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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 28 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />Due to the specialty of drilling techniques, micropiles are generally contracted out as <br />performance specifications (i.e., project structural engineers specify design capacity of piles, <br />minimum required strength of grout, and strength of steel casing and reinforcement), and the <br />contractor is responsible for design, installation, and quality assurance. <br />4.6 DRIVEN PILE AND DRILLED MICROPILE FOUNDATION RECOMMENDATIONS <br />For preliminary design purposes, HWA recommends driven, closed-end, steel pipe piles for <br />support of the proposed Effluent Pump Station and other proposed settlement-sensitive structures <br />and pipelines. HWA understands that BC selected 18-inch-diameter, 5/8-inch wall, steel pipe <br />sections filled with concrete to support the Effluent Pump Station, Combined Sewer Control <br />Valve Vault (CS Vault 30-01), and other pile-supported structures. Where overhead clearance is <br />a concern, HWA understands that BC selected to install 8-inch-diameter drilled micropiles. <br />Note that piles will be required to be embedded into the dense glacial soils (i.e., competent soil <br />layer below liquefiable soils) to achieve required capacities and sufficient support to resist down <br />drag and structural loading conditions. Approximate depths to competent soil layers below <br />liquefiable soils are shown on Figures 4A and 4B. <br />4.6.1 Vertical Axial Capacity <br />Piles to support the proposed Effluent Pump Station, CS Vault 30-01, and other designated <br />pipelines, manholes, and vaults should be designed for both static and seismic loading <br />conditions. Applied loads for static loading conditions include dead and live loads. During static <br />loading, the axial capacity of a single pile is equal to the tip capacity and the skin friction <br />developed along the entire length of the pile. Applied loads for the seismic loading case typically <br />include dead loads and inertial loading caused by earthquake shaking. The axial capacity of a <br />single pile for the extreme event (seismic) is assumed to be equal to the tip capacity and the <br />portion of the skin capacity developed below the lowest liquefiable layer (i.e., into dense glacial <br />soils). Uplift pile capacity will be developed from frictional resistance in the dense glacial soils. <br />For the seismic loading condition, down drag loads (see Section 4.6.2) should also be included. <br />Ultimate pile capacities of 18-inch-diameter open-ended steel pipe piles and 8-inch-diameter <br />micropiles were evaluated using AASHTO LRFD Bridge Design Specifications methods under <br />static and seismic conditions. The capacities are based on the strength of the supporting soils for <br />the estimated pile tip elevations and should include a factor of safety of at least 2 on the <br />calculated ultimate capacities for static loading conditions and a factor of safety of 1 on the <br />calculated ultimate capacity for seismic loading conditions. HWA recommends that dynamic pile <br />testing using the Pile Driving Analyzer (PDA) on driven piles be used to confirm design <br />capacities. A summary of ultimate capacities required for all proposed pile-supported areas and <br />respective structures is presented in Table 2.