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Geotechnical Investigation Report Detroit Lake Water Reservoir Detroit, Oregon APPENDIX D – GENERAL CONSTRUCTION INFORMATION D.1 STRUCTURAL FILL Structural fills should be placed over subgrade, which has been prepared in conformance with the “Site Preparation” and “Wet-Weather/Wet-Soil Considerations” sections of this report. A wide range of material may be used as structural fill; however, all material used should be free of organic matter or other unsuitable materials and should meet the specifications provided in the 2008 Oregon Standard Specifications for Construction, Oregon Department of Transportation (ODOT SS), Section 00330 – Earthwork, depending on the application. A brief characterization of some of the acceptable materials and our recommendations for their use as structural fill is provided below. D.1.1 Borrow Material Borrow material for general structural fill construction should meet the requirements set forth in ODOT SS 00330.12 – Borrow Material. The native sand, and silt may be used as structural fill if processed properly. In order to adequately compact the native soils, moisture conditioning (drying) of the soil to within a few percentage points of the optimum moisture content will be required. Drying may prove infeasible due to rainy weather. Soil amendments using Portland cement or lime may be needed to adequately process the native materials. When used as structural fill, native soils should be placed in lifts with a maximum uncompacted thickness of 6 to 8 inches and compacted to not less than 92 percent of the maximum dry density, as determined by ASTM D 1557. If suitable common borrow material is not available, use of selected general backfill as specified in ODOT SS 00330.13 –Selected General Backfill should be considered. D.1.2 Selected Granular Backfill Selected granular backfill used during periods of wet weather for structural fill construction should meet the specifications provided in ODOT SS 00330.14 – Selected Granular Backfill. Selected granular backfill should be placed in lifts with a maximum uncompacted thickness of 8 to 12 inches and be compacted to not less than 92 percent of the maximum dry density as determined by ASTM D 1557. During the wet season or when wet subgrade conditions exist, the initial lift should be approximately 18 inches in uncompacted thickness and should be compacted by rolling with a smooth-drum roller without using vibratory action. Where selected granular backfill is placed over soft-soil subgrades, we recommend a geotextile be placed as a barrier between the subgrade and selected granular backfill. The geotextile should meet specifications provided in ODOT SS 2320.10 – Geosynthetics, Acceptance, and in Table 02320-1 (p. 734) for soil separation. The geotextile should be installed in conformance with ODOT SS 0350.00 – Geosynthetic Installation. Selected Stone Backfill (ODOT SS 00330.15) and Stone Embankment Material (ODOT SS 00330.16) can also be used for the construction of general structural fill. We however recommend that the larger size material (>6 inches) should be placed in the deeper portions of the fill and should not be used within 2 feet of the pavement subgrade. Considerations should also be given to the future excavation of utilities through this material since it is relatively difficult to excavate through larger size material. November 23, 2009 Project No. 72852.000 D-1