10200 25TH AVE SE Geotech Report 2018-01-02 MF Import

i : Proposed Modernization and Additions to Subsurjace Ezp[oration, Geolagic Hazardr, Eisenhower Middle Schoal and Geotechnica!Engineering Repon Evere�t, Wasiiinqton Gea[ogic HaZards and Mitigations can disrupt the grain-to-grain contact, increase the pore pressure, and result in a decrease in soil shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is supported by pore pressure alone. Liquefaction can result in deformation of the sediment and settlement of � �rlying structures. Areas most susceptible to liquefaction indude those areas underlain by non-cohesive silt and sand with low relative densities, accompanied by a shallow water table. The encountered stratigraphy has a low potential for liquefaction due to the relatively high densiry of most of the site soils, and rypically high silt content. We did not complete a rigorous liquefaction analysis and none is recommended for this site. 5.4 Ground Motion The project site is !ocated within a Zone 3 rating for seismic activity on a scale of 1 (lowest) to 4 (highest) based on the Sersmic Zone Map ofihe United Stares, Figure No. 16-2 in the 1997 edition of the Uniform Be�ildi�:g Code (UBC). This zonation is based on past earthquake activiry in the Puget Sound region. As such, design recommendations in the report accommodate the possible effect of seismic activiry in areas with a Zone 3 rating, corresponding to a peak ground acceleration oF 0.3g (a Richter magnitude 7.5 earthquake occurriag directly beneath tl�e site), in accordance with UBC guidelines. This seismic zone factor for this site should be �sed with soil type Sc. Alternatively, guidelines presented in the 2003 Inten:ationa! Building Code (IBC), Sectiun 1615, may be used. Information presented in Figure 1615(1) indicates a mapped spectral acceleration for short periods of S� = 1.26. Information presented in Figure 1615(2) indicates a mapped spectral acceleration for a 1 second period of Si = 0.43. B;�sed on the results of subsurface expioration and on an estimation of soil proper;ies at depth utilizing available geologic data, Site Class "C" in conformance with Table 1615.1.1 may be used. Site coefficients F� = 1.0 and F� = 1.37 in conformance with IBC Tables 1615.1.2(1) and ]615(2), respectively, may be used. 6.0 EROSION HAZARDS AND NiITIGATION To miti�ate and reduce the erosion hazard potential a�d off-site soil transport during and posr- construction, we recommend the following: I. No water should be direct:d to tlow over site slopes during construction activities. 2. All storm water from impermeable surfaces should be tighdined into an approved storm water drainage system or temporary ..�oraee facilities and should never be allowrd to flow over site slopes. Jnnuan 33, Z�d �ISSOCl,ITED f.IR1'H SGE,VCES. GVC. I ' .HTlJ-�1"EJi7i3AJ-Pro�ertsL'(AJ7J8�KE'�ll'p. :t=A" Page 8 �I