1004 BROADWAY EVCC STUDENT HOUSING - PUBLIC WORKS 2017-01-13

Geotechnical Report - Revised Proposed Apa�rtrnents: 1002, 1006, and 1008 Broadway Street, Everett, Washington May 12, 2015 Lateral forces from seismic loading and unbalanced lateral earth pc•essures may be resisted by a combination af 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 deterniined using an equivalent fluid weight of 350 pc£ This value ineludes a factor of safety of 1.5, assurning the footing is backfilled with structural fill. A friction coefficient of 0.35 may be used to determine tlie frictional resistance at the base of the footings. The coefficient includes a factor of saf'ety of ].S. 4.4.4 Wal! Drainage Provisions for wall drainage sltould 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 I S-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 6400, may be used in iieu of the clean c�ushed 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 backf 11 should consist of imported, free draining granular material or a soil meeting thc rcquirements of Gravel Borrow as defined in Section 9-03.14(1) of the WSDOT Sta��daj•d Specifications for Roczcl, Bridge, arrd Mi�rricipal Co�istri�clio�r (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 predomin�tely 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 optimuin moisture content, placed in loose, horizontal lifts less than 8 inches in thickness, and systematica3ly conipacted to a dense and relatively unyielding condition and to at least 95 percent of the maximum dry density, as deterrnined using test method ASTM D-1557� Within 5 feet of the wall, the backfill should be coinpacted with hand-operated equipment to at least 90 pet•cent of the maximum dry density. IS-04� lUU8 Bruadwny, Itcviscd I�i1�L' 9 P2I1�i�C�, �31C.