Date of Award
Doctor of Philosophy
The damages brought by landslides of soft sensitive clay are so extensive that the safety of existing structures are threatened and new constructions are hindered. Traditional methods of soil improvement are usually inadequate, expensive and in some cases impossible. New method of soil improvement is therefore needed. With the advancing technology of electrostatics, two methods of electrical strengthening of soft sensitive clay are developed towards this goal. Electro-osmosis, the first method, is a phenomenon involving the transport of pore water in capillaries under the influence of a direct current electric potential. An electro-osmotic cell was developed to investigate this process in the laboratory and the results showed that the shear strength of the treated clay was increased by 172% with the concurrent reduction of moisture content by 30% under an applied voltage up to 6 volts. The physical and chemical properties are significantly improved.;A novel technique of electrical strengthening of soil is the application of dielectrophoresis. The process employs an alternating current high voltage, generating a converging electric field towards the electrode by which a net resultant movement of water in the clay mass is produced towards the direction of stronger electric field intensity. The water extraction caused the shear strength to increase drastically as much as 996% with a corresponding moisture content reduction of 22%, under an applied potential of 20 kV.;A field test was then undertaken to assess the effectiveness of these two methods in strengthening the soft sensitive (Leda) clay in Gloucester test fill site. Specially designed copper electrodes were installed for electro-osmotic treatment to prevent gas accumulation around electrodes and to allow pore water in the soil to flow out from the cathodes without pumping. Field vane test results showed that the undrained shear strength increased uniformly by approximately 50% throughout the depth of the electrodes in 32 days of treatment. The soft clay is shown to be "over-consolidated" and the strength in terms of effective stresses also increased. This improved version of electro-osmosis demonstrated its application in engineering practice.;The dielectrophoretic treatment was less effective due to water surrounding electrodes and electric short circuit problem. Nevertheless, this pioneer research enables the accumulation of experience that contributes to the foreseeable success of the process in the future.
Ho, Kai Sing, "Electrical Strengthening Of Soft Sensitive Clays (volumes I And Ii)" (1990). Digitized Theses. 2012.