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A comprehensive experimental investigation on the electroosmotic strengthening of soft sensitive clay was performed to assess the effectiveness of the treatment and to study the mechanism of the process. A specially designed electroosmotic cell was developed to prevent gas accumulation near the electrodes, to allow better electrode-soil contact, and to improve the treatment efficiency. This apparatus also enables the monitoring of the generated negative pore-water pressure along the sample length, settlement, voltage distribution, and current variation during treatment. The investigation covered two different types of soil trimmed at different orientations: the vertically and horizontally trimmed overconsolidated Wallaceburg clay and the vertically trimmed slightly overconsolidated soft sensitive Gloucester (Leda) clay. Results of this study showed that the voltage distribution and induced negative pore pressure at equilibrium along the sample are linear with steady current flow across the sample, indicating that the electrode design in the electroosmosis test apparatus is efficient. The electroosmotic consolidation curve is similar to that of the conventional consolidation curve, and the preconsolidation pressure was increased by 51–88% with an applied voltage up to 6 V. The undrained shear strength increased to a maximum of 172%, and the moisture content decreased by 30%. The technique of electrode reversal is employed, and a relatively uniform strength increase between the electrodes is observed. Key words: electroosmosis, electroosmotic cell, soft sensitive clay, negative pore-water pressure, preconsolidation pressure, stress–strain behaviour.

A field test was undertaken to assess the effectiveness of electroosmosis in strengthening the soft sensitive (Leda) clay at the Gloucester test fill site. Specially designed copper electrodes were installed to prevent gas accumulation around the electrode and to allow pore water in the soil to flow out from the cathode without pumping. The variation of settlement, shear strength, and voltage distribution during treatment was measured, and tube samples were recovered before and after treatment for laboratory tests. The results of field vane tests at different locations within the treated area and at different times indicate that the undrained shear strength increased uniformly by approximately 50% for a period of 32 days throughout the depth of the electrodes. Concurrently, an average surface settlement of 50 mm was achieved. The total power consumption was less than 1% of the total project cost, indicating that the design of the treatment system was efficient. It is evident, therefore, that substantial increase in strength as well as general improvement in soil properties may be achieved by this improved version of electroosmosis. The elimination of pumping improved the economy of the process considerably. It is hoped that the process may receive wider application as a result of these improvements. Key words: electroosmosis, electrode, polarity reversal, Gloucester test fill, soft sensitive clay, uniformity of treatment, power consumption.

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A field test was undertaken to assess the effectiveness of the electroosmotic strengthening of the soft sensitive (Champlain Sea) clay in the Gloucester Test Fill site by using specially designed copper electrodes to improve treatment efficiency. Tube samples, 127 mm in diameter, were recovered before and after field treatment for detailed laboratory tests. Isotropically consolidated undrained triaxial tests with pore-pressure measurements were performed. It was found that the failure envelope after treatment was significantly higher than the initial envelope, indicating that the strength in terms of effective stresses increased. Consolidation tests showed that, as a result of treatment, the preconsolidation pressure increased from 53 to 98 kPa. The soft clay is virtually "overconsolidated" by the process. Additional effects of electroosmosis on the properties of the soft clay are the increase in plasticity, carbonate content, and salinity and the decrease in sensitivity. There is, therefore, a general improvement in soil properties after treatment, both in terms of total and effective stresses. Key words: electroosmosis, soft sensitive clay, failure envelope, sensitivity, preconsolidation pressure, pH value.