Agenda - Council - 09/14/2021 - Laserfiche WebLink

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Oversizing In areas where the excavations for soil corrections extend below the proposed footing elevations, the excavations require oversizing. We recommend the perimeter of the excavation be extended a foot outside the proposed footprint for every foot below footing grade (1H:1V oversizing). The purpose of the oversizing is to provide lateral support of the foundation. Fill Material Fill required to attain site grades may consist of any debris -free, non -organic mineral soil. Except, we recommend that fill or backfill placed in wet excavations or within 2 feet of the groundwater table consist of granular soil (sand) with less than 5 percent passing the number 200 sieve and at least 50 percent retained on the number 40 sieve. The on -site soils appear to be generally suitable for reuse as structural fill or backfill. Soils that will be used or reused as fill or backfill will could require some moisture conditioning (wetting) to meet the recommend compaction levels. Clayey soils (SB-10 and SB-12) that will be reused as fill or backfill will likely require significant drying to meet the recommend compaction levels. Summer months are typically more favorable for drying wet soils. Topsoil or soils that are black in color are not suitable for reuse as structural fill or backfill. Backfilling We recommend any loose sands or soil disturbed during excavation activities be surface compacted to increase their density and uniformity prior to placing additional fill and/or footings. We recommend the exposed soil be surface compacted with a large self- propelled vibratory compactor operating in vibratory mode. We recommend that backfill placed to attain site grades be compacted to a minimum of 95 percent of its standard Proctor density (ASTM D 698). Granular fill classified as SP or SP-SM should be placed within 65 percent to 105 percent of its optimum moisture content as determined by the standard Proctor. Other fill soils should be placed within 3 percentage points above and 1 percentage point below its optimum moisture content as determined by the standard Proctor. All fill should be placed in thin lifts and be compacted with a large self- propelled vibratory compactor operating in vibratory mode. Foundations We recommend the perimeter footings bear a minimum of 42 inches below the exterior grade for frost protection. Interior footings may be placed immediately below the slab provided construction does not occur during below freezing weather conditions. Foundation elements in unheated areas should bear at least 5 feet below exterior grade for frost protection. We anticipate the foundations and floor slabs will bear on compacted engineered fill (sand fill) or native alluvial sand soils. With the building pad prepared as recommended, it is our opinion the footings can be designed for a net allowable bearing pressure up to 2,000 pounds per square foot (psf). We anticipate total and differential settlement of the foundations will be less than 1 inch and 1/2 inch, respectively, across a 30-foot span. 8