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 5.1.2 Cantilevered Soldier Piles with Timber Lagging Shoring For an excavation that has less than 12 to 15 feet of vertical face, a cantilevered soldier pile shoring wall may be considered. Soldier pile shoring consists of vertical steel beams, typically installed 6 to 8 feet apart along the proposed excavation, spanned by timber lagging. Prior to the start of excavation, the steel H-beams are installed in pre-drilled holes that are backfilled with structural concrete and lean mix concrete. As the excavation proceeds downward and the steel piles are exposed,timber lagging is installed between the flanges of the H-beams to support the soils exposed in the excavation. The basement walls may then be formed and cast against the shoring. The earth pressures depicted on Figure 3 should be used for design. The lateral earth pressures should be increased for surcharge loads resulting from adjacent structures, including the retaining wall located west of the site, construction equipment, or excavated soil stockpiles if they are located within the height dimension(H) of the wall. Above the bottom of excavation, the recommended active earth and surcharge pressures should be applied over the full width of pile spacing. Below the bottom of excavation, the active pressures should be applied over one pile diameter, and the passive resistance should be applied over two times the pile diameter. The upper two feet of the passive pressure should be neglected to allow for disturbance of the ground surface in front of the wall. Voids behind the timber lagging should be backfilled with control density fill(CDF). The joints between the lagging will allow groundwater to seep through the shoring. Drainage should be provided to collect seepage and prevent hydrostatic pressures from building up behind the wall and concrete facing. A sheet drain consisting of Miradrain 6000, or equivalent, should extend the full height of the wall and should be spaced evenly between the soldier piles. The sheet drain should be connected to a perforated collection pipe or weepholes placed along the base of the wall to remove seepage. The timber lagging may be designed for 50 percent of the recommended lateral earth pressures,to account for the effects of arching. 17-233 1020 North Broadway Page 12 PanGEO,Inc.