1710 W MARINE VIEW DR Geotech Report 2023-12-29

■ The concrete mixture for the rigid inclusions should have a minimum compressive strength (fc') at 28 days of 3,000 pounds per square inch (psi). Refer to ground improvement specifications that will be included in separate design drawing submittals for PGL site for additional details. ■ Rigid inclusions should be overlain by a 2-foot-thick layer of crushed surfacing base course (CSBC) to act as a load transfer pad (LTP) between the foundation elements and the rigid inclusions (compacted in accordance with the geotechnical engineer's recommendations). ■ The CSBC should comply with Washington State Department of Transportation (WSDOT) Standard Specification Section 9-03.9(3), Base Course, and restrict fines to maximum 5 percent passing Number 200 sieve. 5.2.2. Post -improvement Recommendations 5.2.2.1. Design Bearing Capacity We recommend an allowable bearing capacity of 3,000 psf with a FOS of at least 3.0 under static conditions and a modulus of subgrade reaction of 200 pounds per cubic inch (pci) be used for the foundations bearing on the improved ground. 5.2.2.2. Static and Seismic Settlements We anticipated that the static settlement will be less than 1 inch with the implementation of rigid inclusion ground improvement, and the differential static settlements between building foundations should be less than 1/2 inch over a horizontal distance of 50 feet. The seismic settlements are estimated based on the settlement reduction ratio determined based on the area replacement ratio of the rigid inclusions and the stiffness ratio between the soils and rigid inclusions. The post -improved seismic soil settlements are anticipated to be less than 6.0 inches; and the differential seismic settlements are anticipated to be on the order of 0.1 to 0.8 inches over a horizontal distance of 50 feet. 5.2.2.3. Earthquake -Induced Lateral Ground Deformation The post -improvement earthquake -induced lateral ground deformation was estimated by performing global slope stability and Newmark analyses that include the improved area with an increased overall strength. Based on the preliminary rigid inclusion design layout, a conservative area replacement ratio of 3 percent was used in the post -improvement global slope stability evaluation. With an area replacement ratio of 3 percent and a compressive strength of 3,000 psi, the increased composite strength of the improved ground was estimated as 6.5 kilopound per square foot (ksf) for the improved area. The improved area was conservatively applied to the north building only. As shown in the Post -Improvement Slope Stability - Post -Earthquake Condition, Figure 9, the FOS corresponding to the slip surfaces going underneath the potential building footprint is higher than 1.9, which indicates a stable post -earthquake condition after ground improvement. With a stable post - earthquake condition, the post -improvement earthquake -induced lateral spreading is mainly due to the deformations happening during earthquakes. As shown in the Post -Improvement Slope Stability - Seismic Condition, Figure 10, with a failure wedge going underneath the potential building footprint with a FOS of about 1.0, the yield acceleration was estimated as 0.25g. The corresponding earthquake -induced lateral ground deformation was estimated at about 3.1 inches, which is within the allowable lateral displacement criterion of 18 inches per ASCE 7-16. GEOENGINEERS� April 1. 2022 Page 8 Flo, No 06, 6-030-00