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J <br /> AMERICAN ENGINEERING TESTING,INC. AET Project No. 22-00012 <br /> In some areas of the site, topsoil will be present at the planned pavement subgrade elevation(i.e., <br /> bottom of sand subbase). In the heavy-duty pavement areas, where the pavement section <br /> includes 24 inches of sand subbase beneath the aggregate base course, the sand can be placed <br /> directly over the topsoil after the subgrade has passed a test roll. In the light-duty areas,where a <br /> thinner sand subbase is planned, we recommend placing a geotextile separator fabric such as <br /> Mirafi 500X or equivalent over the exposed topsoil. <br /> We recommend that all new fill placed within 3 feet of the top of subgrade elevation be <br /> compacted to a minimum of 100% of the Standard Proctor density (ASTM: D698). This applies <br /> to the sand subbase, new fill, and the underlying native soil that is either reworked or reused as <br /> fill. At depths greater than 3 feet below the subgrade, the degree of compaction can be reduced <br /> to 95% of the Standard Proctor density. The fill should be placed in lifts thin enough to attain the <br /> specified compaction level throughout the entire lift thickness. This normally requires that fill be <br /> placed in loose lifts less than 8 inches thick. <br /> Based on a subgrade consisting of lean clay, we recommend using a Stabilometer value (R- <br /> value) of 10 for the bituminous pavement design. If a 2 foot thick sand subbase is included in the <br /> design, we recommend using an equivalent R-value of 30 for the composite subgrade (sand <br /> subbase over clayey soils); for a 1 foot thick sand subbase, we recommend using an equivalent <br /> R-value of 20 for the composite subgrade. <br /> 6.9.2 Fly Ash Stabilization Alternative <br /> Because of the relatively soft, high water content clay soils on this site, we recommend that you <br /> consider improving the pavement subgrade using fly ash stabilization. The cementitious <br /> products formed during hydration of the fly ash (after it is mixed with the soil) stabilize the soil, <br /> and improve the stability and subgrade support. This would reduce the amount of subcutting of <br /> topsoil because the sand subbase would be eliminated for the light-duty pavements and the <br /> thickness of the sand subbase would be reduced for the heavy-duty pavements. <br /> Page 22 of 28 <br />