1004 BROADWAY EVCC STUDENT HOUSING - PUBLIC WORKS 2017-01-13

Geotechnical Repoi-t - Revised Proposed Apartments: 1002, 1006, and 1008 Broadway Street, Everett, Washington May 12, 2015 3.4 GROUNDWATER Groundwater seepage was not encountered in ow� borings or hand augcrs. The till underlying the site generally has low permeability and perched ground�vater may develop in lenses of more pei7neable soi) within the till foi7nation. If encountei•ed, we anticipate groundwater seepage rates will be light. There will be fluctuations in seepage depeiidin� o�� the seasoii, amowlt of rainiall, surface water iunoff, and other factors. Generally, the water level is higher and seepage rates are greater in tlie wetter, winter months (typically October through May). 4.0 GEOTECHNICAL RECOMMENDATlONS 4.1 SEI51111C DESIGN PARAME'1'ERS The 2012 Intetnational Building Code (IBC) seismic design section provides a basis for seismic design of strvctures. Table 1 below provides seismic design parameters for the site that are in confonnance with the 2012 IBC, which specifes a design earthquake having a 2% probability of occurrence in 50 years (rehu�n interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1— Seismic Design Parlineters Spectral Spectral Site Design Spectral Control Periods Acceleration Acceleration Response Site Coefficients [sec.] Class at 0.2 sec. [g] at I.0 sea �g] Parameters SS S� Fa F�• Sos S�>i To Ts C 1.2fi4 0.481 I.U00 1.319 0.843 0.423 0.100 0.502 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Gi•ound Motion website (2008 data) f'oi• the project latitude and longitude. Liquefactin» Pote�rtial: Lic�uefaction is a pi•ocess that cali occur when soils lose shear• stc•ength for• sliort periods of time during a seismic event. Ground shaking of suf'ficient strength and duration results in the loss of grain-to-grain contact and an increase in pore ��ater pressure, causing tlie soil to behave as a fluid. Soils �vith a potential for � 5-0-1� IOUA 13madway, Reviscd P�1�C S 1�21]i�i�;0, �i7C.