Characteristics of critical state and water volume change for Q₃ unsaturated intact loess

A series of isotropic compression tests with controlled suction and triaxial drained shear tests with controlled suction and net cell pressure are performed on Q₃ intact loess by using a double-walled triaxial test apparatus for unsaturated soils. The influences of the suction, net confining pressure and stress path on the critical state and water volume change of intact unsaturated loess are analyzed. The models describing water ratio versus the net mean stress (e_w-p) under isotropic compression and triaxial shear stress, and the critical state lines (CSLs) on the deviator stress versus the net mean stress (q-p) plane are proposed. The results show that the stress path has significant influences on water volume change of unsaturated intact loess. The pore water drains from the specimen under isotropic compression, and with the increase of the net mean stress, the absorbing or draining water depends on the size of the suction and net confining pressure under shear stress. The logarithmic relationships between water ratio and the net mean stress or its increment present a binary linear under different test conditions. The effects of suction on the CSLs of the deviator stress versus the net mean stress (q-p) decrease as the net confining pressure increases. The CSLs of water ratio versus the net mean stress (e_w-lnp) are parallel under different suctions which are greater than zero.