Efficiency of electro-osmosis in soft soils

Abstract

The rekindled interest in Electro-osmosis was revived due to the need for more rapid consolidation of soft clay in certain application as well as the availability of conductive polymeric material. Hence, the research on a??Efficiency of Consolidation in Soft Soilsa?? was initiated. Exploiting the use of Electro-osmosis for consolidation on clay soils was the object. Clay soils have the advantage to be consolidated by EO because their inherent surface negative charge on the surface induce excess cations in a neutral soil. Under an electric potential gradient, these cations move. The solvated water molecules around them are thus attracted to the electrodes. With water drainage, soil consolidates, and be strengthened.A laboratory investigation and a fieldwork were performed to evaluate the efficiency of Electro-osmosis on local soft marine clay. In the laboratory testing program, soft clay soils underwent a top-down electro-osmotic treatment in an EO Cell which was modified from the standard oedometer cell. Steel electrodes were used in this series of tests. The EO Cell initially housed a clay specimen of 70mm diameter and 20mm height but was further improved to house a bigger sample of 70mm diameter and 100mm height. Testing conditions varied include the voltage gradient applied to the soil, the initial overburden pressure, and the duration of electro-osmotic treatment. Settlement and current variation were measured during the electro-osmotic treatment. The aftermath parameters investigated were compressibility and consolidation properties (e-log pa?? curve and Cv), strength properties (shear strength and water content), the long-term compressibility/creep characteristics (Ca). Following on, a large-scale field trial, comprised of two plots of land 50m by 50m, studied the ability of the innovated conductive polymeric drain, i.e. EVD, to initiate Electro-osmosis in the soft clay stratum underlain by thick deposits of surcharged sand. Various configurations, at different spatial arrangements, of EVD were employed. The response of settlement, pore pressure, current, and voltage were monitored with EO treatment time. The self-designed voltage probe picked up voltage signals channeled into soil. Field vane shear test gave the shear strength of soil before and after the electro-osmotic treatment.Soft soil was strengthened with the successful passage of electricity. Occurrence of electrochemical reactions was the main cause, with dewatering effects contributing marginally. In using non-metallic electrode, the conductivity of the medium is a cornerstone for the success of electro-osmotic treatment. For significant settlement to occur, a threshold voltage gradient has to be overcome. Initial preconsolidation pressure must not be too high for effective electro-osmotic consolidation. The consolidation properties, Cc, Cs, and Ca, decreased after electro-osmotic treatment. Similarly, Cv increased with electro-osmotic treatment. These beneficial effects may minimize the subsequent settlement of the EO treated clay when it is subjected to further surcharging. With these encouraging results, further investigation of EO by use of polymeric conductive vertical drains are recommended.