5700 23RD DR W 2018-06-28 - Laserfiche WebLink

November 29,2016 Project No.T-5922-6 With a lower building elevation of 416.34 feet the excavation for the site will extend approximately ten feet below current site grades. At this depth, we expect, the foundations should be below the fill material observed on-site and into the native Advance outwash soils. If loose soils (such as those observed in previous Test Pit TP-3) are encountered at the building foundation subgrade,we recommend overexcavating the loose material and replacing it with structural fill that meets the requirements below. Alternatively,the building foundations can be lowered to bear on suitable soils. In general,the silty sand soils encountered at the site contain a sufficient amount of soil fines and will be difficult to compact as structural fill when too wet. The ability to use these silty sand soils from site excavations as structural fill will depend on its moisture content and the prevailing weather conditions at the time of construction. The underlying clean outwash sand and gravel observed has a low percentage of soil fines and should be suitable for use as structural fill in most weather conditions. Depending on how the site is graded and the available volume of cleaner outwash soils,the contractor should be prepared to import free-draining granular material for use as structural fill and backfill during the wet season. Detailed recommendations regarding these issues and other geotechnical design considerations are provided in the following sections of this report. These recommendations should be incorporated into the final design drawings and construction specifications. 5.2 Site Preparation and Grading To prepare the site for construction,all vegetation, organic surface soils, and other deleterious materials should be stripped from the proposed building, patio, and retaining wall areas. Topsoil and fill soils containing excessive organic material,will not be suitable for use as structural fill, but may be used for limited depths in nonstructural areas or for landscaping purposes. Exposed soils will be highly susceptible to disturbance from normal construction activity particularly when wet. Placement of a four-to six-inch protective layer of clean crushed rock should be planned to minimize disturbance and impacts to the bearing subgrades during wet weather conditions. Once clearing and stripping operations are complete, cut and fill operations can be initiated to establish desired grades. Prior to placing fill, all exposed bearing surfaces should be observed by a representative of Terra Associates to verify soil conditions are as expected and suitable for support of new fill. Our representative may request a proofroll using heavy rubber-tired equipment to determine if any isolated soft and yielding areas are present. If excessively yielding areas are observed, and they cannot be stabilized in place by compaction, the affected soils should be excavated and removed to firm bearing and grade restored with new structural fill. Beneath embankment fills or roadway subgrade, if the depth of excavation to remove unstable soils is excessive, the use of geotextile fabrics, such as Mirafi 500X or an equivalent fabric, can be used in conjunction with clean granular structural fill. Our experience has shown that, in general, a minimum of 18 inches of a clean, granular structural fill placed and compacted over the geotextile fabric should establish a stable bearing surface. Page No. 5