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• systems to prevent subgrade wetting. Because of the relatively moisture-sensitive, poorly <br />draining soils that will form the subgrade, surface grades should be maintained such that water <br />will easily run-off. <br />The following drainage precautions should be observed during construction and <br />maintained at all times after each structure has been completed. <br />(1) Excessive wetting or drying of foundation excavations and under-slab orunder-pavement <br />areas should be avoided during construction. <br />(2) The ground surface surrounding the exterior of structures or adjacent to pavements <br />should be sloped to drain away in all directions. We recommend a minimum slope of <br />12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the <br />first 10 feet in paved areas. <br />• (3) Roof downspouts and other drains should discharge well beyond the limits of all backfill. <br />PAVEMENTS <br />For the pavement requirements at this project, we have assumed that roads, parking and <br />staging areas will be designed for heavy truck traffic, and that an all-weather, high friction <br />surface is desired. Some pavements may be limited to automobile or light wck traffic. <br />Pavement design procedures are based on strength properties of the subgrade and pavement <br />materials, along with the design traffic conditions. Clayey soils, such as those encountered at <br />depth on this site, are moisture-sensitive and can present problems by losing strength if a source <br />' of moisture is present. Therefore, precautions with regard to surface drainage should be taken <br />to provide for adequate pavement performance. Expansive soils are problematic only if wetted <br />• <br />29 <br />