Numerical study of the effect of rock anisotropy on stresses around an opening located in the fractured rock mass

Abstract

The fractured rock mass is a discontinuous, heterogeneous, anisotropic medium in nature, including single, multiple or a network of joints with regular or irregular patterns located between the intact rocks. Anisotropy, as an inherent feature of rock mass, is a factor that causes the mechanical properties of rock to be various in different directions, so it is very important and necessary to be considered in the design of rock engineering structures. This study aims to investigate the effect of rock anisotropy on induced stresses around an opening like a borehole located in the fractured rock mass. For this purpose, the combination of discrete fracture network (DFN) method to construct a geometric model of rock mass, with distinct element method (DEM) to the numerical analysis of stress, was used. All coupled DEM-DFN models were developed based on the field data of the rock and joint system of the Sellafield site in the UK. The discrete fracture network models with different degrees of anisotropy, including a circular opening with two different cross-section areas placed at the center of model, were used for stress analysis. In each type of model, by applying different boundary conditions, the magnitude of induced stresses at selected points around opening is calculated, and then the obtained results are compared with the Kirsch method as a popular closed-form solution. The numerical results of this study showed that the presence of irregular joints with different orientations in the model caused anisotropy in the magnitude of induced stresses obtained around the opening. This is an important issue that the Kirsch method is not able to consider in the calculations. • Fractured rock mass is a discontinuous, heterogeneous and anisotropic medium including network of joints with the stochastic pattern located between intact rocks. • Anisotropy is a factor that causes the mechanical properties of rock to be various in different directions. • Coupled DEM-DFN models are developed to numerical analysis of stress around a borehole. • Presence of irregular joints with different orientations caused anisotropy in the amount of induced stresses around the borehole.