Experimental investigation of local chemo-mechanical behaviour and temporal development of osmotic consolidation in expansive clay

Abstract

A series of one-dimensional cation infiltration tests under different drainage/infiltration conditions, infiltration times, ion concentrations (Na+), and vertical stresses were performed to comprehensively understand the osmotic consolidation of bentonite. The local behaviour of the specimen was captured on a digital camera through a transparent acrylic oedometer ring by tracking the movements of the marker sands on the side of the specimen. The Na+ concentration of the pore fluid throughout the specimen was measured after the test to investigate the spatiotemporal relationships between consolidation behaviour and cation infiltration. In the initial period of infiltration, the pore water pressure measured at the undrained bottom increased. A local swelling behaviour inside the specimen was observed during osmotic consolidation. The low permeability of expansive soils obstructs osmotically induced water drainage from the interlayer space of the expansive clay mineral, especially in regions far from the drainage boundary. This transition of pore water pressure affects the local mechanical behaviour; the dissipation of pore water pressure is followed by settlement. Therefore, the process of osmotic consolidation is totally longer than that of pure mechanical consolidation.