Numerical and experimental investigation of the effect of interstitial liquid viscosity on the collapse of wet granular columns

[Display omitted] •Numerical and experimental study on the collapse of wet granular columns.•Consistent collapse in DEM simulation incorporating both capillary and viscous force models.•Predicting final profiles of granular columns with Bo for low Ca (Ca ∼ 10−3)•Collapsed profiles depending on Bo and Ga with intermediate Ca (Ca ∼ 10−1)•Bo solely controlling the final profiles with high Ca (Ca > 100) The collapse of wet granular columns with high- and low-viscosity interstitial liquid is investigated through experiments and numerical simulations. By incorporating both capillary and viscous force models of interstitial liquid in the Discrete Element Method (DEM), simulations have been conducted and reproduced consistent collapse processes with the experiment. The influence of water content, contact angle, particle diameter, liquid surface tension, and viscosity is explored over a large parameter space using DEM. For wet granular columns with low-viscosity interstitial liquid of water, the final profile of the collapsed column can be predicted by Bond number (Bo), a ratio of particle gravity to capillary force. For wet granular columns where the inertial effect dominates and both capillary and viscous forces are significant, dimensional analysis is employed to characterize the collapse, indicating that the collapsed profile can be predicted by Bo and Galileo number (Ga). Using water and silicone oils with different viscosities as interstitial liquids, simulations show that the collapsed profile depends on Bo with a low capillary number (Ca ∼ 10−3), Bo and Ga when Ca is intermediate (Ca ∼ 10−1). When Ca is high (Ca > 100), the final profile is solely controlled by Bo and a rolling-collapsed regime is observed.