COLLAPSE OF SATURATED SOIL DUE TO REDUCTION IN CONFINEMENT

The potential for collapse due to a reduction in confinement is evalua ted for two very different soils: a uniformly graded sand and an undis turbed clayey colluvial soil. Soil specimens were consolidated anisotr opically and subjected to constant-shear-drained (CSD) tests. During t he CSD lest, the effective confining pressure is gradually reduced whi le the shear stress is held constant. Only for very loose specimens is collapse observed before the failure envelope or steady state is reac hed. In general, specimens subjected to the CSD stress path behave dif ferently than specimens of similar initial density and confining press ure subjected to typical compression stress paths. This observation in dicates that knowledge of the stress path is necessary to accurately p redict the collapse potential, and thereby the potential for flow fail ure, of loose saturated soils.