U. S. Department of the Interior 

Mission Statement 

As the Nation's principal conservation agency, the Department of 

the Interior has responsibility for most of our nationally-owned 

public lands and natural resources. This includes fostering 

sound use of our land and water resources; protecting our fish, 

wildlife, and biological diversity; preserving the environmental 

and cultural values of our national parks and historical places; and 

providing for the enjoyment of life through outdoor recreation. 

The Department assesses our energy and mineral resources and 

works to ensure that their development is in the best interests of 

all our people by encouraging stewardship and citizen participation in their care. The Department also has a major responsibility 

for American Indian reservation communities and for people who 

live in island territories under U.S. administration. 
Report of Investigations 9552 

Timing and Duration of Subsidence 

Due to Longwall Mining 

By Paul W. Jeran and Michael A. Trevits 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Bruce Babbitt, Secretary 

BUREAU OF MINES 

Rhea Lydia Graham, Director 
International Standard Serial Number 

ISSN 1066-5552 
CONTENTS 

bbstract ........................................................................... Introduction ........................................................................ Fieldstudies ........................................................................ IDeformations ....................................................................... Summary .......................................................................... I References ......................................................................... 

1 ILLUSTRATIONS 

Monitoringarray ................................................................. Subsidence during long-term study versus time ........................................... Subsidence during first 60 days ....................................................... Final subsidence versus face position .................................................. Final subsidence versus time ........................................................ Locationofmines ................................................................ Faceadvances ................................................................... Subsidence at centerline points versus time .............................................. Subsidence at centerline points versus face position ........................................ Subsidence at centerline points versus face position-overburden ratio ........................... Subsidence 30.48 m from centerline versus time .......................................... Subsidence 30.48 m from centerline versus face position .................................... Subsidence 30.48 m from centerline versus face position-overburden ratio ....................... Subsidence 30.48 m inside rib versus time ............................................... Subsidence 30.48 m inside rib versus face position ......................................... Subsidence 30.48 m inside rib versus face position-overburden ratio ............................ Subsidence at rib points versus time ................................................... Subsidence at rib points versus face position ............................................. Subsidence at rib points versus face position-overburden ratio ................................ Inclination difference at mine A ...................................................... Inclination difference at mine B ...................................................... Inclination difference at mine C ...................................................... Inclination difference at mine D ...................................................... 

1 TABLE 

1 1 . Study sites information ............................................................ 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

Metric Units 

m meter mm/m millimeter per minute 

m/d meter per day Pet percent 

U. S. Customary Units 

ft foot ft/d foot per day 
TIMING AND DURATION OF SUBSIDENCE DUE TO LONGWALL MINING 

By Paul W. ~eran' and Michael A. rev its* 

ABSTRACT 

Subsidence data gathered by the U.S. Bureau of Mines over a series of longwall panels in the 

Pittsburgh Coalbed were studied to obtain insight as to the role of time in the subsidence process. It 

was found that subsidence began essentially with undermining and was completed within 1 year. The 

progress of the subsidence was dependent upon location above the panel. Subsidence in the central area 

of the subsidence trough, where subsidence is the greatest, was about 90 pct complete by the time the 

face had progressed a distance equal to one overburden thickness beyond a particular surface point. 

For a point over the rib of the longwall panel, the subsidence was only about 60 pct complete at this 

time. Data from three other sites in the northern Appalachian Coal Basin were analyzed to determine 

if an anomaly or the true characteristics of the subsidence process had been observed. All sites behaved 

similarly in the central portion of the subsidence trough. However, the subsidence of points over and 

adjacent to the ribs of the longwall panels was site specific. The fact that movement across the width 

of the panel was not uniform should be taken into account in assessing damages or the potential for 

damages resulting from mining-induced subsidence. 

'~eolo~ist. 

2~upe~sory geologist. 

Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

The mining of a large rectangular block of coal by the 

longwall method results in the development of a troughshaped depression of the surface above the extracted area. 

The process of subsidence is dynamic, as surface movement begins with undermining and continues until some 

maximum displacement has occurred; the magnitude of the 

displacement is controlled primarily by the thickness of the 

extraction, the width of the panel, and the overburden 

thickness and geology. At the end of the subsidence process, equilibrium is achieved and the resulting surface deformations become static. Any subsequent movement of 

the surface results not from subsidence but from the altering of the conditions affecting the rock strata disturbed by 

subsidence (e.g., injection or removal of fluids, erection of 

structures). 

During any discussion of potential subsidence with longwall mine operators and particularly with surface property 

owners, several questions always arise: How much subsidence will occur? What will be affecte.d? When will subsidence begin? How long will the process of subsidence 

last? Answers to the first two questions can be estimated 

using the geometry of mining as input into the U.S. Bureau of Mines (USBM) subsidence prediction model for 

the northern Appalachian Coal Field The latter two 

questions are the subject of this report. 

Subsidence monitoring is typically carried out in two 

directions: along the centerline of the panel to obtain 

data that will show the maximum amount of subsidence 

and the duration of the dynamic phase of movement and 

across the panel (perpendicular to the centerline) to 

evaluate the lateral extent of surface deformations, the 

final cross section of the developed subsidence trough, and 

the distribution of final deformations. These are the static 

result of the subsidence process, and any further movement must be attributed to some other cause. 

Subsidence prediction is typically limited to the final 

shape of the subsidence trough. Practically all predictive 

models address this aspect of mining-induced ground 

movement. 

Study of subsidence data gathered along the centerlines 

of a number of longwall panels in the northern Appalachian Coal Basin, by Adamek and Jeran (2), has shown that 

the subsidence process starts with the undermining of a 

surface point and is 90 pct completed by the time the 

longwall face has been advanced a distance equal to the 

thickness of the overburden beyond that point. Adamek 

and Jeran determined that the speed with which the face 

is advanced has no effect on the magnitude of surface 

deformations, the final movement is usually achieved with 

mining of the adjacent panel, and the magnitude of surface 

deformations that occur during dynamic subsidence is 

always less than the magnitude of the static case (2). 

Examination of manmade features on the surface has 

shown that they are affected by the forces applied to them 

throughout the subsidence process. Therefore, the final 

static shape of the subsidence trough cannot be used to 

fully explain the degradation of the surface features or how 

they came to their final condition. It has also been observed that the degree of degradation is dependent upon 

location within the subsidence trough (3). 

This report presents results from continuing studies on 

subsidence, in particular on its timing and duration. This 

work is in support of the USBM mission to mitigate the 

environmental impacts of mining. 

FIELD STUDIES 

Lfm~Temz study 

As has been noted above, the description of dynamic 

subsidence has been limited to movement along the centerline. However, does this behavior occur equally across 

the developing subsidence trough? To obtain some insight 

into this question, long-term subsidence data were needed. 

At one site in northern West Virginia, the USBM monitored a series of longwall panels in the Pittsburgh Coalbed, 

remote from previous high-extraction mining. Monitoring 

was conducted for over 2 years, during which time four 

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

adjacent longwall panels were mined. Surface monuments 

were installed over the first three panels (figure I), and 

monitoring was conducted over the portions of the array 

that were actively moving because of undermining. Periodic measurements were also made of the priorly undermined portions of the array to determine final movement. 

Above the first two panels, no further vertical movement 

was detected after the subsequent adjacent panel was 

mined (4). 

To simphfy the analysis, four monuments across the 

first panel, as shown in figure 1, were selected: A, above 

the centerline, B, 30.48 m (100 ft) from the centerline, C, 

30.48 m (100 ft) inside the rib abutting the barrier pillar, 

at the end of this report. 
dermining. After that period, the two central monuments 

(A and B) behaved similarly and the behavior of the monument 30.48 m (100 ft) inside the rib (C) lagged slightly 

behind. The rib monument (D) behaved differently. 

From the above, it can be concluded that subsidence of 

the monuments within the panel limits is governed by face 

position and time. Subsidence of the monument over the 

rib, after its initial movement, is governed more by time. 

Since these observations represent information from 

only one site, other sites, with shorter durations of study, 

were investigated to confirm or deny our observations. 

overburden thickness (2), a slower rate of subsidence for 

mine B could be the expected result. When the percentage of final subsidence was plotted against face position 

(figure 9), mines A and B (Pittsburgh Coalbed) were in 

agreement, with mines C and D differing. It should be 

noted, however, that mines C and D had lesser overburden 

thicknesses. When plotted against face position in terms 

of overburden thickness (figure lo), all sites were in closer 

agreement. Note, in figure 10, for the centerline monuments, subsidence at all sites was about 90 pct complete 

when the face had advanced the thickness of the overburden beyond the monument location. These observations 

agree with the findings of the earlier study by Adamek and 

Jeran (2). 

Table 1.--Study sites information 

Panel 

Mine width 

m fi 

A .. . . . 190.5 625 

8 . . . . . 182.9 600 

C . . . . . 289.6 950 

D . . . . . 182.9 600 

Over- Average 

burden face advance Coalbed 

m ft m/d R/d 

210.3-213.4 690-700 6.55 21.5 Pittsburgh. 

277.4-298.7 91 0-980 3.05 10.0 Pittsburgh. 

118.9126.5 3-15 4.94 16.2 Kittanning. 

143.3-155.4 470-510 11 -83 38.8 Freeport. 
The same plots were made for the monuments 30.48 m 

(100 ft) from the centerline for the four sites under study 

(figures 11-13). Again, as for the centerline points, the 

plot of subsidence versus face position in terms of overburden thickness shows the closest agreement, and again, 

over 90 pct of the final subsidence was completed when 

the face had advanced the thickness of the overburden past 

each point. 

Plots for subsidence at the monuments 30.48 m (100 ft) 

inside the rib versus time and face position (figures 14-15) 

are similar to those for the more centrally located monuments. However, the plot of the percentage of final subsidence versus face position-overburden ratio (figure 16) 

shows that this location at mine D lagged behind the same 

location at the other three mines, indicating retardation 

of the subsidence process. The overburden at this site 

I 

I Panel 1 I 

I I 

I1 I Panel 2 1 1 

contains ~i~cantly more and thicker sandstone units. 

These stiffer members bridge farther over the gob than the 

less resistant strata at the other sites. Additional time is 

needed for the stiffer units to bend into the gob area. 

The similar plots for the rib monuments (figures 17-19) 

show a different characteristic. Plots of the percentage of 

final subsidence versus face position (figure 18) and face 

position in terms of overburden thickness (figure 19) do 

not show the same trends as observed for subsidence at 

the other points. The plot of percentage of final subsidence versus time (figure 17), however, shows that within a 

month of undermining, these monuments had completed 

from 40 to 70 pct of their final subsidence. This indicates 

that the process of subsidence over the rib is very much 

site dependent and time appears to play a very si&icant 

role. 

I 

I Panel 

I 

I 

I T 

Panel 

u 

Scale, m 
15 

\ r/ 

\ 100 - 1 

I \ - - .9 

\ \ : /Monument A 

lo - \& Face, panel I \ \ t - -1.0 

\ \ \ 1 1 I \ I r\ I 1 

0 -1.1 

100 200 300 400 500 600 700 800 

TIME, days 

Subsi&nce cfiuing lovtgtenn study wmus time1 I 1 I I I 1 1 I 1 + 

Monument D - 

- I 

- 

- Monument C - 

- - 

Monuments - undermined - - 

- - 

- - 

- 

- 

I 

- I 1 1 I L 

0 10 20 30 40 50 60 

TIME, days 

Subsidence muingjkt 60 dizys. 
Fip 4 

0 50 100 150 200 2 50 300 

FACE POSITION, m 

1 1 I I 1 I 1 1 I I I I 1 

- 

KEY 

- A 

- -0- c ....... D - 

- - 

- - 

- - 

- - 

- 

Final subsidence versus faeposith. 

Fip 5 

TIME, days 

Final subsidence versus time. 
u 

Scale, miles 

Fi, 7

- KEY - 

- Mine A - 

- Mine 6 - 

+ Mine C - Mine D - 

- 

- - 

- - 

- - 

- 

- 

- 

- 

- 

TIME, days 

Face advances. 
KEY 

- Mine A 

-0-0 Mine B 

-a- Mine C 

a a a a Mine D 

TIME, days 

Subsidence atc~poinb versus rimerime 

KEY 

- Mine A 000- Mine B 

-*- Mine C 

a a a a Mine D 

0 50 1 00 1 50 200 250 300 

FACE POSITION, m 

Subsideme at centertine p&s vlersus face position. 
Fi' 10 

FACE POSITION-OVERBURDEN RATIO 

Subsidence at centerlLte pub& vlersus face posjtiovt-twdM doFi' ll 

KEY 

- Mine A 

---- Mine B 

-0- Mine C ooooooo Mine D 

TIME, days 

Subsidence 30.48 rn jiwn centerline versus time. 
Fipz 12 

0 50 1 00 1 50 200 250 300 

FACE POSITION, m 

I I 1 1 1 I 1 1 1 I r I 

-*.* 1 I 

- 

- - 

- 

- - Mine A - 

---- Mine B - -*- Mine C - 

- . . . . . . a Mine D - 

- - 

- 

- 

- 

I I I I I I I I I I 1 1 1 

Subsidence 30.48 m jiwn cenhdhw versus face position. 

Fipz 13 

- 0.5 0 0.5 1 .O 1.5 

FACE POSITION-OVERBURDEN RATIO 

1 

- 

- - KEY 

Mine A 

- 

- 00.. Mine B 

-a- Mine C - 

- ..mamma Mine D - 

- - 

- - 

- - 

- - 

- - 

C ......a - f - 

1 I I I I I 1 1 

Subsidence 30.48 m jiwn centerIine vmsus face position-overburden mtio. 
- 

KEY 

Mine A 

-000 Mine B 

-*- Mine C 

....... Mine D 

TIME, days 

Subdime 30.48 m inside rib vmw limeFi' 15 

I 1 1 I 1 1 I 1 1 I 1 I I 

- pa-.-*-• I 

- 

- 

- - 

- - 

- - 

- Mine A 

- 0 0 0- Mine B - 

- -*- Mine C ....... Mine D - 

- - 

- 

- 

.. 1 I I 1 1 I 1 I 1 I 1 I 1 . - 

- 50 0 50 1 00 1 50 200 250 300 

FACE POSITION, m 

Subdime 30.48 m inside rib versus fme podium 
Figure 16 

KEY 

- Mine A 

-0-0 Mine 6 

-0- Mine C 

....... Mine D 

FACE POSITION-OVERBURDEN RATIO 

Subdimce 30.48 rn inside rib versus face position&M mtio. 

Figure 17 

-40 -30 -20 -10 0 10 20 30 40 50 

TIME, days 

I I l'l'lrl'l'l'l' 

- - 

- KEY - 

- Mine A 

- ---- Mine 6 

-.- Mine C - *.***** Mine D 

- 

- 

- - 

- - 

- - 

**. . - - 

Subdhce at rib pi& wmu time. 
Figam 18 

100 I I I I 1 I 1 I 1 I I I 

90 - - 

KEY 80 - - Mine A C 0-0- g 70- Mine B 

-*- Mine C 

60- eeeoeeo Mine D 

- 

V) 

1 30 - - 

- 

- 

- 

-50 0 50 1 00 1 50 2 00 250 300 

FACE POSITION, m 

Subdknce at rib points vmw fmepdoa 

Figam 19 

100 - 1 I 1 1 1 I 1 1 I I 1 

90 - - 

80 - KEY 

- Mine A t 

g 70- ---- Mine B 

-*- Mine C 

60- *.**..* Mine D 

Z 

50- s - 

V) 

40 - 

v> 

1 30 - 

a 

- 20- 

LL 

- 

- 

- 

-1 .O -0.5 0 0.5 1 .O 1.5 2 .O 

FACE POSITION-OVERBURDEN RATIO 

Subsidence at rib points versus fme position+vetburden nab. 
E + FP/H = 1.0 

\ 

E 12 - -*- Final 

E 

il0 - 

8- 

- z 

6 =- 

Z - 

4 - 

2 - 

i 

lh'z'K///',l ////;////'I /"l I / / 

I I I I 

-225 -200 -175 -150 -125 -100 -75 -50 -25 0 

LOCATION, m 

Ix1-n a3jJme ai mine A. (FP/N = face position+durden mtio-) 
,200 -150 -100 -50 0 50 100 150 200 250 300 

LOCATION, m 

-0- FP/H = 1.0 

- +- Final 

Inc- d@me at mine C (FP/H = facejmiiion-ovwbwden ralio.) 
I I 1 I 1 I I I I 1 1 r 

- fi - 

- 1 \ 

KEY - 

- + FP/H = 1.0 - 

-*- Final - 

- 

- 

d 

- 

- 

- 

- 

- - 

- - 

- 

- 

0 20 40 60 80 1 00 1 20 140 

LOCATION, m 

Im&u&on d$ktmce at mine D. (FPD = foce position-ove~wden mtio.) 

SUMMARY 

Subsidence data from four sites in the northern Appalachian Coal Basin were studied. These data show that for 

locations in the central portion of the developing subsidence trough (within 30.48 m (100 ft) of the centerline) 

subsidence develops relative to face position and overburden thickness and is about 90 pct complete when the 

face has advanced the thickness of the overburden beyond 

the point in question. Above the rib of the panel the process of subsidence is very much site dependent and time appears to play a si@icant role, in that when the face has 

advanced the thickness of the overburden past a monument only 40 to 70 pct of the movement has taken place. 

The remainder of the surface movement, irrespective of 

location above the longwall panel, takes up to a year to 

complete. 

The monuments 30.48 m (100 ft) inside the rib exhibited movements that were characteristically between those 

of the centerline and rib area monuments. With slow to 

moderate face advance (3.05 to 6.55 m/d), the subsidence 

process was similar to that over the central portion of the 

panel, with over 80 pct of the final movement completed 

when the face had advanced the thickness of the overburden past a monument. However, with fast face advance 

(11.83 m/d), there appeared to be some retardation or lag 

in the subsidence process. 

At the sites studied, the preponderance of the surface 

deformations had occurred by the time that the longwall 

face had been mined one overburden thickness past each 

profile. The additional deformations were small. All 

of these factors should be taken into account in assessing damages or the potential for damages resulting from 

mining-induced subsidence. 
REFERENCES 

1. Jeran, P. W., V. Adamek, and M. A. Trevits. A Subsidence 

Prediction Model for Longwall Mine Design. Paper in Proceedings of 

the Longwall USA Conference (Pittsburgh, PA, June 1986). Maclean 

Hunter Publ., 1986, pp. 101-112. 

2. Adamek, V., P. W. Jeran, and M. A. Trevits. Static and Dynamic 

Subsidence Prediction in the Northern Appalachian Ckal Region Based 

on the Use of a Variable Subsidence Coefficient. Paper in Proceedings 

3rd Workshop on Subsidence Due to Underground Mining (WV Univ., 

Morgantown, WV, June 1-5, 1992). WV Univ., 1992, pp. 10-21. 

3. Walker, J. S., and M. A. Trevits. Effects of Longwall Mining on 

Surface Structures. Paper in Proceedings Mine Subsidence-Prediction 

and Control (33rd Annu. Meet. Assoc. Eng. Geol., Pittsburgh, PA, Oct. 

1990). AAPG, 1990, pp. 141-143. 

4. Jeran, P. W., and V. Adamek. Subsidence Due to Undermining 

of Sloping Terrain: A Case Study. USBM RI 9205, 1988, 10 pp. 

5. Adamek, V., and P. W. Jeran. Evaluation of Surface Deformation 

Characteristics Over Longwall Panels in the Northern Appalachian Coalfield. Paper in Proceedings of First Conference on State-of-the-Art of 

Ground Control in Longwall Mining and Mining Subsidence (Honolulu, 

HI, Sept. 5-9, 1982). Soc. Min. Eng. AIME, 1982, pp. 18S198.