79

ABSTRACT 

 The Harris No. 1 Mine, located in Boone County, WV, has been 

longwalling the Eagle Coalbed for over 30 years. Harris has 

experienced numerous interactions associated with the extensive 

room-and-pillar and longwall mining operations which have been 

conducted in the overlying No. 2 Gas Coalbed. The problems have 

included roof falls, excessive rib sloughage, and gateroad and 

bleeder entry closure. A detailed evaluation of the multiple seam 

experiences at Harris No. 1 Mine was conducted as part of the 

National Institute for Occupational Safety and Health (NIOSH) 

nation-wide multiple seam mining case history data base. One 

observation from the Harris gateroad case histories was that 

smaller, critically loaded, upper seam pillars seemed to cause more 

severe ground conditions than did wider pillars. The LaModel 

program was used to investigate this supposition, and the results 

confirmed that “critical” sized pillars do transmit the highest 

amounts of stress to adjacent seams. In addition, the data suggest 

that the probability of a major multiple seam mining interaction 

increases when the depth of cover is 1,000 ft or greater and when 

the Eagle seam pillars have a Analysis of Longwall Pillar stability 

factor less than 1.50. 

INTRODUCTION 

 The National Institute for Occupational Safety and Health has 

recently completed a comprehensive nation-wide data base of 

multiple seam mining case histories. To collect the case histories, 

underground geotechnical evaluations were conducted at more than 

45 U.S. coal mines. The data is currently being analyzed in order 

to ascertain the relative importance of the various contributory 

mining and geologic parameters responsible for multiple seam 

mining interactions. The ultimate goal is to provide the mining 

community with a design methodology for multiple seam mining 

which will aid in determining the likelihood of adverse interactions 

so that corrective measures can be taken to prevent injuries and 

fatalities. 

 During the study, 22 multiple seam case histories were collected 

from the Harris No. 1 Mine, more than at any other mine site. An 

area was deemed to be a case history if a multiple seam interaction 

occurred or should have been anticipated. This accumulation of 

such a significant number of cases over a relatively small 

geographic area presented an excellent opportunity to conduct a 

study which would evaluate the current state-of-the-art in multiple 

seam design. In other words, can the criteria that engineers employ 

to predict whether or not a multiple seam interaction will occur be 

used to explain Harris’ experiences? 

 The Harris No. 1 Mine is operated by Eastern Associated Coal 

Corporation which is a subsidiary of Peabody Energy. Harris is 

located in Wharton, WV, and began operations in 1966 (figure 1). 

Since then, Harris has driven and retreat mined over 60 longwall 

panels in the Eagle Coalbed. The No. 2 Gas Coalbed is situated 

approximately 200 ft above the Harris Mine workings. Both 

longwall and room-and-pillar retreat mining have been conducted 

in the No. 2 Gas. In many cases, remnant structures such as barrier 

pillars, isolated gateroads (gateroads which are bordered by gob on 

both sides), etc. that were left in the 2 Gas have caused difficult 

ground conditions in Harris due to downward load transfer. In 

other instances, upper seam structures have not noticeably impacted 

mining. From the mine planning perspective, the paramount 

question is: When will multiple seam problems occur and how 

severe will the interaction be? The purpose of this investigation 

was to shed some light on these questions by conducting detailed 

analyses of Harris’ experiences. 

Wharton

Charleston

Figure 1. Harris No. 1 M ine location map.

Multiple Seam Mining Interactions: 

Case Histories From the Harris No. 1 Mine 

Frank E. Chase, Research Geologist 

NIOSH-Pittsburgh Research Laboratory 

Pittsburgh, PA 

Phyllip Worley, Senior Manager of Engineering 

Peabody Energy 

Wharton, WV 

Christopher Mark, Supervisory Mining Engineer 

NIOSH-Pittsburgh Research Laboratory 

Pittsburgh, PA 
80

GEOLOGIC SETTING 

 The topography above Harris No. 1 Mine is fairly rugged. The 

valleys are narrow and “V” shaped and ridges are steep and 

prominent. These physiographical features can cause rapid changes 

in cover over relatively short horizontal distances. The overburden 

at Harris ranges from 100 ft at the drift to slightly over 1,400 ft 

under the highest ridges. As is the case with most Central 

Appalachian coal mines, the overburden is relatively competent. 

 Previous researchers (1-3) have determined correlations between 

multiple seam interactions and the interburden competency, 

thickness, and number of interbeds (number of distinct rock units 

within the interburden); therefore, considerable emphasis was 

placed on obtaining core hole information as close to the case 

history sites as possible. The information on interburden 

characteristics is listed in the Appendix. As indicated in the 

Appendix, the interburden between the Eagle and No. 2 Gas ranges 

in thickness from 176 to 213 ft. 

 

 Figure 2 is a generalized stratigraphic column of the interburden 

between the No. 2 Gas and Eagle Coalbeds. It should also be noted 

that the major sandstone and shale units shown in figure 2 vary in 

thickness. For example, in a few of the core holes the upper two 

sandstone units merge into a 100 ft thick unit. The same can be 

said for the lower two sandstone units. These rock unit thickness 

variations suggest ancient stream channel activity. Usually, the 

interburden contains 6 distinct rock units; however, the actual 

number varies from 4 to 7. In general, the interburden is rather 

competent, with the percentage of sandstone, sandy shale, and 

limestone ranging from 59 to 80 percent. The coalbeds between 

the Eagle and No. 2 Gas shown in figure 2 have not been mined 

above Harris. 

 Another factor identified in determining the magnitude of the 

interaction is the immediate roof rock competency (4). The shale 

unit shown in figure 2 directly above the Eagle Coalbed varies in 

thickness from 0 to 10 ft. In areas of Harris, this shale unit can 

either be laminated, sandy, or nonexistent (replaced by a sandstone 

scour). These fluctuations explain the range in Coal Mine Roof 

Rating (5) values from 44 to 71. These values indicate that the 

immediate roof rock is moderately strong to strong. 

 

GATEROAD DESIGN AND SUPPORT 

 Harris began longwall operations with a 300 ft wide plow face 

and 40 ton walking frames in 1966. Since then, numerous 

technological innovations have lead to improvements in the 

longwall systems and gateroad supplemental supports employed. 

Currently, Harris is mining 3.2 million clean tons of coal per year. 

Gateroad pillar design and supplemental support selection have 

also gone through an evolutionary process at Harris based on the 

performance of past longwall faces and gateroads. In fact, twelve 

different gateroad designs which incorporated various elements of a 

3-entry, 4-entry, and yield pillar designs have been tried at Harris. 

The gateroad system design was progressively refined and 

calibrated through the back analyses of previous successful and not 

so successful mining attempts. 

 The engineers at Harris utilize the novel approach of integrating 

the multiple seam stress transfer values obtained from the LaModel 

program (6) into the Analysis of Longwall Pillar Stability program 

(7) in order to obtain a more realistic stability factor (SF). This 

methodology is described in the Discussion section of this paper. 

For the past 5 years, Harris has been using a 3 entry gateroad 

system with entries on 90 ft centers and crosscuts on 140 ft centers. 

This system has worked well and no gateroad blockages have 

occurred since its usage began. Based on past experiences, during 

mine design Harris’ engineers adhere to the following “rules-ofthumb” as much as possible: 1) the long axis of the panel to be 

mined should be parallel to 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 (8). 

 Harris uses 5 ft full column resin bolts on 4 ft centers in the 

headgate entry. In the remaining gates and bleeders 4 ft full 

column resin bolts on 4 ft centers are standard. The roof control 

plan also stipulates that a minimum of 2 crib equivalents be 

installed every 12 ft in the tailgate. Floor heave has always been a 

major concern at Harris. Because conventional cribs (both 4 and 9 

point) are inclined to roll out when subjected to heave, Harris 

began using 30 inch engineered timber supports. These supports 

have performed well, in that the floor tends to heave up around the 

supports. 

 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. In highly stressed areas, 

either 2 or 4, 12 ft long cable bolts are installed in between each 

row of primary supports. Sometimes, additional engineered timber 

supports are warranted in tailgate locations. The spacing of these 

supports is dependent upon the expected level of stress. 

No. 2 G as

Lower No. 2 G as

Pow ellton "A"

Pow ellton

M atewan

U pper Eagle

Eagle

Legend

 Coal

 Shale

 Sandstone

0

50'

100'

150'

200'

Figure 2. Generalized interburden stratigraphy. 
81

CASE HISTORY ANALYSES 

 A detailed examination of both the No. 2 Gas and Harris No. 1 

workings (figure 3) revealed 22 case histories where multiple seam 

interactions happened or might have been anticipated. In each case 

history, gateroads were driven and panels were extracted under 

various upper seam structures, and the outcomes are listed in the 

Appendix. Overburden depth, interburden thickness and 

composition, and additional consequential mining parameters, 

which are thought to determine whether or not interactions will 

occur (1-3) are also listed in the Appendix. Prior to the analyses, 

the data base was separated into two categories, gate entry 

workings (17 cases) or longwall face stability (5 cases) because of 

the major differences between the two. A rating system from 1 to 6 

(see the Appendix for details) was developed to numerically 

evaluate the conditions or degree of interaction for each case. For 

the purpose of analyses, conditions 1 and 2 were combined and 

categorized as being a minor interaction because the interactions 

were barely negligible to minor. Conditions 3 through 6 were 

combined and designated as being a major interaction because the 

interactions were troublesome to major and warranted that special 

measures to be taken. 

 A series of XY scatter plots were generated in order to examine 

the various mining and geologic parameters for correlations. 

Figure 4 indicates that 6 out of 7 of the major interaction gateroad 

workings cases occurred when Harris’ depth of cover was 1,000 ft 

or greater and the Analysis of Longwall Pillar Stability Factor 

(ALPS) was 1.5 or less. Further, figure 5 points out that 5 out of 7 

of the major interaction cases occurred when the No. 2 Gas ALPS 

Figure 3. No. 2 Gas workings superimposed on Harris No. 1 Mine. 
82

SF was less than 1.0 and the depth of cover was 1,000 ft or more in 

Harris. Finally, figure 6 illustrates a weak correlation between 

problematic cases and a No. 2 Gas overburden/interburden ratio of 

3.9 or greater. As for the five longwall face stability cases, the only 

parallels that could be drawn were that the depth of cover was 

primarily 1,000 ft or greater, and the immediate roof rock was 

enerally relatively weak. Upper seam pillar design did not appear 

to be an issue; however, both it and the findings mentioned in this 

section warrant additional examination and discussion. 

UPPER SEAM PILLAR DESIGN 

 As indicated in the previous section, most of the multiple seam 

interaction problems in Harris’ gate entries occurred when the 

upper seam ALPS SF’s were less than 1.00. At first, it might seem 

counter-intuitive that smaller upper seam pillars would cause more 

severe stress conditions in an underlying seam than would wider 

pillars. However, a consideration of the load distribution in the 

upper seam pillars provides an explanation. Essentially, three load 

distributions are possible, as shown in figure 7: 

• A) illustrates a small, yielded pillar that carries a 

relatively small load; 

• B) illustrates a wide pillar, with localized high stress 

zones near the ribs but a lightly loaded core, and, 

• C) illustrates the load distribution of a “critical pillar,” 

with a highly loaded core. 

 The critical pillar would result in the most severe “footprint” on 

the lower seam, because it produces an intensified downward 

“point load” type of stress transfer to the underlying workings. The 

wide pillar may carry a larger total load, but because that load is 

distributed over a much larger area, its effect on the lower seam is 

less noticeable. A good analogy would be the imprints that a petite 

woman in high heels might make in wet sand compared with those 

made by a sizeable football player wearing tennis shoes. 

 LaModel, a displacement-discontinuity boundary element 

program was used to evaluate the hypothesis described above. The 

models were run using standard default parameters and yield zones. 

Figure 8 displays the basic layout of the two mine designs which 

were modeled. In the Harris design case, a three entry longwall 

gate entry development section (oriented from top to bottom on 

figure 8) was driven on 120 ft entry and crosscut centers in a 6 ft 

high reserve. The pillars had an ALPS SF of 3.07 and the depth of 

cover was 1,200 ft. A three entry isolated gateroad system 

(oriented from left to right on figure 8) was then situated 200 ft 

above Harris. The crosscut center spacing in the No. 2 Gas 

remained constant at 140 ft. The entry centers were varied from 30 

to 180 ft in 10 ft increments for each LaModel run and the mining 

height was 6 ft. As illustrated in figure 8, the No. 2 Gas and Harris 

workings are situated perpendicular to one another so that four 

pillars were stacked in the center of the LaModel grid. Figure 8 

also displays the LaModel analysis results for a No. 2 Gas gateroad 

system with 60 ft wide pillars. Figure 8 clearly shows that the 

multiple seam stress transfer magnitudes in Harris are the highest 

beneath the isolated gateroads. Conversely, the de-stressing effects 

of the overlying gob are also evident in figure 8. 

Figure 4. Relationship between degree of interaction and the 

Harris No. 1 ALPS stability factors and overburden. 

0

200

400

600

800

1000

1200

1400

012345

ALPS Stability Factors

Overburden (ft)

MINOR INTERACTION

MAJOR INTERACTION

Figure 6. Relationship between degree of interaction and the No. 

2 Gas overburden/interburden ratio and Harris No. 1 overburden. 

0

200

400

600

800

1000

1200

1400

01234567

No. 2 Gas Overburden/Interburden Ratio

Harris No. 1 Overburden (ft)

MINOR INTERACTION

MAJOR INTERACTION

A B C

Figure 7. Pillar loads distribution diagrams: 

(A) yielded (B) wide (C) critical 

Figure 5. Relationship between degree of interaction and the No. 2 

Gas ALPS stability factors and Harris No. 1 overburden. 

0

200

400

600

800

1000

1200

1400

01234

No. 2 Gas Stability Factors

Harris No. 1 Overburden (ft)

"Minor Interaction"

Major Interaction
83

 Figure 9 displays the peak multiple seam stress transfer value and 

the ALPS SF for each pillar width modeled. Figure 9 illustrates the 

wide range in multiple seam peak stress transfer values which are 

dependent on the width of the pillar. When analyzing figure 9, the 

multiple seam stress transfer curve appears to have three distinct 

regions that correspond to the three upper seam load distributions 

shown in figure 7. The peak or “critical” multiple seam stress 

transfer values occur when the chain pillars in the upper seam are 

in the 50 to 90 ft range. The models indicated that the cores of 

these pillars were all heavily loaded. On the left side of the critical 

pillar region, the models showed that the stresses in the cores of 

smaller, upper seam pillars were much lower than for the critical 

pillars. The smaller the pillar, the lower the peak stress, and the 

less the multiple seam stress experienced in the lower seam. On the 

right side of the critical pillar region, as the upper seam pillars get 

wider, they distribute their load more evenly. The result is a steady 

decreasing trend in downward stress transfer as the pillar width is 

increased up to around 130 ft. Once the pillar reaches a certain 

width, there is essentially no interaction between the two highstress zones at the ribs and the peak stress transfer levels out at 

approximately 350 psi. 

DISCUSSION 

 For want of a better adjective, the term “critical” was used to 

describe the pillars whose size transferred the highest multiple 

seam stress values. Obviously the word critical conjures up 

different meanings depending on whether you are designing deep 

cover gateroad yield pillars or mining in bump prone ground 

conditions. However, from a multiple seam aspect, the LaModel 

analyses indicate that critically-sized upper seam pillars can 

increase the lower seam pillar stresses substantially. In this study, 

the LaModel results were used to calculate the average stress 

increase in a Harris tailgate pillar system caused by isolated No. 2 

Gas gateroads on 80 ft wide entry centers. The calculated average 

multiple seam pillar stress was 396 psi, which is approximately 

equivalent to increasing the depth of cover by 360 ft. Therefore, a 

Harris tailgate system which was initially designed for 1,200 ft of 

overburden and having a conservative ALPS SF of 1.23 was, in 

actuality, being subjected to cover loads equivalent to 1,560 ft of 

overburden which effectively reduces the ALPS SF to 0.88. This 

example emphasizes the importance of both estimating and 

incorporating multiple seam stress transfer into the pillar design 

process. It implies that wider pillars with higher ALPS SF’s should 

be employed; however, gateroad developmental constraints also 

need to be considered. The engineers at Harris are currently using 

this methodology to design gateroad pillar systems and, based on 

past experiences, an ALPS SF in the 1.0 to 1.2 range (taking into 

account the additional multiple seam stress) has been determined to 

provide satisfactory results. It should be noted that the stress 

transfer values and critical pillar dimension widths previously 

mentioned are case specific and will vary depending upon the input 

parameters. 

Multiple Seam Stress SCALE

 -500

 -385

 -270

 -160

 -50

 70

 185

 300

 410

 525

 635

 ( psi )

Figure 8. LaModel output for 60 ft wide No. 2 

Gas pillars. 

Figure 9. Peak multiple seam stress transfer values and the ALPS SF’s for modeled pillar widths. 

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120 140 160 180

No. 2 GAS PILLAR WIDTH (ft)

MULTIPLE SEAM STRESS (PSI) .

0

0.5

1

1.5

2

2.5

3

3.5

ALPS STABILITY FACTOR .

MULTIPLE SEAM STRESS

ALPS SAFETY FACTOR

 WIDE

PILLAR

ZONE

CRITICAL

PILLAR

ZONE

YIELDED

 PILLAR

 ZONE
84

 As stated in the case history analyses section, 6 out of the 7 major 

interactions occurred when the Harris depth of cover was 1,000 ft 

or greater and when the ALPS SF was less than 1.50 (figure 4). 

The cover relationship is noteworthy, in that, most operators 

maintain that there is a correspondence between multiple seam 

interaction difficulties and overburden. Typically, operators state 

that troubles generally begin occurring at roughly 800 ft of cover. 

Essentially, it takes a certain amount of cover load to cause 

downward load transfer problems. One possible explanation for 

the higher cover value at Harris may be interburden competency. It 

is conceivable that the three sandstone units which comprise 59 to 

80 percent of the interburden are bridging, and therefore 

dampening the downward load transfer. As for the Harris ALPS 

SF’s, figure 4 suggests that the probability of a major interaction 

occurring decrease as the stability factor increases. The same can 

be said for the No. 2 Gas ALPS SF’s. As shown in figure 5, 5 out 

of 7, or 71 pct of the major interaction cases occurred when the No. 

2 Gas ALPS SF was less than 1.0 and the depth of cover was 1,000 

ft or more in Harris. Based on the above mentioned findings, a 

certain amount of concern and supplemental support are probably 

warranted when dealing with deep cover and lower upper and 

lower seam ALPS SF’s. Like the old longwall adage goes, “it is 

better to be safe than be shut down.” (It should be noted that 

multiple seam stress transfer values were not taken into account 

when determining the ALPS SF’s listed in the Appendix or shown 

on the figures.) 

 Data analyses also indicated that there was no relationship 

between the degree of interaction and the percentage of competent 

interburden. The same can be said for the interburden 

thickness/number of beds ratio. Conversely, there was a weak 

correlation with immediate roof rock competency. Generally, the 

Coal Mine Roof Rating (CMRR) was higher for the minor 

interaction cases. Another weak association previously indicated 

was the overburden/interburden thickness ratio value of 3.9. As a 

rule-of-thumb, problems generally do not occur until this ratio 

reaches 7 or 8. However, critically sized pillars may be an 

overriding factor in this particular situation. 

CONCLUSIONS 

 The most significant findings of this investigation was that the 

size of the remnant upper seam structure can influence the extent of 

the multiple seam interaction. More specifically, this study 

suggests that smaller critically loaded upper seam pillars are more 

likely to cause lower seam ground control problems than are wider 

pillars. The LaModel program was used to examine this 

supposition and the results verified this premise. 

 This investigation also demonstrated how effective a tool 

LaModel is in determining multiple seam stress transfer 

magnitudes. Once this value is obtained, it can be incorporated into 

the ALPS or ARMPS programs to obtain a more realistic stability 

factor. 

 The back analyses of 17 gateroad case histories at Harris No. 1 

indicate that the probability of a major multiple seam mining 

interaction occurring increases when: 1) the depth of cover is 

1,000 ft or greater, 2) the upper seam pillars are critically loaded, 

and 3) the Eagle seam pillars have a non-adjusted ALPS SF 

(excludes multiple seam load transfer) less than 1.50. In areas 

where these criteria are met, Harris engineers have mitigated 

problems through pillar design modifications and the installation of 

supplemental support. Based on past experiences, the engineers at 

Harris have determined that an adjusted ALPS SF in the 1.0 to 1.2 

range provides satisfactory results. 

 Finally, the analyses also identified a weak correlation between 

the degree of multiple seam interaction and the immediate roof 

rock competency (CMRR) and the overburden/ interburden 

thickness ratio. However, no relationship between the degree of 

interaction and the percentage of competent interburden or the 

interburden thickness/number of beds ratio was evident. This may 

be attributable to the lack of variability in this site specific data 

base. Possibly, the conclusions drawn from the analyses of the 

nation-wide multiple seam mining data base will concur with 

previous researchers’ findings. 

ACKNOWLEDGMENTS 

 The authors would like to express their gratitude to Dr. Keith 

Heasley for his technical advice during the data analysis, 

interpretation, and review phases of this project. They would also 

like to acknowledge the contributions of John Marshall and 

Kimberly Mitchell for their assistance in preparing the illustrations 

and formatting the manuscript. Special thanks also go to Eastern 

Associated Coal Corp. and Peabody Energy for providing the 

mining data and for allowing their valuable experiences to be 

published. 

REFERENCES 

1. Holland, C.T. Effects of Unmined Seams of Coal by Mining 

Seams Above and Below. Proc. WV Academy of Science, 1947, p. 

113-132. 

2. Stemple, D.T. A Study of Problems Encountered in MultipleSeam Mining in Eastern United States. MS Thesis, Virginia 

Polytechnic Institute and State University, Blacksburg, 1956, 188 

pp. 

3. Haycocks, C., M. Karmis, and B. Ehgartner. Multiple-Seam 

Mine Design. Paper in Proceedings of the International 

Symposium on Ground Control in Longwall Coal Mining and 

Mining Subsidence-State of the Art. AIME, 1982, pp. 59-65. 

4. Luo, J., C. Haycocks and M. Karmis. Gate Road Design in 

Overlying Multiple Seam Mines. SME Preprint 97-107, 1997, 11 

pp. 

5. Molinda, G.M. and C. Mark. Coal Mine Roof Rating (CMRR) a 

Practical Rock Mass Classification for Coal Mines, USBM IC 

9387, 1994, 83 pp. 

6. Heasley, K.A. Numerical Modeling of Coal Mines With a 

Laminated Displacement-Discontinuity Code, Ph.D. Thesis, 

Colorado School of Mines, 1998, 187 p. 

7. Mark, C. Pillar Design Methods for Longwall Mining. USBM 

IC 9247, 1990 p. 53. 

8. Hsiung, S.M. and S.S. Peng. Design Guidelines for Multiple 

Seam Mining, COAL MINING, Part I, 24 (9), Sept. 1987, pp. 42-

46 and Part II, 24 (10), Oct. 1987, pp 48-50. 
85

APPENDIX 

Harris No. 1 Case History Data Base 

Case H h LC SF INT COMP 

INT % 

No. 2

Gas h LC SF H/

INT

INT/ # 

Beds Angle CMRR Rating and Comments 

1 750 6.6 TGL 1.34 180 62 6.0 ISO 1.69 3.2 25.7 33 54 (1) No problems were encountered while 

crossing under isolated gateroads. 

2 925 6.3 TGL 1.01 180 62 6.0 ISO 0.69 4.1 25.7 33 54 (1) No problems were encountered while 

crossing under isolated gateroads. 

3 469 6.6 HGL 4.03 180 62 6.0 BL 3.49 1.6 25.7 33 54 

(1) Headgate was driven under bleeder 

entries without any problems. Panel was 

recovered without gateroad cribbing. 

4 875 6.7 HGL 1.86 176 59 6.0 HGL 1.15 4 25.1 32 63 

(1) No problems were encountered during 

gateroad advance or panel retreat under 

gateroad pillars. 

5 725 6.8 TGL 1.37 199 72 6.5 BL 2.90 2.6 33.2 0 47 

(1) Gateroads were successfully driven 

under longwall bleeder entries the entire 

length of the panel. 

6 800 6.8 TGL 1.18 180 62 6.0 ISO 1.50 3.3 25.7 33 54 

(2) Additional gate entry cribbing was 

required while crossing under isolated 

gateroads. 

7 1000 6.1 TGL 0.90 193 74 6.0 ISO 0.93 4.2 32.2 33 56 

(2) Additional gate entry cribbing was 

required while crossing under isolated 

gateroads. 

8 1100 6.2 Dev 2.29 193 74 6.0 ISO 0.75 4.7 32.2 33 56 

(2) Poor ground conditions required cable 

bolting on development while crossing 

under isolated gateroads. 

9 800 6.8 TGL 1.20 193 74 6.0 ISO 0.87 3.1 32.2 33 56 

(2) Additional gate entry cribbing was 

required while crossing under isolated 

gateroads. 

10 1050 7.2 Dev 2.16 193 74 6.0 ISO 0.85 4.4 32.2 33 56 (2) Poor ground conditions required cable 

bolting under isolated gateroads. 

11 1000 7.1 TGL 1.07 201 80 6.0 ISO 0.60 3.9 50.3 25 44 

(3) Tailgate entries located below isolated 

gateroads experienced several roof falls. 

Numerous tensioned cable bolts were 

installed on 4 foot centers. 

12 1200 7.3 TGL 0.52 201 80 6.0 ISO 0.34 5 50.3 25 44 

(3) During face recovery, tailgate entries 

situated below isolated gateroads 

experienced excessive floor heave and 

roof falls. 

13 1200 6.9 HGL 1.18 176 59 6.0 BL 0.95 5.8 25.1 32 63 (4) During panel recovery, 500 ft of 

tailgate closed. 

14 800 6.1 TGL 1.30 180 62 6.0 BL 1.88 3.4 25.7 33 54 (4) During panel recovery, 1200 ft of the 

headgate entry heaved closed. 

15 1000 6.3 HGL 1.49 199 72 6.5 ISO 0.78 4 33.2 0 47 (5) During panel recovery, the tailgate 

squeezed closed under a headgate. 

16 1000 6.2 BL 1.46 178 71 6.0 BL 1.42 4.6 35.6 58 71 (5) During panel recovery, 750 ft of a 4 

entry bleeder system squeezed shut. 

17 1200 5.8 HGL 1.44 192 66 6.0 BL 0.86 5.3 32 76 44 

(5) The headgate squeezed closed 

beneath bleeder entries after panel 

extraction. 

18 1181 6.8 LW 

Face N/A 192 66 6.0 ISO 0.73 5.2 32 14 44 (2) Two feet of face heave occurred while 

mining under isolated gateroads. 

19 1000 6.7 LW 

Face N/A 199 72 6.5 ISO 0.69 4 33.2 0 47 (2) Two feet of face heave occurred while 

mining under isolated gateroads. 

20 675 7.6 LW 

Face N/A 199 72 6.5 ISO 1.77 2.4 33.2 0 47 (2) Two feet of face heave occurred while 

mining under isolated gateroads. 

21 1200 5.7 LW 

Face N/A 178 79 5.1 LC2 15.86 5.7 44.5 63 62 (5) Longwall face went on squeeze under 

a gob/barrier pillar boundary. 

22 1200 6.6 LW 

Face N/A 213 71 6.5 BL 1.22 4.6 35.5 90 44 

(5) Roof falls and weight on the face 

halted recovery under bleeder/gob 

boundary. 
86

 Legend Rating Scale 

Angle Intersection Angle 1

BL Bleeder Loading 

Panel was developed and retreat mined with little or noevidence 

of multiple seam interactions. 

CMRR Coal Mine Roof Rating 

COMP Competent 2

DEV Development Loading 

H Mining Height (ft) 

Panel was developed and retreat mined with minor to moderate 

floor heave (less than 2 feet) and/or rib sloughage (less than 4 

feet). Infrequent roof falls may also have occurred. 

h Overburden (ft) 

HGL Headgate Loading 3

INT Interburden Thickness (ft) 

Panel was developed with minor difficulties. On retreat, pillars 

were occassionally abandoned due to roof falls and/or heavy 

pillar loading. 

ISO Isolated Loading 

LC Loading Condition 2 (ARMPS) 4

LC2 Loading Condition 

Panel was developed with greater difficulties and several pillars 

were lost on retreat due to adverse conditions. 

LW Longwall 

N/A Not Applicable 5

SF Stability Factor 

Panel was extremely difficult to advance and could not be retreat 

mined. 

TGL Tailgate Loading 

# Beds Number of Beds in Interburden 6

% Percentage 

Ground conditions necessitated that the panel be abandoned on 

development or deteriorating conditions over time closed the 

section