OCCURRENCE AND REMEDIATION OF COAL MINE 

BUMPS: A HISTORICAL REVIEW 

By Anthony T. lannacchione' and Joseph C. 2elanko2 

ABSTRACT 

One of the most difficult, longstanding engineering 

problems associated with coal mining is the catastrophic 

failure of cog mine structures known as bumps. For more 

than 70 years, researchers and practitioners have assembled a wealth of technical information on coal bumps 

in an attempt to understand and control them. However, 

many technical issues raised long ago are still being 

debated today. This paper examines past experiences and 

recognizes achievements in the realm of coal bumps. U.S. 

Bureau of Mines (USBM) researchers collected and analyzed 172 coal bump incident reports and compiled the 

pertinent statistics into a database. Actual field studied are 

also discussed. Examination of past experience has shown 

that there is no one set of defining characteristics that is 

responsible for coal bumps. In all cases, bumps occur 

when complex arrangements of geology, stress, and mining 

conditions interact to interfere with the orderly dissipation 

of stress. However, it is evident from the database that a 

tremendous reservoir of knowledge has been established 

from past experience that has unquestionably limited the 

severity of coal mine bumps in the United States. 

INTRODUCTION 

Coal mine bumps have presented serious mining problems in the United States throughout the 20th century. 

Fatalities and injuries have resulted when these destructive 

events occurred at the working face of the mine. Persistent bump problems have caused the abandonment of 

large coal reserves and have led to premature mine 

closure. 

Through the years, a variety of techniques were proposed and implemented to mitigate bumps. Mining history 

is rich with examples of innovative proposals that, at 

best, temporarily alleviated this complex problem. From 

the 1930's to the present, the U.S. Bureau of Mines 

(USBM) has conducted fundamental research on the geologic environments and failure mechanisms responsible for 

coal mine bumps and on methods to control them. This 

work supports the USBM's mission to improve safety for 

l~upe~sory civil engineer. 

2~ining engineer. 

miners by eliminating their exposure to hazardous 

underground conditions. 

During the 1930's, USBM research indicated that both 

geology and mining practice (geometry and sequence) play 

key functions in bump occurrence. Strong, stiff roof and 

floor strata not prone to failing or heaving were cited as 

contributing factors when combined with deep overburden. 

Various poor mining practices that tended to concentrate 

stresses near the working face were identified and discouraged. Although such qualitative geologic descriptions 

and design rules-of-thumb have persisted through the 

years, the need to better quantify bump-prone conditions 

remains. 

Mine operators find little comfort in generalities when 

they have experienced a bump and must determine if 

another is imminent. Specific questions about the influence of individual factors and the interaction among factors arise but are often ficdt to answer owing to the 

limited experience at a given mine site. Often, many 

Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 
parameters change simultaneously (for example, strength 

and stiffness of roof and floor, proximity of strong lithologic units to a coalbed, depth of overburden, mine geometry, and mining rate). 

To better establish the range of circumstances under 

which bumps take place, the USBM compiled the Coal 

Bump Database, which contains information about bumps 

that have occurred in the United States since 1936. More 

than 172 coal mine bumps have been identified from various documents, including U.S. Mine Safety and Health 

Administration (MSHA) Reports of Investigation (Fatal and Nonfatal), USlBM reports, mining conference 

proceedings, and mining company reports and memoranda. 

Information pertinent to mine design and geologic characterization of bump-prone ground has been extracted 

from the documents and assembled in a spreadsheet. It is 

the mining community's charge to rethink its understanding of bump phenomena while exploring innovative 

techniques to mitigate occurrences. Fresentatio~p of historical information in this format facilitates a reevaluation of 

the broad range of geologic and operational conditions 

under which bumps have been encountered and will help 

preserve knoyledge acquired through experience. 

BACKGROUND 

The earliest U.S. coal mine bump included in the 

USBM Coal Bump Database dates back to 1936. However, several reports indicate that bumps had constituted 

a serious problem even earlier. For example, Watts (30)3 

reported bumps at the Sunnyside No. 1 Mine in Utah, and 

Rice (27) documented several bumps in the Cumberland 

Coalfield in eastern Kentuclq. Bryson (3) indicates that 

bumps occurred in the Cumberland Coallield as early as 

1923 and became very troublesome from 1930 to 1934. In 

most cases, specific information on the events as described 

by these experts is not available, and thus these events 

have not been included in the database. However, the 

descriptions of various causes and attempted remedies for 

bumps provide valuable anecdotal information. 

Notable among the early work on coal mine bumps are 

reports by Rice (27) and Holland and Thomas (14). Rice 

classifies bumps into two general types: pressure bumps 

and shock bumps. According to Rice, pressure bumps are 

thin-pillar mining, the barriers are segmented into a series 

of yield pillars too small to maintain significant stress 

levels or stored strain energy. Efforts in both Eastern and 

Western U.S. coalfields were also directed to maintaining 

low stress levels through planned destressing activities, 

such as large-hole auger drilling (28) and volley fxing (25). 

Despite technical advances in the 1950's, analyses of 

bump records from 1959 to 1984 (12) indicate that bumps 

still occurred at an alarming rate. Current information 

shows that bump-related accidents resulted in 42 fatalities 

since 1960 (table I), 14 in the Eastern United States and 

28 in the Western United States. Continuing bump problems probably stemmed in part from the same unfavorable 

mining conditions and practices discussed by HoPLand and 

Thomas. 

Table 1.4kronological dirstribwtion of bump events included 

in USBM Coal Bump Database 

caused when pillar stress exceeds bearing strength. Shock 

bumps are induced by breaking of thick, massive strata at Time period Number of bumps Fatalities Injuries 

a considerable distance above the coalbed, which causes :9::::9 : : : : : : : : 1 1 0 

9 7 18 the immediate mine roof to transmit a shock wave to the 1950-59 . . . , . , . 38 28 43 

cod. Rice indicates several conditions favoring bumps, 1960-69 . . . , . . , . 27 13 36 

including thick overburden, strong overlying strata, and 

a strong floor not prone to heaving. Holland and Thomas 

define a similar range of conditions based on their examination of more than 117 instances of bumps in West 

Virginia, Kentucky, Utah, and Virginia. Their investigation 

also demonstrated that most bumps had been caused by 

improper mining methods and practices. 

Reports from the 1950's document technical advances 

for mining in bump-prone ground. For example, Tahan 

and Schroder (29) describe a novel barrier-splitting 

technique called the thin-pillar mining method. In 

3~talic numbers in parentheses refer to items in the list of references 

at the end of this paper. 

The advent of the continuous mining machine resulted 

in different problems requiring new control solutions. The 

mobility and versatility of the continuous miner led to the 

development of novel pillar splitting and extraction sequencing designs for bump control. 

With the widespread utilization of the longwall mining 

method over the last 15 years in the United States, bump 

problems have continued to threaten the safe mining of 

coal. One fatality on an advancing longwall face, several 
injuries on retreating longwall faces, and at least one mine 

closure have been attributed to bumps (18). However, 

ingenuity and experience have prevailed, and several innovative designs for controlling bumps in longwall mines 

have been developed. Two designs focus on altering the 

size and shape of gate entry pillars. The conventional 

pillar design approach relies on increasing the gate pillar 

dimensions so that the pillars will prevent abutment load 

ride-over onto the active longwall face (32). The yield 

pillar approach effectively reduces gate pillar dimensions 

so that the pillars will yield in a controlled fashion, thereby eliminating tailgate pillar bumps and aiding in the 

controlled fracturing of the main roof (7, 21). A third 

approach, the advancing longwall method, eliminates the 

need for developing gate road pillar systems; advancing 

longwalls were first used in. the United States at MidContinent Resource's coal mines in the 1970's (19, 26). 

M of these methods have some drawbacks, but they generally represent innovative design philosophies for controlling bumps. 

U.S. coal bumps have been associated with a variety of 

conditions. Perhaps the most general conditions conducive 

to bumps are stiff, massive strata and high stresses. In 

some instances, these conditions are pervasive; in others, 

they are altered locally by geology or mining. For example, geologic structures such as faults or sandstone 

channels have, in some cases, affected the occurrence of 

bumps. Similarly, extraction sequences and mine layouts 

(e.g., multiple-seam mining scenarios) influence the way 

stresses are concentrated around mine openings and thus 

play a role in bump occurrence. Holland and Thomas (14, 

p. 34) state that the relationship between factors and 

circumstances causing bumps "actually is very complex, 

especially in a quantitative sense." Unique combinations 

of geology and mining systems have required many sitespecific bump-control designs. Such designs must continually evolve as new geologic and mining scenarios are encountered. Solutions to new design challenges can result 

from evaluating past experiences. 

OVERVIEW OF USBM COAL BUMP DATABASE 

The USBM Coal Bump Database includes 172 specific 

bump events that occurred in four Eastern States and 

three Western States (figure 1). The database was constructed from USBM and MSIW coal bump accident and 

incident reports written between October 12, 1936, and 

January 21, 1993. A total of 87 fatalities and 163 injuries 

were identified. The 1980's witnessed the greatest outbreak of bumps, accounting for 31 pct of the total, while 

the second largest percentage occurred during the 1950's 

(23 pct). West Virginia recorded the greatest number of 

documented bumps (53), followed by Virginia (40), Colorado (30), Utah (26), and Kentucky (19). Alabama and 

Washington each had one reported bump event. 

Analysis of information in the Coal Bump Database 

indicates that bumps have occurred in a variety of mining 

systems and operations. For example, pillar retreat mining 

accounted for 35 pct of the bumps, barrier-splitting for 

26 pct, longwall mining for 25 pct, and development mining for 14 pct. Of the longwall incidents, 33 pct affected 

the longwall face, 19 pct the tailgate entries, 36 pct both 

the longwall face and the tailgate entries, and 6 pct the 

headgate entries. Generating 67 pct of the total, the act of 

excavating was associated with the greatest number of incidents. The coal-loading operation at the face accounted 

for another 22 pct of the total. Other, less-frequent bump 

incidents occurred during shot fring (5 pct) and 

installation of support (6 pct). Additionally, 22 pct of the 

bumps took place during nonproduction shifts. One event 

reportedly occurred in an abandoned section. 

The database includes reports on individual bump 

events from more than 50 mines. As table 2 indicates, 

some mines account for a single bump record, whereas 20 

or more events have been documented at two sites. With 

such high numbers of bumps at individual mines, it is not 

surprising that an impressive list of bump-control efforts 

has been developed. Unique mine designs have been employed to redistribute excessive stress conditions, for example, the thin-pillar method at the Gary No. 2 Mine and 

pillar-splitting methods at the Olga, Beatrice, and Cottonwood Mines. Innovative support strategies have been 

documented, ranging from yielding leg arches used at the 

Sunnyside Mines to material-filled cribs employed at several eastern Kentucky drift mines. The virtues and shortcomings of destressing techniques, including shot firing, 

auger drilling, and water infusion, have been identified. 

For example, extensive use of auger techniques with hole 

diameters ranging from 9 to 49 cm was attempted in the 

Gary district until a major bump during drilling resulted in 

fatalities in the early 1950's. 

Information pertinent to mine design and geologic characterization of bump-prone ground was extracted from 

source documents for each mine and assembled into a 

computer spreadsheet. The spreadsheet format facilitates 

the identification of common conditions contributing to 

bumps and provides a means of readily evaluating the 

broad range of experiences. Moreover, the range of documented experiences shows that bumps manifest themselves 

in different ways with varying effects. 
Table 2.--4J.S. coal mines included in USBM Coal Bump Database 

Mine Company 

Bartley No . 3 ........ Island Creek Corp ........... Beatrice ............ Beatrice Pocahontas Co ....... Belina No . 1 ........ Valley Camp of Utah. hc ...... Braztah No . 3 ........ Braztah Corp ............... Brookside .......... Kentucky Jellico Coal Co ...... Buchanan No . 1 ...... Consolidation Coal Co ........ C-2 ............... Harlan Cumberland Coal Co ... Castle Gate ......... Castle Gate Coal Co ......... Castle Gate No . 2 ..... Carbon Fuel Coal Co ......... Cottonwood ......... Energy West Mining Co ....... Deer Creek .......... Energy West Mining Co ....... Dehue .............. Youngstown Mines Corp ...... Dutch Creek No . 1 .... Mid-Continent Resources. Inc ... Federal No . 1 ........ Federal Mining Corp ......... Gary No . 2 .......... U.S. Steel Mining Co.. Inc ..... Gary No . 6 .......... U.S. Steel Mining Co.. Inc ..... Glen Rogers No . 2 .... Raleigh Wyoming Mining Co ... H-2 ............... Harlan Cumberland Coal Co ... Harewood .......... Allied Chemical Corp ......... Holden ............. Howe Sound Co ............ Kenilworth .......... Carbon Fuel Coal Co ......... L . S . Wood .......... Mid-Continent Resources. Inc ... Lynch No . 37 ........ Arch of Kentucky. Inc ......... Maple Meadow ...... Maple Meadow Mining Co ..... Marathon No . 1 ...... Harlan Wallins Coal Co.. Inc .... Mary Helen No . 2 ..... Mary Helen Coal Corp ........ Mary Helen No . 3 ..... Mary Helen Coal Corp ........ Milburn No . 4 ....... Milburn Colliery Co .......... Mine No . 10 ......... Wisconsin Steel Coal Mines ... Moss No . 2 ......... Clinchfield Coal Co. ......... Moss No . 3 ......... Clinchfield Coal Co .......... No . D-1 ............. W~sconsin Steel Coal Mines ... No . 1 .............. Turtle Creek Coal Co ......... No . 2 .............. Chafin Coal Co ............. No . 2 .............. Clinchfield Coal Corp ......... No . 4 .............. Jim Walter Resources. Inc ..... No . 9 .............. Jewell Eagle Coal Co ......... No . 17 ............. Island Creek Corp. .......... No . 21 ............. W-P Coal Co ............... No . 27 ............. Island Creek Corp ........... No . 31 ............. Peabody Coal Co ............ Olga .............. Olga Coal Co ............... Price River No . 3 ..... Price River Coal Co .......... Soldier Canyon ...... Soldier Creek Coal Co ........ Somerset ........... U.S. Steel ................ Sunnyside No . 1 ...... Kaiser Steel Corp ............ Sunnyside No . 2 ...... Kaiser Steel Corp ............ Trail Mountain No . 9 ... Beaver Creek Coal Co ........ VP No . 3 ........... Virginia Pocahontas Co ....... VP No . 6 ........... Island Creek Corp ........... Wilberg ............ Emery Mining Corp .......... NA ................ NA ...................... NA ................ NA ...................... NA ................ NA ...................... NA ................ NA ...................... NA Not available . 

City 

Bartley ........ Keen Mountain . . Clear Greek .... Helper ........ Brookside ...... Mavisdale ...... Dione ......... Helper ........ Helper ........ Huntington ..... Huntington ..... Dehue ........ Redstone ...... Elkhorn City .... Gary .......... Gary .......... Glen Rogers .... Louellen ....... Longacre ...... Holden ........ Kenilworth ..... Redstone ...... Cumberland .... Fairdale ....... Verdo ......... Coalgood ...... Coalgood ...... Milburn ........ Benham ....... Clinchfield ..... Duty .......... Benham ....... Coalgood ...... Rita .......... Dante ......... Brookwood ..... Melville ........ Red Jacket ..... Stirrat ......... Ragland ....... Kenvir ......... Coalwood ...... Helper ........ Wellington ..... Somerset ...... Sunnyside ..... Sunnyside ..... Orangeville ..... Vansant ....... Mavisdale ...... Orangeville ..... N A ........... N A ........... N A ........... N A ........... 

County State 

McDowell .... WV 

Buchanan .... VA 

Carbon ...... UT 

Carbon ...... UT 

Harlan ...... KY 

Buchanan .... VA 

Harlan ...... KY 

Carbon ...... UT 

Carbon ...... UT 

Emery ...... UT 

Emery ...... UT 

Logan ....... WV 

Pitkin ....... CO 

Pike ........ KY 

McDowell .... WV 

McDowell .... WV 

Wyoming .... WV 

Harlan ...... KY 

Fayette ...... WV 

Chelan ...... WA 

Carbon ...... UT 

Pitkin ....... CO 

Harlan ...... KY 

Raleigh ...... W 

Harlan ...... KY 

Harlan ...... KY 

Harlan ...... KY 

Fayette ...... W 

Harlan ...... KY 

Russell ...... VA 

Dickenson .... VA 

Harlan ...... KY 

Harlan ...... KY 

Logan ....... WV 

Russell ...... VA 

Tuscaloosa ... AL 

Logan .... 7 W 

Mingo ....... W 

Logan ....... WV 

Mingo ....... WV 

Lee ......... VA 

McDowell .... W 

Carbon ...... UT 

Carbon ...... UT 

Gunnison .... CO 

Carbon ...... UT 

Carbon ...... UT 

Emery ...... UT 

Buchanan .... VA 

Buchanan .... VA 

Emery ...... UT 

NA ......... CO 

NA ......... KY 

NA ......... KY 

NA ......... CO 

No. of Coalbed bumps 

N A ............. Pocahontas No . 3 . . Upper O'Connor ... Subseam No . 3 .... Harlan ........... Pocahontas No . 3 . . Creech .......... Subseam No . 3 .... N A ............. Hiawatha ........ Blind Canyon ..... Eagle ........... B .............. Elswick .......... Pocahontas No . 4 . . Pocahontas No . 4 . . Beckley ......... Harlan .......... Eagle ........... N A ............. Castlegate D ...... B .............. Harlan .......... Beckley .,....... Darby ........... Harlan .......... Harlan .......... No . 2 Gas ........ Harlan .......... Tiller ............. Thick Tiller ....... D above Kellioka ... Harlan .......... Upper Cedar Grove 

Upper Banner ..... Blue Creek ....... Eagle ........... Cedar Grove ...... Chilton .......... N A ............. Darby ........... Pocahontas No . 4 . . Castlegate sub 3 ... Rock Canyon ..... C above Kellioka ... Lower Sunnyside . . Upper Sunnyside . . Hiawatha ........ Pocahontas No . 3 . . Pocahontas No . 3 . . Hiawatha ........ B .............. N A ............. N A .............. Middle B ......... 
F;gure 7 

Major U.S. Coal Basins Where Coal Mine Bumps Have Historically Been a Problem. 

FACTORS CONDUCIVE TO BUMPS 

Although specific mechanisms that trigger coal mine 

bumps are not well established, it is generally recognized 

that high stresses play a key role in bumps. Retreat mining and barrier-splitting often intern9 the stresses. 

Abutment loading on pillar retreat lines and longwall gate 

roads can be extreme, especially when mining is conducted 

between stiff subjacent and superjacent strata. By design, 

barriers are intended to carry abutment loads in various 

situations, and thus barrier-splitting operations often involve high-stress environments. In development mining, 

stress redistribution generally affects areas near the openings. In areas of thick overburden (for example, > 600 m), 

the redistribution of stresses caused by development mining alone may generate coal mine bumps. 

High-stress conditions conducive to generating coal 

mine bumps are associated with a variety of factors. Caving characteristics of main roof units may have a significant impact on stress levels at a room-and-pillar retreat 

line or retreating longwall face. Geologic structures such 

as displacement faults, massive sandstone paleochannels, 

and rolls are important because of their ability to concentrate stress and control the caving and heaving characteristics of strata. Unfavorable mining practices or configurations (for example, multiple-seam interactions) can 

concentrate stresses in specific locations. Undoubtedly, 

these factors play a role in many of the bumps included in 

the USBM Coal Bump Database. Nevertheless, the simplest indicator of bump potential appears to be the presence of thick overburden. Overburden information is 

included in the database for more than 50 mines that have 

experienced bumps. Overburden thickness at these sites 

ranges from 143 to 760 m, but at most of the sites, overburden ranges from 400 to 550 m. Only 10 mines experienced bumps where overburden thickness was less than 

300 m, while 9 were operating under more than 600 m 

when bumps occurred. 

As indicated earlier, a variety of geologic factors have 

influenced the occurrence of bumps. In describing natural 

conditions conducive to coal bumps, a common factor in 

both US. and foreign mines is the proximity of the bumpprone coalbed to strong, thick, rigid strata (2). Of the 

172 events comprising the USBM Coal Bump Database, 
lithologic descriptions of the mine roof are included for 

95 bump sites. In 86 instances, reference is made to the 

presence of sandrtone immediately above to within a few 

meters of the coalbed. Terms such as "strong," "funn," 

"massive," and "thick" are used to describe the sandstone 

units. In 30 instances, a shale, sandy shale, siltstone, or 

mudstone unit of varying thickness was found to occur 

between the coalbed and the overlying sandstone units. 

Geologic descriptions of the mine floor are included for 

more than 80 sites. Shale is the predominant floor lithology in the database; the presence of sandstone in the floor 

is noted in only 25 pct of the site descriptions. Terms such 

as "hard and "dense" are common descriptions of floor 

lithologies. 

The implications of multiple-seam mining interactions 

in generating strata control problems are well documented 

(5-6). These problems can be the result of both stress 

concentration or strata displacement and can be experienced when the interburden is as thick as a few hundred 

meters. However, problems are more severe when the 

interburden is less than 10 m thick. Ground conditions 

in upper coalbeds may be disturbed by strata movements 

associated with previous workings in a lower coalbed. This 

type of interaction may result in diEicult mine roof conditions but has not been identified as a factor contributing 

to bumps. Stress concentrations occwing in multipleseam mining scenarios, however, have been associated with 

bumps; 15 bumps in the database occurred in such 

settings. In most cases, mining in a lower coalbed 

encountered zones of high stress beneath barriers or 

isolated pillar sections in a previously mined upper 

codbed. 

Rice suggested that "a structurally strong coal" not 

prone to crushing easily would favor bumps (27, p. 4). 

However, more recent research suggests that the physical 

properties of coal are not necessarily key factors in bump 

occurrence. For example, Babcock and Bickel(1984) performed laboratory studies on coal samples from 15 mines 

in 11 coalbeds. Their study concluded that many, if not 

most, coals can fail violently given the proper conditions of 

stress and constraint. The database appears to support 

this conclusion, for it demonstrates that coal bumps have 

been experienced in at least 25 US. coalbeds (table 3). 

The height of Eastern U.S. coalbeds ranged from 1 to 

3 m; Western U.S. coalbeds were ~i~canly higher, 

ranging from 1.8 to 4.3 m. 

RDS ASSOCIATED Wlf H BUMPS 

Coal mine bumps are dynamic phenomena; numerous 

fatalities and injuries have been a direct result of miners 

being struck by coal forcefully ejected during a bump. 

Approximately 80 pct of the fatalities documented in the 

database were caused directly by displaced coal either hitting the individual or by forcing the individual into nearby 

equipment or mine ribs. However, other hazards have 

also been associated with coal mine bumps, including roof 

falls and ignitions of methane and coal dust. i 

Table 3.4.S. coaibeds associated with coal mine bumps 

Coalbed State Thickness. m 

Eastern United States: 

Beckley ................................ BlueCreek ............................. Cedar Grove and Upper Cedar Grove .......... Chilton ................................ Creech ................................ Darby ................................. Eagle .................................. Elswick ................................ Harlan ................................. No.2Gas .............................. Pocahontas No. 3 ........................ Pocahontas No. 4 ........................ Tiller .................................. Upper Banner ........................... Western United States: 

...................................... 

Blind Canyon ............................. C............................,........ 

Castlegate D ............................ Dutch Creek M .......................... Hiawatha ............................... Middle B ................................ Rockcanyon ............................ Subseam No. 3 .......................... Upper and Lower Sunnyside ................ 

WV 

AL 

WV 

WV 

KY 

KY-VA 

WV 

KY 

KY 

WV 

VA 

WV 

VA 

VA 
Ten incidents in the database document mine roof falls 

that occurred in conjunction with bumps. Prior to the 

widespread use cf roof bolting for primary support, bumps 

had the potential to create roof instabilities simply by 

dislodging posts and crossbars. With the introduction of 

roof bolting, however, the effect of bumps on supports was 

lessened. Nevertheless, bumps appear to continue to contribute to roof falls by disturbing the stability of the roof 

rock directly. In one case, for example, a bump caused 

roof rock to be released along a slip between longwall 

chocks and the face, resulting in a fatality. This associated 

hazard appears to be most prevalent during pillar mining, 

particularly in the Uinta Coalfields of Utah. 

Ignitions of methane gas and dust associated with coal 

bumps are somewhat rare, but they are among the most 

devastating incidents in terms of the numbers of miners 

killed or injured. For example, on March 14,1945, a pillar 

bump at the Kenilworth Mine caused the trailing cable of 

a loading machine to be pulled with such force that it was 

severed and created a short circuit that led to arcing (15). 

Thick coal dust resulting from the violent bump, coupled 

with methane gas, probably from the adjacent gob area, 

ignited, severely burning 12 miners. Seven of the injured 

miners eventually died as a result of the accident. 

Ignitions are more prevalent in deep pillar extraction 

areas and during longwall mining. However, one bumprelated ignition reportedly occurred during development 

mining. Mid-Continent Resources has experienced severe 

problems with extensive methane gas emissions in association with bumps at its mines, which have been referred to 

as gas outbursts. The most devastating gas-driven bump 

occurred on April 15, 1981, at the Dutch Creek No. 1 

Mine in Colorado. A massive outburst of gas and coal 

occurred approximately 2 h after mining through a fault on 

the development section for the No. 102 longwall. Fifteen 

miners were killed and three were injured in the resultant 

mine explosion. Five less severe events occurred at the 

company's L. S. Wood Mine, where significant quantities 

of methane gas were measured in the mine air after face 

bumps. 

COMPARATIVE MAGNITUDE OF BUMPS 

A sense of relative event magnitude can be gained by 

assessing observed destruction and measured seismicity for 

a number of events documented in the USBM Coal Bump 

Database. In terms of observable damage underground, 

bumps ranged in magnitude from those that dislodged a 

portion of a single rib to three that partially destroyed 

large sections of pillars. On June 3, 1985, the Olga Mine 

in southern West Virginia experienced a series of bumps 

that eventually affected, to varying degrees, approximately 

100 coal pillars (8). Fortunately, this event occurred over 

an idle weekend when no miners were on the section. 

However, only a few meters of bumped rib coal can have 

devastating effects. For example, a continuous mining 

machine helper at the Belina No. 1 Mine was seriously 

injured on March 19, 1981, while standing next to a rib 

where only a few meters of coal were expelled. 

Numerous reports have been made concerning the degree to which bumps are felt on the surface, sometimes as 

far as 3 km away. Seismological observatories around the 

world have recorded some of the more powerful incidents. 

Eleven bumps from the database have Richter magnitudes 

of 3 or greater, with three in Virginia having magnitudes 

of 4 or greater (table 4).. 

Table 4.-Levels of mining-induced seismicity 

registered at U.S. coal mines 

Mine State Richter Date 

magnitude 

Olga .............. WV 3.4 Apr. 26, 1965. 

Moss No. 2 . . . . . . . . . VA. '3.5 and 4.5 Julv 30, 1970. 

Moss No. 2 . . . . . . . . . VA 

Beatrice ............ VA 

Jim Walter Resources, Inc., No. 4 . . AL 

VP No. 3 . . . . . . . . . . . VA 

Buchanan No. 1 . . . . . . VA 

Buchanan No. 1 . . . . . . VA 

Lynch No. 37 . . . . . . . . KY 

Deer CreekCottonwood ........ UT 

Soldier Creek . . . . . . . . UT 

Lynch No. 37 . . . . . . . . KY 

Lynch No. 37 . . . . . . . . KY 

May 7, 1986. 

Mar. 4, 1987. 

Apr. 14, 1988. 

Apr. 10, 1989. 

Nov. 22, 1989. 

Mar. 15, 1991. 

Jan. 21,.6993. 

Aug. 3, 1994. 

Oct. 5. 1994. 

 rebu bump shock 12 h and 6 h, respectively, before bump occurrence underground. 

An explanation for the range in levels of observed 

seismicity may be found by examining the mechanisms 

responsible for many of the rock bursts in deep South 

African and Canadian hard-rock mines. Morrison and 

MacDonald (22) have shown that rock bursts are often 

associated with slip along preexisting geologic discontinuities adjacent to mine openings. S tick-slip movements 

on these discontinuities produce a sharp, instantaneous 

acceleration within the strata around the mine structure. 

As seismic waves propagate through the mine, pillars are 

compressed, then extended. This causes an immediate 

increase in load, resulting in a potentially unstable stress 

state. During the next instant, load is removed, which 

lowers confinement and can initiate an unstable state. 

The level of mining-induced seismic activity coming 

from U.S. coalfields suggests that earthquake-like sources 

may indeed be partially responsible for pillar damage underground. Evidence at one site suggests that the seismic 

source was over 30 m above the mine opening and may 

have been associated with slip between large blocks of 
strata over or adjacent to longwall gob areas. At other energy into a mine opening. These data suggest that there 

sites, the source of the seismicity appears to be within the is a weak correlation between the magnitude of surmine structure. These events generally have lower values face shaking and the degree of destruction experienced 

of seismicity, possibly resulting from the dissipation of underground. 

BUMP EXPERIENCES AT SPECIFIC MINES 

The sections below provide an overview of many events 

represented in the USBM Coal Bump Database. The 

authors refer often to the L. S. Wood, Gary No. 2 and 

No. 6, Moss No. 2, and Beatrice Mines to highlight various 

aspects of U.S. bump experiences. Therefore, a brief 

description of these operations is warranted. 

L. S. Wood Mine 

The L. S. Wood Mine near Redstone, CO, was developed in the 2-m-thick B Coalbed in the early 1970's by 

Mid-Continent Resources. Initially, the mine employed 

approximately three continuous mining machines and 

developed pillar sections to the left and right of its main 

entry system (figure 2). Because the mine was originally 

a drift mine, overburden in the early years was low. 

However, overburden rapidly increased as the main entries 

were developed downdip. By the time the first longwall 

became operational, the overburden was approaching 

depths of 500 m. The mine was plagued with methane gas 

emissions and displacement faults. 

Gary No. 2 and No. 6 Mines 

The Gary No. 2 and No. 6 Mines, operated by U.S. 

Steel Mining Co., were first opened in 1903 in the Pocahontas No. 4 Coalbed (9). These mines are located adjacent to each other in McDowell County in southern 

West Virginia. The coalbed crops out on the mine property, but rugged terrain accounts for overburden thicknesses approaching 460 m. In conjunction with thick overburden, strong roof and floor lithologies are present. The 

mine roof over much of the property includes a massive 

sandstone up to 45 m thick. 

The Gary Mines have a long, fairly well-documented 

coal bump history. Duckwall (9) noted that bumps 

Figure 2 % 

Location and Dates of Bumps Reported at L. S. Wood Mine, Redstone, 

Pitkin County, CO. 

11 \ 

Oct. 17, 1980 

- 

Scale, m 
occurred as early as 1930 on the mine property, but they 

did not appear to be sdrious events. Records were not 

maintained until 1945, when injuries were associated with 

bumps. From 1945 through the 1950's, the history of 

bumps at these mines and U.S. Steel's efforts to prevent 

them were well documented through company memoranda, eTSBM reports, journal articles, and conference 

papers. 

Bumps at the Gary Mines in the 1950's were associated 

with a variety of factors (figure 3). Mining in the first half 

of the 20th century undoubtedly resulted in the bumpprone mining scenarios faced in the 1950's. For example, 

mining was conducted adjacent to gob areas created decades earlier, retreat sections operated on groups of pillars 

of irregular sizes and shapes, and much of the mining was 

directed to recovering barriers between old workings. 

Moss No. 2 Mine 

The Moss No. 2 Mine near Dante, VA, was extensively 

mined by Clinchfield Coal Co., from the 1950's to the 

1970's in 1.2 m of the Tiller Coalbed. During this time, 

five bumps were recorded and are part of the USBM 

database (figure 4). The mine utilized a multientry development system, followed by room-and-pillar mining. 

Extraction of pillars was accomplished primarily by the 

split-and-fender method. Rooms were typically driven23 m 

apart and 6 m wide with crosscuts every 23 m. More than 

100 sections were developed and pillared using some variation of this method. One of the Grst longwall sections in 

the United States was employed at this site in the late 

1960's and 1970's. Twenty-two longwall panels of varying 

length were extracted. 

Many conditions associated with bumps were found at 

this mine. Overburden at the mine ranged Erom zero at 

outcrop to greater than 400 m under the highest ridges. 

The roof stratum was dominated by thick sequences of 

massive sandstone. Numerous paleochannels scoured the 

coalbed, limiting the development of the mine in several 

areas. Locally, this massive roof had the ability to span 

large areas of the gob. Additionally, thick pockets of shale 

were noted adjacent to the sandstone channels. The floor 

stratum was almost always referred to as a hard, dense, 

silty shale. The Moss No. 2 Mine property was also overlain by the minable Upper and Lower Banner Coalbeds. 

The Upper Banner Coalbed was about 250 m above the 

Tiller Coalbed, but it undoubtedly had a considerable 

effect on the stress transfer process. 

Beatrice Mine 

The Beatrice Mine near Keen Mountain, VA, reported 

24 bumps between 1972 and 1981 (figure 5). This high 

number of occurrences spanned the spectrum of mining 

conditions. Therefore, examples from this operation will 

be referred to often in this paper. The Beatrice Mine 

worked about 2 m of the Pocahontas No. 3 Coalbed at 

overburden ranging from 300 m near the shaft bottom to 

over 700 m under the highest ridges. A massive, quartziterich sandstone was found throughout the property. In 

places, this extremely hard stratum came in direct contact 

with the coalbed. However, in most locations, a very 

competent siltstone occupied the interval between the 

coalbed and the overlying sandstone. The floor was often 

reported as a sandy shale. No mining occurred above or 

below the Beatrice Mine. 

BUMPS ASSOCIATED WITH 

VARIOUS MINING METHODS 

The examples below have been grouped according to 

the type of mining system at various bump sites. These 

mining systems can generally be categorized as (1) development mining, (2) pillar retreat mining, (3) barrier 

splitting, and (4) longwall mining. This grouping facilitates 

descriptions of the impact of the particular mining method 

on bump occurrence. Examples of bumps associated with 

the various mining methods are intended to highlight the 

shortcomings and/or successes of each mining method and 

related practices and to indicate the influence of conditions 

and circumstances unrelated to mining method. .$ 

Development Mining 

Development mining refers to the extension of entries 

and crosscuts into undeveloped portions of the coal reserve. Generally, extension of mains, submains, butt sections, gate roads, and setup and bleeder entries represent 

development work. Because this activity involves the initial 

stages of mining and does not produce abutment loading, 

bumps should be generated less frequently. 

Twenty-one bumps were identified in the total USBM 

database as occurring during development mining (table 5). Three were in the Eastern United States and 18 

were in Utah and Colorado. 

The L. S. Wood Mine experienced nine bumps during 

development of the Main Slope section between July 1980 

and April 1982. All these bumps were associated with 

overburden greater than 600 m. Four bumps took place 

near one of two adjacent gobs (figure 2). Although the 

bumps exhibited tremendous force, the skilled work force 

at the mine was always able to avoid being "caught" by the 

bump so no miners were injured in any of these events. 

Eight bumps occurred during or shortly after mining and 

displaced large volumes of rib coal near the mining zone. 
Large barrier pillars 

0 - 1000 

Scale, m 

h 

Circled numbers indicate number of bumps at various locations. 
Fr"g61re 4 

Location and Dates of Bumps' Reported at Moss No. 2 Mine, Russell County, VA. 

Significant quantities of methane gas were liberated in 

association with several bumps. After the bump on April 

13, 1981, methane concentrations measured as high as 

5 pct. Five of the bumps occurred under more than 750 m 

of overburden far from the gob or faults. In situ coalbed 

gas pressures were undoubtedly high, for these bumps 

showed high methane emission characteristics. These 

events may be better defined as gas outbursts. The bump 

problems at the L. S. Wood Mine and two other MidContinent operations were severe enough to warrant the 

elimination of gate entries by employing the advancing 

longwall system. 

At the Beatrice Mine, development work was underway 

in the No. 9 unit section off the Skip South Mains, approximately 70 m from an adjacent gob area (figure 6), 

when there was a violent bump in the face area on July 24, 

1976, that injured three miners. Abutment loading from 

the adjacent gob area may have contributed to the bump. 

Therefore, this event could be explained as resdting from 

the barrier-splitting operations. However, because the gob 

was 70 m away and the solid block of coal being mined 

was approximately 230 m wide, it appears more appropriate to categorize it as a development bump. Other significant factors at this site were the very massive, stiff, 

siltstone roof and floor strata and overburden averaging 

600 m in depth. 

Table 5.4onditions associated with development mining 

Mine 

L.S. Wood . . . . 

Beatrice Mine . . 

Deer Creek . . . . Dutch Creek 

No. 1 . . . . . . . Sunnyside No. 2 

Total . . . 

Number of 

bumps 

4 

9 

2 

1 

1 

1 

Condition 

Close to gob section. 

Overburden deeper than 600 m. 

Destressing . Close to gob section. 

Overburden deeper than 600 m. 

Close to gob section. 

Displacement faults. 

Displacement faults. 
Figure 5 

ed at Beatrice Mine, Buchanan County, VA. 

im 

j 

cIzzIl LEGEND 

0 

0 

I 

Date of Bump Occurrenc 

I 

I,I~0000 

I 

I I 

I 

Dl 

I 

Scale, m 
Figure 6 

Violent Bump During Development of Pillar Section Within Beatrice Mine That Injured Three 

Miners. 

Scale, m 

Bump 

can cantilever, adding load to the pillar. Mining in the 

yielded rib releases confinement and may result in violent 

solid-core failure. 

Pillars adjacent to gob areas experience elevated loading conditions from the unsupported strata above the gob 

(figure 8A). Certain mining geometries, such as a large 

pillar surrounded by smaller pillars, can concentrate stress 

(figure 8B). Large pillars can be imagined as stiff struehues that tend to deform or converge less than smaller, 

less stiff pillars. These larger structures tend to gather 

load, increasing the potential for violent failure as the 

smaller pillars are extracted within and around them. 

In addition, section-wide mine plans and extraction 

sequences can contribute to bumps. For example, overlapping abutment pressures from converging gob lines 

Pillar Retreat Mining 

Many bumps have been recorded on continuous miner 

sections where rows of chain pillars l5 to 30 m wide were 

extracted near the gob. Individual chain pillars are extracted very rapidly, causing loads to shift before the adjacent pillars can redistribute load in a controlled manner. 

Pillars in such a range of sizes appear to have difficulty 

accommodating excessive amounts of strain energy, thereby increasing the likelihood that the pillars will bump. 

When a pillar is adjacent to the gob, the combination of 

considerable rib crushing and abutment loading can produce great confining pressures on the solid core (figure 7). 

With few exceptions, massive strata exist in the immediate 

and main roof overlying bump-prone coal. These strata 
Flgure 7 

Generalized Vertical Stress Distribution Within 

Coal Pillar. 

1 Newly created yield zone 

Peak stress zone 

Yielded Solid 

Rib Core 

Distance from rib, x 

(figures 8C and 80) and overlying large pillars or barriers 

in multiple-seam mining operations can cause excessive 

pressures (figure &). Fortunately, all of the preceding 

conditions lend themselves to engineering solutions, many 

of which are discussed later with actual examples. 

FdQ pillar retreat bumps have been identified in the 

USBM database. Forty-eight occurred in conjunction with 

full-extr action mining, whereas two occurred during partial 

pillar mining. Geology, destressing, and multiple-seam 

mining were the principal contributing conditions associated with bumps during pillar retreat mining operations. 

Six events were associated with unique geologic conditions, 

three with destressing, and two with multiple-seam mining. 

On February 16, 1951, a large bump occurred in the 

Gary No. 2 Mine, killing four miners and injuring six (figure 9). The force of the bump threw four miners against 

the loading machine, while others were thrown against 

cribs and timbers. One miner 50 m away was injured by 

the force of the bump. Earth tremors were felt on the 

surface within a 3-km radius of the bump's center. This 

bump, however, dislodged only a relatively small amount 

of coal. This event may well exemphfy mining-induced 

seisrnicitywithmagnitudes similar to those shown in table 4. 

Possibly the overlying strata had shifted by a considerable 

amount toward the gob, releasing large amounts of energy 

but not significantly damaging the mine workings. 

Three pillar retreat bumps were reported at the Moss 

No. 2 Mine. The first occurred on August 4,1960, in the 

2 Right section (figure 10). Extensive arrangements of pillars and pillar remnants had been left during mining, giving the strata above the gob a support system that inhibited the roof caving process. 

The second bump occurred on December 12, 1967, in 

the 6 Right section (figure 11). This bump was associated 

with a small overhang of roof that was in turn associated 

with a distinctive change in roof lithology. The inby part 

of the section had been free of bumps because of the 

weaker interbedded shale-and-sandstone roof. The second 

bump took place within the transition zone to the more 

competent sandstone roof. 

The third bump, on July 30, 1970, had several contributing factors (figure 12). The Upper Banner Coalbed 

was mined 250 m above the Moss No. 2 Mine. The bump 

occurred as the section was retreating from under the 

overlying remnant pillars. A considerable amount of stress 

must have been transferred through these remnant pillars. 

The bump was obviously violent, for it displaced the continuous mining machine several meters (figure 13). 

A bump in the No. 1 South section of the Beatrice 

Mine on May 30, 1978 (figure 14), was similar to those 

experienced earlier at the Olga Mine, which had led to the 

development of the Olga pillar extraction sequencing 

technique. This method is discussed in greater detail on 

page 60. Such a sequence uses a continuous mining machine to mine certain highly stressed pillars selectively and 

move abutment stresses within a mine section in a 

controlled manner. 

Barrier-splitting is generally done in association with 

full-extraction pillar operations, most often during the final 

stages of a mine's life when the barrier pillars along the 

main access entries are extracted. However, a barrier 

block is sometimes mined in conjunction with a pillar retreat section for some operational reason. Typically, a 

mine will begin to extract barriers in the most remote 

portions of the mine and work back toward the main portalareas. Use of the barrier-splitting technique has decreased owing to inherent dficulties associated with this 

process. 

The USBM database contains references to 36 bumps 

associated with barrier-splitting operations. As indicated 

earlier, barrier-splitting often involves high-stress environments because these pillars are designed to carry abutment 
Figure 8 

Generalized Examples Showing Hew Different Full-Extraction Mining Scenarios 

Transfer Load to Pillar Structures. 

A Distance A' Displacement 

@ Plan view 

KEY 

Load 

Gob 

transfer 

@ Plan view @ Plan view 

. / /'/ [I . 

\ I/ / / Upper coalbed 

Interburden 

I -1 I I I -1 Lower coalbed 

@ Cross-sectional view 

@ Plan view 
Figure 9 

0 - 50 

Scale, m 
Figure 70 

Effects of Pillar Remnants and Hanging Roof Strata on Pillar Retreat Bump at Moss No. 2 Mine, 

August 4, 1960. 

loads. The stress fields and geologies at these operations 

generally provide conditions conducive to bumps. There 

were a few instances in which anomalous factors controlled 

the occurrence of bumps during barrier-splitting. Of the 

36 bumps associated with barrier-splitting operations, only 

two were associated with multiple-sea. mining and four 

were associated with destressing techniques. Also, in most 

cases, injuries were the result of contact with bumped coal. 

Associated hazards were limited to one roof fall at the 

Peabody No. 31 Mine and an ignition at the Gary No. 6 

Mine. 

Bumps at the Gary No. 2 and No. 6 Mines in the early 

1950's illustrate the nature of events typical of barriersplitting operations. At the No. 6 Mine, barrier-splitting 

was used in several locations as sections developed decades earlier were retreated. Development of the mine 

over a long period by hand-loading resulted in an irregular 

mine plan; bumps occurred under a variety of circumstances and often involved complex geometries that resulted in excessive stress concentrations. Cut sequencing 

in bump-prone areas at the No. 6 Mine apparently evolved 

on a case-by-case basis to accommodate the irregular 

nature of the remaining coal reserves. However, over 

time, reserves at the Gary No. 2 Mine were developed and 

retreated using a more consistent method that eventually 

evolved into the thin-pillar mining system, described on 

pages 60-61. 

Figure 15 illustrates the Gary No. 2 Mine plan in the 

vicinity of a bump in the 12-Left section in January 1951. 

In this mining plan, four-entry development sections were 

driven at intervals off a set of main entries. Sections were 

separated Gom one another by a barrier block that was 

developed just ahead of the retreat line during second 

mining. However, as indicated in figure 15, bumps were 
Figure I I 

Effects of Roof Strata Characteristics on Pillar Retreat Bump at 

Moss No. 2 Mine, December 12, 4 967. 

encountered in some locations. USBM researchers, including Holland, found several factors they believed influenced bumps in this system and elsewhere in the Gary 

No. 2 and No. 6 Mines. For example, pillars of irregular 

sizes were located adjacent to the retreat line, secondary 

development was done within the abutment zone, and 

rooms were not driven in proper sequence. As a result of 

these and several other related issues, U.S. Steel, the 

owner, developed another mine plan for the Gary No. 2 

Mine. 

The next-generation mine plan differed from earlier 

ones in several respects. Figure 16 indicates, for example, 

that secondary development took place farther outby the 

retreat line and adjacent sections were retreated simultaneously; when all sections were activated, the length of 

the pillar line was approximately 670 m. Nevertheless, 

bumps were encountered in early 1952. Company perand falling. Duckwall (c. 1952) notes that "it was possible 

to travel a distance of [60 m] or more into the mined-out 

area which was free of falls" in 18 Left. Based on observations of strata behavior and bump experiences at the Gary 

No. 2 Mine, U.S. Steel engineers sought to incorporate 

beneficial aspects of each of the mining systems into a new 

system, which became known as the thin-pillar mining 

method. 

The Gary mines exhibited a long history of coal bumps 

under a variety of circumstances. The same held true for 

both the Moss No. 2 Mine (figure 17) and the Beatrice 

Mine (figure 18). In contrast, the Moss No. 3 Mine in 

Dickenson County, VA, experienced an isolated bump occurrence; that is, conditions conducive to bumps apparently 

were not pervasive at the site. Mining began in 1958 at 

the Moss No. 3 Mine, portal A, and proceeded for nearly 

20 years without a reported coal bump event. However, 

sonnel indicated that poor caving in the gob inby 18 Left on November 4,1977, bump conditions were encountered 

contributed to squeeze and bump conditions. Secondary during barrier-splitting operations, resulting in the death 

development well in advance of the retreat line appeared of a continuous mining machine helper (figure 19). 

to allow the pillars to crush and the massive sandstone The Thick Tiller Coalbed reportedly averaged 3 m 

main roof to settle into the gob rather than breaking thick, in the area of the Moss No. 3 bump. The barrier 
Figure 72 

Effects of Overlying Remnant Pillars on Pillar Retreat Bump at Moss No. 2 Mine, 

July 30, 1970. 
Figure 13 

at Moss No. 2 Mine, July 30, 1970. 

Cave 

Breaker post 

Scale, m 

Note position of caved roof line and postbump continuous mining machine (solid 

lines). 
Figure 74 

Pillar Retreat Bump at Beatrice Mine, May 30, 1978. 

No. 1 South 

Bump 0 50 I 

Scale, m 

Note use of sequential pillar mining technique. 
Figure 75 

Barrier-Splitting Bumps in Adjacent Sections With Similar Layout Positions, Gary No. 2 

0 - 50 

Scale, m 
Figure 76 

Multiple Bump Events During Splitting of 18 Left Barrier at Gary No. 2 Mine, 1952. 

Star denotes location of mountain bump. 
Figure 7 7 
F;gure 78 

Barrier-Splitting Bump at Beatrice Mine, December I I, 1980. 

Skip south section 

I 

/ 

Gob 

Scale, rn 
Figure 19 

Effects of Multiple-Seam Mining on Barrier-Splitting Bumps at Moss 

Scale, m 

Upper Banner Coalbed 
pillar measured about 116 m long by 43 m wide. Adjacent 

pillars were generally square and appeared to be spaced 

on 24-m centers. Reports of the Moss No. 3 coal bump 

did not indicate overburden or interburden thickness between the Thick Tiller and superjacent Upper Banner 

Coalbeds at the bump site. However, it was concluded that 

the combined effects of abutment loads generated as a result of barrier-splitting and retreating, along with concentrated stresses caused by overmini.ng, created an excessive 

stress condition. Isolated pillars that were left in the 

Upper Banner Coalbed during second mining apparently 

intensified the stress interaction (figure 19). 

Longwall Mining 

Since 1970, coal bumps have occurred with gate entry 

systems and along the faces of U.S. longwall mines. In 

many cases, these bumps were located where the gate 

entry pillars were unable to prevent abutment loads from 

"riding over" onto the mined longwall panel (17). In other 

instances, the bumps responded to either gob caving adjacent to the longwall face or were associated with excessive gas pressures. 

The USBM database contains 36 longwall coal bumps. 

Of these, 12 occurred along the longwall face, 7 within the 

tailgate, 2 within the headgate, 13 both along the face and 

within the tailgate entries, and 2 in setup or bleeder 

entries adjacent to the longwall panels. The most influential condition was the presence of multiple-seam mining, 

which was found in seven of the events. Five bumps occurred during destressing. Rolls in the structure of the 

coalbed being mined played an important function in two 

bumps at the Beatrice Mine. The most sigdicant hazard 

associated with longwall mining bumps was ignition. Four 

such events were identified in the database, all of which 

occurred in Western U.S. longwall mines. 

The early experience of longwall mining at the Moss 

No. 2 Mine clearly exemplifies how inadequate gate entry 

pillar design can contribute to bumps. Clinchfield Coal 

Co., the owner, was one of the first companies to implement longwall technology in the United States. The first 

longwall was laid out next to a mined-out room-and-pillar 

section approximately 480 m long and 170 m wide. This 

longwall panel was 60 m wide and 530 m long and was 

completed on October 11, 1969. Owing to the industry's 

lack of experience with the longwall mining system at that 

time, chain pillars measuring 17 by 17 m were believed to 

be an appropriate size between the first and second longwall panels (figure 20). The second longwall was 80 m 

wide and 600 m long. At the time of the bump, in which 

the longwall foreman was injured, the longwall face had 

retreated approximately 400 m. 

Several contributing conditions were readily apparent. 

Multiple-seam mining occurred in the overlying Lower and 

Upper Banner Coalbeds. At the time of the bump, the 

longwall itself was progressing from under a group of unmined pillars (figure 20). Additionally, a large sandstone 

channel was located about 450 m inby the face and evidently contributed to the poor caving characteristics in the 

main roof member. Finally, the chain pillars left to protect the longwall panel were of inadequate size and too 

weak to withstand abutment loading from the adjacent gob 

areas. 

The Beatrice Mine had extensive experience with 

bumps during longwall mining in its southern portion during the early 1970's (figure 5). Early longwall equipment 

included a plow and 94 hydraulic legs and canopy units 

having a capacity of 127 t. Many of the same conditions 

responsible for bumps at the Moss No. 2 Mine were also 

found at the Beatrice Mine. Overburden in the south 

longwall district ranged from 700 to 760 m. Roof strata in 

these areas apparently changed from a laminated shale 

and sandstone sequence with coal streaks to predominately 

sandstone intermixed with siltstone layers. The gate entry 

design at the Beatrice Mine consisted of a yield-yieldabutment system. The pillars were 24 m long and none 

were offset. The yield and abutment pillars were 9 and 

24 m wide, respectively. 

The first coal bumps associated with longwall mining at 

the Beatrice Mine took place in March 1972 on the tailgate of No. 3 development. At approximately the same 

panel location on the next panel, another bump occurred 

on January 26, 1973 (figure 21). Twenty minutes before, 

the section had been quiet. The bump exploded three 

chain pillars and completely filled the adjacent entries with 

loose coal. Several more bumps' occurred during the mining of this and the adjacent panel. These events did not 

appear to be particularly dficult to address and did not 

result in any injuries. 

A devastating bump two panels later in the tailgate 

entry of No. 6 development (figure 22) killed one miner 

and signrficantly injured three others. One of these miners 

was approximately 150 m away from the immediate bump 

location. The event was 350 m from the startup rooms in 

a longwall panel 140 m wide by 910 m long. A stall machine was utilized to keep the tail side of the longwall face 

advanced about 10 m ahead of the face conveyor (figure 23). This system was used to eliminate removal of the 

previously set cribs during retreat of the longwall face. 

James Gilley, a recognized authority on coal bumps (31), 

referred to this occurrence as a "shock impact bump." The 
Figure 20 

Effects of Overlying Remnant Pillars and Underdesigned Entry Pillars on Longwall Pillar Bump 
Figure 2 7 

Longwall Tailgate Entry Pillar Bump at Beatrice Mine, January 26, 1973. 

0 

, 

50 

Scale, m 

Direction of Mining 

Figure 22 

Fatal Longwall Panel Bump Near Tailgate Entry at Beatrice Mine, May 15, 1974. 

Expulsion of coal No. 6 development 

No. 3 Plow off 1 South off 1 West 

No. 7 development 
Figure 23 

Detailed View of Bump at Beatrice Mine, May 15, 1974. 

Pillar size: App. 24 x 24 m 11 

Victim / 

0 

0 

10 

Scale, m 

This section of longwall panel was referred to as the "stall area." R indicates miners. 
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on March 20, 1980, six narrow pillars bumped, two of 21, 1980, approximately 50 m from the location of the 

them violently (I I). No miners were injured in this tail- bump occurring on May 8, 1978. The July 21 bump took 

gate bump. Because the floor in the roll area resisted place over a weekend, so no miners were on the section; 

heaving for a distance of 200 m, the operator decided to the exact time of occurrence could not be estimated. 

volley fire or shot fire ribs of three abutment pillars outby 

SUMMARY OF RECOMMENDATIONS TO MITIGATE COAL MINE BUMPS 

When coal pillar bumps first occurred in eastern 

Kentucky (3), local mine officials, workers, mining engineers, and many others tried to explain their cause. Numerous methods of prevention were suggested and attempted unsuccessfully. Most of the bumps were located 

along the retreating pillar line where several of the 

following conditions existed: (1) uneven pillar lines, (2) 

irregular pillar sizes, (3) overburden greater than 300 m, 

(4) strong mine roof and floor strata, and (5) overhanging 

or cantilevering gob. Since that time, several prominent 

mining engineers, consultants, inspectors, and researchers 

have developed recommendations and methods to mitigate 

bump hazards in room-and-pillar mines. 

RECOMMENDATIONS BY HISTORICAL EXPERTS 

Recommendations by Rice 

Rice (27) proposed that two types of bumps, termed 

"presspre bumps" and "shock bumps," caused the observed 

mining problems. Pressure bumps were caused when 

stress on moderately sized coal pillars became too great 

for the pillars' bearing strength. Shock bumps were 

induced by breaking of thick, massive strata above the 

coalbed, which transmitted a shock wave through the rock 

to the stressed coal pillars. Faulty mining methods were 

then identified where (1) pillars were too small, (2) 

projecting pillars were left behind the retreat line, (3) 

pillars were narrowed to points, and (4) pillars were 

extracted in separate groups without any attention being 

paid to a long, continuous retreat line. 

Based on these observations, Rice recommended two 

operational methods for controlling bumps: straight retreat lines and rock-filled cribs. Keeping retreating pillar 

lines straight eliminated pillar points projecting into the 

gob. This practice was fairly easy to initiate and had 

favorable results. Rock-filled cribs, for a cushioned support of the roof rock, were also tried with positive results. 

Generally, the cribs were ordinary mine post timbers 1.1 m 

long, not less than 0.2 m thick, set on 6-m centers. Each 

crib was tightly packed with a fill of rock material. 

The cribs were designed and placed so that the mine roof 

could converge gently without rupture of the immediate 

strata. This action decreased the potential for sandstone 

breaks within the gob, which were believed to cause many 

shock bumps. 

Bryson (3) described a detailed field test of this design 

method at a deep mine in the Harlan Coalbed, 

Cumberland Mining District, under 430 m of cover. 

Bumps had killed five miners at this particular site. Figure 25 shows the test area, which was approximately 210 m 

wide and adjacent to a large gob area. Rooms were driven approximately 91 m between the support entries, which 

were about 10.7 m wide. Prior to the extraction phase, the 

study area was composed of a series of narrow (10.7 m 

wide) and large (43 m wide) pillars. As the section was 

mined, 16 roof-to-floor convergence stations and 64 rockfaed cribs were installed. 

After the area was extracted, convergence began. Bryson reported that a few roof rock cracks gradually widened 

to as much as 41 cm without causing mine roof collapse. 

Convergence continued until the roof and floor almost 

met. In general, the strata settled by cracking and grinding noisily, but did not develop many large breaks. Only 

one bump occurred during coal extraction when the pillar 

line was not kept straight. 

Recommendations by Holland and Thomas 

Holland and Thomas (14) expanded on Rice's general 

recommendations regarding pillar extraction procedures 

and offered the following 10 measures to minimize pillar 

bumps: 

1. Recover all coal in a pillar operation. 

2. Avoid pillar line points. 

3. Keep the roof spans projecting over the gob as short 

as possible or provide support so that the roof beds do not 

fracture. 

4. Do not conduct development work in abutment 

areas. 

5. Do not split pillars on or near the extraction line. 
Figure 25 

DISTANCE FROM EXTRACTED ZONE, m 

+ Roof-to-floor convergence 

Rock-filled cribs 

-- Pillars extracted during test 

0 30 60 90 I I I 1 

Scale, m 
6. Use the open-ended extraction technique with lifts 

of not more than 4.3 m. 

7. Leave one or two rows of pillars adjacent to old gob 

areas. 

8. Maintain pillars at the same size and shape. 

9. Keep development entries narrow, approximately 

4.3 m. 

10. Note areas of rolls, changes in dip, and changes in 

coal thickness and hardness. Use this information in 

designing the mining system. 

Although many of the rules still apply to modern roomand-pillar operations, several are no longer pertinent by 

today's standards, however they may be useful as new 

mining methods are developed. For example, continuous 

mining machines require regular mining patterns and 

entries larger than 4.3 m to operate. It is also necessary 

to conduct development work in abutment areas during 

the final stages of a mine's life. This is necessary as the 

mine pulls back along main entries, extracting the remaining large barriers. The practice of a retreating 

longwall through existing openings may change this 

assump tion. 

Recommendations by Peperakis 

Peperakis (25) summarized experiences in the use of 

novel engineering designs at the Sunnyside Mines prior to 

the introduction of longwd mining techniques in the early 

1960's. Many of Sunnyside's bumps initiated roof falls of 

the immediate shales and thin laminated sandstones beneath the massive main sandstone roof rock. Bumps initiated during development were associated with a series of 

faults trending along strike. Displacements ranged from 

1 to 8 m. Peperakis identified the following seven measures to minimize bumps: 

1. Conduct long-hole shooting. 

2. Cut up large blocks into smaller, more uniform 

pillars ahead of the retreating pillar line. 

3. Do not split large blocks during development. 

4. Break large development blocks ahead of retreat 

pillar lines into uniformly sized blocks. 

5. Use substantial supplemental support. 

6. Use yieldable steel arch supports to minimize roof 

falls associated with bumps. 

7. Use hydraulic backfill to reduce stress transfer 

during bumps. 

Osterwald (23) noted that many other oriented structural features (for example, shatter zones, cleavage, pyrite 

veins, and cylindrical and smooth fractures) were found in 

bump-prone areas. He suggested that mine layouts could 

take advantage of these features to reduce stress concentrations, thereby decreasing bump incidences. 

OTHER BUMP MITIGATION RECOMMENDATIONS 

OIlga PiPiar Erjt-Graetian Sequencing Technique 

A novel pillar extraction sequencing technique was developed principally by Olga Mining Co. in the 1970's to 

control bumps. This technique involved mining numerous 

places over three to four rows of pillars to direct the overburden loads gradually away from the pillar line where 

most miners and machines were located. An idealized 

schematic of the extraction sequence is shown in figure 26. 

By design, all coal pillars three rows away from the retreating pillar line have at least a "bump" cut. This bump 

cut is a 6.1- by 6.1-m cut of coal taken from a typical size 

of chain pillar (18.3 by 21.3 m). The frequent audible 

thumps during extraction explain the terminology. The 

two pillar rows closest to the gob line are split in half by 

extending the bump cut entirely through the pillar. Finally, the pillar wings, or fenders, are extracted in the row 

closest to the gob line. 

This innovative design was evaluated by the USBM 

using an extensive rock mechanics instrument array to 

determine how the strata responded during mining (4). 

The response of the strata was measured by 44 coal cells 

(borehole platened flatjacks) and more than 70 convergence stations. Observations at the field site indicated 

that the technique redistributed stress effectively. Pressures were transferred farther than would normally be 

expected-up to eight pillar rows away from the pillar line. 

This redistribution effectively transferred the load over a 

very large area, greatly minimizing bump hazards. 

Recently, USBM researchers have attempted to evaluate this extraction technique using numerical modeling 

(33). Several idealized mining scenarios were modeled by 

a USBM-developed boundary-element program with nonlinear material types and an energy-release-rate subroutine. The study found this novel pillar splitting and extraction sequencing method superior in reducing bump 

potential to more traditional techniques, such as single 

split-and- fender, pocket-and-wing, and open-ending. 

U.S. Steel's Thin-Pillar Methodl 

Coal bumps often occur during extraction of the large 

barriers adjacent to main entries. Violent bumps during 

barrier-splitting appeared to be especially troublesome 

during the 1950's in southern West Virginia. Engineers at 

U.S. Steel Mining Co., a major coal producer in the 
Figure 26 

Idealized Pillar Extraction Sequencing Technique for Bump Control During Room-and-Pillar 

Mining. 

Row 

Row 

I I I I I I I I 

I I I I I I 

I I I I I I 

I 1 Bump cuts 

I I 

Row 

1 Center splitting 

This technique was developed by Olga Mining in the 1970's. Numbers indicate cutting sequence. 

region, developed a method of splitting large barriers 

adjacent to main entry systems (29). They found that pi.- 

lars smaller than 14 m or larger than 49 m almost never 

bumped. An extraction method known as thin-pillar mining was developed that systematically cut the large barriers 

into pillars with widths smaller than 14 m, leaving a barrier 

pillar remnant, which was either destressed or left in place. 

When implementing a thin-pillar mining system for 

barrier extraction, multiple entries are first driven within 

the barrier directly adjacent to the main entries. The 

remaining solid barrier is,located between the newly advanced headings and the stabilized gob. The mining of 

barrier and predeveloped chain pillars proceeds simultaneously (figure 27). Barriers are split from the recently 

driven headings adjacent to the active gob back toward the 

next solid barrier. These headings are very close, isolating yield pillars about 6.1 m wide. These yield pillars 

fail in a controlled manner, shedding high stresses both to 

the active gob areas and farther into the solid barrier. 

When the remaining barrier approaches 49 by 49 m, a 

critical-size pillar is formed. This large abutment pillar is 

called a "bump block" and is left to avert a bump. These 

large blocks aid in breaking the roof at the pillar line and 

protecting the remainder of the section from excessive 

convergence. 

The thin-pillar mining system has many forms, but it is 

generally employed when extracting the barriers left to 

protect main entries. The smaller pillars tend to yield to 

the high stresses imposed on them by overburden and normal mining. The adoption of this technique greatly reduced bumps in the Gary Mining District. 
Figure 27 

Typical Mining Sequence Utilizing Thin-Pillar Method. 

Old gob 

//// / ///////A// ////////////4/ 

//////////// /' 

/.'/// ////////Y// 

/////////// /,, / 

)/// I// 

/ // Active gob I/ / 

'//// / / ,/// / /I/ / 

// ///, / // /I// 

//// //////// 

, / 

/,// / // /I/ / ----- 7'?%7 77'/ / 

Old gob 

This method was developed by U. S. Steel in the 1950's. Numbers indicate cutting sequence. 

Longwall Gate Entry Design Techniques 

As a result of the longwall gate entry bump problems 

discussed above, two different design philosophies have 

emerged in the United States based primarily upon regional geologic conditions and mining preferences. Standard gate entry designs in the Southern Appalachian coal 

basin consist of three or more entries with at least one 

row of abutment pillars, whereas two- and three-entry 

systems with yield pillars are a more common gate entry 

design in the Uinta and Piceance Creek Basins. Many 

mines in the Southern Appalachian Basin require multiple 

gate entries because of methane gas emission problems. 

Several of the bump-prone longwall mines operating in the 

Southern Appalachian Basin employ three- and four-entry 

designs with a combination of yield and abutment pillars. 

The most common designs used in the Uinta and Piceance 

Creek Basins consist of one or two yield pillars. 

Abutment Design 

A well-designed abutment gate entry design supports a 

considerable amount of the abutment loads generated 

from both the adjacent gob and the approaching longwall 

face. This method is well suited for longwalls of moderate 

depth (300 to 600 m) that have substantial methane gas 

emission problems. In bump-prone ground, typical sizes 

of gate entry pillars (15 to 25 m wide) fail prior to the 

passage of the longwall mining face. To control the abutment load ride-over problem, gate entry pillars have been 

widened so that they do not fail during panel extraction. 

Redesign of the gate entry was accomplished by increasing 
the width of the abutment pillar. This caused the abutment pillars to fail much later in the mining sequence (13). 

This design eliminated abutment load ride-overs from the 

adjacent gob panels onto the actively mined panel. As a 

result of implementing this technique, the incidence of 

bumps at problem mines has been greatly reduced. Although this method has proven successM, it may have 

limitations when overburden is extreme (about 750 m), 

depending on coalbed thickness. These conditions may 

require extremely large abutment pillars, which may be 

impractical. 

Viellding Design 

Yield pillar designs allow the gate entry system to deform under the weight of the approaching panel abutments, thereby diverting substantial load to the nearby 

solid coal panel. This method of stress control for gate 

entries is well suited for two-entry designs. The first U.S. 

applications were pioneered in the early 1960's at the 

Sunnyside Mine in the Uinta Basin (16). At that time, 

longwall mining had been practiced in the United States 

for only about 10 years, and entry design methods for 

bump-prone ground were not well developed. Perhaps 

without fully realizing the advantages of a two- versus a 

multiple-entry yielding system, operators made the decision 

to develop only two entries primarily to limit the amount 

of ground to be opened up prior to panel retreat. Nearly 

30 years later, this system has continued to be successful 

in eliminating entry pillar bumps during panel development and retreat operations, especially in areas overlain by 

up to 600 m of overburden. 

Not all mines have experienced Sunnyside's success with 

a yield pillar design. A nearby mine attempting to emulate 

this very profitable design had difficulties in developing 

small pillars without generating serious bumps and routinely lost si@cant portions of tailgate entries to large 

bumps. It soon became evident that the successful application of yielding designs depended partly on the geology 

surrounding the pillar system. Competent mine roof and 

floor conditions are necessary to maintain stability during 

the higher rates of entry closure experienced with this 

system. 

Two-entry gate systems more commonly employ pillar 

designs that yield during or shortly after development. By 

design, the narrower gate entries typically generate sigllificant side abutment stresses, which are capable of destroying most conventional chain pillars even at moderate 

overburden. Mere two-entry systems are impractical, 

yield pillars have been used effectively in multientry 

systems, but such systems are more commonly used in 

conjunction with abutment pillar designs. In either application, yield pillar designs have proven to be an effective 

alternative in mitigating bump hazards in deep U.S. coal 

mines. 

Destressing 

Several forms of destressing were identified within the 

USBM Coal Bump Database. These included (1) volley 

firing or shot firing, (2) auger drilling, (3) water infusion, 

(4) hydraulic fracturing, and (5) partial mining. If conducted with deliberation, destressing generally aids in 

releasing excessive stresses in a controlled manner. However, many examples in the database demonstrate that 

bumps may occur in conjunction with destressing the coal. 

Shot Firing 

Shot firing fractures coal, thereby extending the yielded 

coal zone. This process injects energy into stressed coal, 

causing seismic shock. The shock waves temporarily release confinement, initiating violent failure under a controlled condition. However, there is little that is engineered about this method. Typically, the shot holes are 

loaded with explosives, but the amount of explosive needed 

is poorly defined. The most appropriate lengths and spacings of blastholes are also unknown. Generally, all shots 

are initiated simultaneously. It is commonly believed that 

the destressed zone is defined by the length of the blasthole. Jackson (19) noted that Mid-Continent Resources 

mines in Colorado used shot fuing to move the peak stress 

zone into the solid core of the longwall panel when this 

zone was less than 5 m from the rib. Polish mines have 

long used shot firing to break and shear cantilevered roof 

strata. 

Auger Drilling 

Auger drilling was first practiced at the Gary No. 2 

Mine in the mid-1950's when 61-cm holes were drilled 

from the sides of highly stressed barrier pillars (29). 

Unfortunately, these large-diame ter boreholes were prone 

to triggering large bumps. Up to 1,000 t of coal was 

ejected from the coal ribs by the largest events, causing 

this method to be judged too hazardous to use routinely. 

As a result of European research, which suggested that 

auger holes less than 10 cm could not initiate a coal bump, 

auger destress drilling has regained limited favor in recent 

years. 

The Olga Mine routinely used this method to redistribute stress away from active work areas (4). As the auger 
holes entered the more highly stressed coal 3 to 4 m from 

the rib, the amount of coal produced rose dramatically. 

Si@cant amounts of coal were recovered at a gradual 

pace, often 10 to 20 times the volume of a 10-cm-dim 

hole. In effect, augering affected the areas of highest 

stress in the pillars without removing any of the confining 

fractured and yielded rib coal. Undoubtedly, this technique is very effective in mining highly stressed coal pillars 

when other alternatives are unsuccessful. 

Water Infusion 

Water lubricates fracture surfaces within a rock mass; 

therefore, water infused into a coalbed can initiate slippage 

between rock surfaces, thus lowering the state of confinement on the surface and the amount of energy stored within the rock. This technique has been tried successfully in 

Europe, but has received only limited use in the United 

States. This probably stems from the difficulty of infusing water into U.S. coalbeds. Water infusion has been 

attempted in many mines to control respirable dust and 

methane gas migration. It has been most successful in 

coalbeds that have a well-developed cleat system that 

controls permeability. 

Because water infusion is impractical when the coalbed 

is highly stressed, destressing must be completed prior to 

retreat mining, for holes will not remain open long. Successful water infusion generally requires the coalbed to 

accept and transmit fluid readily. The equipment must be 

capable of pumping water at or above hydrostatic pressure. 

Two U.S. coal mines have attempted to use water infusion to destress coalbeds. Lessley (20) discusses use of 

the technique in a room-and-pillar section in a Virginia 

coal mine. Several 4- to 9-m-long holes were drilled into 

pillars. Injection pressures averaged 3.7 MPa, with the 

coal pillar accepting between 0.1 and 3 m3 of fresh water. 

Microseismic monitoring indicated that only small amounts 

of energy were released during infusion. 

Hydraulic Fracturing 

In some mines, it has been dif%icult to achieve good 

caving into full-extraction gob areas. This is believed to be 

a function of the ability of massive units to span the gob. 

It has been proposed that caving could be induced with 

hydraulic techniques near vertical breaks within the main 

roof beam. This technique was attempted at Arch of Kentucky's Lynch No. 37 Mine in southeastern Kentucky, but 

little data from this experiment are available. 

Partial Pillaring 

A unique application of pillar destressing was attempted 

at Energy West Mining CO.'S Deer Creek Mine in Utah in 

1987. A remotely controlled continuous mining machine 

was used to split seven chain pillars outby a retreating 

longwd face. Pillars in the 7th Right gate entries were 

progressively narrowed from 12 to 9 m wide to accommodate the change from a three- to a two-entry gate design. 

Upon retreat, this longwall panel encountered severe pressure in the pillar transition zone, producing bumps and 

damaging the longwall shearer and adjacent tailgate pillars. 

It was determined that pillar splitting could provide the 

safest means of destressing the chain pillws in the transition area (figure 28). Several operational precautions were 

taken to decrease the dangers of initiating a bump during 

splitting, with apparent success. 

Olbse~ationar I Techniques 

Because many bumps are very sensitive to slight 

changes in geology, considerable attention should be 

placed on observing the condition of the yielded coal. The 

depth and character of the fractured coal zone reveals the 

location of the peak stress zone and therefore the potential 

for violent failure. Numerous techniques are available to 

acquire this idormation. If the ribs are generally crushed, 

but locally appear straight and solid, the peak stress zone 

may be close to the pillar edge. If the ribs are difficult to 

cut or drill, an abnormally high peak stress zone may be 

present. A sandstone channel scour may signal a change 

in the character of the contact zone. Generally, the irregular nature of the scours provide higher shearing resistance. The appearance of a "red-coal" zone within the contact zone is perhaps the most dramatic indicator of the 

imminent occurrence of a coal mine bump. This condition 

reflects the coalbed's inability to resist the shearing forces 

generated by the tremendous confinement applied to the 

coal in a localized area. The red-coal zone probably 

represents coal that has been mechanically altered because 

of the presence of excessive amounts of shear strain. 

USBM researchers have observed this condition at three 

bump-prone mines: the Olga and Gary Mines in southern West Virginia and the Lynch No. 37 Mine in eastern 

Kentucky. 

Auger drilling also has been used to probe for areas of 

highly stressed coal (24). Often after a particular mining 

section has bumped, small-diameter (5 cm) auger holes 

are drilled into the face with hand-held units. Drill hole 
Fjgure 28 

Example of Partial Pillar Destressing Method Employed at Deer Creek Mine, Emery County, UT. 

7th right 

0 

I 

2 5 

Scale, rn 

Numbers indicate mining sequence. 

cuttings are often monitored, but generally the operator is 

most interested in determining when drilling difficulty or 

drill string seizures occur. At these points, it is assumed 

that the drill hole has entered an area of high stress. Several holes are drilled across the problem working face at 

distances of 2 to 6 m apart. If the peak stress zone (figure 7) is close to the entry (less than 2 m), the situation 

is generally considered critical, and mining is temporarily 

halted or some destressing technique is attempted. If the 

peak stress zone is greater than 5 m from the entry, conditions are generally considered safe for additional mining 

at the face. One should note that no reliable criteria exist 

to guide an operator in selecting how often a face should 

be probed or in choosing drilling parameters or patterns. 

Longwall mines such as the Dutch Creek No. 1 and Lynch 

No. 37 Miues have utilized auger drilling to choose areas 

to be destressed. 

The Coal Bump Database compiled by the USBM con- c. In longwall sections when geologic structures are 

tains a wealth of knowledge from past experience that has encountered, and 

undoubtedly reduced the severity of coal mine bumps in d. In either room-and-pillar or longwall sections 

the United States. hi^ paper has elaborated on the most when overburden, abutment, or shock loads are excessive. 

successful designs for both room-and-pillar and longwall 3. Supplemental support has been usefd in mk~11.g 

mining. The following are the principal observations de- bump damage. Rockefilled cribs allow gob to converge 

veloped from mining in bump-prone strata: gently without rupturing. Combinations of cribs, crossbars, 

and props reduce the severity of bumps in main entries. 

Wood cribs and yielding arches in combination with rock 1. The potential for bump occurrence increases when bolts help support weak, immediate mine roof during mining in stiff roof and floor rock. Strata of this nature bumps, which reduces associated roof falls. 

found within the Southern *ppalachian7 4. The use of straight retreating pdar lines and total 

Uinta, and Piceance Creek Basins. extraction of all coal can eliminate projections of bump- 2. Bumps can occur- prone material into the gob. 

a. In development sections when faults and igneous 5. Developing or splitting large blocks of coal into 

dikes are approached, smaller, uniform blocks ahead of the retreating pillar line 

b. In room-and-pillar sections when cantilevering causes the coal to yield in a controlled manner before it is 

roof is encountered, extracted and allows the roof to bend gently. 
6. Sequential splitting of pillars away from the retreating pillar line can effectively move excessive stress 

away from the working face in a controlled manner. 

7. Sizing gate entry pillars large enough to contain 

induced stresses can effectively reduce bump occurrences. 

8. Sizing gate entry pillars to yield in a controlled 

manner can assist fracturing of the main roof and, in some 

instances, decrease the magnitude of abutment and/or 

shock loads onto the longwall face. 

Most past and present U.S. bump-control designs have 

helped control the manner in which the roof rock breaks 

and have regulated the manner in which stresses are 

redistributed. These techniques have mostly been very 

successful, but they have not been applied over a wide 

range of geologic and mining conditions. As production 

rates and overburden depths increase and new mining 

systems are designed, the mining industry will be required 

to engineer new bump-control techniques. My evaluating 

past experiences, analyzing current and projected conditions, and investigating innovative design techniques in 

the field, the requisite technology can be developed to 

keep bump-prone U.S. mines safer for underground mine 

workers. 

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