Post on 24-Feb-2016
description
The Ground Response Curve, Pillar Loadingand Pillar Failure
G.S. (Essie) EsterhuizenChris MarkMichael Murphy
The findings and conclusions in this presentation are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.
Background
• Review of retreat pillar mining• Role of overburden response
in loading and failure of pillars
Gob
Gob
Gob
• Overburden response• Pillar loading• Pillar failure
Overburden response
Stiff strong overburden Weak-soft overburden
Overburden response can determine whether pillars fail or not
Well developed pressure arch Poorly developed pressure arch
Stre
ss
Overburden stress
Convergence20%0 10% 30%
1600
Weak
Overburden behavior can be represented by a “ground response curve”
Strong
Load transferred to abutments
by arching
Load carried by internal supports
Load transferred to abutmentsby arching
Ground response curves can be estimated using realistic numerical models
Extraction panels
Coal bed
3500 ft
2500 ft
Strong beds
Ground response development conditions
Ground response recorded at center of panel
2,000
1,500
1,000
500
0
Stre
ss (p
si)
Overburden stress
Convergence (inches)0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Width 80 ft
Effect of panel width on ground response Development conditions - Depth 1500 ft - Western US geology
2,000
1,500
1,000
500
0
Stre
ss (p
si)
Overburden stress
Convergence (inches)0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Width 80 ft
Width 150 ft
Effect of panel width on ground response Development conditions - Depth 1500 ft - Western US geology
2,000
1,500
1,000
500
0
Stre
ss (p
si)
Overburden stress
Convergence (inches)0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Width 80 ft
Width 150 ftWidth 250 ft
Effect of panel width on ground response Development conditions - Depth 1500 ft - Western US geology
2,000
1,500
1,000
500
0
Stre
ss (p
si)
Overburden stress
Convergence (inches)0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Width 80 ft
Width 150 ftWidth 250 ft
Width 500 ft
Effect of panel width on ground response Development conditions - Depth 1500 ft - Western US geology
2,000
1,500
1,000
500
0
Stre
ss (p
si)
Overburden stress
Convergence (inches)0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Width 1000 ft
Width 80 ft
Width 150 ftWidth 250 ft
Width 500 ft
Effect of panel width on ground response Development conditions - Depth 1500 ft - Western US geology
Ground response at the pillar extraction line
Ground response was recorded at center of extraction line
Gob
Extraction line
Ground response at the pillar extraction line Panel width 500 ft at 1500 ft depth – Western US geology
0.05 0.10 0.15 0.20 0.25 0.30 0.35
Stre
ss (M
Pa)
Convergence (m)
At extraction line
Development conditions
6,000
4,500
3,000
1,500
0
Stre
ss (p
si)
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Convergence (inches)
Overburden stress
Pillar response
Pillar response curves
0.0
3.4
6.9
10.3
13.8
17.2
20.7
24.1
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
3,500
3,000
2,500
2,000
1,500
1,000
500
0.0
W:H = 6
W:H = 8
W:H = 4
W:H = 3
Stre
ss (p
si)
Distributed stress over entire panel
Combined pillar and ground response curvesPillar W:H = 8
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
2,000
1,800
1,500
1,200
900
600
300
0.0
W:H = 8
Stre
ss (p
si)
Overburden stress
Effect of panel width on pillar loadingPillar W:H = 8
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
2,000
1,800
1,500
1,200
900
600
300
0.0
W:H = 8
Stre
ss (p
si)
Overburden stress
Effect of panel width on pillar loadingPillar W:H = 8
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 100 200 300 400 500 600 700 800 900 1000
Perc
enta
ge o
f ove
rbur
den
stre
ss
Panel width (ft)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
2,000
1,800
1,500
1,200
900
600
300
0.0
W:H = 6
Stre
ss (p
si)
Effect of panel width on pillar loadingPillar W:H = 6
Overburden stress
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
2,000
1,800
1,500
1,200
900
600
300
0.0
W:H = 3
Stre
ss(p
si)
Effect of panel width on pillar loadingYield pillar W:H = 3
Overburden stress
80 ft
0.0
3.4
6.9
10.3
13.8
17.2
20.7
24.1
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
3,500
3,000
2,500
2,000
1,500
1,000
500
0.0
W:H = 8
Stre
ss (p
si)
Extraction line
Development
Pillar loading at the extraction line500 ft wide panel at 1500 ft depth Western US geology
0.0
3.4
6.9
10.3
13.8
17.2
20.7
24.1
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
3,500
3,000
2,500
2,000
1,500
1,000
500
0.0
W:H = 8
Stre
ss (p
si)
Pillar loading at the extraction line500 ft wide panel at 1500 ft depth Western US geology
Extraction line
Development
0.0
3.4
6.9
10.3
13.8
17.2
20.7
24.1
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
3,500
3,000
2,500
2,000
1,500
1,000
500
0.0
W:H = 6
W:H = 8
Stre
ss (p
si)
Pillar loading at the extraction line500 ft wide panel at 1500 ft depth Western US geology
Extraction line
Development
0.0
3.4
6.9
10.3
13.8
17.2
20.7
24.1
0% 2% 4% 6% 8% 10%
Stre
ss (p
si)
Convergence
3,500
3,000
2,500
2,000
1,500
1,000
500
0.0
W:H = 6
W:H = 8
W:H = 4
Stre
ss (p
si)
Pillar loading at the extraction line500 ft wide panel at 1500 ft depth Western US geology
Extraction line
Development
Pillar failure
Structural failure of pillars
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0.0% 2.0% 4.0% 6.0% 8.0% 10.0%
Stre
ss (M
Pa)
Convergence
W:H = 6
Structural strength = peak resistance
Structural failure
Functional failure of pillars
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10%
Stre
ss (M
Pa)
Strain
Functional failure
Convergence
Conclusions
• Ground response and pressure arch formation are affected by:– Rock stiffness and strength– Panel width
• Ground response affects:– Pillar loading– Ultimate success/failure of pillars
• Ground response evaluation has demonstrated:– Importance of panel width on success of pillar mining– Structural failure of pillars does not necessarily imply functional failure– Functional failure appears to be related to ultimate pillar strain (%conv)