3535 RIVERFRONT BLVD Geotech Report 2023-02-22

September 24, 2018 HWA Project No. 2015-061-21 the anticipated settlement of compressible materials at the crane location induced by the significant depths of proposed new fill. Downdrag loading for 16-inch and 18-inch diameter piles was evaluated using LRFD methods in general conformance with the procedures referenced in the FHWA Design and Construction of Driven Pile Foundations (Hannigan, et al., 1997). For the crane foundation piles, downdrag loading will occur to approximately Elev. -7 feet. The downdrag loading associated with a 16-inch diameter pile is about 60 kips. For an 18-inch diameter pile, the downdrag loads are estimated to be 90 kips. A load factor of 1.1 is recommended to be applied to downdrag loading (WSDOT, 2016). Downdrag forces will also be exerted on the piles due to settlement of liquefied materials during the Extreme Event Limit State. Potentially liquefiable materials extend to El. -37 feet, equal to a pile penetration depth of about 60 feet below the proposed ground surface of the crane structure. All materials above this elevation will exert downdrag loading associated with the residual strength for liquefied materials, and the full strength for non-liquefied materials. However, downdrag is expected to be higher for smaller events as layers that are predicted to liquefy for the design event may not liquefy for smaller events. Thus, we provide the resulting estimated downdrag force using the full-strength properties of the soils above the lowest liquefiable layer likely to liquefy in smaller events (Elev. -20 ft) and the residual in the lowest liquefiable layer from Elev. -20 to -37 ft. The resulting load exerted on a 16-inch diameter pile for the liquefied state is 210 kips. The downdrag force exerted on an 18-inch diameter pile during the liquefied state is 280 kips. A load factor of 1.0 is recommended to be applied to downdrag loading for the Extreme Event Limit State (WSDOT, 2016). Piles will need to be driven a sufficient depth into the non-liquefiable materials to support the loads of the Extreme Event State, which should be verified during driving. A minimum tip elevation should be required to be about 5 feet into the non-liquefiable material which is Elev. -42 feet. Concrete Slab at Crane Structure In design discussions with KPFF, we understand that the portion of the concrete slab within the sheet pile wall will be structurally supported by the sheet and/or crane foundation piles. West of the sheet piles, however, the slab is planned to be constructed on grade. Based on our analyses with regard to settlements due to grading fill placement, we anticipate of the order of 2 to 3 inches of settlement between the structurally supported slab and the slab-on-grade. However, there could be more, depending upon the variability in subsurface conditions. Given the predicted settlements, we recommend some manner of narrow transfer slab section be included between the two slabs that could articulate off the structurally supported portion to the slab-on- grade portion. This will allow the grade-supported slab portion to settle independent of the structural portion and will minimize the damage to the slab, as well as provide for a smoother surface transition between the slab sections. Final Geotechnical Report-3-Acre Park.docx 20 HWA GeoSciences Inc.