Influence of particle size on vertical plate penetration into dense cohesionless granular materials (large-scale DEM simulation using real particle size)

The influence of the particle size on the vertical plate penetration into dense cohesionless granular materials was numerically investigated. Simulations were performed in quasi-two-dimensional conditions by changing the mean particle diameters d(50) but maintaining the plate thickness B from B/d(50) = 63-2.6. The initial bulk packing fraction was kept high, irrespective of the particle size. In the smallest particle size case (B/d(50) = 63), the size ratio reached almost the same level as that in the laboratory experiments using natural sand particles. The results demonstrated that the mean penetration resistance force acting on the plate tip surface increases with a decrease of B/d(50), while the tangential force acting on the side surfaces does not change with B/d(50). Tip resistances increase linearly with the penetration depth, while the tangential resistances increase with the square of the depth regardless of B/d(50). The behavior of the resistance fluctuations changes qualitatively between B/d(50) = 31 and 21. For all cases, we confirmed the formation of a wedge-shaped flow with a high forward velocity in front of the plate tip. The wedge flow width was larger than the plate thickness by almost a mean particle diameter, and was responsible for the increase in the mean resistance depending on the particle size. For the large B/d(50) cases only, the resistance exhibited quasi-periodic fluctuations, which was attributable to the intermittent nucleation and disappearance of the shear bands. Moreover, we investigated the dependence of B/d(50) on the band evolutions by analyzing the band thickness.