931 BROADWAY SEPA 016 - 008 - TEUTSCH PARTNERS Geotech Report 2025-04-14

Geotechnical Report Proposed Student Housing: 931 Broadway Street, Everett, Washington December 8, 2015 4.4.2 Surcharge Surcharge loads, where present, should also be included in the design of retaining walls. We recommend a lateral load coefficient of 0.3 be used to compute the lateral pressure on 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, on-site soils are not suitable for use as wall backfill. 15-275 931 Broadway,Everett Page // 9y PanGEO, Inc.