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Mr. Greg Bertch <br />January 18, 2017 <br />Our stability analyses was performed along three critical slope sections delineated as Cross -Sections A -A', B-B', <br />and C-C'. The cross-section locations are shown on Figure 1. Stability analysis along these sections was <br />performed using the computer program Slide 7.0. Our analysis considered both static and the pseudostatic <br />(seismic) conditions. A horizontal acceleration of 0.16g was used in the pseudostatic analysis to simulate slope <br />performance under earthquake loading. This value is based on the maximum considered earthquake (MCE) peak <br />ground acceleration (PGA) adjusted for pseudostatic analysis following procedures outlined in Section 6.2.2 of <br />the FHWA NHI-11-032 Seismic Design — Geotechnical Features Manual. <br />Soil conditions/geologic units modeled in the sections are based on our test pit field explorations, previous <br />explorations completed by others, and geologic reconnaissance of the slope. Test Pit and Test Boring Logs used <br />for the analysis are attached to this letter. Strength parameters assigned to the soils are based on our experience <br />with similar soil types and local standard practice. Values assigned are summarized in the following table: <br />Table 1— Slope Stability Analysis Soil Parameters <br />Soil Type <br />Unit Weight (pcf) <br />Friction Angle (degrees) <br />Cohesion (psi) <br />New structural fill <br />125 <br />34 <br />0 <br />Existing fill <br />120 <br />32 <br />0 <br />Dense to very dense silty SAND <br />with gravel <br />125 <br />36 <br />50 <br />Dense to very dense SAND with <br />varying amounts of silt and gravel <br />125 <br />38 <br />0 <br />Water <br />62.4 <br />0 <br />0 <br />The results of our slope stability analysis, as shown by the lowest safety factors for each cross section, are <br />presented in the following table: <br />Table 2 — Slope Stability Analysis Results <br />Cross Sections Analyzed (Post Construction) <br />Minimum Safety Factors <br />A -A' <br />1.734 <br />Seismic FS =1.214 <br />1.615 <br />B-B' <br />Seismic FS =1.141 <br />C-C' <br />1.580 <br />Seismic FS =1.122 <br />The results of our analysis indicate that the eastern steep slope will be stable post construction and that the pond <br />can be constructed as shown on the drawings without any adverse impacts to the global stability of the slope. <br />Graphical output of the analysis is attached for City of Everett review. <br />Project No. T-7342 <br />I <br />