Size dependences of the mechanical behaviors of basalt rock blocks with hidden joints analyzed using a hybrid DFN–FDEM model

Abstract Due to the extremely complex origin, Baihetan basalt typically contains hidden joints, which strongly affect its mechanical properties. Therefore, studying the size effect of the mechanical behaviors of basalt is important to accurately obtain the values of the engineering design parameters. In this study, the distribution characteristics of the length and orientation of hidden joints in basalt rock blocks were analyzed. Subsequently, a synthetic rock mass (SRM) method comprising a discrete fracture network (DFN) model and a combined finite-discrete element method (FDEM) model was used to characterize the basalt rock block with hidden joints. The scale dependences of the mechanical behaviors of the block were systematically explored. The representative element volume (REV) size of the block with hidden joints was found to be 500 mm as determined by the size effect analysis of the geometrical and mechanical properties. Under uniaxial compression, the intact sample presented elastic and brittle mechanical characteristics, whereas the rock block containing cracks exhibited elastoplastic mechanical characteristics. The peak strength of the intact sample was linearly related to the confining pressure, whereas this relationship was nonlinear in the case of the rock block containing cracks. The brittle-to-ductile transformation pressure of the rock block decreased with increasing sample size. The failure modes of basalt changed with increasing sample size, from fragmentation failure of the intact rock to failure controlled by the local structure and then to splitting failure under the REV size. The results of this research can help advance our understanding of the mechanical behaviors and failure mechanism of basalt, so as to more accurately guide the formulation of engineering design schemes.