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32 Piping and Utility Connections Piping and utility connections between structures and equipment should be designed to accommodate differential settlements and/or to be realigned during the life of the project. FLEXIBLE PAVEMENTS The access road at the site is to be constructed with an asphaltic concrete (AC) pavement section. Subgrade The existing native subgrade soils consist of uncontrolled fill that is composed of silty sand, silty sand with glass or glass. An R-value of 48 was measured on a compacted sample of silty sand. This value is considered applica- ble for these materials when compacted to meet requirements for structural fill. The R-value for the silty sands in their present in-situ condition would be variable and locally less than this value. An R-value for locations where glass predominates would be much lower. We recommend that subgrade in the paved traffic area consist of compacted structural fill. The fill materials can either be on-site silty sand or import materials meeting the requirement for structural fill materials in the Earthwork section of this report. The compacted subgrade should be at least 2. ft thick. This may require overexcavation and recompaction of native materials, depending upon: (a) the difference in elevation between the final grade and existing surface, and (b) the combined thickness of AC and base. The top 12 inches of compacted subgrade should be placed and compacted to in excess of 95 percent relative compaction as determined by ASTM 1557. A minimum of 90 percent relative compaction is recommended for the bottom portion of the compacted subgrade. Base Material The base materials should be a select granular material meeting State of California, Department of Transportation specifications for Class 2 aggregate 1144A/CC-32 11- —