1020 N BROADWAY EVCC STUDENT HOUSING Geotech Report 2022-10-25

Proposal for Geotechnical Engineering Services Proposed Apartments: 1020 North Broadway,Everett,Washington September 27,2017 the wall face resulting from surcharge loads located within a horizontal distance of one- half the wall height. 4.4.3 Lateral Resistance Lateral forces from seismic loading and unbalanced lateral earth pressures may be resisted by a combination of passive earth pressures acting against the embedded portions of the foundations and by friction acting on the base of the wall foundation. Passive resistance values may be determined using an equivalent fluid weight of 350 pcf. This value includes a factor of safety of 1.5, assuming the footing is backfilled with structural fill. A friction coefficient of 0.35 may be used to determine the frictional resistance at the base of the footings. The coefficient includes a factor of safety of 1.5. 4.4.4 Wall Drainage Provisions for wall drainage should consist of a 4-inch diameter perforated drainpipe placed behind and at the base of the wall footings, embedded in 12 to 18 inches of clean crushed rock or pea gravel wrapped with a layer of filter fabric. A minimum 18-inch wide zone of free draining granular soils (i.e.pea gravel or washed rock)is recommended to be placed adjacent to the wall for the full height of the wall. Alternatively, a composite drainage material, such as Miradrain 6000, may be used in lieu of the clean crushed rock or pea gravel. The drainpipe at the base of the wall should be graded to direct water to a suitable outlet. 4.4.5 Wall Backfill Wall backfill should consist of imported, free draining granular material or a soil meeting the requirements of Gravel Borrow as defined in Section 9-03.14(1) of the WSDOT Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT 2014). In areas where space is limited between the wall and the face of excavation, pea gravel may be used as backfill without compaction. In our opinion, the predominately silty sand and silt soils underlying the site are not suitable for use as wall backfill. Wall backfill should be moisture conditioned to within about 3 percent of optimum moisture content, placed in loose, horizontal lifts less than 8 inches in thickness, and systematically compacted to a dense and relatively unyielding condition and to at least 95 17-233 1020 North Broadway Page 9 PanGEO,Inc.