Behaviors of wetting-induced failure for unsaturated intact loess

The tests are performed on intact loess under two separate hydro-mechanical paths: constant-suction triaxial shearing and constant-shear stress wetting in steps, using the triaxial equipment for shearing and permeability of unsaturated soils.The variation characteristics of stress-strain and critical state identified from shearing and wetting are analyzed.The influences of hydro-mechanical path on the wetting-induced failure of intact loess are discussed.The necessary conditions are clarified when wetting-induced failure occurs.The results show that the critical state lines(CSLs)on the deviator stress versus the net mean stress(q-p)plane from constant-suction triaxial shearing tests are non-parallel straight lines, while the data of the critical state points collapse along a single line much closer to the saturated CSL on the deviator stress versus effective mean stress(q-p′)plane.The data of critical state points from constant-q wetting tests tend to merge together on q-p′plane, which can well be described by the linear form of the Mohr-Coulomb strength theory.The contribution of suction to the shear strength of the loess is dependent on the hydro-mechanical path, and the values of strength parameters are lower obtained by the latter tests than those of the former tests.The threshold values of shear stress level and suction are identified, which can be used to judge whether the wetting-induced the intact loess failure may occur.The expressions for those threshold values are obtained by combining with the proposed water retention model considering the influences of shear stress.