Chaofa Zhao

Different types of cohesive forces, such as van der Waals forces, electrostatic forces and capillary forces occur in granular materials. For wet granular materials, capillary forces are larger than the other cohesive forces. Hence, cohesion in wet granular materials originates from capillary forces between the constituting particles.

At the particle scale, we have obtained analytical expressions for rupture distances and capillary forces of capillary bridges under volume control (where the liquid volume is kept constant) and suction control (where the pressure difference between the surrounding gas and the liquid inside the capillary bridge is kept constant). These expressions for the pendular regime are based on the governing Young-Laplace equation. We have found that the properties of capillary bridges between two spherical particles under suction and volume control are significantly different, in particular for the rupture distances.
To investigate the influence of the hydraulic loading path on the hydromechanical behaviour of wet granular materials, we have conducted Discrete Element Method (DEM) simulations. In these simulations, the properties of capillary bridges between spherical particles are represented by the newly developed expressions that are suitable for capillary bridges under volume as well as suction control. The DEM simulation results show macro-scale differences of the behaviour that originate from the interparticle capillary bridges at the micro-scale under volume and suction control.