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• The subsurface conditions encountered in [be test holes were variable and generally consisted of a thin <br />veneer of clay and gavel fill materials overlying a layer of existing pit run sand and gravels which in <br />turn were underlain by natural clays. <br />A thin veneer, 1 to 2 inches [hick, of day and gravel fill materials was encountered at the roadway <br />surface. The clay and gravel fill materials were very soft and wet. Pit run sand and gravels were <br />encountered below the thin layer of day and gravel fill and these gravels ranged from 9 to f2 inches in <br />thickness. The subgrade soils encountered beneath the sand and gravel layer generally consisted of <br />clays to the maximum depth investigated. The clays generally classified as CL soils in accordance with <br />the Unified Soil Classification System. The clays will generally provide fair to poor subgrade support <br />for [he gravel sections. Free groundwater was not encountered in the test holes a[ the time of [his <br />investigation. <br />Pavement Recommendations: The subgrade soils encountered along the subject roadway were <br />somewhat variable and generally consisted of a layer of existing pit run sand and gravel materials <br />overlying natural clays. The existing sand and gravels were in fair to good condition; therefore, a <br />strength coefficient of 0.09 was used in the design of the new gravel section. The clays classified as A-6 <br />to A-7-6 soils in accordance with the American Association of State Highway Transportation Offcials <br />(AASHTO) classification system. Using [he group index values obtained on the subgrade soil samples, <br />a correlated soils resilient modulus of 5,000 psi was used in the design process. <br />• II is our understanding that [he subject roadway is used as an access road and is typically subjected to <br />light traffic volumes related to pickup trucks and occasional delivery and construction trucks; therefore, <br />we have assumed an 18 kip equivalent single axle loading (FSAL) of 6,500 for this roadway. <br />The gravel section presented below is 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 a minimum of 4 inches of new road base gravels be placed over the existing pit <br />run sands and gravels after the overlying clay and gravel fill materials are removed. <br />Subarade/Gravel Preparation: Prior to placing the new gravel section on the roadway, we recommend <br />that all of the loose and soft materials be removed and the underlying sands and gravels be reshaped <br />and recompacted to at least 95% of [he standard Proctor density determined in accordance with ASTM <br />D698. <br />The new base course materials placed on the roadway should be compacted to at leas[ 95% of [he <br />maximum modified Proctor density at or near the optimum moisture content, determined i^ <br />accordance with ASTM D1557. The base course gravels should be approved by the soils engineer, <br />prior to placement. We recommend [hat the road base gravels placed on the roadways meet the <br />requirements for Class V or Vi base course in accordance with the Colorado Department of <br />• Transportation specifications. <br />-t R ac~ <br />