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Positive surface drainage should be provided around all permanent cut and fill slopes to direct surface <br />• drainage away from the slope faces. All cut and fill slopes and other stripped areas should be protected <br />against erosion by revegetation or other methods. We recommend that a maximum of 4-inches of topsoil <br />be placed back over the disturbed slopes. <br />Pavement Section Recommendations <br />Based on the subsurface conditions encountered across the site and our experience with similar projects, we <br />recommend that the haul road be constructed with a composite section consisting of 6 inches of base course <br />gravels overlying a minimum of 18 inches of subbase (pit run) gravels. <br />The base course materials should consist of a well-graded aggregate base course material, which meets <br />CDOT Class 6 or 5 grading and durability requirements. <br />We recommend that the roadway areas be prepared by sub-excavating and re-compacting the existing <br />natural soils to provide uniform support for the gravel sections. We recommend the removal of any topsoil <br />and organic materials from under the roadways. We also recommend that the exposed subgrade materials <br />be scarified to a depth of at least 6 inches and be moisture conditioned to near the optimum moisture <br />content and then be compacted to at least 98% of the maximum standard Proctor density in accordance with <br />ASTM D-698. After the subgrade soils have been properly moisture treated and recompacted, the subgrade <br />should be proof rolled with a heavily loaded pneumatic tired vehicle and any areas which deform <br />excessively under the wheel loads should be removed and replaced or stabilized prior to placement of the <br />gravel sections. <br />Slope Stability Evaluation <br />The stability of proposed cut and embankment fill slopes for the cuttings pit and sedimentation ponds were <br />assessed by computing theoretical factors of safety (against slope failure) for the proposed slope <br />configurations. A factor of safety in this case is calculated by summing the forces resisting slope <br />movement (i.e. soil strength generated along a theoretical failure plane) and dividing that sum by the <br />driving forces of the slope (i.e. the weight or mass of the soil and groundwater). We have chosen a <br />minimum factor of safety of 1.5 for this project, which is the minimum specified factor of safety for Class <br />B or C dams that are full and under steady state seepage saturation conditions. <br />By inputting slope geometry and soil strength values into the slope stability program GEO-SLOPE, <br />strength and geometry values can be easily varied to help assess the factors of safety for the proposed <br />C7 <br />Job Number: 08-8241 NWCC, Inc. Page 9