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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 gravel fill materials overlying natural clays. <br />The gravel layer ranged from 19 to 21 inches in thickness. The near surface subgrade soils encountered <br />beneath the gravel layer generally consisted of clays to the maximum depth investigated. The clays <br />generally classified as CL soils in accordance with [he Unified Soil Classification System. The clays will <br />generally provide poor to fair subgrade support for the proposed gravel sections. Free groundwater <br />was not encountered in the test holes at the time of drilling. <br />Pavement Recommendations: The subgrade sails encountered along the subject roadway were <br />somewhat variable and generally consisted of a Layer of gravel fdl materials overlying natural clays. <br />The existing gravel fill ma[eriaLs were in fair to poor condition; therefore, a strength coefficient of 0.6 <br />was used in the design of the new gravel section. The clays classified as A-7-6 to A-6 soils in <br />accordance with the American Association of State Highway Transportation Officials (AASHTO) <br />classification system. Using [he group index values obtained on the subgrade soil samples, a correlated <br />soils resilient modulus of 5,000 psi was used in the design process. <br />It is our understanding [hat the subject roadway is used as a haul road and will generally be subjected <br />• to moderate to high traffic volumes related to off-road haul trucks and eazth moving equipment. <br />Therefore, we have assumed an 18 kip equivalent single axle loading (ESAL) of 120,000 for this <br />roadway. <br />The gravel sections presented below are based on the field 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 6 <br />inches of pit run gravels and 4 inches of road base gavels. The new gravel section should be placed <br />over the existing gravels. <br />SubPrade/Gravel Preparation: Prior to placing the new gravel sections on the roadway, we <br />recommend that all of the loose and soft materials be removed and the existing gravels be reshaped <br />and recompacted to at leas[ 95% of the standard Proctor density determined in accordance with ASTM <br />D698. <br />The new subbase gravels and base course materials placed on the roadway should be compacted [o at <br />leas[ 95% of [he maximum modified Proctor density at or near the optimum moisture content, <br />determined in accordance with ASTM D1557. The base course and subbase gravels should be <br />approved by the soils engineer, prior to placement. We recommend that [he road bast gravels placed <br />• on [he roadways meet the requirements for Class V or VI base course in accordance with [he Colorado <br />11`~ a ~ <br />