3000 41ST ST Geotech Report 2025-12-31

PNW Home Builders, LLC ES-2598.03 May 2, 2013 Page 8 Provided the building will be supported as described above, the following parameters. can be used for design of new foundations: • Allowable soil bearing capacity 2,500 psf • Passive earth pressure 300 pcf(equivalent fluid) •. Coefficient of friction 0.35 A one-third increase in the allowable soil bearing capacity can assumed for short-term wind and seismic loading conditions. The above passive pressure and friction values include a factor-of- safety of 1.5. With structural loading as expected, total settlement in the range of one inch and differential settlement of approximately one-half inch is anticipated. The majority of the settlements, excluding those induced by the surcharge or preload programs, should occur during construction, as dead loads are applied. Seismic Design Considerations The International Building Code (IBC) specifies several soil profiles that are used as a basis for seismic design of structures. Based on the soil conditions observed at the test sites resulting in liquefaction potential, Site Class F should be used for design. If the 2009 IBC is applicable to' this project, Table 1613.5.2 yields the appropriate site class. If the 2012 IBC is applicable, Section 1613.3.2 recognizes Chapter 20 of the American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures (ASCE 7), where Table 20.3-1 yields the appropriate site class. It should be noted that a site response analysis in accordance with Section 21.1 of ASCE 7 shall be performed for Site Class F soils. Liquefaction In our opinion, the younger alluvium deposits reported on the site have a high susceptibility to liquefaction-induced settlement. Liquefaction is a phenomenon where saturated or loose soils suddenly lose internal strength in response to increased pore water pressures resulting from an earthquake or other intense ground shaking. The on-site sand, silt, and organic layers consistent with younger alluvium deposits are generally in a moist to wet condition, which is the primary basis for our conclusion. Groundwater seepage was reported at depths ranging from approximately 3 to 14 feet below existing grades. Given the time of year the explorations were conducted (January. 2007), these elevations likely reflect the seasonal high static groundwater elevations. In our opinion, liquefaction-induced settlement may be in the range of two to three inches and would likely not occur uniformly. Mitigating measures are provided by utilizing an applicable surcharge or preload program, which will improve near-surface soil structural capacity and provide a consistent and stable subgrade for foundation support. The placement of a biaxial geogrid along the foundation alignment and/or a deeper layer of structural fill beneath the foundations will provide a greater measure of protection from the effects of differential settlement. ESNW can provide additional soil improvement methods if the settlement estimates in this report are not tolerable. Earth Solutions NW,LLC