3D discrete analysis of damage evolution of hard rock under tension

Abstract

Geomechanical studies largely focus on failure and deformation processes of hard rock under compression. However, damage evolution during tensile loading conditions is not well understood in terms of revealing the local deformations. The subject of this work is discrete analysis of strain localization related to microcracking process under tensile stresses. For this purpose, a three-dimensional discrete element modeling approach is used to calibrate the mechanical responses of Forsmark granite as a typical example of hard rock. A series of uniaxial/triaxial compressive and direct tensile test simulations are initially performed on the numerical samples to ensure that the calibrated model represents accurately the mechanical failure process of the real rock in terms of failure and stress-strain relationship. Subsequently, a detailed micromechanical analysis is carried out on the numerical samples under uniaxial tensile stress loading condition. The model results show that microcracks emerge at approximately 62.5% of the peak stress. At 87.5% of the yielding point, the damage related to the diffuse microcracking propagates irrepressibly and the strain localizes in specific regions within the numerical sample which indicates the location of a macro-fracture that develops after the failure. Here, the displacement fields are also calculated during the propagation of the damage. Specifically during the early stages of the loading, the flow directions of the displacement vectors form a subhorizontal split line approximately in the center of the sample, which might also predict the location of the forthcoming damage zone. These results may provide a fundamental basis on the evolution of tensile damage process related to microcracking taking place in hard rock where many underground applications are performed.