Swelling pressure of compacted expansive soil over a wide suction range

Abstract A series of wetting experiments was performed on a compacted expansive clay to evaluate the swelling pressure generated over a wide suction range. Both osmotic and vapor equilibrium techniques were introduced and implemented to apply the suction required in the swelling pressure measurements. It is shown that, associated with the evolution of the microstructure of soil during wetting, the development of swelling pressure with decreasing suction is nonmonotonic. The soil water retention characteristics were independent of dry density at high suction in the adsorption regime, and a threshold suction was identified to distinguish adsorbed and capillary waters. The development of swelling pressure was closely related to the water retention characteristics. At high suction, the swelling pressure stems mainly from interlayer hydration; at low suction, however, the swelling pressure was controlled by the development of double layers, accompanied by the collapse of some macropores. The nuclear magnetic resonance (NMR) technique was introduced to determine the specific amount of adsorbed and capillary water contents, shedding new insights into the swelling behavior of compacted expansive soil during the wetting process under confined conditions.