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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 36 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />4.6.4 Lateral Evaluation – Effluent Pump Station, CS Vault 30-01, and OMES <br />Generator Pad <br />HWA understands that BC will use lateral soil spring constants for design of piles supporting the <br />Effluent Pump Station, CS Vault 30-01, and the OMES generator pad. The software program <br />LPILE 2022.12.10 (Ensoft) was used to obtain the lateral soil spring constants for a single, <br />vertical, 18-inch-diameter steel pipe pile for the Effluent Pump Station, CS Vault 30-01, and <br />OMES generator pad structures. <br />HWA based the analyses on the following assumptions and information provided by BC: <br />• Pile cap and tip elevations for the relevant structures presented in Table 2, Section 4.6.1, <br />were used in the analyses. <br />• HWA understands that 18-inch-diameter, 5/8-inch-wall steel pipe piles filled (after <br />driving) with concrete will be used for the structures. <br />Lateral soil spring constants for the 18-inch-diameter piles are presented in Appendix G. <br />4.6.5 Impact of Lateral Spreading on Pile Capacity <br />HWA understands that a ground improvement buttress is proposed west of the Effluent Pump <br />Station; the intent of the ground improvement is to reduce lateral spreading loads for the Effluent <br />Pump Station, CS Vault 30-01, and associated infrastructure east of the buttress. <br />Based on the conditions observed in borings HWA-10P, HWA-11, HWA-12, HWA-13P, HWA- <br />15, and HWA-16P, liquefiable soil with the potential for lateral spreading extends from <br />elevations of approximately 10 feet to -66 feet. Other pile-supported structures are anticipated at <br />locations other than those where lateral spreading is mitigated by the ground improvement <br />buttress. Although these other structures are likely to have some level of protection from <br />liquefaction-induced lateral spreading (provided indirectly by the ground improvement buttress <br />and other pile-supported structures), lateral spreading loads on these structures should still be <br />anticipated. HWA understands that smaller pile-supported structures (other than the Effluent <br />Pump Station and Area 40 Stormwater treatment system) will be designed to only accommodate <br />associated liquefaction-induced settlements. HWA did not provide liquefaction-induced lateral <br />loads. <br />4.6.6 Micropile Design Considerations <br />Recommendations for the design of drilled micropiles are summarized below: