Site Investigation and Laboratory Results on Treasure Island Natural Shoal Deposit

Treasure Island is located in the central San Francisco Bay, immediately north of Yerba Buena Island, between the active San Andreas and Hayward faults. The island was constructed by placing hydraulic sand fill within a perimeter of rock dikes. The original objectives of the study are: (1) to evaluate the potential for pore pressure generation and characterize the stress-strain response in the shoal deposit, along with the resulting lateral movements; and (2) to estimate the amount of settlement that may occur due to post-cyclic reconsolidation of the shoal deposit. The results of this study demonstrate that the dynamic behavior of the natural shoal differs from that of the fill and is influenced by variations in clay content, as well as the unique soil structure shaped by the site-specific depositional environment. To assess these soil characteristics, multiple borings, Cone Penetration Tests (CPTs), and cyclic laboratory tests were performed by ENGEO between 2008 and 2021. The site investigation data is intended to be made publicly accessible through this project.