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<br />• The subsurface conditions encountered in the test holes were variable and generally consisted of a thin <br />layer of gravel £dl materials overlying natural clays. <br />The existing gravel layer ranged from 3 to 10 inches in thickness. The near surface subgrade soils <br />encountered beneath the gravel layer generally consisted of clays to [he maximum depth investigated. <br />The clays generally classified as CL soils in accordance with the Unified Soil Classification System. <br />The clays will generally provide poor to Fair subgrade support for [he proposed gravel sections. Free <br />groundwater was not encountered in the test holes at the time of drilling. <br />Pavement Recommendations: The subgrade soils encountered along the proposed roadway were <br />somewhat variable and generally consisted of a very thin layer of gravel fdl materials overlying natural <br />clays. The existing gravels were in poor to fau condition; therefore, a strength coeeficient of 0.06 was <br />used in the design of the new gravel section. The underlying 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 the group index values obtained on [he subgrade soil samples, a correlated <br />soils resilient modulus of 5,000 psi was used in the design process. <br />It is our understanding that the subject roadway will be used as a haul road which will generally be <br />subjected to moderate to high traffic volumes related to otf-road haul [rucks and earth moving <br />equipment. Therefore, we have assumed an 18 kip equivalent single axle loading (ESAL) of 120,000 <br />for this 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 [he gravel section to be constructed for [his roadway consist of a minimum of 16 <br />inches of pit run gravels and 4 inches of road base gravels. The new gravel section should be placed <br />over the existing gravels. <br />Su erode/Gravel Preparation: Prior to placing [he gravel sections on the roadway, we recommend <br />[hat all of the loose and soft materials be removed and [he exposed gravels be reshaped and <br />recompacted [o at least 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 to at <br />least 95% of the 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 [ha[ the road base gravels placed <br />on the roadways meet the requirements for Class V or VI base course in accordance with the Colorado <br />Department of Transportation specifications. In addition, the subbase gravels should meet [he <br />requirements for Class II or Class III base course. <br />• <br />1({x(0 <br />