Introduction to anion-exchange membranes and their use in electro-osmotic consolidation

Electro-osmotic consolidation has long been of interest to the geotechnical community due to its potential to improve on current methods of clay soil consolidation. However, electro-osmotic consolidation is not widely used because of the change in soil pH and increase in soil resistance with long-term application of electrical current. This paper studies the efficiency of a novel method of using anion-exchange membranes to minimise the change in soil pH, and hence to prevent change in soil resistance. Settlements were measured for electro-osmotic tests subjected to different voltages with and without a membrane. The results showed that the membrane was always more effective in removing water, particularly at voltages below the limiting current. This demonstrates that using an ion-exchange membrane during electro-osmosis will remove significantly more water than conventional electro-osmosis for the same applied voltage. This occurs because the anion-exchange membrane blocks the migration of hydrogen ions formed near the anode into the soil, which would in turn increase soil electrical resistance. The increase in efficiency could finally push electro-osmotic treatment into the market as a viable solution for soil consolidation projects.