SME Annual Meeting 

Feb. 25-Feb. 28, 2007, Denver, CO

1 Copyright © 2007 by SME 

MULTIPLE SEAM LONGWALL MINING IN THE U.S.—LESSONS FOR GROUND CONTROL

C. Mark, NIOSH, Pittsburgh, PA 

Abstract

Relatively few longwall mines in the U.S. operate under multiple 

seam conditions where the two seams are less than 200 ft apart. This 

paper describes the experience of six that do. These operations are 

located in PA, WV and UT, and include examples of both undermining 

and overmining. Some operate above or beneath their own workings,

others are in historic mining districts and must contend with abandoned 

mines that are decades old. The lessons that these mines have

learned cover a broad range of topics, including: 

• Whether to stack gateroads or place them under old gob

areas; 

• How to size pillars and select artificial support to cross 

longwall stop lines; 

• How to use yield pillars to minimize multiple seam stresses 

and coal bump potential, and; 

• When to anticipate the creation of pathways for gas, water,

or oxygen between current and abandoned gobs.

Introduction

Multiple seam interactions can cause roof falls, rib spalling, and

floor heave, disrupting mining operations and threatening the safety of

miners. In early 2006, a West Virginia coal miner was killed by rib roll

that occurred in a high-stress zone beneath a remnant pillar structure

in an overlying mine (MSHA, 2006). Longwalls may be uniquely 

vulnerable to multiple seam interactions, because they tend to operate

under deep cover, generate large abutment stresses, and have little

flexibility to avoid localized zones of difficult conditions. 

For the past several years NIOSH has been conducting research

with the goal of developing better techniques to predict the location 

and severity of multiple seam interactions. In the course of this 

investigation, more than 40 mines were visited across the U.S. 

coalfields, including a number of longwalls. The study also drew upon

past studies conducted by the author and an extensive literature 

review. The purpose of this paper is to discuss the potential impacts of

multiple seam mining on longwalls, based on an evaluation of the

different geologic environments in which longwall mining is conducted,

combined with analyses of past case histories. 

Overview

Figure 1 shows the 5 major regions for underground coal mining

in the U.S. Also shown are the numbers of operating longwall faces in

each region (Fiscor, 2006). 

The Central Appalachian region of southern WV, eastern KY, and

southwestern VA is the most significant coalfield from standpoint of

multiple seam mining. Mining has been ongoing in Central Appalachia

for nearly 150 years, and recent studies have indicated that perhaps 

70% of the ultimate reserve base in the region has already been mined 

(Bate and Kvitkovich, 2004). One consequence of the maturity of the 

central Appalachian coal fields is that most underground reserves have

been impacted by past mining activity. The mountains of the central

Appalachian coalfields are honeycombed with worked-out mines, 

located above, below, and adjacent to today’s and tomorrow’s 

operations. 

Although longwall mining has a long history in central Appalachia,

including the first mechanized faces in the US (Barczak, 1992), the 10

longwalls active there today account for less than 20% of the region’s 

underground production (DOE-EIA, 2006; Fiscor, 2006). Of these, 

three are extracting the very deepest mineable seam in the area, the 

Pocahontas No. 3, without any significant mining above or below. The 

others are operating in multiple seam environments, and two case

histories are discussed in some detail later in the paper. 

Figure 1. Underground coal mining regions in the U.S., showing the

number of longwall faces in each.

The Western U.S. is the next most important area for multiple

seam mining. Here, in the states of UT, CO, WY, and NM, nearly 95%

underground production comes from the 13 longwall operations (DOEEIA, 2006; Fiscor, 2006). Approximately half of these are operating in 

multiple seam configurations, including several mines in the Price, UT 

area and three others in the North Fork Valley near Paonia, CO. 

In contrast to central Appalachia, in the west the same mining

company is usually responsible for all the mining on a property. As a 

result, a greater degree of multiple seam planning is normally possible. 

Recently, however, one North Fork Valley mine was forced to abandon

a panel prematurely when an interaction associated with an 

abandoned mine resulted in roof falls in the headgate (Buchsbaum,

2006). 

Multiple seam interactions in western longwalls can also

contribute to the deadly bump hazard because of the deep cover and

strong roof and floor rock (Peperakis, 1968). To minimize the hazard,

many western longwalls employ yield pillar gate entry designs. Some 

of the lessons that have been learned from their experience are 

discussed later in this paper. 

The Northern Appalachian region is home to nearly one-third of

the nation’s longwalls, 17 faces producing 87 million annual tons 

(DOE-EIA, 2006; Fiscor, 2006). Currently, all but one of those

longwalls is extracting the Pittsburgh seam. The Freeport seam, the

nearest mineable coalbed beneath the Pittsburgh, is over 600 ft below, 

and it has never been extracted beneath any Pittsburgh longwall. 

There has been some mining in the Sewickley seam that overlies the 

Pittsburgh, and in the distant past it caused some disruption in the 

Pittsburgh (Zachar, 1952), but it has not been known to impact the 

modern longwall mines. 
SME Annual Meeting 

Feb. 25-Feb. 28, 2007, Denver, CO 

2 Copyright © 2007 by SME 

Though none are operating today, in the recent past longwalls 

have operated in the Sewickley seam and other seams in central PA. 

These operations provided two examples of longwall mining above

abandoned works that are discussed below. 

More than 90% of the underground coal produced in the Illinois 

Basin comes from two seams, the Springfield 5/Kentucky 9 and the

Herrin 6/Kentucky 11 (DOE/EIA, 2006). These seams are often less 

than 80 ft apart, so there is significant potential for multiple seam

interaction. However, today there are just two longwall mines 

operating in the Illinois Basin. One of these does work both seams,

but the mining has been planned so that the workings in one seam

have never crossed previously-mined gob areas in the other seam.

Seven longwalls are currently active in the Alabama coalfields.

Six of these are extracting the Blue Creek seam, which is again the

deepest mineable seam in the section, lying hundreds of feet below the 

nearest mineable overlying seam. The only non-Blue Creek Alabama

longwall is also free of multiple seam interactions. 

Hazards Associated with Multiple Seam Mining

Ground instability is usually the greatest hazard due to multiple

seam interaction. Interactions may be classed into four major 

categories, depending on the mining method, the mining sequence,

and the thickness of the interburden. Other potential hazards are 

associated with water, gas, and oxygen-deficient air. 

Undermining, the first category of interaction, occurs when the

upper seam has been mined first and the lower seam is the active

seam (figure 2). In an undermining situation, damage is caused by 

load transfer from highly stressed structures associated with fullextraction mining in the overlying seam. 

Figure 2. Undermining interaction. 

Overmining, the second type of interaction, occurs when the

upper seam is extracted after mining is complete in the lower seam 

(figure 3). Load transfer occurs in this situation just as it does in

undermining (in other words, gob-solid boundaries and remnant pillars 

cause stress concentrations both above and below). In addition,

however, full extraction of the lower seam normally results in

subsidence of the overlying beds, potentially damaging the roof. 

Dynamic interactions occur whenever active mining occurs above

or beneath open entries that are in use. The most severe dynamic 

interactions occur when a lower seam is longwalled or pillared,

resulting in subsidence of the overlying workings. While there have 

been several relatively recent cases in which longwalls were extracted

as far as 550 ft beneath open main entries caused extensive damage 

to the upper mine (Ellenberger et al., 2003; Mark, 2006), there do not

appear to be any instances in the U.S. where a working longwall was 

the victim of a dynamic interaction.

Ultra-close mining is the fourth type of interaction, and the only 

one that applies to development mining. The primary concern is failure 

of the interburden between the two seams. Ultra-close interactions are

unlikely when the two seams are more than 20-30 ft apart. 

Figure 3. Overmining interaction. 

Other hazards include the potential for inundation from an

overlying, flooded mine, particularly where full extraction in the lower 

seam can create a direct pathway between the upper and lower seam

gobs. In one example, the first longwall panel at a Kentucky mine

encountered a major inflow from workings 150 ft above. In this 

instance the water posed no hazard to the miners, but the lack of

pumping capacity in the lower seam resulted in major mining delays

(Mark et al., 1998). Fractures in rock above subsided gob areas can

also fill with methane or oxygen-deficient air, resulting in inflows of gas

or blackdamp when they are intersected by overmining. 

Overmining Interactions: Two Case Histories from Pennsylvania 

Two Pennsylvania longwalls, both of which are now closed,

provide examples of the potential for overmining previously extracted 

areas. The first example was a successful one, the second less so. 

In Cambria County, near Ebensburg PA, Bethlehem Mines Corp. 

No. 33 Mine employed longwall methods to extract the B seam (Middle

Kittanning) and the overlying C Prime seam (Upper Kittaning). The

mining was sequenced so that extraction was completed in the B seam 

first. More than 25 longwall panels were later recovered in the upper 

seam over almost two decades (Bauer et al., 1992). 

The B seam averaged about 5 ft in thickness, and its depth of 

cover was 500 to 800 ft. High horizontal stresses were typical of the

lower seam, where they caused extensive damage to the gate entries 

during both development and longwall retreat (Mark and Mucho, 1994). 

The C Prime seam was typically 3.5 ft thick, with an additional 1 ft

of drawrock normally extracted. The immediate roof consisted of

interbedded sandstone and shale, with a CMRR of about 50. The 

interburden between the seams averaged 105 ft, and consisted mainly 

of shales and sandy shales. Typically at least 10 years was allowed to

elapse between the completion of mining in the lower seam and

development in the upper. Contrary to usual multi-seam practice, the

gate entries in the C-Prime were superpositioned above the gates in 

the lower seam (figure 4). In general, conditions were quite good both

on development and longwall retreat. Six-ft long fully-grouted resin

bolts, supplemented in the tailgate by two rows of wooden posts,

provided adequate roof support. Only in one instance, when an 

attempt was made to develop a gate road slightly over the gob, were

poor ground conditions attributed to multiple seam interactions.

Conditions along the longwall face were also benign, and were not 

noticeably different near the panel edges than they were in the center 

of the subsidence trough. 

Interestingly, ground conditions in the upper seam actually 

seemed to be worse above virgin, undisturbed B seam areas than they 

were above areas where the B seam was mined out. Above the virgin 

areas, C Prime workings encountered severe ground conditions and 

methane emissions. It seemed that perhaps the subsidence

associated with the extraction of the B seam relieved the horizontal 

stresses and removed the methane that would otherwise have been

present. 
SME Annual Meeting 

Feb. 25-Feb. 28, 2007, Denver, CO 

3 Copyright © 2007 by SME 

Figure 4. Stacked gateroad layout at the No. 33 Mine (Bauer et al.,

1992). 

The second example of overmining was provided by the New 

Warwick mine, which was located in Greene County, PA. New

Warwick worked the Sewickley seam, beneath 500 to 900 ft of cover.

The Sewickley roof was a dark sandy shale with a CMRR of about 40. 

The Pittsburgh was approximately 100 ft below the Sewickley,

and underneath one panel it had been worked by high-extraction roomand-pillar methods (figure 5). Analysis indicated that many of the small

fenders that had been left in the Pittsburgh had probably yielded,

transferring much of their load to a few large, isolated remnant pillars 

(Heasley and Chekan, 1999). Severe pillar spalling and poor roof

conditions were encountered when developing gate entries above

these remnants.

The inby portion of the Sewickley longwall panel, where the cover 

was shallowest, was developed and longwalled with little difficulty. 

However, stress mapping and LAMODEL analysis indicated that the 

most severe interactions would occur beneath the deepest cover, near 

the mouth of the panel (Heasley and Chekan, 1999). When the

longwall face reached this area, ground control problems included face

spalling and headgate roof instability. The conditions were so severe 

that the longwall face had to be stopped 50 ft short of the recovery 

chute, which greatly complicated recovery of the longwall. 

Undermining Interactions: Two Case Histories 

from Central Appalachia

Two mines in southern WV provide examples of longwalls 

undermining full-extraction workings in an upper seam. The first, the 

Harris No. 1 Mine is operated by Peabody Energy. During the past 30 

years Harris has mined more than 60 longwall panels in the Eagle coal

seam. The depth of cover exceeds 1400 ft beneath the highest ridges.

The roof is fairly typical of Central Appalachia, consisting of strong

shale and sandstone, with CMRR values normally in the 45-60 range 

(Chase et al., 2005). 

The Eagle is located 180-200 ft beneath the No. 2 Gas seam.

Figure 6 is a generalized stratigraphic column of the interburden that

shows that it contains a high percentage of massive sandstone. The

No. 2 Gas has also been extensively mined. The longwall panels in 

the upper seam were much smaller than the recent Harris panels, and 

they also lie in several different orientations. As a result, in many 

cases it has not been possible to plan the lower seam workings to

minimize the potential for interaction. 

Chase et al. (2005) evaluated 17 locations where gate entries at

Harris crossed beneath remnant pillar structures in the upper seam. In

about 60% of these cases, development and retreat mining were

successful, though it was often necessary to install cable bolts or other 

secondary support to control the ground conditions. In seven cases,

however, the interactions were serious enough that the headgate or 

tailgate squeezed shut during panel recovery. Most of these cases 

occurred beneath chain pillars where the depth of cover exceeded 

1,000 ft (figure 7). 

Figure 5. Map of the New Warwick Mine in the Sewickley seam, and

the underlying Pittsburgh seam workings (Heasley and Chekan, 1999). 

There have also been several instances when poor ground

conditions on the face were attributed to overlying structures. Most

often the problem was severe floor heave, though in two instances roof

control was lost at the face. All but one of these five incidents occurred

more than a decade ago, when the longwall hydraulic face supports 

were much less capable than they are today. 

Based on past experiences, mine planners at Harris try to adhere

to the following “rules-of-thumb:” 

1) The long axis of the panel to be mined should parallel that of 

the upper seam panel; 

2) The future headgate should be positioned under, and as 

close to the center of the gob as possible, and; 

3) Avoid advancing the longwall face under a gob/solid

boundary. 

The engineers at Harris also use the LaModel program to identify 

high vertical stress areas which are caused by deep cover, abutment 

loads, and/or multiple seam stress transfer (Heasley and Agioutantis, 

2001). Once multiple seam stress transfer magnitudes are obtained,

they can be incorporated into the ALPS or ARMPS programs to obtain 

more realistic pillar stability factors.

At WV Mine B, longwall mining was initially conducted in the

Lower Cedar Grove seam before being moved to the underlying Alma 

seam. The interburden between the two seams was only 60 to 90 ft,

and consisted largely of sandstone. In the highly mountainous terrain

the cover varied from 300 to 1100 ft (Vandergrift et al., 2000). The

lower seam roof is typically a strong siltstone or fine-grained

sandstone, with a CMRR in excess of 55. 
SME Annual Meeting 

Feb. 25-Feb. 28, 2007, Denver, CO 

4 Copyright © 2007 by SME 

Figure 6. Stratigraphic column from the Harris Mine, Boone County,

WV. 

Figure 7. Harris mine longwalls in the underlying Eagle seam (light

gray) crossing beneath upper seam chain pillars (dark gray). 

Following an extensive LaModel study, the lower seam layout was

planned to minimize the potential for interactions. Particular care was 

taken to ensure that no development crossed beneath the heavily 

loaded upper seam chain pillars. The lower seam mains were

developed beneath the overlying ones, but the longwalls were laid out

so that the gates were offset by approximately one-quarter of a panel 

width (figure 8). Because the lower seam panels were longer than the

overlying ones, the gates crossed both the upper seam start- and stopline barrier pillars. At both crossings, the entry widths were reduced to 

18 ft and the crosscut spacing was increased. Extra support, including 

truss bolts and steel props, were installed in the belt entry. 

Figure 8. Multi-seam longwall layout employed in the Lower Cedar 

Grove seam (Vandergrift et al., 2000) 

The first panels were retreated in the lower seam are shown in 

figure 8. No serious gate entry stability problems were encountered,

though the high stress zones beneath the stop and start lines were 

clearly visible, particularly when the depth of cover exceeded 800 ft.

Although the upper seam chain pillars were located above the longwall 

face, they did not seriously impact ground conditions either. As one

miner put it, “beneath the chain pillars, the coal was so broken that the 

shearer didn’t have to cut anything, all it had to do was load.” Several

of these faces were also successfully retreated across the upper seam

start pillars. 

The next two panels were not as successful, however. They were

oriented perpendicular to the initial panels, and crossed a 110 ft wide 

remnant barrier pillar located under about 800 ft of cover between two

pillared areas in the upper seam. It was difficult to develop the gates

across this structure, but when the longwall face approached it the

conditions on the face became so severe that the panel was 

abandoned early. To prevent a similar event, the second panel was 

also recovered before it reached the remnant barrier. 

Subsequently, eight additional longwall panels have been

extracted in the lower seam. The most serious difficulties have been

associated with an unsuccessful attempt to stack the gate roads. The

roof in this area consisted of an unusually thick shale, and the 

conditions became so severe once the depth of cover exceeded 800 ft 

that the development was abandoned. 

Multiple Seam Longwall Mining with Yield Pillars in Utah 

Longwall mines in Utah work in a region characterized by rugged 

canyon-and-mesa topography, where cover depths can reach 3,000 ft.

The roof and floor strata tend to be relatively strong 15,000 to 25,000

psi, and the overburden consists largely of massive sandstone units 

that can be as much as 500 ft thick. Many of the mining properties

also contain two or more thick coal seams in close proximity (Barron et

al., 1994). 

Unique among US coal operations, Utah longwalls rely almost

exclusively on yielding pillar gate entry designs. According to DeMarco

(2000), yielding pillar gate systems were developed to: 

1. Mitigate the severe coal bumps (dynamic coal seam

failures), most commonly experienced in the tailgate entries;

and: 

2. Abate the high stress concentrations associated with 

remnant gate pillars during close-proximity multi-seam

mining. 

Based on his comprehensive study of yielding pillar case

histories, DeMarco (2000) concluded that successful gate entry 

systems: 
SME Annual Meeting 

Feb. 25-Feb. 28, 2007, Denver, CO 

5 Copyright © 2007 by SME 

• Are largely limited to settings where the immediate roof is 

strong enough to withstand large deformations (the CMRR in 

every successful case history exceeded 50); 

• Employ chain pillar width-to-height ratios of less than 5 to

ensure that timely, nonviolent yielding occurs during first

panel mining, and; 

• Normally require that artificial roof support plays a major 

role. 

At Utah Mine A, approximately 20 lower seam longwalls have

been extracted beneath upper seam panels. The interburden has 

ranged from 60-90 ft, with maximum depths of cover from 1,400 to 

2,100 ft. Upper seam mining was typically completed 3 to 5 years 

before development began beneath it. Both seams employ two-entry 

gate systems, with 30 ft wide yield pillars. The roof in the lower seam

is variable, but typically a strong sandstone either lies directly on the 

coal or can be reached with roof bolts, so the CMRR is usually near 

70. 

In the very first multiple seam application at this mine, the gate

entries were stacked. A 160 ft massive roof fall ensued, and the gate

had to be re-driven. Since then, all gate entries have been driven

beneath the upper seam gob, normally offset at least 100 ft from the

upper gate. Lower seam panels have usually been designed so that 

they begin and end under the upper seam gob. However, figure 9 

shows a multi-panel layout where several of the longwall faces did 

cross the stop lines of the overlying panels. The depth of cover at the 

crossings was less than 1,400 ft in every case. 

Figure 9. Layout of yield pillar longwall panels at Utah Mine A. 

No special support is normally required to develop the gates

underneath the upper seam stop lines. However, when the cover 

exceeds about 1600 ft, bumps are more likely to occur if the gate 

crosses the stop line near the middle of the overlying panel, rather than

near the edge where the upper seam stop line barrier pillar has been 

slightly “softened” by the presence of the upper seam gates. 

One of the big advantages of being a two-seam longwall mine is 

that, other than the chain pillars, there should be no isolated remnant 

pillars in the overlying gob. One incident at mine A illustrates just how

important this advantage is. A “barrier pillar” was created in the upper 

seam between the longwall start line and some bleeder entries. When

the lower seam longwall had mined beneath the bleeders and partially 

beneath the barrier, a major bump occurred along approximately 80%

of the face (figure 10). The depth of cover at this location was in

excess of 2,000 ft. Subsequently, the set-up rooms in the lower seam

were always placed under the gob if the cover exceeded 1,400 ft. 

In general face conditions have been excellent in the lower seam.

Although the imprint of the overlying yield pillars could clearly be seen

in the roof and coal face, it caused no problems. Under deep cover the

panels start outby the upper set-up rooms, and stop inby the upper 

seam stop line, so nearly all the longwall mining has been beneath

gob. 

Figure 10. Cross-section showing panel geometry at the time of a 

large face bump at Utah Mine A. 

With a 10 ft extraction height in the lower seam, and as little as 60

ft of interburden, it seems likely that subsidence fractures can create

hydraulic connections between the gobs of the two seams. None the

less, there has been just one instance where water from an

insufficiently dewatered area entered the lower seam mine in sufficient 

quantities to obstruct production. 

At Utah Mine B, the two seams are 50-75 ft apart. The cover is 

lighter than at Mine A, reaching a maximum of about 1,100 ft, but the 

roof is weaker, with a CMRR averaging about 50. Bumps have not 

been a problem at this operation, but roof control is a significant

concern. 

The upper seam panels at Mine B have all employed three-entry 

gates, with 30-ft wide yield pillars. A total of nine lower seam panels 

have been extracted. As was the case in Utah Mine A, it is possible to 

“see” the upper seam pillars on the face and in the set-up rooms of the 

lower seam, but they have never caused problems.

The lower seam panels at Mine B have been planned so that they

are set up, mined, and stopped all under the gob of the upper seam.

The critical zone of interaction has been where the gates cross the

upper seam stop line barriers. These have been troublesome and

require substantial artificial support. Currently, cable bolts are installed 

in these areas as primary support on development, in a pattern of four,

12-16 ft long cables per row, with rows on 4-ft centers. Over time,

Mine B has also found that conditions are better if larger pillars 

(currently 100 ft centers) are used to cross the barriers (figure 11).

Figure 11. Layout of stop-line crossings employed at Utah Mine B.

Another design issue is the location of the lower seam set-up

room. In the first lower seam panels, the set-up was developed just 40

ft inside the gob from the edge of the upper seam set–up (figure 12).

Conditions were less than favorable. They improved considerably 

when the offset was increased to 100 ft. 

A mine planner at Mine B observed that one undesirable

characteristic of multiple seam interactions is that “they just keep

coming.” In one instance, a long-term mains crossed beneath an

upper seam gob line. Over 4 years, more than 4 ft of floor heave

developed, and the roof was cable bolted three times but still 

eventually failed.
SME Annual Meeting 

Feb. 25-Feb. 28, 2007, Denver, CO 

6 Copyright © 2007 by SME 

Figure 12. Set-up room offset at Mine B. (A) 40 ft offset. (B) 100 ft

offset. 

Spontaneous combustion is another safety concern at Mine B. In 

one of the panels where the set-up was developed with a 40 ft offset,

the caving behind the longwall created a connection that allowed 

oxygen to reach the upper seam bleeder system. A heating 

developed, which was fortunately detected and quickly extinguished. 

There have also been several instances of large water inflows to the

lower seam, despite numerous holes drilled from the lower seam into 

low areas of the upper seam gob to drain water pools from the upper 

seam workings before undermining. 

Conclusions 

Although few U.S. longwalls face serious multiseam challenges,

some valuable lessons can be learned from those that do. These 

include: 

• Gate entry configuration: The first question that often faces 

mine planners is whether to stack the gateroads or offset

them. Most of the U.S. longwall mines have preferred to

offset their gateroads at least 100 ft from the gates in the

previous seam. Some have had bad experiences when they

tried stacking. However, the No. 33 Mine successfully 

employed a stacked gate configuration for many years, and

the Harris Mine has used stacked pillars on occasion. 

• If the offset design is employed, then the gate entries must

be developed across the gob-solid boundary at the stop line

of the previous seam longwall. The experience of the mines 

described in this paper is that this crossing may require a

special pillar design or extra roof support, but it has not 

usually been a major concern. 

• Panel layout: The preferred layout is one in which the panel

start positions are set up outby the overlying or underlying

set up room, and stop before they reach the stop line of the 

previous panel. This way all longwall mining is beneath the

old gob area (except for the coal beneath the chain pillars.) 

However, there are a number of instances where these

mines have successfully brought their faces across old stop

lines or set up rooms, at least occasionally. 

• Longwall face conditions have rarely been a problem at any 

of these mines, whether they are overmining, mining 

underneath large chain pillars, or crossing gob-solid 

boundaries. The most difficult interactions have been 

associated with large remnant pillars that were left in the 

previously mined seam, particularly when the remnant

barrier was oriented parallel with the longwall face. 

• Roof strength: The experience of these mines is that roof

strength is a major factor determining the success of multiple

seam mining. For example, the weaker roof at Utah Mine B

has caused it to generally have more trouble than Utah Mine

A, even though Mine A’s cover is significantly greater.

Similarly, New Warwick has weaker roof than Mine 33, and

also encountered greater difficulties. 

• Planning: The ability to preplan the multiple seam mining on

a property is a major advantage. Mines that overmine or 

undermine their own longwall panels can more easily 

overlap the panels, offset the gates, and longwall almost 

entirely under gob areas. Most importantly, they can ensure

that isolated remnant pillars are not left in the gob. The

experience of the Utah mines also shows that yield pillars

can also be a very useful planning option, so long as the roof 

strength is adequate. 

• Those mines, like Harris and New Warwick, which do not

have the luxury of preplanning all the mining in advance

have been forced to deal with remnant structures and gob 

areas at odd angles. For instance, it seems that perhaps the

extra 100 ft of interburden at Harris compared to WV Mine B 

may have compensated for Harris’ more difficult remnant 

structures. 

As the demand for coal continues to expand, mining companies

are considering a number of new multiseam longwall mines in such

areas as central Illinois and the Hunter Valley in Australia. Hopefully,

these future operations will be safer because they have benefited from 

the experience of the operations described in these case studies. 

References 

Barczak, T.M. (1992), "The History and Future of Longwall Mining,"

U.S. Department of the Interior, Bureau of Mines, IC 9316, 26 pp. 

Barron, L.R., M.J. DeMarco, and R.O. Kneisley (1994), "Longwall Gate

Road Stability in Four Deep Western U.S. Coal Mines," U.S.

Department of the Interior, Bureau of Mines, IC 9406. 

Bate, R.L. and J.F. Kvitkovich (2004), "Quantifying the Coal Reserve

Dilemma in the Central Appalachian Mining Region," SME 

preprint 04-108, 8 pp. 

Bauer, E.R., G.J. Cheken and G.P. Sames (1992), "Influence of

Subjacent Gob on Longwall Development Mining in the Upper 

Kittanning Coalbed of South Central Pennsylvania," U.S.

Department of the Interior, Bureau of Mines, RI 9538. 

Buchsbaum, L (2006), "Longwall Mining Thrives in Colorado’s North

Fork Valley;" Coal Age, August, pp. 28-34. 

Chase, F.E., P. Worley and C. Mark (2005), "Multiple Seam Mining 

Interactions: Case Histories from the Harris No. 1 Mine," in

Proceedings of the 24th International Conference on Ground

Control in Mining, Morgantown, WV, pp. 79-86. 

DeMarco, M. (2000), "Review of Current Yielding Gate Road Design 

Approaches and Applications in U.S. Longwall Operations,"

Appendix 11 to Volume 1 of UNSW/SCT Collaborative ACARP

Project C9018 – Final Report, ACARP, 2005, 74 pp. 

DOE-EIA (2006), Annual Coal Report, 2005, Available at the Energy

Information Administration website 

http://www.eia.doe.gov/fuelcoal.html . 

Ellenberger, J.E., F.E. Chase and C. Mark (2003), "Case Histories of

Multiple Seam Coal Mining to Advance Mine Design," in

Proceedings of the 22nd International Conference on Ground

Control in Mining, Morgantown, WV, pp. 59-64. 

Fiscor, S. (2006), "U.S. Longwall Census 2006," Coal Age, 111(2):26-

30. 

Heasley, K.A. and G.J. Chekan (1999). "Practical Boundary-Element 

Modeling for Mine Planning," in Proceedings of the 2nd

International Workshop on Coal Pillar Mechanics and Design,

NIOSH IC 9448, pp. 73-87. 

Heasley, K.A. and Z. Agioutantis (2001), "LAMODEL – A Boundary

Element Program for Coal Mine Design," in Proceedings of the

10th International Conference on Computer Methods and

Advances in Geomechanics, University of Arizona, Jan. 7-12, pp. 

1679-1682. 

Mark, C. (2006), "Extreme Multiple Seam Mining in the Central 

Appalachian Coalfields," SME Preprint 06-060, 8 pp.

Mark, C. and T.P. Mucho (1994), " Longwall Mine Design for Control of 

Horizontal Stress," in Proceedings of the USBM Technology 

Transfer Seminar, USBM SP 94-01, pp. 53-76. 
SME Annual Meeting 

Feb. 25-Feb. 28, 2007, Denver, CO 

7 Copyright © 2007 by SME 

Mark, C., T.P. Mucho and D.R. Dolinar (1998), "Horizontal Stress and 

Longwall Headgate Ground Control," Mining Engineering, 

January, pp. 61-68. 

MSHA (2006), "Underground Coal Mine, Fatal Rib Roof Accident, 

Report of Investigation, Feb. 1, 2006," 

www.msha.gov/fatals/2006/ftl06c18.asp . 

Peperakis, J. (1968), "Multiple Seam Mining With Longwall," Min Cong. 

Jrnl, January, pp. 27-29. 

Vandergrift, T.L., T.R. Ross, C.W. Hawley and J.A. Rusnak (2000), 

"Mine Planning for Longwall And Pillar Retreat Panels Subject to 

Seam Interaction Effects," in Proceedings of the 19th International 

Conference on Ground Control in Mining, Morgantown, WV, pp. 

204-212. 

Zachar, F.R. (1952), "Some Effects of Sewickley Seam Mining on Later 

Pittsburgh Seam Mining," Min. Eng., July, pp. 687-692.