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~ • <br />occurring between the overburden clays ands underlying sands and gravels and a factor of safety of 1.29 was <br />determined for a surface failure (sloughing) occurring in the sands and gravels. <br />The minimum calculated theoretical factor of safety for the cut slopes excavated to a l (horizontal) to 1 (vertical) <br />configuration will be 1.71 under static conditions for an overall slope failure occurring at the top of the cut slope. <br />A minimum factor of safety of 1.01 was determined for a surface failure (sloughing) occurring in [he sands and <br />gravels. <br />Generally, a minimum theoretical factor of safety ranging from 1.3 to 1.5 is desirable for cu[ slopes. A factor of <br />safety of less than l.3 but greater than l.0 indicates some degree of risk of failure and a theoretical factor of <br />~ safety of less than 1.0 indicates the slope will probably fail. <br />Based on the above results, we recommend that the cut slopes constructed in the [Wining azea be excavated no <br />steeper than to a 1(horizontal) : 1(vertical) slope configuration. This recommendation is for temporary cut slopes <br />and is based on the assumption that the excavations will be dewa[ered and that the overburden spoils will be <br />placed back against the excavated slope shortly after the sands and gravels have been removed. If the excavated <br />azeas are not going to be backfilled (reclaimed) shortly after [hey aze constructed, then we recommend that they be <br />excavated to a 2(horizontal) : 1(vertical) slope configuration. <br />To prevent damage to the existing gas line easement which crosses the site and the existing fencelines which are <br />situated along the north, south and west property lines, from the excavation operations and minor sloughing of the <br />topsoil layer, we recommend that the top of the cut slope be simated at least 5 feet from the edge of the easement <br />or fencelines. <br />It is our understanding that the pit excavations will be filled in with the overburden spoils and that the final slope <br />configuration will be 3(horizontal) 1(vertical) or flatter. Based on our experience with similaz projects, we <br />believe that the slopes constructed to a 3(horizontal) : 1(vertical) slope configuration should be stable as long as <br />~ the fill materials aze adequately compacted and well drained. We recommend that the spoils be compacted [o at <br />least 85 % of the maximum modified Proctor density. <br />HAUL ROAD RECOMII~NDATTONS <br />Based on our experience with similaz projects, the proposed traffic loads and the subsurface conditions <br />encountered a[ the site, we recommend that the haul road be constructed with a structural section consisting of a[ <br />least 2 feet of properly compacted pit run sand and gravel fill materials. The sands and gravels excavated from <br />the proposed pi[ will be suitable for use in the haul road. <br />• lob No. 9g-35114 Northwest Colondo Consultants, Inc. Page 6 <br />