Micromechanical modelling of erosion due to evaporation in a partially wet granular slope

Small quantities of water in a granular slope increase the overall stability and justify the large slope angle which is sometime observable in nature. However, the evaporation usually changes the water content of soil, especially in very shallow layers, leading to a soil strength reduction and the trigger of erosion processes. This work presents some numerical tests simulating a small slope physical model constituted of monosized glass ballotini in a pendular state. After a brief review of the different theories describing the capillary bridge which forms between two spheres and its effects on inter-particle forces, this paper deals with the implementation of the minimum energy approach within a discrete element model (DEM). Some numerical triaxial tests with different water contents and confinement stresses were performed: the analyses permitted to emphasize the shear strength increase occurring at low water content. Moreover, moving from the observations performed in the physical model, a law relating the evaporation rate with depth and air–water interface was also included in the DEM. Finally, the improved DEM was successfully adopted in the simulation of the erosion process occurring in the physical model: it very well captures the formation of a talus slope profile, typical of the long-term evolution of granular slopes. The monitoring of soil displacements and suction distribution during the numerical test also allows for the evaluation of erosion mechanisms: for instance, both in experimental and numerical tests, it was observed a rigid displacement at the slope toe after the initial phase of shallow erosion