Structures Produced in Clays by Electric Potentials and their Relation to Natural Structures

Abstract

If an electric potential is applied by means of two electrodes to a remoulded soil containing a proportion of particles of colloidal size, such as London clay, the soil develops a structure which is similar in appearance to that of the clay in its natural state. This phenomenon was observed by me in 1931 on a great variety of fine-grained soils. In recent investigations carried out on London clay and Wyoming bentonite, I found that the electro-osmotic transport of pore water towards the cathode results in the formation of cracks in the soil around and between the electrodes, the pattern of the cracks following the equipotential lines. These cracks, which are filled with free water, become more widely spaced with increasing distance from point electrodes. Originating from these basic cracks an irregular pattern of additional fissures is formed. When the soil becomes consolidated, as, for example, by continued electro-osmotic drainage or drying, the fissures and cracks close up but the structure remains even in the completely dry state and is readily revealed on breaking up the soil. Fig. 1 shows such a pattern in a gel of 2 per cent by dry weight of Wyoming bentonite, after a potential gradient of 0-2 volts per cm. was applied for forty hours. Surrounding the copper cathode (the thick electrode) concentric fissures in the process of formation can be seen.