Geotechnical Evaluation for the Treasure Island New Ferry Terminal Foundations-Paper

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The Treasure Island Ferry Terminal lies on hydraulic sand fill over shallow shoal deposits, soft Young Bay Mud, and deeper Older Bay Deposits. Offshore, Young Bay Mud is approximately 30–60 feet thick and is weak and compressible. The site is exposed to strong earthquake shaking, liquefaction, lateral spreading, shoreline instability, and seismic forces on offshore foundations.<br /><br />A detailed geotechnical investigation and site-response analyses were used to establish seismic design motions and assess foundations. The terminal’s shore-side improvements could experience damaging movement if the fill alone were improved. Engineers therefore designed a deep-soil-mix (DSM) buttress, with additional fill improvement and surcharge. Analyses indicated that movement behind the buttress would generally be limited to 2–6 inches, with the DSM expected to remain largely elastic during the design earthquake.<br /><br />Offshore movement could not be practically eliminated. Accordingly, the ferry pier and float were supported on 48-inch steel monopiles, while the breakwater used concrete sheet piles supported by 24-inch concrete batter piles. These deep foundations were designed to resist soil–pile interaction and kinematic loads from lateral movement of offshore deposits.<br /><br />Construction conditions required a breakwater redesign: denser-than-expected fill and shoal deposits prevented pile installation near shore. A rock berm was built to bridge the gap and provide scour protection. Settlement analyses considered immediate movement and long-term consolidation, including substantial potential settlement where the berm rested on bay sediments.<br /><br />The project demonstrates how site-specific seismic analysis, ground improvement, deep foundations, and construction-stage adaptation were combined to address challenging marine soils and earthquake hazards.

Keywords

Treasure Island Ferry Terminal

geotechnical investigation

liquefaction

lateral spreading

Young Bay Mud

deep-soil-mix buttress

seismic design motions

steel monopiles

breakwater redesign

construction settlement