The objective of this paper is to investigate the failure process of brittle rock in particle scale under compression with different confining pressures. Three-dimensional discrete element code PFC3D is adopted to perform the numerical simulations where intact rock is represented by an assembly of rigid spheres bonded at their contacts. The numerical model is firstly calibrated by comparing the simulation results to the laboratory data of Beishan Granite. Good agreement can be found between the numerical and experimental results in terms of uniaxial compression strength, Young’s modulus and Poisson’s ratio. Responses at particle scale are further investigated in order to gain insights of the micro mechanisms of the failure process of brittle rock. Increment of micro cracks is examined under different confining pressures. The development of micro cracks to a major fracture is investigated by exploring the location of cracks occurring at different strain intervals. Orientation distribution of micro cracks is linked to the orientation distribution of stress acting on parallel bonds. Moreover, the effects of confining pressure are examined by comparing results from uniaxial compression test to those of triaxial compression tests. With the increase of confining pressure, the micro crack failure mode changes from tensile to shear.
Rock anisotropy is one of the most distinctive features that must be considered in rock mechanics. In this study, two-dimensional discrete element simulations are conducted to investigate the strength and deformation behavior of inherently anisotropic rocks which display different behaviors in response to load with respect to the different orientations of the plane of weakness. In the numerical model, intact rock is represented by bonding rigid particles at their contacts together. The inherent anisotropy is modeled by artificially removing any parallel bonds dipping around a certain angle to the loading direction and replacing them with smooth joint contacts. The numerical model is validated by comparing the strength and elastic modulus with previous experimental results. The failure patterns can be classified into: split cross weak layers, shear along weak layers and split along weak layers, which also agree with that observed in laboratory. The angle range plays an important role on the response of numerical model which can be used to represent the degree of anisotropy. The numerical model proposed in this study provides a new way to investigate the mechanical behavior of anisotropic rock. Future studies can be carried out to investigate the strength criterion of anisotropic rock based on this approach.