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Geotechnical Engineering ; Vport Irerracon <br /> SN4924 —Silver Lake North Cell Tower Everett, Washington <br /> October 24, 2014 Terracon Project No. 81145043 <br /> groundwater table may occur due to seasonal and longer term variations in the amount of <br /> precipitation and runoff, future construction and other factors not evident at the time the boring <br /> was drilled. <br /> 4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION <br /> 4.1 Geotechnical Considerations <br /> Based on the results of the subsurface exploration, laboratory testing, and our analyses, it is our <br /> opinion that the site is suitable for the proposed construction. The tower may be supported on <br /> either a reinforced concrete mat foundation bearing on native medium dense to very dense silty <br /> sand soils or a drilled shaft foundation with a minimum embedment of 10 feet bgs. Based on <br /> mapped geologic conditions and our field observations, the presence of scattered large cobbles <br /> or boulders could potentially cause difficulty during construction of a drilled shaft foundation. <br /> Geotechnical engineering recommendations for design and construction of foundation systems <br /> and other earthwork phases of the project are outlined below. The recommendations contained <br /> in this report are based upon engineering analyses, and our current understanding of the <br /> proposed project. <br /> 4.2 Earthwork <br /> Earthwork on the project should be observed and evaluated by Terracon. The evaluation of <br /> earthwork should include observation and testing of engineered fill, subgrade preparation, <br /> foundation bearing soils, observation of drilled shaft construction, and other geotechnical <br /> elements involved with construction of the project. <br /> 4.2.1 Site Preparation <br /> All existing vegetation, including grass, roots, loose or soft soil/rock and other unsuitable materials <br /> should be removed from beneath proposed structural slabs and the tower foundation. After <br /> removal of unsuitable materials and prior to placing fill, soft or disturbed areas encountered during <br /> subgrade preparation should be removed and replaced with suitable structural fill as described <br /> below. Pumping or unstable soils are not suitable for supporting structure foundations and should <br /> be removed and replaced with structural fill. <br /> The design recommendations presented in this report are based on the observed soil/rock <br /> conditions at the specific exploration location. <br /> 4.2.2 Subgrade Preparations <br /> If a concrete mat foundation is selected to support the tower, we recommend the subgrades be <br /> stripped of unsuitable materials and should be evaluated by a qualified geotechnical engineer to <br /> identify any unsuitable areas. <br /> 3 <br />