4027 4TH ST SE 2018-01-01 MF Import

January 14, 2003 HWA Proiect No. 2002-146-21 4.2 SEISMIC DEStGN CR[TERIA 4Z.1 Ge¢eral The project site lies within Seismic Zone 3 as defined in the Uniform Building Code (UBC, 1997). Zone 3 includes the Puget Sound region, and represents an area of significant seismic risk. For comparison, much of Califomia and southem Alaska are in Seismic Zone 4, which designates an area of higher seismic risk. Consequently, moderate levels of earthquake shaking should be anticipated during the design life of the new maintenance building. Based on the subsurface conditions observed during our exploration program, UBC Soil Type 3F inay be assumed for the soils supportin� the proposed new building. The site specific seismic response spectra appropriate for this site is addressed in section 4.2.3, Site Response. 4.2.2 Liquefaction The soft soils at the site aze generally cohesive end the non-cohesive sands aze generally medium dense to dense. In our opinion, there is the potential for isolated sand lenses in the upper portion and lower of the soil pro6le to liquefy during a design level seismic event. However, the installation of a driven pile foundation will both densify the soil in the immediate viciniry of the piles and place the building load below the sands with the greatest liquefaction potential. 4.2.3 Site Response E3ecause the site soils aze susceptible to liquefaction, they classify as UBC Type SF Soils. r�s such, UBC requires a site-specific seismic site response evaluation be perfomied. Sitc-specific spectra were developed using the equivalent linear ground :esponse analysis program ProShake (EduPro Civil Systems, 1999). The analysis involved four basic steps: 1) creation of a generalized soil profile considered to be representative of soil conditions below the buiiding; 2) selection of five earthquake records with an average response specVa ehat closely matches probabilistic hazard data prepared by USGS (Frankel, et. al, 1996) for the project area; 3) calculation of the response of the soil profile to the various earthquake records; and 4) pazametric analyses of input paruneters to account for uncertainties in soil characteristics. A generalized representative soil profile was created using the geotechnicai data gathered during our exploration program. Sheaz wave velocities were estimated using available data for similar soils and various empirical relationships (e.g., [mai and Tonouchi, 1982). A suite of five earthquake records was then selected and scaled such that the average response spectra for the suitc closely matched the USGS hard ground spectral ordinates 2002146 repun - fina� $ H\VA GEOSCIENCES IN� I