1707 SCENIC DR Geotech Report 2022-10-25

Snohomish County Public Utility District No.1 March 31,2015 Page 3 TABLE 1. RECOMMENDED MSE WALL DESIGN PARAMETERS Soil Properties Backfill Soil Retained Soil Foundation Bearing Soil (Reinforced Zone) (Existing Fill or New Fill) 2 inches of Structural Fill Glacial Till Unit Weight(pcf) 125 125 125 125 Friction Angle(deg) 36 36 36 36 Cohesion(psf) 0 0 0 0 Notes: psf-pounds per square foot pcf-pounds per cubic foot Groundwater For purposes of design,we recommend that the groundwater be assumed at the base of the wall, provided that adequate wall drainage is provided as shown in the Typical Section of the project plans. Surcharge Loading The MSE wall was designed for a live load of 250 psf for traffic loading.GeoEngineers should be consulted to evaluate other surcharge loading conditions so that modifications can be made to our design and recommendations,as appropriate. Earthquake Loads Based on the 2002 United States Geologic Survey (USGS) probabilistic seismic hazard maps, the peak ground acceleration (PGA) expected at the site from an earthquake with a 10 percent probability of exceedance in 50 years is approximately 0.37g.The global stability was evaluated utilizing half of the PGA (0.186g)for pseudo-static seismic analysis. Wall Stability Analysis Stability analyses were performed for the wall to determine the margin of safety against sliding and overturning. The methods of analyses compute the ratio of forces (or moments) resisting movement, as compared to forces(or moments)tending to cause movement.Our design includes safety factors for sliding and overturning in excess of 1.5 and 2.0, respectively (the respective minimum safety factors normally used for stability against sliding and overturning).Bearing capacity for the wall was also analyzed and found to be sufficient for wall support. Provided the wall is founded on native undisturbed glacial soils, or on structural fill overlying dense native soils global wall stability is also adequate in both static and seismic conditions. Geogrld Soil Reinforcement for MSE Wall The minimum required grid strength and length is shown on the typical section and elevation and includes that necessary to provide both internal geogrid and wall to geogrid connection strength, and long term global stability. Geosynthetic reinforcement shall consist of geogrid manufactured specifically for soil reinforcement applications and shall be manufactured from high tenacity polyester yarn or high-density polyethylene.The wall has been designed using Tensar UX11OOMSE geogrids vertically spaced at 1.5-foot intervals.The geogrid reinforcement is typically 10 feet long,except for the upper most geogrid layer,which is 16 feet long.Any changes in design or products should be approved by GeoEngineers. GEOENGINEER rue No.0482-027-02