2320 CALIFORNIA ST Geotech Report 2025-07-25

Administration Building Office Expansion Everett,Washington New hot mix asphalt(HMA) pavement sections should consist of at least 2 inches HMA over 4 inches of base course in light-duty pavement areas and at least 3 inches HMA over 6 inches of base course in heavy-duty pavement areas. The glacial soils observed generally contain a high percentage of fines and are highly moisture sensitive. ' The on-site soils may be used as structural fill during dry weather conditions (typically June through September) provided the material is properly moisture conditioned. Imported Gravel Borrow should be used as structural fill during wet weather conditions and during the wet season (typically October through ' May). It may be necessary to construct a 2-foot compacted till layer in areas where sand lenses are observed within the pond. Permanent cut and fill slopes within the detention pond be no steeper than 3H:1V and should be protected from erosion by an erosion control blanket and hydroseeding. An infiltration rate of no more than 0.06 inches/hour should be used in design. ' These geotechnical issues and other considerations are discussed further and recommendations pertaining to the geotechnical aspects of the project are presented in the following sections. Earthquake Engineering 2009 IBC Seismic Design Information ' We recommend the 2009 International Building Code (IBC) parameters for Site Class, short period spectral response acceleration(Ss), 1-second period spectral response acceleration (Si), and Seismic Coefficients FA and Fv presented in Table 1. These values are equivalent to the 2006 IBC parameters and can be used if the project will be designed per the 2006 IBC. TABLE 1. IBC SEISMIC PARAMETERS 2009 IBC Parameter Recommended Value Site Class C ' Short Period Spectral Response Acceleration,Ss(percent g) 125 1-Second Period Spectral Response Acceleration,Si(percent g) 44 Seismic Coefficient, FA 1.0 Seismic Coefficient,Fv z 1.36 Liquefaction Liquefaction refers to a condition where vibration or shaking of the ground, usually from earthquake forces, results in development of excess pore pressures in saturated soils and subsequent loss of strength in the deposits of soil so affected. In our opinion,the dense glacial till observed at the site will not liquefy under the design earthquake. Shallow Foundations We recommend that the planned addition be supported on conventional spread footings bearing on competent undisturbed dense to very dense glacial till as described below. GEOENGINEERS October 30,2009 Page 3 ' File No.0482-031-02