Laserfiche WebLink
~ i <br />non to low plastic, soft to medium stiff, moist to very moist and black to dark brown in color. A sample of the • <br />sills and clays classified as a ML-CL soil in accordance with the Unified Soil Classification System. An <br />unconfined compressive strength test was conducted on a relatively undisturbed sample of the silts and clays. The <br />test results indicate that these materials exhibited an unconfined compressive strength value of 700 psf. <br />Natural sands artd gravels with occasional interbedded sand lenses were encountered below the topsoil and silt <br />materials in all of the test holes. The sands and gravels were clean to silty, fine to coazse grained with cobbles <br />and occasional boulders, non plastic, medium dense to dense, moist to wet and brown to gray in color. Samples <br />of the sands ar~d gravels classified as GP, GP-SP and SP-SM soils in accordance with the Unified Soil <br />Classification System. <br />Occasional sand lenses were also encountered as interbeds within the natural sands and gravels. The sand.lenses <br />were encountered mainly in the southern portion of the site (see test hole logs IA, 2A & 3A) and ranged from 2 to <br />3 feet in thicltness. The sands were generally clean to slightly silty, fine [o coazse grained with occasional <br />gravels, non plastic, medium dense, wet and light brown to brown in color. A sample of the sands classified as <br />an SP soil in accordance with the Unified Soil Classification System. A direct sheaz test conducted on a sample of <br />the sands indicates that the this material will exhibit an ultimate internal angle of friction (phi angle) of 39.2 <br />degrees under leading conditions similaz to those we anticipate will be encountered during the mining operation. <br />The direct shear test results are shown in Appendix A. • <br />Free groundwater was encountered in all of the test holes and test pits at depWs ranging from approximately 5 and <br />6.5 feet below the existing grotmd surface a[ [he time of [his investigation. It should also be noted that <br />groundwater levels vazied from approximately 5 to 13 feet a[ the time of the previous investigation. Based on <br />these measurements, it appears tbat the groundwater table was encountered at elevations ranging from 6,486 [o <br />6,490 feet at the time of this investigation. It should be noted that groundwater conditions can be expected to <br />fluctuate with changes in precipitation, runoff and the flows in the Yampa River and Trout Creek. <br />SLOPE STABILTTY ANALYSIS <br />To calculate the overall theoretical stability of [he cut slopes to be constructed during the mining operations, the <br />slope stability program SB-SLOPE was employed. This program is a comprehensive slope stability program for <br />microcomputers which uses the "Simplified Bishop Method of Slices" to calculate theoretical factors of safety <br />against slope failure for given slope configurations, soil strength and unit weigh[ values, as well as groundwater <br />levels. The cut slope analyses and data aze presented in Appendix B and a discussion and summary of the results <br />are discussed bt:low. <br />The soil strength parameters used during the stability analysis were obtained from the laboratory tests conducted <br />on a relatively undisturbed sample of the natural silt and clay materials and on a remolded sample of the natural • <br />Job No. W-0304 Northwest Colorado Consultants, Inc. Page 4 <br />