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~ . <br />Natural sands and gravels were encountered below the clays and extended to the maximum depth investigated, 48 <br />feet. The sands and gravels were clean to silty, fine to coarse grained with occasional cobbles, non plastic, dense <br />to very dense, moist to wet and brown in color. The sands and gravels classified as SP-GP soils in accordance <br />with the Unified Soil Classification System. The direct sheaz tests conducted on a sample of the sands and gravels <br />indicates that the sands and gravels will exhibit an internal angle of friction (phi angle) of 45.6 degrees under <br />loading conditions similar to those to be encountered during construction of the cut slopes. The direct sheaz test <br />results are shown in Appendix A. <br />Free groundwater was encountered in the test holes drilled during both investigations at depths ranging from 15 to <br />33 fee[ below the existing ground surface. Based on the measurements made by our firm, it appears that the <br />~ groundwater table was encountered at elevations ranging from 6,591 to 6,597 feet at the time of this investigation. <br />It should be noted that groundwater conditions can be expected to Fluctuate with changes in precipitation and <br />mnoff. <br />SLOPE STABII.TTY ANALYSIS <br />To determine the overall theoretical stability of the cut slopes to be constructed during the mining operations, we <br />used the slope stability program SB-SLOPE. This program is a comprehensive slope stability program for <br />microcomputers using the "Simplified Bishop Method of Slices". The slope configurations used in our analysis <br />were obtained from our discussions with the client regarding the proposed slope configurations. The cut slope <br />analyses and data aze presented in Appendix B and a discussion and summary of the results are discussed below. <br />The soil parameters used during the stability analysis were obtained from the laboratory tests conducted on the <br />relatively undisturbed samples of the natural clays and on remolded samples of the sands and gravels obtained <br />from [he test pit. Based on the laboratory test results, we used a unit weight of 125.0 pcf, cohesion value of 900 <br />psf and a internal angle of friction (phi) angle of 0 degrees for the clays. For the namral sands and gravels, we <br />used a unit weight of l40 pcf, a cohesion value of 0 pcf and a internal angle of friction (phi) of 45 degrees. <br />The subsurface profile used in the analyses was considered to be a "worst case" scenario and was assumed to be <br />where the deepest cut will occur in the pit. The subsurface profile used in the analysis consisted of approximately <br />10 feet of clays overlying sands and gravels to the base of the excavation. The elevation of the top of the cut <br />slope was taken as 6,622 feet and the elevation at the toe of the excavation was 6,592 feet. A groundwater <br />elevation of 6,602 feet was also used in the analyses. <br />Based on our calculations and analysis, the minimum calculated theoretical factor of safety for cut slopes <br />excavated [o a 2 (horizontal) to 1 (vertical) configuration will be 2.13 under static conditions for an overall slope <br />failure occurring at the top of the cut slope. A minimum Cactor of safety of 4.12 was determined for a failure <br />• Job No. 98-3504 Northwest COIOrJdO Consultuvns, Inc. Page 5 <br />