Thesis: MyungHo Lee

M.Sc Thesis, St. Catherine's College, Hilary Term 2000

An Experimental and Analytical Study of Electrokinetic Consolidation

Summary

This thesis describes settling process of clay particles in suspension and subsequent consolidation behaviour of Speswhite Kaolin clay under the influence of electrokinetics.

Comprehensive experimental investigations on soil behaviour under different stress conditions (e.g. electrokinetics, self-weight, and hydraulic gradient) were performed and reported. For comparing soil behaviour under electrokinetics with self-weight consolidation, the electrode configuration of closed anode and open cathode (the anode at the base of the cathode at the top of the soil) was used. One of the problems with this electrode arrangement was the gas produced at the anode electrode entering the soil and destroying the developing structure of soils. This problem was overcome by developing a specially designed electrokinetic cell.

The density measurements of soil were achieved by an accurate and non-destructive X-ray technique, and pore pressures were also measured during the process. The experimental results revealed that the electrically induced surface settlement was greater in magnitude and faster in rate than that under self-weight stresses; the dissipation rate of excess pore pressure was directly related to the applied electric field strength; the density in the anode region was increased significantly by the development of effective stress die to the effect of electroosmosis; the movement of acid and base fronts due to electrolysis was identified by the variation of pH; and the development of the denser layer at the soil surface was caused by the additional effects of electrokinetics, such as the variation of zeta potential and voltage gradient.

Numerical simulations using the simple diffusion equation with constant coefficients were investigate in order to predict the soil behaviour under the influence of electrokinetics. The normal small strain assumption (equivalent to the boundary remaining fixed) made in previous solutions of the equation has been replaced by boundary movement coupled with the requirement of conservation of mass.

Remarkably good agreement between the measured and simulated surface settlement, density, and excess pore pressure profiles has been achieved using the method above, with appropriate soil parameters, such as C_c, C_v, K_h, and K_e.