4735 GLENHAVEN DR Geotech Report 2022-10-25

41, S Geotechnical Engineering Evaluation NGA File No. 1113119 Dutton Foundation Stabilization and Slope Evaluation July 3,2019 �"1 Everett,Washington Page 4 �� SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2018 International Building Code (IBC) for seismic site classification for this project. Since dense to very dense soils are interpreted to underlie the site at depth, the site best fits the IBC description for Site Class D. Table 1 below provides seismic design parameters for the site that are in conformance with the 2018 IBC, which specifies a design earthquake having a 2%probability of occurrence in 50 years(return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1—2018 IBC Seismic Design Parameters Site Class Spectral Acceleration Spectral Acceleration Site Coefficients Design Spectral at 0.2 sec.(g) at 1.0 sec. (g) Response Ss S i Parameters Fa F, SDS SDi D 1.408 0.535 1.000 1.500 0.939 0.535 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website(2008 data)for the project latitude and longitude. 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 very dense glacial 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. We reviewed data from the Soil Survey of the Snohomish County Area, Washington, by the Natural Resources Conservation Service (NRCS). The soils on the site are listed as Alderwood-Urban land complex, 8 to 15 percent slopes and Everett very gravelly sandy loam, 15 to 30 percent slopes. The erosion hazard rating for the site soils are listed as moderate. Based on our experience in the area and our observations in the field, it is our opinion that the soils encountered around the residence would have a slight to moderate erosion hazard for areas where the native soils aren't exposed. NELSON GEOTECHNICAL ASSOCIATES,INC.