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Blast-Induced Liquefaction and Determination of Soil-Density Changes with Ground-Penetrating Radar, Treasure Island, CA

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Objectives
The objective of this study was to observe the effects of liquefaction on soil density. To achieve this, PVC-cased boreholes were placed approximately 8 m away from the piles, and blast charges were then placed between the piles and the boreholes, roughly equidistant from each. As such, the radar site would experience similar blast intensity as the pile group, but was isolated from pile-group loading following the blast. Blasts consisted of eight 0.5 kg explosive charges placed in a circular pattern around the pile group, and approximately 3.5 meters below the excavated surface (3 meters below the ground water surface). For each blast, elevated pore water pressures were measured, sand boils were observed, and settlements were recorded. Extensive sand boiling and water flow to the surface were also observed adjacent to the radar borehole array such that we are confident that liquefaction occurred within the tomographic plane. Piezometer sensor data indicate that a 4-m thick zone liquefied within the soil column.

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