Environmental Engineering Reference
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FIGURE 10.14
Finite-element mesh for coal mine conditions beneath site near Wilkes-Barre, Pennsylvania. (Mabry, R.E.,
Proceedings of ASCE, 14th Symposium on Rock Mechanics, University Park, PA, 1973. With permission.)
TABLE 10.3
Summary of Finite-Element Analysis of Coal Mine Study a
Condition
Safety Factor
Cumulative
Maximum Distortion within Plant Site
against Pillar
Settlement
Angular
Horizontal Strain
Failure
(cm)
Rotation (rad)
( tension)
Weathering in all veins
1.0
20.0
10 6
12.0
10 6
Collapse in Hillman, R
50%
0.80
4.0
3.6
10 −4
1.7
10 −4
Collapse in Mills and
0.89 to 0.99
29.0
3.0
10 −3
10.1
10 −4
40%
Collapse in Mills, R
Hillman, R
30%
1.1
63.2
4.8
10 −3
19.2
10 −4
a
From Mabry, R. E., Proceedings of ASCE, 14th Symposium on Rock Mechanics , University Park, PA, June 1972.
With permission.
10.3.6
Subsidence Prevention and Control and Foundation Support
New Mines
In general, new mines should be excavated on the basis of either total extraction, permitting
collapse to occur during mining operations (if not detrimental to existing overlying struc-
tures), or partial extraction, leaving sufficient pillar sections to prevent collapse and result-
ing subsidence at some future date. Legget (1972) cites the case where the harbor area of the
city of Duisburg, West Germany, was purposely lowered 1.75 m by careful, progressive long-
wall mining of coal seams beneath the city, without damage to overlying structures.
Old Mines
Solutions are based on predicted distortions and their probability of occurrence.
Case 1
No or small surface distortions are anticipated when conditions include adequate pillar
support, or complete collapse has occurred, or the mined coal seam is at substantial depth
overlain by competent rock. Foundations may include mats, doubly reinforced continuous
 
 
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