

Two other bumps were experienced under 700 to 800 ft of 

strata (fig. 19). Mine personnel indicate that no bumps have 

been recorded under creekbeds, plausibly as a result of lower 

overburden thicknesses in such areas. Additionally, mine 

personnel note that where surface fractures have been 

recognized just off the crests of mountains on the mine property, there have been no bumps in the mine below. Mine 

personnel believe that these fractures may extend to a depth 

of 200 ft and theorize that they may relieve some of the 

stresses imposed by greater overburden thicknesses. 
Overburden thickness 9' overburden thickness contour l lne 

500 to 1,000 ft Contour Interval = 100 ft 

1 Owrburden thickness - Mine of mine worklngs 

[pM)n1*500n ---Ou~ofPoca~n~sNo.4Coalbed 

Wbn of bump 

0 6mo 

Scale, ft 

FIgure I B.-Overburden map for mlne 2. 
Bump Occurrence 

The incidence of bumps in mine 2 dates from about 1946. 

Prior to that time hand-loading technology was employed. 

By 1950 over 85 pct of the production was from mechanical 

mining machines. Continuous miners eventually replaced 

all the conventional and hand-loading stations (2). 

It has been speculated whether the manifestation of 

bumps was brought about by the advent of mechanized 

mining or the mining of coal at greater depth. Thirty-two 

separate bump accidents occurred from June 1945 to April 

1951, resulting in 66 injuries and 7 fatalities at mine 2. 

Analysis of these events led mining engineers and management of the mine to a number of conclusions about bumps 

in the Pocahontas No. 4 Coalbed. Bumps do not occur where 

the depth of overburden is less than 600 ft or strong massive 

adjacent strata are not present. Irregularly sized pillars, 

especially large pillars spaced among yielding pillars, led 

to an increased probability of bumps. Coal losses in the form 

of pillar remnants in the gob increase abutment pressures 

outby the pillar line. Abutment pressures move outby at 

approximately the same rate as the retreating pillar line. 

Finally, they found that a coal pillar with a length or width 

dimension of 45 ft or less will yield and not bump, and 

generally a coal pillar with a minimum dimension of 160 

ft is too large to bump. 

The thin-pillar mining system, designed in the 1950's 

to combat bumps during the mining of barrier blocks, is still 

in use today. Figure 20 is a schematic of the thin-pillar 

mining system; the five entries labeled A, B, C, D, and E 

are developed in advance. The entries are driven on centers 

of 65 to 75 ft with breakthroughs every 90 ft. Further refinement of the system revealed that 65-ft centers produced optimum balance between pillar softening and squeeze 

prevention. 

The important feature of the thin-pillar method is that 

it incorporates a bare minimum of barrier splitting outby 

the pillar line. Barrier splitting is limited to the active gob 

edge of the barrier pillar. The rigid portion of the barrier 

pillar is carrying the main roof load, and its gob sides 

become crushed and softened. All barrier splitting is confined to the yielded portion of the barrier pillar, and mining 

in the highly stressed core is avoided. When the outby end 

of the barrier is approached, the critical size of the pillar, 

generally considered to be 160 by 160 ft, is formed. This 

bump block is left to avoid a potential bump. 

/Old gob 

Solid coal 

Figure 20.-Thin-pillar mining method diagram, mine 2. 
Solid coal 

B 

...... .,: . .:>: ........... . . ....... ,,:..;,.',;;':. t.':..'...... :. .;;.:::..;:-::ii':.. .... :a',. .,., ... ., .... - :, . >,'.',, :.'..- .,'Old gob t,::,, :.... :::i."; ... .......... ..: ............ .* .. 1. r 

Figure-21 .-Results of auger drilling of bump block left by thin-pillar mining method, mine 2. 
~nnn-rFigure 22.-Thin-pillar mining method as used to retreat old mains located between two gobs, mine 2. 
sinuous washouts with associated rolls in the mine are attributed to channeling processes prior to the deposition of 

sandstone. The paucity of corehole information precluded 

the construction of a sandstone isolith map of the mine 

property. 

Structural Setting and Overburden Thickness 

The axis of a syncline, trending northeast-southwest, 

lies just east of the center of mine 3 (fig. 24). The Pocahontas No. 3 Coalbed dips gently toward the axis of this basin, 

more steeply on the eastern flank than on the west. 

A thrust fault has been recognized in mine 3 and may 

be related to a similar fault in an adjacent mine (fig. 24). 

This fault strikes N 20" W and has 13 ft of displacement. 

No crushing of rocks in the proximity of the fault was visible; however, upon development of the entry that encountered the fault, some fault gouge was observed. No 

clastic dikes have been recorded; however, kettlebottoms 

are fairly common. 

Overburden thicknesses at mine 3 are extreme; this 

mine is the deepest of the five examined in this study. Depth 

of cover ranges from just under 1,200 ft to in excess of 2,400 

ft (fig. 25). Bumps have been noted to occur at various depths 

throughout the mine, but, according to mine personnel, the 

majority of bumps are experienced under greater than 2,200 

ft of overburden. The locations of several previous bump 

occurrences are indicated on figure 25. All but one of these 

bumps took place under more than 2,200 ft of cover. 

1-1 Shale roof 

Bright, banded coal 

Shale binder 

Bright, banded, fairly 

blocky coal 

Friable coal with 

sulfur staining 

I-) Fissile,gray shale floor 

Figure 23.-Generalized stratigraphic column for mine 3. 

LEGEND 

,40, Structure contour line 

(Contour interval = I0 ft) 

= Fault 

Location of bump 

7 Outline of mine workings 

0 - 3,000 6,000 

Scale, ft 

Figure 24.-Structure contour map for mine 3, drawn from elevation of top of Pocahontas No. 3 Coalbed. 
n- 17 LEGEND 

I Overburden thickness ,1ro0/ Overburden thickness contour line 

1,000 to 1,500 f t Contour interval = I00 ft 

Overburden thickness @ Location of bump lao0 to 2m ft- Outline of mine workings 

Overburden thickness 

2,000 to 2900 f t 0 3,000 6000 

Scale, ft 

Figure 25.-Overburden map for mine 3. 
71 \ 6/ '5 4 - 

LEGEND 

7 Longwall ponel 

0 - 500 lPOO @ Bump 

Scale. ft 1 Outline of longwall panels 

q Overburden thickness contour line 

%,(Contour interval =200 ft) 

L 

Solid coal 

Figure 27.-Plan view of longwall gate road entries and location of bump event, mine 3. 

Figure 26.-Locations of retreating longwall bump events and 

overburden thicknesses, mine 3. 

Figure 28.-Plan view of shot-fire softening technique, used 

on tail entry longwall gate roads for bump control, mine 3. 
Head Tail 

Figure 29.-Plan view of modified bump control gate road 

design, mine 3. 

LEGEND 0 100 200 

- 2.5 -Convergence 

(Contour interval 

contour = 0.5 in) 

- 

Scale, f t 

Figure 30.-Convergence contour map for room-and-pillar 

retreat mining, mine 3. 

Water infusion 

0 

10 20 30 40 50 

TIME, days 

Figure 31.-Graph of convergence effects of water infusion 

of pillar C (fig. 30), mine 3. 
northeasternmost portion of the studied area, the sandstone 

is generally 40 to 60 ft thick (fig. 33). 

Structural Setting and Overburden Thickness 

Mine 4, located in the Appalachian Plateaus 

physiographic province, is situated in a relatively uncomplicated structural setting. Structural contour lines, 

drawn on the top of the Chilton Coalbed, trend northeastsouthwest (fig. 34). The mine lies on the east flank of the 

Handlev svncline: therefore. the coalbed dro~s in elevation 

Shaly coal 

Bright coal 

Claystone floor 

toward the northhest. No faults or clastic dies have been 

observed in the area of mine 4. Figure 32.-Generalized stratigraphic column for mine 4. 
LEGEND 

,40' Sandstone thickness contour line 

(Contour interval = 10 ft) 

Corehole data point 

@ Location of bump 

---- Outcrop of Chilton Coalbed 

3 Outline of mine workings 

1 I I 1 

Scale, f t 

Figure 33.-Sandstone thickness map of Lower Winifrede Sandstone, which immediately overlies Chilton Coalbed, mine 4. 
LEGEND 

,1400- Structure contour line 

(Contour interval = I0 f t) 

@ Location of bump 

Scale, f t 

---- Outcrop of Chilton Coalbed 

, 

d 

, Outline of mine workings 

Figure 34.-Structure contour map for mine 4, drawn from elevation of top of Chilton Coalbed. 
Rgm 35.-OwfW&n rmp lor mhm 4. 
I:: 

LEGEND lml Bump location 

Gob areas 

It 'I Outline of unsurveyed '' ''I mine workings 

Outline of surveyed mine workings 

I I I 

Scale, ft 

Figure 37.-Overview of bump accident area, mine 4. 

- .- - 
LEGEND 0 40 80 - I I 

Indicates locations of pillars that bumped Scale, ft * Estimates of roof rock conditions after bump 

occurrence made by company and Federal 

investigators 

2 Pillar 

Figure 38.-Plan view of immediate area of bump accident, mine 4. 

A closer view of the accident area is mapped in figure 

38. Note the standing gob directly inby and to the left of 

pillar 4, where the pin machine or roof bolter was located. 

The fall of immediate roof only in the gob area of pillars 

1 and 2 also is significant. The combination of the stress 

transferred from the yield pillars directly adjacent to pillar 

5 (fig. 37) by the rigid roof and the standing gob led to the 

bump event. Five rows of pillars were then left as a barrier 

(fig. 37), full extraction was discontinued, and a partial extraction procedure was instituted. This pillar splitting 

reduced the total extraction ratio to less than 60 pct. 

MINE 5 

Stratigraphic Relationships 

Mine 5 operates in the No. 2 Gas Coalbed of the 

Kanawha Formation (Pottsville Group, Pennsylvanian 

System) near Milburn, WV. The mine straddles the boundary between Fayette and Raleigh Counties. The name "No. 

2 Gas" has been applied to the lower bench of the Campbell Creek Coalbed, which is split along the Kanawha River 

southeastward of Campbell Creek, Kanawha County (12). 

Throughout the mine, the No. 2 Gas Coalbed is 43 to 63 

in thick. The coalbed is friable and displays multiple 

benches, each separated by binders of bone or shale (fig. 39). 

A persistent bone binder, noted at several locations in the 

mine, occurs approximately 1 ft from the top of the coalbed. A thicker, more prominent and continuous bone layer 

is also found approximately 1 ft above the bottom of the 

coalbed. Mine personnel believe that this binder stores 

energy from overburden pressure. Therefore, they recommend the removal of the lower parting first when mining 

commences. 

The floor consists of a medium-gray shale of variable 

thickness that is underlain by a sandstone approximately 

30 ft thick. Five coalbeds are known to exist below the No. 

2 Gas, two of which are mined in this area. Above the No. 

2 Gas Coalbed is a brown sandstone that displays variable 

characteristics, with a reduction in structural competence 

occurring where laminations are present (12). In general, 

the sandstone lends itself well to room-and-pillar retreat 

mining. In fact no unexpected roof falls have been reported 

in the mine. In places, the sandstone is separated from the 

coalbed by a thin layer of dark shale that tends to peel off 
along the bottom bedding plane of the sandstone and fall. 

Fifteen coalbeds occur in strata overlying the coalbed, but 

none of these is mined in the area. The hard, competent 

strata enclosing the No. 2 Gas Coalbed tend to converge 

at points and produce some bottom heaving. The few 

washouts present most likely resulted from paleochannel 

activity prior to deposition of the overlying brown 

sandstone. 

Drill-hole information was not available for the construction of a sandstone isolith map of the mine area. 

Therefore, no assessment of sandstone geometry was possible. However, as mentioned previously, the sandstone 

displays variable features and these are coupled with 

changes in coal character and sulfur content. Mine personnel attribute these variations to fluctuating environmental conditions during the deposition of the coalbed and 

overlying strata. 

Structural Setting and Overburden Thickness 

Mine 5 lies in the Appalachian Plateaus physiographic 

province and is situated approximately 15 miles southeast 

Approximately 300 st of coal was displaced by the bump; 

the location of the dislodged coal is diagramed on figure 42. 

One miner was slightly injured by the dislodged coal (13). 

It is theorized that the bump was caused by the extraction of pillars located on a pillar point. A pillar point, as 

defined by previous researchers (I), is a pillar located at the 

intersection of at least two gob areas. In this case, the pillars 

were located between three gob areas (fig. 42). Abutment 

pressure was transferred from three gobs onto the section. 

This pressure, combined with unstable roof conditions 

created by the failure of pillar remnants inby the section, 

caused the bump. 

This event was unique among those studied, for three 

reasons: (1) The center of the bump was not the pillar 

containing the working face, (2) a 6- to 12-in separation 

was formed between the roof and the top of the affected 

pillars, and (3) roof support timbers were broken into a 

V-shape, but were loosely held between the roof and bottom. 

These results seem to indicate that the roof transmitted a 

hammerlike blow to pillars A, B, and C (fig. 42). This type 

of failure was defined by previous researchers as a shock 

bump (1). 
LEGEND 

,2140- Structure contour line 

(Contour interval= 10 ft) 

@ Location of bump 

---- Outcrop of No. 2 Gas 

Coalbed 

2' Outline of mine workings 

I I 1 

Scale, ft 

Figure 40.-Structure contour map for mine 5, drawn from elevation of top of No. 2 Gas Coalbed. 
Owrburdan thickness ,d Overburden thtcknerr contour llne 

500 to 1,WO ft Contour Interval 100 ft 

8 Location of bump - Outline of mine worklngs 

--- Outcrop of No, 2 

Gaa Coalbed - 

Scale, ft 

agum 41.--Overkrrden map for mlne 5. 
KdJ 'UA 71.2 :/A YLJ Y/,J ?A V'j vA r(' (r- - zi 

L 

LEGEND 

and pil- / 

pW Indicates bump location \UDnC)a 18 Miningsequence 

Q (-J a a Bump pillar 

N 0 100 200 300 

I I I J 

~Daaoaoo~ Scale, ft 

Figure 42.-Plan view of area of bump accident, mine 5. 
Aspects of Occurrence, Cause, and Control. BuMines B 535,1954, 

37 PP. 

2. Hayduk, M. (US. Steel). Private communication, 1985; 

available upon request from A. A. Campoli, BuMines, Pittsburgh, 

PA. 

3. Goode, C. A., A. Zona, and A. A. Campoli. Controlling Coal 

Mine Bumps. Coal Min., v. 21, No. 10, 1984, pp. 48-53. 

4. Hennen, R. V. Wyoming and McDowell Counties. WV Geol. 

Surv. County Rep., 1915, 783 pp. 

5. Blankenship, C., and A. T. Castanon. Multiple Fatal Bump 

Accident (Outburst). MSHA (4015 Wilson Boulevard, Arlington, 

VA 222031, 1983, 17 pp. 

6. Miller, T. C., and R. Sporic. Development of a Hydraulic Device 

for Measuring Relative Pressure Changes in Coal During Mining: 

A Progress Report. BuMines RI 6571, 1964, 13 pp. 

7. Talman, W. G., and J. L. Schroder, Jr. Control of Mountain 

Bumps in the Pocahontas No. 4 Seam. Min. Eng. (Littleton, CO), 

Aug. 1958, pp. 877-891; Sept. 1958, pp. 982-1004B. 

Bump Accident. MSHA (Drawer AA, Richlands, VA 24641), 1974, 

12 PP. 

9. Diamond, W. P., and J. R. Levine. Direct Method Determination of the Gas Content of Coal: Procedures and Results. BuMines 

RI 8515, 1981, 36 pp. 

10. Kissell, F. N. The Methane Migration and Storage 

Characteristics of the Pittsburgh, Pocahontas No. 3, and Oklahoma 

Hartshorne Coalbeds. BuMines RI 7667, 1972, 22 pp. 

11. Davis, J. E. Fatal Outburst of Coal Accident. MSHA (P.O. 

Box 112, Mt. Hope, WV 25880), 1983, 26 pp. 

12. Hennen, R. V. Fayette County. WV Geol. Surv. County . Rep., . 

1919, 1002 

13. Grose. H. S. Nonfatal Fall of Rib Accident (Coal Outburst). 

MSHA (p.0: Box 112, Mt. Hope, WV 258801, 1984, 9 pp.