615 75TH ST SE Geotech Report 2022-10-25

Subsurface Exploration, Geologic Hazard, and Boardwalk Condominium, Building C Geotechnical Engineering Report Everett, Washington Design Recommendations 11.0 PIPE PILE FOUNDATIONS The pipe pile foundations recommended herein are intended to mitigate the condominium foundations near the slope/rockery crest where future movement is most likely. Some risk of future landsliding in the property will remain even with the mitigation measures installed. Our subsurface exploration of the area indicates that loose fill and native glacial soils are located beneath the project area as described above. We anticipate the loose deposits are at least approximately 12 feet thick below existing grades in the areas of the proposed foundation improvements. The pipe piles will penetrate through the unsuitable loose soils into the medium dense and very dense soils at depth. Once a structural engineer has developed plans indicating the locations of the pipe piles, AESI should review the underpinning plan once completed to verify conformance with the recommendations of this report. 11.1 Pipe Piles Due to restricted site access, we recommend that foundations consist of small-diameter, driven pipe piles. Pipe piles should consist of 2-inch inside-diameter steel pipe, typically driven with a pneumatic hammer through the soft soils to embedment in the underlying, bearing layer. For pipe piling driven to refusal, we recommend using an allowable bearing capacity of 4,000 pounds per pile (4 kips). Refusal is defined as less than 1 inch of vertical movement after 60 seconds of sustained driving with a 90-pound jack hammer. Medium dense soils that are suitable for support of the piles are anticipated at a minimum depth of approximately 10 feet below existing grades; however, the piles will penetrate significantly deeper into the bearing soils. We recommend starting at the corner and working east along the foundation line. The piles will likely continue to shorten as the depth of fill decreases. We suggest planning for at least 40 feet to the east of the corner with the possibility of going farther. Anticipated settlements of a pipe pile-supported grade beam should be less than 0.5 inches. Vertically driven pipe piles should not be used to provide lateral support. Since pipe piles are driven until specific refusal criteria are achieved, rather than to a specific depth, accurate estimation of pile lengths is not possible. We recommend that AESI be retained to observe pile installation to confirm that our recommendations have been implemented to verify that appropriate installation procedures are used, and that the appropriate refusal criteria are achieved. The City of Everett will more than likely require this inspection as a condition of the building permit. September 12, 2012 ASSOCIATED EARTH SCIENCES, INC. FSM/[d-EE120288A8-Projects 1201202881EEIWP Page 10