Effect of Particle Size Distributions (PSDs) on ground responses induced by tunnelling in dense coarse-grained soils: A DEM investigation

Tunnelling-induced ground responses in coarse-grained soils often exhibit complex behaviours such as soil arching and progressive ground instability. However, the effect of particle size distributions (PSDs) on ground responses in tunnelling remains largely unexplored. This study provides new insights into PSD's effect on tunnelling ground response and the underlying mechanism based on granular skeleton quantification. The coarse-grained soils with 9 typical PSDs were modelled by the discrete element method (DEM) with varied granular skeleton structures. A representative volume element (RVE) assembly method, with a novel iterationbased specimen generation method, is developed to build ground models incorporating millions of soil grains, where an eccentric displacement boundary was embedded for reproducing the tunnel volume losses. The results demonstrated that the change in skeleton structures from fine-grains to coarse-grains dominated leads to the acceleration of soil arch emergence and the deceleration of soil arch collapse-rebuilding. With an increase in ded, the strengthened soil arch leads to a more evident deformation localization in ground, and results in more significant hysteresis of ground instability from the tunnel to the surface. The effect of PSDs on ground responses becomes prominent as the overburden thickness decreases and the tunnel volume loss increases, and a decrease in ded would increase the risk of overall failure in tunnelling.