Algorithm for generation of 3D polyhedrons for simulation of rock particles by DEM and its application to tunneling in boulder-soil matrix

Abstract

The shape of rock particle can profoundly affect its mechanical behaviors due to the interlocking force associated with morphological features. In this study, a hybrid extension method encompassing both convexity control and overlap detection was developed to generate three-dimensional (3D) polyhedrons for simulating irregularly shaped rock particles by discrete-element-method (DEM). Based on a random initial tetrahedron, a polyhedron can be extended from a simple shape to a complex one by adding new tetrahedrons. To control polyhedron convexity, a two-step method derived from the definition of convexity was proposed in this study. Moreover, the enhanced Gilbert–Johnson–Keerthi (GJK) algorithm was applied for overlap detection during the extension process of polyhedron generation. With the proposed hybrid extension method (HEM), a numerical model for simulation of tunnelling in boulder-soil matrix was built in the commercial DEM software; then, extensive parametric studies were performed to explore the influence of several factors (boulder size, orientation, position, and morphology) on tunnelling. The simulation results demonstrate the efficiency and reliability of the proposed algorithm and revealed the ground movement patterns in case an undetected large boulder was accidently encountered by tunnelling at shallow depth.