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C CORNERSTONE EARTH GROUP 6.3 TEMPORARY CUT AND FILL SLOPES The contractor is responsible for maintaining all temporary slopes and providing temporary shoring where required. Temporary shoring, bracing, and cuts/fills should be performed in accordance with the strictest government safety standards. On a preliminary basis, the upper 10 feet at the site may be classified as OSHA Site C materials. Excavations performed during site demolition and fill removal should be sloped at 3:1 (horizontal:vertical)tyithin the upper 5 feet below building subgrade. Excavations extending more than 5 feet below building subgrade and excavations in pavement and flatwork areas should be slope at a 1:1 inclination unless the OSHA soil classification indicates that slope should not exceed 1.5:1. 6.4 SUBGRADE PREPARATION After site clearing and demolition is complete, and prior to backfilling any excavations resulting from fill removal or demolition, the excavation subgrade and subgrade within areas to receive additional site fills, slabs-on-grade and/or pavements should be scarified to a depth of 6 inches, moisture conditioned, and compacted in accordance with the "Compaction" section below. 6.5 SUBGRADE STABILIZATION MEASURES r' Soil subgrade and fill materials, especially soils with high fines contents such as clay and silt \_ materials, can become unstable due to high moisture content, whether from high in-situ moisture contents or from winter rains. As the moisture content increases over the laboratory optimum, more likely the materials will be subject to softening and yielding (pumping) from construction loading or become unworkable during placement and compaction. As discussed in the "Subsurface" section in this report, the in-situ moisture contents are about 5 to 8 percent below to 5 percent over the estimated laboratory optimum in the upper 10 feet of the soil profile. The contractor should anticipate moisture conditioning the soils prior to reusing them as fill; however, moisture contents greater than 2 percent above the laboratory optimum will likely cause silty and clayey soils to begin "pumping" under the weight of construction equipment. In addition, repetitive rubber-tire loading will likely further de-stabilize the soils. During winter construction, areas that are prone to water-related impacts typically include undercut street subgrade areas, cul-de-sac or "hammer-head" streets, or other low areas where surface water runoff is likely to pond. Utility crossings where native soil backfill materials are used can also be susceptible to deflection under the weight of construction equipment. These areas are typically difficult to dry out after winter rains due to saturated subgrade soils that often extend to depths on the order of 24 to 48 inches below finished subgrade. There are several methods to address potential unstable soil conditions and facilitate fill placement and trench backfill. Some of the methods are briefly discussed below. Implementation of the appropriate stabilization measures should be evaluated on a case-by- case basis according to the project construction goals and the particular site conditions. Ponderosa Active Adult Community Page 13 132-2-1