1910 MERRILL CREEK PKY 2018-11-15

� Mr. Darren Peugh January 19, 2004 The soil conditions we observed at the hand-excavated test holes in the area of the water quality pond consisted of dense, compacted silty sand with gravel fill. As we understand, this fill was placed for construction of the access roadway. The approximate location of the previously excavated test pits and our recent hand auger borings are shown on Figure 2. Logs describing soil conditions observed are attached as Fib re 3. GEOLOGIC HAZARDS Seismic The Puget Sound area falls within Seismic Zone 3 as classified by the 1997 Uniform Building Code (UBC). Based on the soil conditions encountered and the local geology, Table 16-J of the 1997 UBC indicates that soil type S� should be used in structural design. Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations. Liquefaction mainly affects geologically recent deposits of fine-grained sands that are below the groundwater table. Soils of this nature derive their strength from intergranular friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction; thus, eliminating the soil's strength. Based on the results of our study, in our opinion, there is no risk for soil liquefaction to occur at this site. Slope Stability Title 19, Chapter 37 of the Everett Municipal Code, categorizes slopes with gradients in excess of 40 percent as geologically hazardous areas. The code requires that properties designated as geologically hazardous areas have a standard buffer of 25 feet from the top, toe, and sides of the slope. To evaluate the impact of the planned development on the stability of the slopes, we completed stability analyses using the computer program WINSTABL on three slope cross-sections. These sections were located through the southeast building corner, the east side of the building where the building foundation is about ten feet from the top of the slope, and off the northeast site corner through the proposed water quality pond. The analyses were performed for existing and post-construction conditions. The post-construction analyses included pseudostatic or seismic analysis using a horizontal acceleration value of 0.17g to simulate loading during a seismic event. The following tables summarize the results of the analyses listing the safety factors for the critical failure surfaces generated by the analyses. Southeast CoYner Slope Conditions Analyzed Minimum Safet Factors Static Pseudostatic Existing conditions 1.54 1.10 After construction 1.54 1.10 Proj ect No. T-5471 Page No. 3