Abstract:
Simulation of rock blasting is a challenging task in computational mechanics given the multiphysics and multiscale nature of the phenomenon. Among the several numerical methods available to deal with this problem, the Extended Finite Element Method (XFEM) presents some advantages since it can perform arbitrary crack propagation without remeshing and elements containing a crack are not required to conform to crack edges. In this research XFEM is applied to investigate rock blasting based on the phantom node method where discontinuities in the displacement fields are introduced through new degrees of freedom in overlapping elements. Some specific aspects related to the fracturing of a rock mass subjected to a general bench blast are discussed, such as the influence of mesh refinement, the effects of the stress-loading rate and the number and distribution of preexisting cracks around the blast hole. The numerical results are compared with those obtained by other authors using different numerical approaches, which confirms the suitability of XFEM to simulate dynamic fracture propagation problems.
Introduction
Rock blasting is widely used for excavations in mining and civil engineering works. Damage to the rock structure during blasting may occur as a result of the stress waves (dynamic load) and the overpressure of the explosive gases (quasi-static load) that create new cracks and widen the already existing ones (Liu and Katsabanis, 1997).
One of the most used methods for simulation of crack propagation is the finite element method, where the evolution of cracks in time is followed through successive mesh updates in order to represent the new geometry of the fractured body. This approach, besides being computationally inefficient and lengthy, may also yield loss of numerical accuracy when variables of interest are mapped and interpolated from the old to the new finite element mesh.
On the other hand, the Extended Finite Element Method (XFEM) is able to model cracks without remeshing (Belytschko and Black, 1999; Moës et al., 1999). The representation of cracks is ensured by special enriched functions in conjunction with additional degrees of freedom, which gives numerical results of greater accuracy and lower computational times. XFEM is a very attractive option to simulate initiation and propagation of cracks.