Instability analysis and simulation of water infiltration into an unsaturated elasto-viscoplastic material

A linear instability analysis was performed in order to investigate which variables have a significant effect on the onset of the instability of an unsaturated viscoplastic material subjected to water infiltration. It was found that the onset of the growing instability of the material system mainly depends on the specific moisture capacity, the suction, and the hardening parameter. Then, in order to simulate the water infiltration process of a one-dimensional unsaturated soil column, a multiphase coupled elasto-viscoplastic finite element analysis was performed based on the theory of porous media. The results of the numerical simulations are discussed with respect to the effect of the specific moisture capacity and the initial suction on the development of volumetric strain. We found that rapid transitions from unsaturated to saturated states and higher levels of initial suction lead to the contractive behavior of the material and instability. The instability detected by the numerical results is consistent with the theoretical results obtained through the linear instability analysis.