2710 14TH ST BLDG A Geotech Report 2023-12-29

' 4.1.3.2015 IBC Seismic Design Information ' We recommend the use of the 2015 IBC parameters listed in Table 1 for soil profile type, short period spectral response acceleration (Ss), 1-second period spectral response acceleration (Si) and seismic coefficients (FA and Fv) for the project site. TABLE 1. 2015 IBC PARAMTERS 2015 IBC Parameter Recommended Value Soil Profile Type C Short Period Spectral Response Acceleration, Ss (percent g) 126.2 ' 1-Second Period Spectral Response Acceleration, Sl (percent g) 48.0 Seismic Coefficient, FA 1.0 Seismic Coefficient, Fv 1.32 ' 4.2. Shallow Foundations We recommend that the proposed buildings be supported on shallow spread footings founded on the dense to very dense glacial till and/or stiff to hard glaciolacustrine deposits encountered in our test pits. Shallow spread footings may also be supported on properly compacted structural fill extending down to the dense to very dense glacial till or stiff to hard glaciolacustrine deposits. Existing fill and unsuitable weathered glacial soils should be removed from under the planned buildings foundations. ' For shallow foundation support, we recommend widths of at least 18 and 36 inches, respectively, for continuous wall and isolated column footings supporting the proposed buildings. The design frost depth in ' the Puget Sound area is 12 inches; therefore, we recommend that exterior footings for the buildings be founded at least 18 inches below lowest adjacent finished grade. Interior footings should be founded at least 12 inches below bottom of slab or adjacent finished grade. The following recommendations for the building foundations are based on the subsurface conditions observed in the test pits. 4.2.1.Allowable Bearing Pressures ' Unsuitable soils consisting of fill, topsoil, and/or highly weathered glacial soils will vary across the site and must be removed from below planned footings. Based on our test pits, these unsuitable soils range from 2.5 to 6.5 feet, 3 to 6 feet, and 4 to 5.5 feet across Sites 1, 2, and 3, respectively. Therefore, depending ' on the foundation locations and design elevations, overexcavation under the footings may be necessary. We recommend the following: ' ■ Shallow Foundations on Dense Glacial Till: For foundations extending to and bearing on competent undisturbed dense to very dense native glacial till, foundations may be designed using an allowable soil bearing pressure of 6,000 psf for isolated spread footings and continuous footings. Controlled ' density fill (CDF) or lean concrete may be used below footings to support 6,000 psf, provided that it extends down to dense to very dense glacial till. ' GEoENGINEER5 October3O.2O19 Page6 File No. 21288-002-00