Electrochemical cementation of calcareous sand for offshore foundations

A laboratory-floor experimental study was conducted on the electrochemical cementation of calcareous sand for offshore foundations. A caisson, 200 mm in diameter and 400 mm long, was embedded in a calcareous sand under seawater. The calcareous sand and seawater were recovered from the coast of Western Australia. Installed around the caisson were 12 electrodes, made of perforated steel pipes 14 mm in diameter and 450 mm long and filled with soluble CaCl2 granules as a cementing agent. A dc voltage of 8 volts with current intermittence and polarity reversal was applied over a period of 7 days to transport the cementing agent into the pores of the calcareous sand. The results of the treatment were assessed by a pullout resistance test, after which the caisson was pushed back into the soil and the treatment repeated to simulate post-failure recovery. The results showed that the pullout resistance of the foundation model after the electrochemical treatment increased by 140% prior to failure and increased by 255% post-failure, as compared with that of the control test. The cementation generated by the electrochemical treatment was evidenced by the attachment of cemented soil to the electrodes and caisson. The cementation effects were further confirmed by the mineralogical, chemical and XRF analyses, which indicated formation of synthetic calcite, calcium iron chlorate and iron oxide, compounds known as cementation agents in soils.