PILLAR MECHANICS OF COAL MINE BURSTS: A CONTROL STRATEGY 

Anthony T. lannacchione, M.S., Supervisory Geologist 

Joseph C. Zelanko, B.S., Mining Engineer 

U.S. Bureau of Mines 

U.S.A. 

ABSTRACT 

One of the most difficult and longstanding engineering problems associated with coal mining is the 

catastrophic failure phenomenon known as coal mine bursts (known in the United States as bumps). For 

more than 70 years, researchers and practitioners have attempted to determine whether this destruction 

observed underground is caused by stress conditions within the coal pillar or from distant seismic sources in 

the mine roof and floor strata. The role of confinement and the extent of failure in solid pillars and panels 

have also proven difficult to define. These are important issues, since control solutions need to be based on 

a fundamental understanding of the problem. 

Obsenations by U.S. Bureau of Mines researchers over the last decade have helped to clarify certain 

aspects of these issues. Microseismic sensors and geomechanic field measurements have located areas of 

excess energy release, identified stress conditions in coalbeds close to failure, and recorded the response of 

mine structures prone to bursts. In the present study, data available for a range of U.S. bursts were 

considered in an effort to evaluate both common and distinctive features. Although the attempt revealed little 

commonality, encouraging results were produced by categorizing coal bursts by source mechanisms. When 

a coal burst is thus categorized, differences in environmental factors-such as geology, stress fields, and mining 

methods-are highlighted, and viable control strategies are readily recognized. 

INTRODUCTION 

Analyses made within this paper were based on numerous burst-related investigations reported over the 

past 76 years. The earliest of these was made by Watts (1918) at the Sumyside No. 1 Mine in Utah. 

Reports by Rice (l!%35) and Bryson (1936) indicate that coal mine bursts occurred in the Cumberland Field 

of Kentucky and Virginia as early as 1923 and became very troublesome during the 1930's. In the 1950's, 

bursts continued to be reported in the eastern and western U.S. coalfields (Holland and Thomas, 1954; 

' Peperakis, 1958; Talman and Schroder, 1958), stimulating the develo~lnent of burst control strategies and 

remediation techniques. 

The wealth of kormation developed in the first half of this century provided a strong foundation for 

expanded research investigations during the last decade. Recent efforts were initiated in response to the 

persistent occurrence of bursts in U.S. coalfields. Since 1980, 19 underground mines in three Eastern States 

(figure 1) and two Western States (figure 2) have reported more than 30 coal mine bursts. 

Without further development andappli&tion of burst control measures, the occurrence of burst-related 

problems in the United States will likely increase for several reasons. First, full-extraction mining, with both 

the room-and-pillar and longwall methods, continues to increase. Widespread application of remote control 

continuous mining machines, continuous haulage, and mobile roof supports have made these methods very 

attractive. Second, these full-extraction mining methods are working at deeper mining leveis with higher 

stress conditions. Lastly, clean air legislation in the United States has shifted some production to the lowsulfur regions of the southern Appalachian and western coalfields, where much stronger and stiffer strata 

exist. Strong strata, high stresses, and full-extraction mining are environmental factors long associated with 

coal mine bursts. 
LEGEND 

Mines with reported bumps 

aince 1980 

West Virginia 

10) Maple Meadow 

@ Location of past bump mining areas 

index Map 

Kentu 

\ Logan 

\ @ 

Weich Caw . Mining 

0 - 5 0 ~umbdland 

scale, krn 

Harlan .02/7 @ Big y Stona Gap Virginia 

/ 

-/ .--------- 

Figure 1.-Coal mine bursts in the Eastern Unlted States slnce 1980. 

LEGEND 

index Uap Uinas with reportad bumps 

slncr 1980 

Areos known to conto~n 

minable coalbeds 

Figure 2-Coal mine bursts in the Western Untted States since 1980. 

CATEGORIES OF COAL MINE BURSTS 

For many years, researchers have acknowledged differences between individual coal mine bursts. Such 

distinctions seek to explain apparent differences in the manner in which bursts are manifested underground 

and to incorporate some practical and theoretical considerations of the environments in which these bursts 

occur. In general, three environmental factors appear to be most influential in the occurrence of bursts: 

(1) geology, (2) stress, and (3) mining methods. 
It has long been known that geology plays an important function in bursts. Sandstone, fonned by ancient 

fluvial processes, is the lithology most commonly identitied with bursts. However, to say that sandstone is 

needed for a burst to occur per se would .be incorrect. This is because the strength of sandstone rock masses 

is very diverse. To a large degree, this strength is controlled by geologic discontinuities, which range in scale, 

Often, the largest-scale discontinuity is the basal contact that is formed by the erosional powers of an ancient 

river system. The position and extent of this low shear strength surface can vary widely within U.S. burstprone mine roof strata. Next in scale are trough beds, which represent unique episodes of an individual 

channel within the greater limits of an ancient fluvial system. The trough beds are generally crescent- (arc) 

shaped and can extend tens of meters, often intersecting other discontinuities to form a network of potential 

failure surfaces. These surfaces generdy have moderate shear and very low tensile strengths. Smaller 

discontinuities such as crossbeds, coal stringers, and clay bands occupy scales of up to 1 m and can be found 

in varying intensity within a fluvial channel depending on which depositional environments were at hand. 

Shear and tensile strengths of these discontinuities range from low to moderate. 

A measure of the effect of these properties on sandstone strength can be demonstrated with the 

sandstone Unit Rating measurements contained in the Coal Mine Roof Rating database developed by the 

U.S. Bureau of Mines (Molinda and Mark, 1994). The unconfied compression strength accounts for onethird of the Sandstone Unit Rating, while the other two-thirds is estimated by the intensity of discontinuity 

spacing and its shear strength. This database shows that sandstones have a nonuniform strength distribution 

that spans the spectrum of behaviors from very weak to very strong. 

The interaction of these discontinuities along with the grain-size characteristics and cementing properties 

of the sandstones can produce a wide range of responses during the extraction of adjacent blocks of coal. 

Indeed, some sandstones are known to cave readily, whereas others can bridge tremendous spans of gob. 

It is therefore not surprising that certain types of sandstones can be associated with spefiric burst 

mechanisms. This fact will be alluded to later in this paper. 

The next environmental factor-stress-is extremely important in bursts, since it will largely control the 

states at which the strata will fail. Obviously, high vertical stress conditions can be the direct result of mining 

under deep overburden. This is, however, not necessarily true for horizontal stresses. In the eastern (and 

to a lesser degree the western) US. coalfields, an elevated horizontal stress field, produced by residual 

tectonic processes, has locked geologic discontinuities in place and elevated coal pillar confinement at even 

shallow overburdens. En some instances, the smallest adjustment to this stress field can lower shear resistance 

along these inherent planes of weakness, thereby releasing codiement to the coal pillar or shearing 

resistance to a fault plane and causing a sudden release of energy. 

Clearly, an analysis of the effect of environmental factors on strata behavior is not complete without 

considering the effects of mining practices on exacerbated stress conditions. Holland and Thomas (1954) 

examined 177 coal mine bursts that occurred in the United States from 1925 to 1950 and determined that, 

in many instances, bursts could be averted by avoiding unfavorable mining configurations. Unfavorable 

mining practices contributed to bursts by creating areas of stress concentration within a mine structure. 

In summary, coal pillar yielding and failure may be readily observed underground at almost any fullextraction mining section. Usually, this process proceeds in an orderly manner. Environmentdfir~, 

including geology, stress state, and mining system, can interact to effect a violent failure of coal through one 

of several mechanisms. Categorizing coal mine bursts by mechanism provides a framework for the 

development of more appropriate mine designs and, if necessary, remediation techniques. With this in mind, 

the following discussion will describe three categories of bursts based on mechanism: (1) excessive pressure, 

(2) seismic shock, and (3) loss of confinement. Additionally, remediation procedures are reviewed in light 

of their potential effect on these mechanisms. 

b 

Excessive Pressure' Mechanism 

The fust cod mine burst category is defied by the excessive pressure mechanism. This mechanism has 

been discussed extensively by Holland and Thomas (1954). When excessive loads are applied to mine 

structures, mainly in the form of large abutment pressures, bursts may result. Coal pillars and barriers can 

be concentrators of load owing to a host of conditions. For example, if a pillar is adjacent to the gob, the 

combination of considerable rib crushing and abutment loading can produce high stresses in a confined pillar 

core (figure 3a). Commonly, massive strata exist in the immediate mine roof overlying burst-prone coal, 

which can cantilever, adding load to the pillar. When massive load shifts occur rapidly, the pillar's ultimate 

load-bearing capacity can be exceeded before the coal can shed the load in a controlled manner. Such rapid 

loading can be caused by a swift red of adjacent pillars or by bursting of adjacent pillars. This 

mechanism can be likened to the behavior of a typical rock or coal specimen compressed to failure in a 
testing machine whose postfailure stiffness is less C 

LEGEND than that of the rock. At the point of failure, the - Load +ran,fer energy stored via the extension of the testing E' s -92 c > l7J Gob machine acts to drive the rock sample to fail 

U violently. One surmises that such a situation couid 

A Disfancs A' Displacement occur in the field as well if a similar relationship 

arose between the local mine stiffness and the 

stiffness of coal pillars, panels, or working faces. 

Other mining geometries, such as a large coal 

pillar surrounded by smaller pillars, can concentrate stress (figure 3b). Large pillars can be 

imagined as stiff structures that tend to deform or 

6J Plan view (@ Plan view @ Plan vlew converge less than smaller, less stiff pillars. These 

larger structures will tend to gather load, inneasing the potential for violent failure as pillar extraction occurs within and around them. In addition 

/ / / Upper coalbed to individual pillar geometries, section-wide mine 

Interburden plans and extraction sequences can contribute to 

coal mine bursts. For example, overlapping abuto n o o o u Lowar ~0~1b.d ment pressures from converging gob lines (figures 

3c and 3d) and overlying large pillars or barriers in 

@ cross-~ectional VI~W multiple-seam mining operations can cause exces- 

@ Plan view sive pressure conditions (figure 3e). Fortunately, 

all of the preceding conditions lend themselves i6 

Flgure 3.-Load transfer pattern found In mlnlng engineering solutions. sectlons where excessive pressure bursts occur. Environmental characteristics associated with 

excessive pressure bursts include- 

(I) Geology.Stilf and massive roof and floor strata should over wide mining areas. This type of 

strata is generally comprised of thick sandstone occurring immediately above and below the coalbed. Faulting 

or interne jointing should not occur. Internal geologic discontinuities, such as !arge trotlgh bcds, should be .. - mral. 

(2) Stress.-High overburden stress conditions are generally required. Typically, coal mine bursts are not 

experienced at overburdens less than 200 m.. 

(3) Mining.-Critical coal pillars are located either near full-extraction mining zones or aligned with a 

barrier pillar in a supe jacent or subjacent mine. 

A promis'i development in recent U.S. experience has been the refmement of geologic models 

predicting the locations of excessive pressure coal mine bursts. A combination of in-mine mapping, 

exploration drillhole data, topographic information, and mine plans can provide the necessary data to evaluate 

burst potential. Computer-based geologic information systems provide a means of evaluating interadions 

among factors that contribute to bursts and thus provide insight into the relative burst hazard (Samw and 

Zelanko, 1994). 

The excessive pressure mechanism lends itseif to both anaiyticai and numerical modeiing. For exampie, 

boundary element codes that use nonlinear material properties and energy release rate calculations provide 

a new capacity to test the intuition of mine planners (Zipf, 1992). Mining can now be simulated by extracting 

blocks of "imaginary" coal with a computer model, allowing for the relativz merits of a design to be examined 

without expending any actual mining effort. Heasley and Zelanko 11992) successfully previewed this 

technique by utilizing a boundary element code that calculates dissipated energy as a measure of coal mine 

burst potential. p he-approach & useful due to the persistence of stiff, massive geologic layers that produce 

the characteristic cantilevered spans so often found with excessive pressure bursts. Unfortunately, there are 

uncertainties associated with &en these rock masses, which reduce the capability to predid bursts at 

acceptable levels. Minor changes to material properties input to the codes tend to have considerable 

influence over output results. Close attention must be paid to calibrating the models with known conditions. 

Seismic Shock ~echanism 

The second coal mine burst category consists of a wide grouping of mechanisms associated with coal 

pillan subjected to seismic shocks. The seismic shock burst mechanism was fist introduced by Rice (1935) 

in the late 1920's. Rice indicated that shock bursts stemmed from the failure of thick, massive, rigid strata 
above the coalbed, which 

transmit a seismic shock 

LEGEND wave to the coal below. He 

~ia~dad coal also stated that seismic 

solid coal shocks could be generated 

IIII] coal atice from the sudden failure of Tonmiom - Prashwk strata spanning a gob area or 

f----? - - Stress from 

comprarsaon wave from the impact of a massive 7- .*"' -- stress from 

tanrlon wava volume of rock onto the 

mine floor. Both of these 

c Cohmrlon mechanisms could theoreti7 Shaar strass cally produce a sizable shock 

IUv Normal stras. wave, traveling through the 

a" On ? Vartisol stnss intervening strata and affect- 

% Horizontal strars ing a wide areal distribution 

of coal pillars. 

Investigations in CanadiFigure 4.-Fallure mechanism associated wlth selsmlc shock an deep hard rock mines 

have shown that rock bursts 

are often associated with slip 

along, preexisting geologic 

Mine State Richter Date of discontinuities adjacent to 

magnitude seismic event the mine openings (Morrison 

and MacDonald, 1990). 

Jim Walter Resources No. 4 . Alabama . 3.6 07 May 1986. Stick-slip movements on 

Wrginia Pocahontas No. 3 . . Wrginia . . 3.0 04 March 1987. these discontinuities produce 

Buchanan No. 1 . . . . . . . . . . Wrginia . . 4.0 14 April 1988. a sharp, instantaneous accelLynch No. 37 .'. . . . . . . . . . . Kentucky . 2.3 22 November 1989. eration within the strata 

Cottonwood ............ Utah .... 3.0 15 March 1991. around the mine structure. 

Soldier Can~n . . . . . . . . . . Utah . . . . 3.6 21 January 1993. Seismic waves propagate 

through the mine, compressTabla I. -U.S. mlnlng-Induced selsmlc events slnce 1986. ing then extending the coal 

pillars. This causes an instantaneous increase in load, 

resulting in a potentially unstable stress state (figure 4). During the next instant, load is removed, lowering 

confinement and potentially initiating an unstable state. 

Clearly, the level of mining-induced seismic activity coming from U.S. coalfields suggests that 

"earthquakelike" sources may indeed be partially responsible for coal pillar damage underground. Since 1986, 

seismic events have been recorded from numerous mining sites, producing Richter magnitudes from 23 to 

4.0 (table 1). Sources were associated with longwall and pillar retreat mines in Alabama, Kentucky, Virginia, 

and Utah. Evidence at one of these sites suggests that the seismic source occurred over 30 m above the mine 

opening and may have been associated with slip between large biocks of strata into adjacent gob areas. 

Environmental conditions associated with seismic shock mechanisms include- 

(I) Geology.-Typically stiff sandstones and siltstones with large-scale structures such as faults, persistent 

discontinuities like trough beds, bedding plane and slips, or repeated systems of through-going fractures * within tens of meters of the mine structure. 

(2) Stress.-Highly biaxial stress conditions, Like those found adjacent to full-extraction zones, are generally 

required. When one plane of stress is reduced in the direction of the gob, slip along planes of weakness is 

more easily initiated. 

(3) Mining.-The mining-induced seismicity may be caused by strata shifting toward full-extraction zones 

or may result from entries driving into unmined areas where large-scale faulting is present. 

Unfortunately, temporal prediction at levels acceptable to the mining community has proved to be elusive. 

Problems with realizing reliable coal burst precursors continue to plague this effort. However, many new 

advancements have been achieved in microseismic monitoring, such as real-time display of coal mine burst 

locations, three-dimensional sensor installations, and underground access of data near active mining locations. 

These developments have made microseismic information more accessible to mine personnel so that excessive 

energy release locations can be related quickly to activity observed underground (Coughlin and Wilson, 1993). 
Loss of Confinement Mechanism 

The ,third coal mine burst category is defined by 

the loss of confinement mechanism. Babcock and 

Bickel (1984) first suggested this mechanism based 

primarily upon laboratory investigations. By dramati- 

~ally~reducing the confinement (a,) while maintaining 

the vertical stress state (a,) within a load frame, 

v violent failure was produced in 15 different coal 

Strain materials. They postulated that if this process occurred very rapidly within a coal pillar,, dynamic 

figure 5.-Generzllzed vertical stress dlstrtbutlon coal. Anew peak stress zone is now located farther 

a coal ~IIW. inside the pillar at the boundary between the yield 

zone and the slightly reduced solid coal zone. AddiN~~ re ate d i e 1 d e failure could result. Although their theory was 

somewhat simplistic, it showed that interface or 

Peak stress zone contact interaction between the coal cubes and the 

steel platens of the load frame controlled the failure 

mode. 

tional confinement can be given to the coal from the adjacent mine roof &d floor strata. The amount of 

confinement depends on the contact or interface characteristics (Iannacchione, 1990). 

In most U.S. coalbeds, the contact between the coal and adjacent shale, siltstone, or sandstone is 

V) 

generally sharp. Gradational or irregular contacts are less common and mainly exist where a stiff sandstone 

member is in contact with the coalbed. Sharp contacts typically exhibit shear strength properties, which are 

0 Loaded coal pillars are comprised of two basic 

less than those of coal, whereas gradational contacts assume the characteristics of the coal. 

Planar discontinuities and slickensided surfaces characteristic of sharp contacts provide Little resistance 

V) 

Q) parts: an elastic solid core and an inelastic yielded L 

+ rib. The formation of the yield zone and its role in V) confining the core have been analyzed by many - 

0 researchers (Barron, 1984; Salamon, 1992; Wagner, 

0 . - 1974; Wilson, 1973). In general, the yield zone + 

L develops inward as the edge of the solid coal zone 

Q) 

> fails. At this time, the peak stress state drops to 

some residual strength level, transferring a portion of 

+ Yielded 4-b Solid ti the load to solid coal farther inside the pillar 

(figure 5). This newly fractured slice of coal receives 

Distance from rib, x confinement from the adjacent yielded coal and, 

in turn, provides confinement to the rest of the solid 

to shear displacements. However, in burst-prone ground, a gradational or irregular contact increases the 

frictional resistance at the roof and floor interfaces with the coalbed: allowing the coal to achieve ememeiy 

hxgh peak stresses. The normal growth of the yield zone is slowed by the additional confinement from the, 

contact zone. Movements witbin the contact zone occur in a stick-slip fashion. When slip occurs, 

the elevated stress conditions are finally overcome. A rapid release of shearing resistance triggers movement 

and a massive loss of confinement for the rib coal and the adjacent peak stress zone within the solid core 

(figure 6). 

Environmental conditions that are important in contributing to the loss of confinement mechanism 

include 

(I) Geology.-The contact zone between the coalbed and surrounding strata, usually a stiff sandstone, 

is generally either gradational or rough and irregular if it is a sharp contact. This can be a very localized 

condition, such as a sandstone channel scour that penetrates portions of the coalbed. 

(2) S@ess.-In general, high in situ stresses are needed. These can be .supplied by a high residual 

horizontal stress field, excessive overburden pressure, or abutment pressures from full-extraction mining. 

(3) Mining.-Bursts generally occur at the working face of the mine in association with coal extraction. 

They can therefore occur over a wide range of mining operations, including entry development, longwall 

extraction, and pillar recovery. 

Because this mechanism is very sensitive to small changes in geology, considerable attention should be 

placed on observing the conditions of the yielded coal. The depth and character of the fractured coal zone 
?--- LEGEND 

1 Yielded coal 

I 

1 Solid coal 

Mined coal 

mn Contact analysis zone 

Stress from 

irregular contact 

- - Stress from 

T sharp contact 

Stress from 

c ontoc\ irregular contact 

cf, Fricflon angle 

C . Cohesion 

3 T Shear stress 

on on Normal stress 

O1 Principal stress 

'03 Secondary stress 

Figure 6.-Fallure mechanlsm associated wlth loss of confinement 

reveals the position of magnitude of the peak stress zone and, therefore, the potential for violent failure. 

Numerous techniques are available to acquire this information, including both observational and instrumentbased procedures. If the ribs are generally crushed, but locally appear straight and solid, this may indicate 

that the peak stress zone is close to the coal pillar edge. If the ribs are difficult to cut or drill, this may 

indicate an abnormally high peak stress zone. The presence of a sandstone channel scour may signal the 

change in the character of the contact zone. The irregularity of the scours generally provides higher shearing 

resistance. 

The appearance of a dusting of "red coal" at the contact zone is perhaps the most dramatic indicator of 

the imminence of a coal mine burst. This condition indicates the coalbed's inability of resist shearing forces 

generated by the tremendous confinement locally applied to the coal. The red coal zone probably represents 

coal that has been mechanically altered due to the presence of excessive amounts of shear strain. 

U.S. Bureau of Mines researchers have observed this condition at three different burst-prone mines: the 

Olga and Gary No. 2 Mines in southern West Virginia and the Lynch No. 37 Mine in eastern Kentucky. 

Auger drilling also has been used as a technique to probe for areas of highly stressed coal. Often, after 

a particular mining face has burst, small-diameter (5-cm) auger holes are drilled into the face with handheld 

*~Ls. Dr'ioie cutting are often monitored, but generalby the mining company is most t?teresteb b 

determining when drilling difficulty or drill string seizures occur. At these points, it is assumed that the 

drillhole has entered an area of high stress. A number of holes are drilled across the problem working face 

at distances of 2 to 6 m. If the peak stress zone (figure 5) is close to the entry (less than 2 m), the situation 

is generally deemed critical and mining temporarily ceases or some destre&ing 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. It should be noted that no reliable criteria exist to guide the mining company in 

determining how often a face should be probed or in selecting drilling parameters or patterns. Longwall 

mines such as Dutch Creek in Colorado and Lynch No. 37 in eastern Kentucky have utilized this technique 

to predict the location of destressing. 

A summary of useful designs to reduce the severity and occurrence of coal mine bursts has been 

presented by Iannacchione and DeMarco (1992). In room-and-pillar mining, the use of straight retreating 

coal pillar lines, small and uniform pillars, and sequential splitting of pillars can effectively move excessive 

stress conditions in a controlled manner away from the working face of the mine. In longwall mining, 
by contrast, sizing gate entry pillars either large enough to contain induced stresses or small enough to yield 

in a controlled way can effectively reduce bursts and their magnitude. Such design approaches should be the 

first line of defense against bursts, and remediation measures shouldlbe considered only as a last resort. 

Auger destress drilling was first practiced at the Gary No. 2 Mine, McDowell County, West Virginia, 

in the mid-1950's by augering 61-cm holes from the sides of highly stressed barrier pillars (Talman and 

Schroder, 1958). Unfortunately, these large-diameter boreholes were prone to trigger large coal mine bursts. 

As a result, auger holes with diameters of less than 10 cm have been used recently, because they are believed 

to be incapable of initiating a burst. The augering process effectively shifts the highest stress areas away from 

the coal pillar edge without removing any of the confining fractured and yielded rib coal. This technique may 

prove most effective when the mechanism is believed to be excessive pressure or loss of confinement. 

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." This technique could prove effective with all three categories of coal 

mine bursts. 

Water infused into a coalbed has the ~otential to initiate slippage between rock surfaces, lowering the 

state of confinement on the surface and the energy stored within this system. This technique may prove most 

effective when the mechanism is believed to be excessive pressure or loss of confinement. 

Several other techniques have remained untried, but should be mentioned here. In some instances, it has 

been difficult to achieve good caving into full-extraction gob areas. This is believed to be a function of the 

ability of these massive units to span over the gob. Hydraulic fracture has the potential to induce strata 

caving by propagating a fracture or to induce strata slip by lubricating a significant geologic discontinuity. 

This technique may prove most effective when the mechanism is believed to be excessive pressure or 

seismic shock. 

SUMMARY AND CONCLUSIONS 

U.S. coal mine bursts may be categorized by three distinct source mechanisms: excessive pressure, 

seismic shock, and loss of confinement. These mechanisms define categories with unique geologies, stress 

conditions, and mining scenarios. Categorizing coai bursts in this manner allows spatial prediction and 

establishes rules by which control measures and remediation efforts may be selected. 

In general, coal mine bursts caused by excessive pressure occur in massive strata comprised mainly of 

sandstone, free of persistent geologic discontinuities. Stresses are generated from a combination of 

overburden and abutment loads resulting from mining adjacent to full-extraction zones. This type of burst 

lends itself to empirical, analytical, and numerical design procedures and is often a result of faulty mine plans. 

Therefore, spatial prediction is possible, and engineering designs and control techniques are available 

to mitigate this category of bursts. 

Coal mine bursts caused by seismic shock occur in stiff strata with large-scale discontinuities that afford 

movement, principally into gob zones. Stresses are biaxial, which can assist in fault-slip-type movement. 

A wide variety of mining scenarios can be associated with this category. In general, microseismic monitoring 

techniques are useful in locating zones of seismicity. Once the nature of the seismicity is understood, 

engineering design and control techniques similar to those used for the excessive pressure category can lower 

the overall stress states on a section-wide basis. This would lower the abiIity of a seismic wave to initiate 

structural damage. Shot fuing techniques allow for the reproduction of seismic shock effects under controlled 

situations. Hopefully, additional options, such as prefracturing strata to inducekontrolled movement, can be 

developed in the future. 

Finally, coal mine bursts caused by loss of confinement occur where the contact between coal and mine 

roof or floor resists movement. These zones can be very localized and are generally associated with 

sandstone channel scours. The peak stress zone is generally found exceptionally close to the coal rib. Bursts 

occur in direct response to mining within the yielded coal adjacent to the peak stress zone. This type of burst 

can occur during coal pillaring, working face development, or panel extraction. Burst potential is best 

identified with drilling, but can also be recognized with rock mechanics instrumentation. Mitigation measures 

are limited to destressing techniques, including the use of water infusion to lower coal confinement. 

The above model is provided with the hope that a logical, effective methodology can be recognized that 

will allow for the rapid execution of the most efficient coal mine burst control technique. 
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