Laserfiche WebLink
• T <br /> <br />• The subsurface conditions encountered in [he test holes were variable anti generally consisted of a layer <br />of existing gravel fdl materials overlying natural clays. <br />The existing gravel layer ranged from 9 to 15 inches in thickness. The existing gravels were in fair [o <br />poor condition; therefore, a strength coefficient of 0.06 was used for these materials in the design of [he <br />new gravel section. The near surface subgrade soils encountered beneath the gravel layer generally <br />consisted of clays to the maximum depth investigated. The clays generally classified as CL soils in <br />accordance with the Unified Soil Classification System. The clays will generally provide poor to Fair <br />subgrade support for the proposed gravel sections. Free groundwater was ao[ encountered in the test <br />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 thin layer of gravel Fill materials overlying natural clays. <br />The clays classified as A-7-6 to A-6 soils in accordance with the American Association of State <br />Highway Transportation Officials (AASHTO) classification system. Using [he group index values <br />obtained on the subgrade soil samples, a correlated soils resilient modulus of 5000 psi was used is the <br />design process. <br />[t is our understanding that [he subject roadway will be used as an access road; however, [he roadway is <br />subjected [o a large number of construction and delivery trucks. Therefore, we have assumed an 18 kip <br />equivalent single axle loading (ESAL) of 12D,000 for this roadway. <br />• The gravel sections presented below are based on the field investigation, laboratory test results, the <br />assumed traffic loadings and [he 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 this roadway consist of a minimum of 8 <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 />Subgrade/Gravel Preparation: Prior to placing the new gravel sections on the roadway, we <br />recommend that the existing gravels be reshaped and recompacted to at least 95% of the standard <br />Proctor density determined in accordance with ASTM 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 is accordance with ASTM D1557. The base course and subbase gravels should be <br />approved by the soils engineer, prior [o placement. We recommend that the road base gravels placed <br />on the roadways meet [he 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 />• Draina¢e: The collection and diversion of surface drainage away from the roadway area is extremely <br />important for satisfactory performance of the roadway. The design of surface drainage features should <br />'Tg,ac~ <br />