The paper presents the results of the large-scale laboratory tests conducted on the electrokinetic strengthening of natural marine clay for offshore foundations. A steel cylinder, 200 mm in diameter and 400 mm in length, was adopted as the model of foundation element and it was equipped with eight electrodes equally spaced around the outside wall of the cylinder. Attaching the electrodes on the cylinder with the holding ring facilitated the one-pass installation procedure, so that the cylinder and electrodes could be installed simultaneously. A dc voltage of 5.2 V with polarity reversal was applied over a period of 28 days. A control test with identical configuration to that of the electrokinetic treatment test was also set up to provide baseline data. After the treatment pullout tests were performed on both cylinders and the effect of electrokinetics was evaluated. The results demonstrated that the pullout resistance of the foundation model embedded in natural marine clay increased up to 5 times, after the electrokinetic treatment, as compared with that of the control without treatment. The clay adhered strongly to the cylinder and electrodes, indicating bonding was developed between soil and steel after the treatment. The XRF analysis showed significant increase of iron oxide after the treatment, which is known as a cementation agent in soils. The electrokinetic treatment also accelerated the recovery of friction resistance of the foundation after subjected to failure.
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