Resistive force modeling for shallow cone penetration into dry and wet granular layers

Estimating penetration resistive forces on granular materials is important for applications in various research fields. This paper investigates resistive forces into dry and wet granular layers through theoretical analysis and discrete element simulations. Theoretical model is derived from slip line field theory by assuming materials with cohesion and inter-particle friction. This model indicates that penetration resistive forces are composed of the sum of the buoyancy-like force proportional to the penetration volume and the cohesion-derived force proportional to the penetration cross-sectional area. The model is compared with the simulation results of various cones shallowly penetrating into granular layers with/without liquid-bridge forces between particles. For cohesion-derived force, the simulated resistive forces agree with the theoretical model within a factor of two. For buoyancy-like force, on the other hand, the simulated resistive forces deviate from the theoretical model by up to five times as the cone-tip angle increased. To solve the discrepancy, this paper introduces the correction factor depending on the relationship between stagnant zone and cone shape. As a result, a maximum difference between the proposed model and simulated force are reduced to twice. Thereby, it turns out that the proposed model can compute penetration resistive forces on granular layers in a wide range of cone-tip angles and water content conditions.