Geotechnical Mitigation of Treasure Island Phase1-PPT Presentation

PPT Presentation

Pdf Summary

ENGEO’s August 2021 presentation describes the geotechnical resilience program for Treasure Island development. Before infrastructure improvements, the program aimed to densify sandy hydraulic fill to reduce liquefaction-related settlement, pre-compress soft Young Bay Mud using surcharge to limit future subsidence and support new construction, raise grades for sea-level rise, and strengthen the shoreline and causeway to protect critical infrastructure and maintain access during a major earthquake.<br /><br />Geological investigations identified different shoal deposits: relatively clean, densely packed sand with thin clay bridges, and finer-rich, interbedded clayey sand and clay. The presentation notes that the latter deposits may have added capacity due to their fines, sand-clay mixing, clay cementation, depositional processes, and bioturbation. Laboratory testing included cyclic and monotonic simple shear tests. Engineers also developed and calibrated a two-dimensional finite-element model for seismic analysis.<br /><br />Ground-improvement techniques included wick drains to shorten surcharge periods, vibrocompaction and direct power compaction to densify sandy fill, tamping, surcharge, and deep soil mixing. Field testing evaluated direct power compaction.<br /><br />The presentation’s conclusions emphasize that densification was applied only to hydraulic fill, stone columns were not used, and the development made expanded use of shallow foundations.

Keywords

Treasure Island development

geotechnical resilience

liquefaction mitigation

hydraulic fill densification

Young Bay Mud

surcharge precompression

sea-level rise adaptation

shoreline strengthening

vibrocompaction

deep soil mixing