Collapse behavior of compacted clays in suction-controlled triaxial tests

Using a suction-control led triaxial apparatus for unsaturated soils, a series of tests on a compacted clay was performed to investigate the influences of stress states, water content, void ratio, and matric suction on the collapse behavior. The triaxial tests were carried out under the conditions of (1) different stress ratios and mean stresses, (2) triaxial compression and extension, (3) different initial void ratios of specimens with the same water content, (4) different initial water contents with the same degree of compaction, and (5) different controlled matric suctions. The main conclusions were obtained as follows: (1) The volume change induced by the collapse mainly depends on the initial void ratio and mean net stress under which the collapse occurs, irrespective of imposed matric suction; (2) the amount of collapse is small at both low and high confining stresses, and there exists a maximum value of collapse at a particular mean stress; (3) the shear strain increment induced by collapse depends on stress ratio, triaxial compression, or extension stress; (4) when imposed suction is decreased, large collapse deformation takes place in the samples compacted dry-of-optimum, while little collapse deformation takes place in the samples compacted wet-of-optimum; and (5) the collapse behavior can be explained by the elastoplastic theory for unsaturated soils.