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 5.1.1 Ultrablock Shoring Ultrablocks consist of concrete blocks with a typical dimension of 21/2 feet high, 21/2 feet deep and 5 feet long. Based on the encountered soil conditions, in our opinion, Ultrablocks can be used to shore an excavation with a maximum height of three blocks, or 7%2 feet, with a vertical face. An Ultrablock wall up to four blocks, or 10 feet high, may be constructed, but would need to have a face batter of no steeper than 6V:1H (Vertical:Horizontal). The blocks should be placed in a running bond pattern and the space between the blocks and excavation backfilled with clean crushed rock meeting the requirements for Permeable Ballast in the WSDOT Standard Specifications, Section 9- 03.9(2) (WSDOT, 2014), or an approved equivalent. Clean rounded gravel such as pea gravel or washed gravel/drain rock should not be used to backfill the block wall. The base course of blocks should be embedded at least one foot below the construction subgrade elevation. The grade above the wall may be sloped at a 1H:1V inclination. The Ultrablock temporary shoring may be placed in alignment with the walls of the building and can used as the backform for the permanent basement walls. The joints between the blocks will allow groundwater to seep through the shoring. As the wall will be faced by the concrete basement walls, it will be necessary to provide drainage to collect the seepage and prevent hydrostatic pressures from building up behind the wall and concrete facing. For this application, a geotextile sheet drain incorporating a filter fabric such as Miradrain 6000, or equivalent, should be used. The sheet drain should connect to piping extending through the basement wall that connect to a collector pipe on the inside edge of the perimeter foundation. We recommend the Ultrablocks be stockpiled on site before commencing with the excavation. This will allow for placing the blocks as the excavation progresses. PanGEO personnel should also be on site to observe the stability of the excavation and to monitor the Ultrablock wall construction. If the excavation cannot be accomplished using Ultrablock shoring, then consideration should be given to using a shoring system consisting of cantilevered soldier piles with timber lagging. 17-233 1020 North Broadway Page 11 PanGEO,Inc.