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

Jenurry 14, 2003 HWA Proiect No. 2002-146-21 for eazthquakc events associated with a 475-year retum period (]0 percent probability of exceedrnce in 50 years). Using these earthquake records, ProShake analyses wae performed several times and a parametric sensitivity study was performed for input variables including modulus reduction and damping relationships. Our analyses were completed assuming a damping level of 5 percent. The mean site-speciSc elastic response spectra is presented on Figure 3. UBC Section l63 L5.4 stipulates that Elastic Response Parameters be reduced such that the corresponding design base shear be no less that 80 percent of the base sheaz detecmined using the static force proceduro (Section 1630.2.1). Because the site-specific elastic response spectrum falls below 80 percent of the static force procedure base shear, the site response must be taken as 80 percent of the static force procedure bue shear. Code-based elutic spectrum corresponding to soil type SE and 80 percent of soil Type SE aze presented on Figure 3. For reference, the code-based elastic spectrum corresponding to soil type Sois also presented in Figure 3. The seismic coefficients C, and C�, which correspond to 80 percent of soi) Type SE response spectrum, are 0.29 and 0.67, respectively. 4.3 P[LE FOUNDAT[ONS 4.3.1 General Based on the subsurface conditions encountered, it is our opinion that the new maintenance building should be suppoited using piles. Spread foundations aze not considered feasible for the new building, due to the prevalence of compressible soils which could lead to excessive differential settlement, and also due to potentially liquefiable layers in the upper portion of the alluvium. Our evaluations indicate that driven displacement piling is the most practical and cost-effective deep foundation alternative. Use of drilled shafts is not considered feasible, due to: 1) the very loose, saturated deposits which would require casing the entire shaft length during consWction; and 2) the relatively poor bearing characteristics of soils anticipated at shaft tip elevations, which would result in relatively low bearing capacities for drilled shafts. In conjunction with ihe design team, che preferred choice of pile type has been reduced to either timber piles or precast concrete piies for use on the project. Based on our understanding of the previous foundations consiructed at this site, the apparendy saNs`actory performance of those foundations and conversations with the City of Everett and the design team, we recommend founding thc piles at elevation —35 to provide a foundation that wil( perfortn consistent with the other buildings at the site. Parameters for design of deep foundation systems, including allowable axial and lateral load capacities, construction considerations, and geotechnical monitoring requirements are provided below. Settlement of the piles is addressed in Section 4.4. ?002 N6 «pon • final HWA GEOSCIENCES INC.