Laserfiche WebLink
GeoTest Services, Inc. <br />4320 Thomson Avenue, Everett, WA <br />April 12, 2019 <br />Project No.19-0050 <br />Liquefaction is defined as a significant rise in pore water pressure within a soil mass <br />caused by earthquake -induced cyclic shaking. The shear strength of liquefiable soil is <br />reduced during large and/or long duration earthquakes as the soil consistency <br />approaches that of semi -solid slurry. Liquefaction can result in significant and <br />widespread structural damage if not properly mitigated. Deposits of loose, granular <br />soil below the groundwater table are most susceptible to liquefaction. Damage <br />caused by foundation rotation, lateral spreading, and other ground movements can <br />result from soil liquefaction. <br />Based on the presence of dense to very dense sand and gravel and a relatively deep <br />groundwater table, it is GTS's opinion that the potential for liquefaction underlying the <br />subject property is low. Thus, GTS concurs with the DNR classification of very low <br />liquefaction susceptibility. Furthermore, for these reasons, the subject property would <br />not be classified as a Seismic Hazard. <br />We recommend that the design team utilize seismic design standards per IBC such <br />that the planned structure, including nonstructural components that are <br />permanently attached to building's supports, be designed to resist the effects of <br />earthquake motions. <br />Mitigation of Geologic Hazards <br />The proposed residence will be constructed at roughly the same location as the <br />existing residence, with the western portion of the residence cut partially into the toe <br />of the existing steep slope. As discussed previously, it appears that the core of the <br />existing slope is comprised of Advance Outwash and Till. GTS did not observe any <br />noticeable signs of shallow or deep-seated instability during our visits to the site and <br />during our review of published geological information or aerial imagery. _G2$ <br />recommends that the western foundation wall at is closest to e of the ex' in <br />s ope be designed as a com ination fo dation/retaining wall with a "freeboard" <br />portion to catc any potential debris that may encroac c ose tote proposed <br />build .Atypical "freeboard" height should be at least 5 feet a ove e surrou g <br />finis grades. We can prove e ateral earth pressures and other geotechnical <br />parameters to: the structural engineer upon request. <br />GTS also recommends that erodible soils be addressed as previously recommended <br />in the Erosion Hazards section of this report. Provided that these mitigations are <br />implemented, it is GTS's opinion that the geologic hazards that are present on the site <br />can be adequately mitigated per the Everett Municipal Code. <br />Additional Geotechnical Recommendations <br />GTS can provide additional geotechnical recommendations regarding the new <br />residence (excavation, structural fill requirements, infiltration feasibility, etc.) once the <br />preliminary plans are completed and upon request. Our current scope of services is <br />only intended to identify and provide mitigations for critical areas. Our current <br />9 <br />