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

5.1. Rigid Inclusions Rigid inclusions are generally unreinforced, grouted, or concrete columns installed in weak foundation soils to improve the overall stiffness and strength so that the foundation soils can meet the settlement criteria and achieve the bearing capacity required for support of shallow foundations of a structure. Rigid inclusion elements are formed by constructing unreinforced concrete columns using a continuous - flight, hollow -stem auger attached to a set of leads supported by a crane or installed with a fixed -mast drill rig. The first step in the rigid inclusion placement process consists of drilling the auger into the ground to the specified tip elevation of the rigid inclusion. Concrete is then pumped through the hollow -stem during steady withdrawal of the auger, replacing the soils on the flights of the auger. One benefit of using the augercast method for rigid inclusion installation is that the auger provides support for the soils during the installation process, thus eliminating the need for temporary casing or drilling fluid. 5.2. Rigid Inclusions Design In this project, the rigid inclusions are designed to mitigate the ground deformations and the risk of slope failure within the potential building footprints due to earthquake by stiffening the liquefiable fill and recent deposits so that the foundation design of the buildings meets the performance criteria for bearing pressure, static and seismic settlements, and lateral spreading. The design bearing capacity of the improved foundation soils was estimated based on the axial capacity of each individual rigid inclusion column and the load transfer between the columns and the surrounding soils. Design analyses were completed to estimate the total amount (i.e., number and depth) of the rigid inclusion columns that are required under the foundation; and therefore, the static and seismic settlements meet the performance criteria. 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. 5.2.1. Rigid Inclusion Layout A preliminary rigid inclusion design layout (dated October 7, 2021) was developed for the two buildings at the PGL site based on the foundation plan provided by PND on September 30, 2021. The preliminary rigid inclusion design layout will be updated based on the potential updates in the foundation and utility plans. The preliminary rigid inclusion layout is summarized below. And the detail ground improvement plans, and construction specifications will be included in separate design drawing submittals for PGL site. ■ Two -foot -diameter rigid inclusions. ■ Typical center -to -center spacing is 5 feet 4 inches and 7 feet in a triangular pattern below the building foundations, and 10 feet 6 inches in a square pattern under the slab. Refer to the preliminary rigid inclusion design layout for additional details. ■ Rigid inclusions should extend a minimum of 3 feet into the non -liquefiable layer. According to the geophysical survey results (Section 2.2.1) that indicate a depth of glacially consolidated soils ranging from 27.5 feet to 35.0 feet bgs, by including an extra 2 feet to consider the potential variability in soil condition, the tip elevations are anticipated approximately at -22.0 feet. April 1, 2022 Page 7 CiEOENGINEERS� File No. os 603000