STRESS RATIO EFFECTS ON COLLAPSE OF COMPACTED CLAYEY SAND

A "double-triaxial" test procedure similar to the double-oedometer test was developed to determine the wetting-induced collapse potential of soils subjected to anisotropic stress states. Based on a series of double-triaxial tests performed on a slightly expansive clayey sand, it was established that the magnitude of volumetric strain resulting from a change in stress state or from wetting depends on mean normal total stress and is independent of principal total stress ratio. The individual components of axial and radial strain, however, depend significantly on stress ratio. For a given mean normal total stress, axial collapse increases and radial collapse decreases with increasing stress ratio. Comparison of oedometer and triaxial results indicates that the ratio of horizontal to vertical effective stress after wetting under zero-lateral-strain conditions varies as a function of the wetting-induced axial strain. In the swell region, effective lateral stresses tend toward active, and in the collapse region effective lateral stresses tend toward passive. These results may be used in conjunction with a knowledge of the in situ stresses to evaluate the potential for multidimensional, wetting-induced collapse in soils.