PERMFILE50053

• Permit No: C1980001
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: 3.4 BACKFILLING & GRADING
• Media Type: D
• Archive: No

• STABILITY ANALYSIS
Two separate computer programs, SWASE and REAMS were used to
complete the stability analysis for this report. These programs
were developed by Yang H. Huang at the University of Kentucky in
1978 and have been continuously updated and expanded. The SWASE
program is used to determine the factor of safety of a sliding
block failure. The REAME program determines the factor of safety
of a cylindrical failure. Yang H. Huang recommends running the
SWASE and REAMS programs on slopes with an identifiable plane of
weakness to determine which failure surface is more critical. A
minimum acceptable factor of safety of 1.5 was selected for
stability.
Three separate stability analyses were completed to determine
the slope stability of this area. The first stability analysis
was conducted to determine the required slope of the out-of-pit
spoil that would result in a factor of safety of 1.5 or greater.
The factor of safety for the out-of-pit spoil slope was determined
using the REAME computer program. The REAMS (Rotational
Equilibrium Analysis of Multi-layered Embankments) computer
program is used to determine the factor of safety of a slope based
on a cylindrical failure surface and the simplified Bishop method.
A slope of 3:1 was used as a beginning point for determining the
• factor of safety of the out-of-pit spoil material. The soil
properties for the spoil material shown on TABLE 1 were used for
this stability analysis. The factor of safety for the out-of-pit
spoil at a 3:1 slope was calculated to be 1.875 which is well
above the 1.5 minimum factor of safety required. Since this slope
met the stability requirements, additional factor of safety
calculations for flatter slopes were not necessary.
The second stability analysis was completed using the SWASE
computer program to determine the affect the out-of-pit spoil
would have of the factor of safety of the entire slope. The SWASE
(Sliding Wedge Analysis of Sidehill Embankments) computer program
is used to determine the factor of safety of a slope when one or
more planes of weakness exist within the slope. The weak plane
of this slope was found to exist between the interface of the coal
seam and the underclay. Sase on an analysis of the Wadge and the
Lower Wadge seam, the greatest potential for failure in the slope
was at the Wadge seam since it outcrops in the Trout Creek
embankment. WWL has stated in their 1985 stability analysis
report that the angle of the critical slippage plane through the
overburden sandstone and shale is 57 degrees. According to their
report, this angle was determined from field observations,
compiled geologic information, and a random stability analysis.
Based on WWL's research, the critical slippage angle of 57 degrees
was also used in this study for the factor of safety calculations.
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