Unsaturated wetting deformation characteristics of a granite rockfill under rainfall conditions

Rainfall-induced unsaturated wetting deformation has been one of the main sources of postconstruction deformations of rockfill structures. An experimental study is presented of the unsaturated wetting deformation characteristics of a weakly weathered granite rockfill under different triaxial stress conditions and rainfall intensities investigated by a modified triaxial apparatus equipped with the newly developed rainfall simulator. Results show that the wetting deformation of rockfill materials occurs at a relatively small water content; when the rockfill reaches a critical wetting point (i.e., the effective water content), additional water does not produce more deformations. It is shown that the tested rockfill material has an effective water content of <6.89%, with a corresponding effective degree of saturation of <17.26%. Moreover, the unsaturated wetting deformation can be classified into two components: the instantaneous wetting deformation that occurs during rockfill wetting and exhibits properties of parallelism and the wet-state creep deformation that occurs time-dependently after the rockfill is wetted and shows features similar to those of general creep deformation, suggesting that unsaturated wetting can be considered as a generalized load. Finally, by introducing the two-stage wetting deformation model, the experimental curves of axial strain and volumetric strain against time were well predicted.