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• unit weights, grain size analyses and liquid and plastic limits. The laboratory testing was conducted in <br />general accordance with applicable ASTM and AASHTO specifications. <br />The subsurface conditions encountered in the test holes were variable and generally consisted of a layer <br />of topsoil overlying natural silts, days, sands and sandstone bedrock. <br />The topsoil ranged From 1 to 4 1/2 feet in thickness. The near surface subgrade soils encountered <br />beneath [he topsail layer generally consisted of silts and clays. The silts and days extended to depths <br />ranging from 7 to 24 fee[ below the existing ground surface. The silts and days were slightly [o very <br />sandy with occasional gravels, low [o very low plastic, stiff to very stiff, slightly moist to moist and <br />brown in color. The silts and clays generally classified as CL to ML-CL soils in accordance with [he <br />Unified Soil Classification System. The silts and clays will generally provide poor to fair subgrade <br />support for the proposed gravel sections. Free groundwater was no[ encountered in [he test holes at <br />the time of drilling. <br />Pavement Recommendations: The subgrade soils encountered along the proposed roadway were <br />somewhat variable and generally consisted of a 1 [0 4 foot layer of topsoil overlying natural silts and <br />clays. The silts and clays classified as A-4 to A-6 soils in accordance with the American Association of <br />State Highway Transportation Officials (AASHTO) classification system. Using the group index values <br />obtained on the subgrade soil samples, a correlated soils resilient modulus of 5,000 psi was used in the <br />design process. <br />• It is our understanding [hat the subject roadway will be used as an access road which will generally be <br />subjected to very low traffic volumes, generally consisting of pickup trucks. Therefore, we have <br />assumed an 18 kip equivalent single axle loading (ESAL) of 6,500 for the access road <br />The gravel sections presented below aze based on the Feld investigation, laboratory test results, the <br />assumed traffic loadings and the AASHTO Guide For Design of Pavement Structures (1986). The <br />design calculations are shown in Appendix A. <br />We recommend that the gravel section to be constructed for this roadway consist of a minimum of 8 <br />inches of pit run gravels and 4 inches of road base gravels. An alternate section would consist of 14 <br />inches of pit run gravels and no road base gravels. The new gravel section should be placed on the silts <br />and clays found below the topsoil materials or on properly compacted Fill materials. <br />Subgrade/Gravel Preparation: Prior to placing [he gravel sections on the new roadway, we <br />recommend [hat all of [he topsoil materials be removed and the exposed soils be scarified to a depth of <br />6 inches, brought to within 2 percent of the optimum moisture content and then be recompac[ed to at <br />least 95% of the standard Proctor density determined in accordance with ASTM D698. Any Fill <br />materials placed beneath the roadway should be placed in 6 [0 8 inch lifts and compacted to 95% of the <br />maximum standard Proctor density. <br />• The new subbase gravels and base course materials placed on [he roadway should be compacted [o at <br />leas[ 95% of the maximum modified Proctor density at or near [he optimum moisture content, <br />1 f~ !J~- fo <br />