Two-stage wetting deformation behaviour of rock-fill material

Combined loading–creep–wetting tests were performed to investigate the wetting deformation behaviours of rock-fill material by using a modified triaxial apparatus. Results show that the wetting deformation of rock-fill material can be classified into two components, namely, instantaneous wetting deformation and time-dependent wet-state creep deformation. The former occurs simultaneously with rock-fill wetting and possesses the characteristics of parallelism and non-hardening; the latter occurs over time after the rock-fill is wetted and exhibits features similar to those of general creep deformations in rock-fill material. Wetting deformation is induced by the physical-state weakening of the wetted rock-fill material; the wetting can be intuitively considered as a generalised load. Then, a new constitutive model of two-stage wetting deformation for rock-fill material is proposed. In the model, the instantaneous shear wetting strain is in a hyperbolic relationship with the stress level; the instantaneous volumetric wetting strain is described by the dilatancy equation of conventional triaxial loading; and the time-dependent wet-state creep strain is calculated using a general rock-fill creep model. The new model was also used to simulate triaxial wetting tests of rock-fill material, and its validity and practicability were further evaluated.