10111 9TH AVE W EMERALD COURT APARTMENTS Geotech Report 2022-10-20

Geotechnical Engineering Evaluation NGA File No.910814 Emerald Court Apartment Building November 21,2014 Everett,Washington Page 4 SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2012 International Building Code (IBC). Since mostly dense soils are interpreted to underlie the site at depth,the site conditions best fit the IBC description for Soil Class D for native soils. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the medium dense or better native deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of Snohomish County Area,Washington,by the Soil Conservation Service(SCS)was reviewed to determine the erosion hazard of the on-site soils. The surface soils for this site were mapped as Alderwood-Urban land complex, 2 to 8 percent slopes. The erosion hazard for this material is listed as slight. It is our opinion that the erosion hazard for the site soils should be slight in areas where the site is not disturbed. LABORATORY ANALYSIS We performed four grain-size analyses on selected soil samples obtained from the test pits. Laboratory tests were performed on samples taken from Test Pit 1 at 5.5 feet; Test Pit 2 at 6.8 feet; Test Pit 3 at 2.3 feet;and Test Pit 5 at 8.5 feet. The results of the sieve analyses are presented as Figures 6 through 9. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion from a geotechnical standpoint that the site is compatible with the planned development of a 5-story apartment building structure and associated parking and underground utilities. Our explorations indicated that the site is generally underlain by a thin layer of surficial topsoil and native weathered soil, with dense glacial till below. The native competent soils should provide adequate support for foundation, slab,and pavement loads. We recommend that the planned structure be designed utilizing NELSON GEOTECHNICAL ASSOCIATES,INC.