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results completed on the Hamra] clays and bedrock materials encountered at the site are shown in the <br />attached Table 1. <br />Slone Stability Evaluation: The stability of proposed cut slopes for the pond (2(horizontal) : 1(vertical) was <br />assessed by computing theoretical factors of safet}~ (against slope failure) for the proposed slope configuration. A <br />factor of safety in this case is calculated by summing the forces resisting slope movement (i.e. soil strength <br />generated along a theoretical failure plane) and dividing that sum by the driving forces of the slope (i.e. the weight <br />or mass of the soil and groundwater). We have chosen a minimum factor of safety of 1.5 for this project. By <br />inputting slope geometry and soil strength values into the slope stability program SB-SLOPE, strength and <br />geometry values can be easily varied to help assess the factors of safety for the proposed slopes under varying <br />conditions. This program is a comprehensive slope stabilii< program for microcomputers and uses the "Simplified <br />Bishop Method of Slices" for factor of safety calculations. <br />The strength values used for the overburden soils were obtained from pre~dous strength tests conduced on similaz <br />clay soils for other dam projects in this area. In our analyses, we used a unit weight of 120 pcf, an effective <br />cohesion value of 250 pcf and an effective phi angle of 18 degrees for the Hamra] clays. It should be noted that the <br />values given above are yen' conservative for these types of clays. <br />Based on our calculations and analyses, the minimum calculated theoretical factor of safety for the proposed cut <br />slopes will be 3.95 under static conditions. Generally, z minimum theoretical factor of safety of 1.5 is desirable for <br />these types of slopes. A factor of safety of less than 1.3 but greater than 1.0 indicates some degree of risk of failure <br />and a theoretical factor of safer}' of less than 1.0 indicates the slope will probably fail. The slope stability data and <br />calculations aze shovm in Appendix A. <br />Based on these results, we believe that the proposed cut slopes should be stable at the 2 (Horizontal) to 1 (Vertical) <br />configuration. We strongly recommend that a representative of NWCC observe the cut slopes after they are <br />constmcted to verify that the subsurface/soil conditions aze similaz to those encountered in the test holes. <br />Limitations: This report has been prepared in accordance with generally accepted soil and foundation engineering <br />practices in this azea for use by the client for the construction of the subject sedimentation pond. The conclusions <br />and recommendations submitted in this report are based upon the data obtained from the exploratory test holes <br />advanced during our pre~~ous investigation at the site. The nature and extent of variations between the exploratory <br />test holes may not become evident until the excavations aze completed. If during the construction, the soil, rock <br />and groundwater conditions appear to be different from those described herein, a reevaluation of the <br />recommendations should be made by this office. <br />It is advisable that a c~rtractor familiar with constmction details t}pically used for the local subsoil and climatic <br />conditions be retaine,`,~[`o construct [he structure. If you have any questions regarding this report or if we may be of <br />further service, pleas do not hesitate to contact us. <br />Sincerely; <br />~- "l <br />Brian D. L.E G <br />O~ O ~~' <br />Job Nivnber: OS=Gf~5t1'~A jj ~ ~ ~r,~~p~ NwCC, Inc. Page 2 <br />