1210 W MARINE VIEW DR Geotech Report 2022-10-25

Proposed Port Gardner Substation £ Project No. 1779.01 aC , 15 November 2017 Geoprofessional Consultants the boring B-2 location extended to a depth of approximately 41 feet, with hard silt and clayey silt extending to the boring's 49-foot termination depth. It should be noted that the nature of uncontrolled fill is such that its composition and depth may vary over relatively short distances. Consequently, subsurface conditions between the locations of the borings referenced in this report may vary from those observed at the boring locations. ZGA completed a geotechnical evaluation for the Norton Avenue substation several blocks to the south of the Port Gardner substation site in 2014. The borings advanced for that evaluation did not encounter significant wood debris or other oversize obstructions within the fill. However, substantial wood debris and some metal (chain link fencing)were encountered during the installation of augercast piles in 2016. Groundwater Groundwater was observed at depths of approximately 3 and 3.5 feet below grade while advancing the borings. Groundwater conditions should be expected to fluctuate due to changes in seasonal precipitation,site utilization, possibly tidal fluctuations,and other factors. CONCLUSIONS AND RECOMMENDATIONS Geotechnical Considerations Based on information gathered during the field exploration,laboratory testing,and analysis,we conclude that the proposed substation construction is feasible from the geotechnical perspective provided that the recommendations presented herein are followed during design and construction.The site is underlain by low density uncontrolled fill material overlying medium dense to dense native sand and hard silt, and groundwater is relatively shallow. Our analysis indicates that the low density granular fill material would be prone to liquefaction during a design seismic event. The poor load-bearing characteristics of the fill and the potential for liquefaction will necessitate the use of deep foundations to support the more heavily loaded and settlement-sensitive substation components. Less settlement-sensitive features may be supported in a conventional manner following some subgrade improvement if seismic settlement can be tolerated. Excavations for vaults and conduits will encounter groundwater, most likely necessitating dewatering during construction. Raising site grade to the extent feasible would help to reduce groundwater intrusion into the excavations and the dewatering magnitude. Geotechnical engineering recommendations for site grading, drainage, foundations, and other geotechnically-related aspects of the project are presented in the following sections. The recommendations contained in this report are based upon the results of and the field exploration, laboratory testing, engineering analyses, and our current understanding of the proposed substation design. ASTM and WSDOT specification codes cited herein refer to the current manual published by the American Society for Testing& Materials and the 2010 edition of the WSDOT Standard Specifications for Road, Bridge, and Municipal Construction (Publication M41-10). Page 13