Electrochemical stabilisation for offshore model caissons

A laboratory-floor experimental study was conducted on the electrochemical treatment of calcareous sand for offshore foundations. A steel tube of diameter 200 mm and length 400 mm was used as a model caisson. Calcareous sand and seawater from the coastline of Western Australia were used in the study. Twelve electrodes made of perforated steel pipes, diameter 14 mm, length 450 mm and filled with soluble CaCl₂ granules as a cementing agent, were installed around the caisson. The electrochemical treatment tests were carried out with two electrode layout configurations in parallel with a control test. The electric power was applied via pairs of the steel pipe electrodes in the first configuration whereas the caisson served as one electrode in the second configuration. The applied direct current (d.c.) voltage was 8 V for the first configuration and 6 V for the second. The pullout resistance of the caisson after the treatment was increased by 140% to reach a value of 304%, in comparison with the control. The cementation generated by the treatment was demonstrated by the formation of a soil plug inside the caisson, soil cemented to the surface of the electrodes and caisson, and the significant increases in pullout resistances. The cementation effects were confirmed by electron microscopy images, X-ray fluorescence analyses and X-ray diffraction analyses.