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Geotechnical Engineering Report <br /> Proposed Flight Line Steam Line Project lierracon <br /> ' Boeing Everett Facility• Everett, Washington <br /> January 17, 2012 • Terracon Project No.: 81115085 <br /> ' 4.2.10 Construction Considerations <br /> Earthwork may be difficult during periods of elevated soil moisture and wet weather due to the <br /> moisture sensitive nature of the glacial till soils. Excavated site soils may not be reusable as <br /> engineered fill depending on the soil moisture content and weather conditions at the time of <br /> construction. If soils are stockpiled for future reuse and wet weather is anticipated, the stockpile <br /> should be protected with plastic sheeting that is securely anchored. If on-site soils become <br /> unusable, it may become necessary to import clean, granular soils to complete wet weather site <br /> ' work. <br /> We recommend that the earthwork portion of this project be completed during extended periods <br /> of dry weather if possible. If earthwork is completed during the wet season (typically November <br /> through May) it may be necessary to take extra precautionary measures to protect subgrade <br /> soils. Wet season earthwork may require additional mitigative measures beyond that which <br /> ' would be expected during the drier summer and fall months. <br /> If earthwork takes place during freezing conditions, we recommend that the exposed subgrade <br /> be allowed to thaw and be recompacted prior to placing subsequent lifts of engineered fill. <br /> Alternatively, the frozen soils could be scraped off to expose unfrozen soil. The frozen soils <br /> ' should not be reused as fill unless it is permitted to thaw and be conditioned to a suitable <br /> moisture content. <br /> ' Terracon should be retained during the construction phase of the project to observe earthwork <br /> operations and to perform necessary tests and observations during subgrade preparation, <br /> placement and compaction of structural fill, backfilling of excavations, and just prior to <br /> construction of foundations and floor slabs. <br /> 4.3 Seismic Considerations <br /> 4.3.1 Tectonic Setting <br /> The tectonic setting of western Washington is dominated by the Cascadia Subduction Zone <br /> formed by the Juan de Fuca plate subducting beneath the North American Plate. This setting <br /> leads to intraplate, crustal, and interplate earthquake sources. Seismic hazards relate to risks <br /> of injury to people and damage to property resulting from these three principle earthquake <br /> sources. <br /> I <br /> Responsive • Resourceful • Reliable 11 <br />