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 used in the study were recovered from the coast of Western Australia. Twelve electrodes, made of perforated steel pipes of 14 mm in diameter and 450 mm long, were installed around the caisson. The hollow electrodes were filled with soluble CaCl2 granules as the cementation agent, which were forced into the calcareous sand by an applied intermittent electric current. A dc voltage of 8 volts with current intermittence and polarity reversal was applied over a period of 7 days. A control test with identical configuration to that of the electrochemical treatment test was also set up to provide baseline data. The results of the treatment were assessed by a pullout resistance test. After the pullout test, the caisson was pushed back into the soil sample and the treatment was repeated to simulate post-failure recovery. X-ray diffraction analysis, X-ray fluorescence analysis and electron microscopy imaging for soil particles and chemical analyses for soil pore fluid were conducted on control and treated soil samples. The results showed that the pullout resistance of the foundation model increased by 140% prior to failure and 255% post-failure after the electrochemical treatment, 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 evidenced from the mineralogical and chemical analyses, which indicated formation of new calcite and calcium iron chlorate minerals. In addition, XRF analysis showed significant increase of iron oxide (Fe2O3) an amorphous compound known as a cementation agent in soils.