DEM and experimental analysis of the water retention curve in polydisperse granular media

We investigate the water distribution and the link between suction and water content in granular media. Firstly, we examine the effect of suction on the shape and the volume of the liquid bridge by four different methods. Method I is based on the local expression of the capillary force coupled with the gorge method and Method II is based on the Laplace law. These two methods use the toroidal approximation. Methods III and IV are based on the integration of the differential equation that defines the liquid bridge shape (established from the Laplace law). This local behaviour is then used in a discrete element study of a sample composed of several thousands of grains. We focus our study on the pendular state. A liquid film around the grains involving the continuity of the liquid phase is assumed. The water distribution and the water content associated with a given suction are calculated. Then retention curves of the granular media are built. A parametric study is made to bring to light the effect of macroscopic parameters (grain-size distribution) and physical parameters (liquid/air surface tension and contact angle) on the water retention curve. Finally, numerical data are compared to experimental results.