Effect of the symmetrical eccentric load on the soil arching effect in granular soil via 2D DEM trapdoor tests: An insight from particle motion to mechanical behaviour

The soil arching effect under the symmetrical eccentric load (SEL) is vital for the design of the tunnel or buried pipeline. However, the mechanism of the soil arching effect under the SEL is still unclear. This study conducted three fill heights with eight SEL deviation distances and three loading magnitudes to analyze the soil arching effect, soil deformations, shear band, and mechanical characteristics via the two-dimension (2D) trapdoor tests using the discrete element method (DEM). The results indicate that the ultimate arching ratio (the ratio of the final average vertical stress on the trapdoor to the initial vertical stress) shows a first decrease, then inversely increases, and finally remains stable with increasing deviation distance, and the variation of the ultimate arching ratio under different SELs is not significant in the higher fill materials. The SEL-induced horizontal displacement of particles weakens as the deviation distance and fill height increase. The shear band above the trapdoor gradually expands and converges to the vertical plane as the SEL deviation distance increases. Furthermore, the discussions provided the insight that the soil arching effect under different SELs could be regarded as the shear behaviour in the limited region above the trapdoor.