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5.3 Slone Stability Analysis Model Parameters <br />The purpose of the slope stability analysis was to investigate the <br />potential for: <br />• A deeply seated catastrophic landslide where the failure plane <br />would emanate at the southern rim of the upper refuse bench and <br />terminate at the North Fork of the Gunnison River; <br />• A deeply seated landslide where the failure plane would include <br />passing through the mined out F-seam; <br />• Shallow failure which could endanger the WEM main portal <br />bench; and <br />• Shallow failure of the coal refuse pile. <br />Borehole logs from SOM-7, SOM-8, SOM-127H, and SOM-13, together <br />with aerial photogrammetric maps and ground surveys were used to generate <br />the geologic cross-section employed for slope stability modelling. The cross- <br />section, Figure 5, shows the detail layering of Mesaverde formation sandstone, <br />shale, and coal seams, along with colluvial slope wash overburden and <br />groundwater ree me. The cross-section orientation was selected to align with <br />the maximum topographic gradient, as well as the northeasterly dipping <br />stratigraphy. Boundary coordinates for the geologic strata were entered into <br />a digital computer file to perform the slope stability analysis. <br />Searches for the minimum factor of safety (FOS) were performed using <br />computer softlvare XST.~BL Version 4.1 (released in 1992), written and used <br />for all slope stability and design performed by U.S. Department of Agriculture <br />(USDA) Forest Service engineers and geologists. The analytical portion of <br />XSTABL is a modified version of STABL4 written by the Purdue University <br />Civil Engineering Department, Nest Lafayette, Indiana. The slope stability <br />8 <br />