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Geotechnical Investigation Report Detroit Lake Water Reservoir Detroit, Oregon Aggregate. We recommend the granular wall backfill be separated from general fill, native soil, and/or topsoil using a geotextile fabric that meets the requirements provided in ODOT SS 02320.10 – Geosynthetics, Acceptance and ODOT SS 02320.20 – Geotextile Property Values, Table 02320-1 (p. 734) for separation geotextile. The geotextile should be installed in conformance with ODOT SS 00350 – Geosynthetic Installation. The wall backfill should be compacted to a minimum of 92 percent of the maximum dry density, as determined by ASTM D 1557. However, backfill located within a horizontal distance of 3 feet from the retaining walls should only be compacted to approximately 90 percent of the maximum dry density, as determined by ASTM D 1557. Backfill placed within 3 feet of the wall should be compacted in lifts less than 6-inches thick using hand- operated tamping equipment (such as, jumping jack or vibratory plate compactors). D.1.7 Granular Drain Backfill Material Backfill in a 2-foot zone against the back of retaining walls and for subsurface trench drains should consist of granular drain rock meeting the specifications provided in ODOT SS 00430.11 – Granular Drain Backfill Material. The granular drain rock should be wrapped in a geotextile fabric that meets the specifications provided in ODOT SS 02320.10 – Geosynthetics, Acceptance and ODOT SS 02320.20 – Geotextile Property Values, Table 02320-1 (p. 734) for drainage geotextile. The geotextile should be installed in conformance with ODOT SS 00350 – Geosynthetic Installation. D.1.8 Aggregate Base Rock Aggregate base rock below asphalt concrete pavements should be clean, crushed rock or crushed gravel. The base aggregate should contain no deleterious materials, meet specifications provided in ODOT SS 02630.10 – Dense-Graded Aggregate 1”-0”, and have less than 5 percent by weight passing the U.S. Standard No. 200 Sieve. The aggregate base rock should be compacted to at least 95 percent of the maximum dry density, as determined by ASTM D 1557. D.1.9 Recycled Concrete, Asphalt, and Base Rock Asphalt pavement, concrete, and base rock from the existing site improvements can be used in structural fills, provided no particles greater than 6 inches are present and no hazardous or deleterious material is present. It also must be thoroughly mixed with soil, sand, or gravel such that there are no voids between the fragments. The recycled material should generally conform to ODOT SS 00330.12 – Borrow Material. This material should be approved by the engineer before use. D.2 PERMANENT SLOPES Permanent cut and fill slopes up to 10-feet tall may be built to a gradient as steep as 2H:1V. However, cut slopes over 10-feet tall should be limited to a gradient of 2.5H:1V or should be partially retained by a retaining wall. Slopes that will be maintained by mowing should not be constructed steeper than 3H:1V. Newly constructed fill slopes should be over-built by at least 12 inches, and then trimmed back to the required slope to maintain a firm face. Higher slopes should be individually designed. Access roads and pavements should be located at least 5 feet from the top of cut and fill slopes. Slopes should be planted with appropriate vegetation to provide protection against erosion as November 23, 2009 Project No. 72852.000 D-3