1400 W MARINE VIEW DR WATERFRONT PLACE APARTMENTS Geotech Report 2022-10-25

Summary • A summary of the geotechnical considerations is provided below.The summary is presented for introductory purposes only and should be used in conjunction with the complete recommendations presented in this report. • The building site should be designated Site Class E, per the 2015 IBC. Liquefiable soils are present at the site; however, because the building period is less than 0.5 seconds, the site is designated Site Class E. • The interbedded layers of soft silt and clay within the fill are prone to static settlement under the anticipated foundation load.The static settlement will be mitigated by ground improvement. • The loose to very loose fill and recent deposits below the groundwater elevation are susceptible to liquefaction. The liquefaction hazard presents a liquefaction-induced (seismic)settlement and lateral spreading risk, as such, ground improvement will be designed to mitigate seismic settlement and lateral spreading. • Due to poor soil conditions below the planned development, the preferred foundation support will consist of shallow foundations supported by improved ground. For design purposes, an allowable foundation bearing pressure of 4 kips per square foot(ksf) can be used for foundations bearing on improved ground. is Ground improvement is planned to be completed to mitigate the static settlement of the interbedded layers of soft silt and clay and the potential impacts of liquefaction in the loose fill and recent deposits below the groundwater table. • ■ Slab-on-grade supported on improved ground is considered appropriate for the development. Conventional slabs-on-grade should be underlain by a 4-inch-thick capillary break gravel layer.A vapor retarder should be placed where moisture-sensitive floor coverings are to be used. • Based on the Port of Everett's final Environmental Impact Statement(EIS) dated May 2005, methane gas was detected in subsurface explorations and is the result of the decomposition of organic matter (wood waste) present in the subsurface soils. Methane gas can pose a risk for explosion or oxygen depletion if allowed to accumulate in subsurface voids or structures.We recommend that during design the presence of methane gas be assessed and, if necessary, the design of the development address the risk of methane gas. Our specific geotechnical recommendations are presented in the following sections of this report. Earthquake Engineering Liquefaction Liquefaction is a phenomenon where soils experience a rapid loss of internal strength as pore water pressures increase in response to strong ground shaking. The increased pore water pressure may temporarily meet or exceed soil overburden pressures to produce conditions that allow soil and water to flow, deform, or erupt from the ground surface. Very loose to medium dense sands and low plasticity silts are susceptible to liquefaction.Ground settlement, lateral spreading and/or sand boils may result from soil liquefaction. Structures, such as buildings, supported on or within liquefied soils may suffer foundation • settlement or lateral movement that can be damaging to the buildings. GEOENGINEERS� May31,2017 ? Page 4 File No.22360-003-00