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<br />It appears that the majority of the roadways investigated do not have a sttffident depth of road base <br />gravels. Without an adequate depth of base course gravels, the pavement section will not be sufficient <br />to handle the traffic loads. In addition, the existing road base gravels, which were exposed at the <br />surface of the majority of the roadways, have been contaminated with the on-site clays and do not <br />provide a suitable roadway surface when they become saturated. The gravel depths should be thick <br />enough to allow a sown to be established and maintained along [he roadways. <br />The existing road base materials classified as very poor to good road base materials and will provide <br />variable degrees of support. For design purposes, varying svength coeffdents were used for the <br />existing road base materials. Strength coefficients ranging from 0.03 [0 0.10 were used for the existing <br />road base materials in the design of the new gravel sections. <br />The subgrade soils obtained were somewhat vaziable and generally consisted of clays which classified <br />as CL to CH soils in accordance with the Unified Soil Classification system and A-6 to A-7-6 soils in <br />accordance with the American Association of State Highway Transportation Officials (AASHTO) <br />classification system. Using the group index values obtained on the subgrade soil samples, a correlated <br />soils resilient modulus of 5000 psi was used in the design process. <br />It is our understanding that the majority of the roadways investigated aze not haul roads and are <br />generally subjected to a very low traffic volumes, generally consisting of pickup [rucks. Therefore, we <br />have assumed an 18 kip equivalent single axle loading (ESAL) of 6,500 for the access roads. However, <br />it is our understanding that Haul Road B, the PM Bay Access Road and [he Waste Coal Pile Access <br />road will be subjected to daily trips of haul [rucks and otf-road earth moving equipment, such as front <br />end loaders. Therefore, we have assumed an ESAL of 120,000 for the haul roads. <br />The gravel sections presented below are based on the field investigation, laboratory test results, the <br />assumed traffic loadings and [be AASHTO Guide for Desigo of Pavement Structures (1986). The <br />desigo calculations are shown in Appendix A. <br />Haul Road B: Based on the two test holes advanced along Haul Road B, it appears that this roadway <br />had 19 to 21 inches of existing road base gravels. The road base gravels were in Fair to poor condition; <br />therefore, a strength coefficient of 0.06 was used for the existing road base materials in the design of <br />the new gravel section. Based on our calculations, we recommend that this roadway be surfaced with <br />an additional 6 inches of pi[ run gravels and 4 inches of Class VI base course. <br />PM Bav Access Road: Based on the four test holes advanced along the PM Bay Access Road, i[ <br />appears that this roadway had 9 to 15 inches of existing road base gravels. The road base gravels were <br />in fair to poor condition; therefore, a strength coefficient of 0.06 was used for [he wasting road base <br />materials in the design of [he new gravel section. Based on our calculations, we recommend [hat this <br />roadway be surfaced with an additional 8 inches of pit run gravels and 6 inches of Class VI base course. <br />It is our understanding that a considerable amour[ of subgrade displacement occurs at the north end of <br />the roadway in the vicinity of the storage buildings. We recommend that roadway areas in this portion <br />of the site be reconstructed with a layer of geotextile fabric and a new gravel section. The fabric should <br />Job No. 95--?JJl Northwest Colorado Consultams. [nc. Page 5 <br />