Effect of relative density of 2D granular materials on the arching effect through numerical trapdoor tests

The relative density and the fill height of granular materials influence the arching effect significantly, from either the overall behavior of granular materials or the formation of the arching effect. In this study, a comprehensive comparison of the arching effect at four fill heights with three relative densities is conducted by numerical trapdoor tests using the two-dimensional (2D) discrete element method. The results indicate that the stick–slip behavior of the arching ratio (the ratio of the average vertical stress on the trapdoor to the overburden stress; the ratio decreases to a minimum value, followed by recovering to the ultimate value) is more obvious for the case with lower fill height at a given relative density or that with higher density at a given fill height. The partial and the full arching can be distinguished by whether the loosen zone propagates to the surface. Two different critical states are identified for the partial and the full arching, respectively. These critical states are insensitive to the relative density. A characteristic height is identified around twice the width of the trapdoor, at which the critical state of the partial arching transfers to that of the full arching with the increase of the relative density.