2006-06-07_PERMIT FILE - C1996083

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 6/7/2006
• Doc Name: 02/15/2006 Gob Pile #2 Stability Evaluation TR-42 Buckhorn Geotech Inc
• Section_Exhibit Name: Volume IX Coal Waste Disposal Area No. 2
• Media Type: D
• Archive: No

Table 6. Effective Stress Shear Strength Parameters
From CU Triaxial Testing
Sample
Borehole
4'
Cohesion,
ID
ID
(degrees)
c' (psl)
BS -3
N/A
31
330
SH -1
BG05 -05
34
60
SH -2
BG05 -06
33
60
5.0 INSTRUMENTATION MONITORING
Vibrating wire piezometer and inclinometers have been monitored at regular intervals. The
piezometers give an indication of pore pressures with time and are useful for determining the
proper analysis methods (e.g., drained or undrained) and evaluation of strength parameters.
Inclinometers detect subsurface movement and are used as a warning mechanism of slope
movement (or an indication of stable conditions).
5.1 Vibrating Wire Piezometers
Monitoring of the five vibrating wire piezometers has generally been conducted on a monthly
basis and is on- going. Pore pressure readings are illustrated in Figure 1. In general, the initial
pore pressure readings (taken immediately after installation) are observed to be high. For the
first week or so after installed the pore pressures dropped significantly and finally began to
stabilize. The initial high readings are due to the grout in the borehole. As the grout cured, the
pore pressures were observed to decrease. As the pore pressures in the coal waste reached
equilibrium at the transducer, the readings are observed to stabilize. The lag time is largely
related to the hydraulic conductivity of the coal waste.
Stabilized pore pressures range from 2 to 8 psi. The pressures at VWP -02 and VWP -03, located
in the central interior of the gob stockpile are increasing slightly. The pressure at VWP -05,
located near the central toe of the stockpile appears to be decreasing. Pressures at VWP -04,
located at the western interior of the stockpile, have not changed much for the past three months.
As indicated previously, VWP -01 was likely damaged sometime between November 22, 2005
and January 11, 2006. Diagnostic tests performed indicate that the cable has been damaged and
a short has developed. Remediation of this piezometer is considered unlikely. This piezometer
is essential to the monitoring program will need to be replaced.
Bowie No 2 Gob Pile Stability Dec2005
Project #05- 126 -GEO
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