3500 TERMINAL AVE Geotech Report 2022-10-25

12 I Port of Everett—South Terminal Wharf&Electrical Upgrades—Phase 2 The results of our analysis indicate that liquefaction-induced settlement will be greatest at the north end of the South Terminal,where up to 16 inches of settlement may occur in the native silty sand. Furthermore,settlement in the dredged fill of up to 7 inches is estimated,which may cause significant differential settlement of the wharf between the upland area(which is underlain by the fill)and the pile- supported area west of the top of the construction dike. Tsunami Hazard The tsunami hazard within Puget Sound is controlled by crustal faults.According to the Everett tsunami hazard map prepared by the Washington State Department of Natural Resources(2014) (Attachment 2),a tsunami originating from a magnitude-6.7 Seattle Fault earthquake would likely cause widespread inundation ranging from 0 to 2 feet across the project site. For a magnitude-7.3 Seattle Fault event, inundation estimates range from 0 to 6 feet across the project site. Because of the relatively long return periods of these Seattle Fault events,the tsunami hazard during the design life of the structure is low. Other potential tsunami sources in the area,such as the southern Whidbey Island fault zone,are currently not characterized well enough to create specific scenario models(WSDNR). GEOTECHNICAL ENGINEERING CONCLUSIONS AND RECOMMENDATIONS The following sections provide our conclusions and recommendations pertaining to the geotechnical aspects of the project. Slope Stability The slope stability of the site was analyzed using limit-equilibrium methods and numerical modelling methods to evaluate the stability of the proposed under-wharf slope and wharf system under static, pseudostatic,and post-earthquake liquefied conditions. Numerical modelling using the program FLAC was performed to assess the dynamic behavior of the slope and wharf under various seismic hazard levels. For each loading scenario,two design cases were considered: 1. Current slope geometry and pile layout 2. Current slope geometry and pile layout with proposed additional structural piles In our analysis, lengths of existing piles were estimated using the historical pile driving records from the original Weyerhaeuser Mill as-built drawings(1978)and Shannon&Wilson(2015). If no records were available for a given section, plan pile depths were used.Additionally,we received plans dated March 22,2017 with bathymetry data from KPFF,and developed the stability model geometries to reflect the bathymetry surveys. Slope stability of the site was modeled for the two cross sections A-A'and D-D'with the geometry shown in Figures 3 and 6,respectively,to capture the variability in the presence of soils with high liquefaction potential (ESU 5 and ESU 6).Appendix F describes the procedures used in the slope stability analyses in greater detail. 19232-01 rI December 6,2017 CRO