2017-03-29_REPORT - C1982056

• Permit No: C1982056
• IBM Index Class Name: Report
• Doc Date: 3/29/2017
• Doc Name: Quarterly Subsidence Monitoring Report
• From: Twentymile Coal, LLC
• To: DRMS
• Permit Index Doc Type: Subsidence Report
• Email Name: TNL
• Email Name: DIH
• Media Type: D
• Archive: No

Table 4: CRSP3 Parameter Ranges for Representative Site Conditions
SITE CONDITION
Tan ential Coefficient Restitution Coefficient
Min
Ave Max Min
Ave
Max
Sandstone Cliff Face
0.83
0.85 0.87 0.33
0.35
0.37
Road Pavement
0.83
0.85 0.87 0.33
0.35
0.37
Tallus Covered Upper Foreslo e
0.82
0.835 0.85 0.30
0.315
0.33
Thin Colluvium Overlying Marine
Shales on Upper Foreslo e
0.80
0.835 0.85 0.30
0.315
0.33
Colluvium Covered Lower Foreslo e
0.78
0.805 0.83 0.28
0.29
1 0.30
5. DAMAGE TO THE CLIFF IN THE PHASE I
STUDY AREA
The western limit of the Phase I study area, Zones 1
to 3 experienced cracking, however, no massive
failures were observed during or following under-
mining. Cliff failure occurred several months after
undermining in Phase I Zones 4 and 5. Approxi-
mately twenty boulders were retained by the
remedial trench in Phase I, Zones 4 and 5. Table 5
provides summary data for thirteen of the largest
blocks. Retained boulder size ranged from 10 to 900
tons with an average block weight of 115 tons (1,500
cubic feet). The average boulder weight was 50 tons
(600 cubic feet) when the largest boulder was
removed from consideration.
Table 5: Boulders Retained by the Remedial Trench/Berm
Boulder
Number
Type
Length
Width
Height
Approx.
Volume
(ft3)
Approx.
Mass
(tons)
R1
triangle (3)
34
26
20
12580
944
R2
disk (2)
8
5
4
160
12
R3
cube (1)
13
15
12
2340
176
R4
cube (1)
11
8
7
616
46
R5
disk (2)
6
9
9
486
36
R6
disk (2)
3
4
5
60
5
R7
disk (2)
5
8
7
280
21
R8
cube (1)
6
6
6
216
16
R9
cube 1)
12
16
11
2112
158
R10
triangle (3)
4
7
4.5
126
9
R11
disk (2)
9
9
6
486
36
R12
disk (2)
8
10
5
400
30
R13
cube (1)
2
2
2
8
1
Average
9
10
8
1528
115
Average without 944 ton block
7
8
1 7
608
46
6. REFERENCES
CTI, 1993. Colorado Rockfall Simulation Program
(CRSP), Users Manual for Version 3.0,
Colorado Transportation Institute, December
1993.
Pfeiffer, T.J. and Bowen, T.D. "Computer
Simulation of Rockfalls", Bull. Of Assoc. of
Engineering Geologists, Vol. 26 1989.
Priest, S.D. and Hudson, J. A. "Discontinuity
Spacing in Rock", Int. J. Rock Mech. Min.
Sci. & Geomech. Abstr. Vol. 13,1976.
Priest, S.D. and Hudson, J. A. "Estimation of
Discontinuity Spacing and Trace Length
Using Scanline Surveys", Int. J. Rock Mech.
Min. Sci. & Geomech. Abstr. Vol. 18,1981.
SubTerra, Inc., 1994. Rockfall Hazard Assessment
and Selection of Hazard Control or
Mitigation Measures, report prepared for
Twentymile Coal Company, October, 7,
1994.
TerzaghiI R. D. "Sources of Error In Joint Surveys"
Geotechnique, Vol. 15,1965.