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GEOTECHNICAL REVIEW OF LOW WALL PIT XY
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DATE : 4/21/2009
AGENDA : Review of Low Wall PIT XY Slope Stability Failure
AREA :
SEAM TARGET : C 8
PICTURE :
GEOTECHNICAL ROCK PROPERTIES DATA :
No MaterialsUnit
Weight
InternalFriction
Angle
Cohesion
1 Top Soil 23.10 35.00 36.90
2 Upper Burden Seam C8 22.40 12.90 83.00
3 Seam C8 13.90 21.40 57.00
4 Inner Burden Seam C8-C9 20.60 10.60
42.00
5 Seam C9 15.10 36.10 215.00
6 Inner Burden Seam C9-C10 20.90 26.10
190.00
7 Seam C10 15.10 36.10 215.00
8 Inner Burden Seam C10-C11 23.60 21.90
106.00
9 Seam C11 15.10 36.10 215.00
10 Under Burden Seam C11 21.30 22.00
113.00
11 Water 9.087 - -
12 Road Embankment 17.00 16.00 86.29
Note :
1 Pressure from Dump Truck 785 = 77.943 kPa or 7.948 ton/m2
(full capasity)
33.009 kPa or 3.366 ton/m2 (empty)
2 Horizontal seismic load (model) = 0.02
Picture 1. Cross section of Plan Base PIT XY f rom Mine Plan
Dept. (not on true scale)
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EXPLAINED :
1. Low Wall slope face angle range from 12 degree to 14
degree
2. Calculation not including yet vertical pressure from heavy
vehicle (Dump Truck HD 785)
3. Inner Burden Seam C8-C9 controlled by Mudstone with saturated
condition
4. Seismic load 0.02
5. Slope stability calculation by Slope/W and Bishop Method
6. Resulting of Safety Factor (SF) 1.576
7. With SF number 1.576 indicated Low Wall PIT XY still in safe
condition for further coal mine but need some rules :
a. Execution must be based on plane base
b. No much more water trap (flooding) in PIT that will be
make cracking and swelling Mudstone
c. Mudstone will become weak layer if too much water by flooding
so increasing moisture water content and swelling
that reducing their cohesion number
d. Materials with small number cohesion will be make
small SF number
e. Vertical pressure by heavy vehicle can be trigger
unstable condition if itsn't make with good design
f. Water surface open drain channel must be design in
order to keep away from over topping and seepage
1.576
Factor of S afety: 1.576Total Activating Moment: 1513900Total
Resisting Moment: 2385300Total Resisting Force:Total weight:
67941Total Volume: 3259.5
FOS LOW WALL PIT 8A EAST BLOCK
Distance (m)
0 100 200 30010
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
E l e v a t i o n ( m )
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
Picture 2. Model of FOS Low Wall PIT XY after finishing coal
mine, condition before push back review design which high walland
low w all slope failure occurrence ( ignore heavy vehicle
pressure)
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EXPLAINED :
1. Low Wall slope face angle range from 12 degree to 14
degree
2. Calculation including vertical pressure from heavy vehicle
(Dump Truck HD 785)
3. Inner Burden Seam C8-C9 controlled by Mudstone with saturated
condition
4. Seismic load 0.02
5. Slope stability calculation by Slope/W and Bishop Method
6. Resulting of Safety Factor (SF) 1.373
7. With SF number 1.373 indicated Low Wall PIT XY still in safe
condition for further coal mine like model below :
a. Hauling construction based on plane base (70 meter
eastern section from exisiting)
b. Vertical pressure by heavy vehicle 77.43 kPa
c. Water infiltration model under Seam C8 or Mudstone
roof
COMPARISON PLAN BASE AND EXISTING MODEL PIT 8A EAST BLOCK
PLAN BASE
1.373Factor of Safety: 1.373Total Activating Moment: 266390
Total Resisting Moment: 365740
Total weight: 25341
Total Volume: 1224.2
Horz Seismic Load: 2.e-002
Distance (m)
40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
380 400 420 4405
10
15
20
2530
35
40
45
50
55
60
65
70
75
80
85
E l e v a t i o n ( m )
5
10
15
20
2530
35
40
45
50
55
60
65
70
75
80
85
Picture 3. Model of FOS Low Wall PIT XY based on exsiting
condition and original plan base of hauling road and surfacewater
open drain channel
Hauling Plan
Surface Water open drain channel
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EXPLAINED :
1. Low Wall slope face angle range from 12 degree to 14
degree
2. Calculation including vertical pressure from heavy vehicle
(Dump Truck HD 785)
3. Inner Burden Seam C8-C9 controlled by Mudstone with saturated
condition
4. Seismic load 0.02
5. Slope stability calculation by Slope/W and Bishop Method6.
Resulting of Safety Factor (SF) 1.064
7. With SF number 1.064 indicated Low Wall PIT XY in unsafe
condition for further coal mine like model below :
a. Hauling construction out of plan based and closely top
of Low Wall
b. PIT have been flooding until 10 days and made Mudstome
become weak layer
c. Decreasing cohesion number by flooding that increasing
water moisture content made SF become 1.064
so that Low Wall running to sliding (Slope Failure)
MODEL EXSITING CONDITION WITH PROGRESSIVE HAULING CONSTRUCTION (
70 Meter )
1.064Factor of Safety: 1.064Total Activating Moment: 1020300
Total Resisting Moment: 1085100
Total weight: 51193
Total Volume: 2495.9
Horz Seismic Load: 2.e-002
Distance (m)
40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
380 400 420 440510
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
E l e v a t i o n ( m )
510
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
Picture 4. Model of FOS Low Wall PIT XY based on exsiting
condition with progressive contruction of hauling road from
planbase and PIT Flooding
Hauling Existing
Surface Water open drain channel
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CONTOH MUDSTONE UNTUK PENGAMATAN PADA KONDISI TERENDAM AIR
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TERENDAM 3 HARI
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HASIL SETELAH 6 HARI (TERENDAM 3 HARI)
