Depth-dependent response of a liquefiable sand deposit to repeated electrolysis-induced desaturation

Abstract

Introducing a discrete gas phase into saturated sand reduces the bulk modulus of the pore fluid, but the response of deep deposits to repeated electrolysis-induced desaturation (EID) has received limited field evaluation. A field trial lasting 45 days comprised three energisation cycles of 12 h each at 3 A, separated by 15 days, in a fine sand deposit classified as liquefiable by the site investigation. Nine time domain reflectometry probes at depths of 10, 15 and 20 m recorded bulk electrical conductivity corrected for temperature, and three observation wells measured groundwater head response. Resistivity calibration using the site sand yielded spatially averaged saturation minima of 96.33%, 95.50% and 94.71% at 10 m during cycles 1 ~ 3; the corresponding values were 97.66%, 97.37% and 97.15% at 15 m, and 98.14%, 97.94% and 97.75% at 20 m. Groundwater head peaks corrected against the reference well increased from 9.67 to 14.63 mm. Equivalent circuit resistance increased during successive cycles, for which the total measured energy was 46.26 kWh. Faraday’s law gave a stoichiometric upper bound for gas production of 1.007 mol per cycle. Concurrent changes in bulk resistivity and groundwater head were repeatable across the three cycles, with the greatest inferred desaturation at the upper electrode boundary.