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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 39 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />4.7 NON-PILE-SUPPORTED DESIGN <br />The following discussions and recommendations are provided for proposed structures that are <br />not supported on pile foundations. <br />4.7.1 Lift Station 46 <br />Lift Station 46 Foundation Recommendations <br />The proposed Lift Station 46 (LS 46) will be founded on a slab-on-grade foundation at an <br />approximate elevation of -15 feet. For this structure, HWA recommends a maximum allowable <br />bearing pressure of 3,000 pounds per square foot (psf) for foundations that are bearing directly <br />on firm and unyielding native soils. For short-term wind and seismic loading conditions, this <br />allowable bearing pressure may be increased by 33 percent to resist increased pressures on the <br />edge of the foundation due to over-turning moments. <br />Lift Station 46 Resistance to Lateral Loading <br />Earthquake and unbalanced earth loads will likely subject the proposed LS 46 to lateral forces. <br />Lateral forces will be resisted by a combination of base sliding friction and passive earth <br />pressure against the buried portions of the structure. For footings founded on medium dense <br />coarse-grained soils or structural fill extending to medium dense to coarse grained soils, a <br />coefficient of friction of 0.5 may also be used to resist lateral movement. Passive earth pressures <br />of 250 pounds per cubic foot (pcf) may be utilized for areas where structural fill will be placed <br />directly against walls. For slabs designed as a beam on an elastic foundation, a static modulus of <br />subgrade reaction of 150 pounds per cubic inch (pci) may be used for subgrade soils prepared as <br />recommended. <br />4.7.2 General Shallow Foundations <br />General Foundation Recommendations <br />HWA understands that some of the proposed structures will be supported on shallow foundations <br />above liquefiable soils and within the fill soils. Structures supported on shallow foundations that <br />are susceptible to differential settlements should be designed as mat foundations. <br />Mats or slab-on-grades founded within fill soils and above soils susceptible to liquefaction <br />should be designed for a maximum allowable bearing pressure up to 1,500 psf. The <br />recommended maximum allowable bearing pressure may be increased by 1/3 for short-term <br />transient conditions such as wind and seismic loading conditions <br />General Resistance to Lateral Loading