7500 HARDESON RD Geotech Report 2022-10-25

Geotechnical Engineering Report SSGCHardeson Road Retail Everett,Washington SSGC Project No. 18072 September 18,2018 Table 6. Lateral Earth Pressures Earth Pressure Equivalent Fluid Soil Type Coefficient Pressure(pcf) Active: 0.31. Active: 35 Native Soil At-rest: 0.47 At-rest: 50 Passive: 3.25 Passive: 325 Active: 0.45 Active: 50 Fill At-rest: 0.60 At-rest: 65 w Passive: 2.0 Passive: 200 A factor of safety of about 1.5 should be applied to these values. Additional lateral pressure should be added to these values to model surcharges such as sloped backfill, traffic. construction, or seismic loads. We recommend an active seismic pressure of 7H psf(where H is the height of the subgrade wall) and an at-rest seismic pressure of 11 H. The effects of other surcharge loads should be accounted for as appropriate. Wall Drainage ' Drainage should be provided behind subgrade walls to reduce the potential for hydrostatic pressure developing against the wall. We recommend a minimum 12-inch wide zone of free draining granular soil (WSDOT Section 9-03.12(4), or as approved by the engineer) is placed directly behind the wall. A perforated rigid plastic drain pipe at least 6-inches in diameter should be installed behind the base of the wall within 6-inches of the bottom of the footing. The drain line should be surrounded with the free-draining granular soil zone and sloped to provide flow to an approved storm water receptor.The granular fill zone should extend to within 1 foot of final grade of the wall,where it should be capped with compacted low permeable fill containing sufficient fines to ' reduce infiltration of surface water into the drainage zone. A filter fabric (such as Mirafi I40N, or other approved material) should be placed between native soils and the granular drain material to limit siltation into the drainage zone. Cleanouts are recommended for maintenance of the drain system. Wall Backfill Backfill behind the drainage zone should consist of granular material that satisfies the criteria of Section 9-03.12(2) "Gravel Backfill for Walls" per the 2014 Washington State Department of Transportation (WSDOT) Specifications for Road, Bridge, and Municipal Construction Manual (Publication M 41-10),or as approved by the engineer. Wall backfill should be placed in lifts not exceeding 8 inches and compacted with hand-operated compaction equipment. Compaction of wall backfill should be between 90 to 92 percent of the maximum dry density(MDD) per the ASTM D1557 test method within 3 feet of the back of the wall. At a distance greater than 3 feet behind the back of the wall, backfill can be compacted 12