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June 9,2022 <br /> Page 8 of i5 <br /> Geotechnical Evaluation <br /> Site Preparation <br /> Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic-rich <br /> soil and fill. Based on observations from the site investigation program, it is anticipated that the <br /> stripping depth will be 6 to 18 inches. Deeper excavations may be required below foundation <br /> systems and large trees,where roots extend to greater depths. <br /> The near surface soils include silty-sand with gravel and poorly graded sand trace gravel some silt. <br /> These soils are generally suitable for use as structural fill provided they meet compaction <br /> requirements and are within the 3 percent of the optimum moisture content. <br /> Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of <br /> 3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). <br /> Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted <br /> to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the <br /> ASTM D 1557 test method. <br /> Temporary Excavations <br /> Based on our understanding of the project,we anticipate that the grading could include local cuts <br /> on the order of approximately 9 feet or less for foundation and most of the utility placement. <br /> Temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose <br /> fill and native soils and iH:1V in medium dense native soils. If an excavation is subject to heavy <br /> vibration or surcharge loads, we recommend that the excavations be sloped no steeper than <br /> 2H:1V,where room permits. <br /> Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part <br /> N, Excavation,Trenching,and Shoring. Temporary slopes should be visually inspected daily by a <br /> qualified person during construction activities and the inspections should be documented in daily <br /> reports. The contractor is responsible for maintaining the stability of the temporary cut slopes <br /> and reducing slope erosion during construction. <br /> Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, <br /> and the slopes should be closely monitored until the permanent retaining systems or slope <br /> configurations are complete. Materials should not be stored or equipment operated within 10 feet <br /> of the top of any temporary cut slope. <br /> Soil conditions may not be completely known from the geotechnical investigation. In the case of <br /> temporary cuts,the existing soil conditions may not be completely revealed until the excavation <br /> work exposes the soil. Typically, as excavation work progresses the maximum inclination of <br /> temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental <br /> recommendations can be made. Soil and groundwater conditions can be highly variable. <br /> Scheduling for soil work will need to be adjustable,to deal with unanticipated conditions, so that <br /> the project can proceed and required deadlines can be met. <br /> If any variations or undesirable conditions are encountered during construction, we should be <br /> notified so that supplemental recommendations can be made. If room constraints or <br /> groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed <br /> by the WAC, temporary shoring systems may be required. The contractor should be responsible <br /> for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences <br /> and the project structural engineer review temporary shoring designs prior to installation, to <br /> verify the suitability of the proposed systems. <br /> www.cobaltgeo.com (206)331-1097 <br />