Experimental and numerical investigation on the mechanical properties and progressive failure mechanism of intermittent multi-jointed rock models under uniaxial compression

Abstract

The joint geometry configurations significantly affect the mechanical properties and failure behavior of intermittent jointed rock models under uniaxial compression. Combining laboratory experiments with discrete element method (DEM) simulations, this paper comprehensively investigated the influence of four joint geometrical parameters (i.e., dip angle, joint spacing, persistency, and density) on the mechanical properties and progressive failure behavior of intermittent jointed rock models. Our experimental results indicate that the uniaxial compression strength (UCS) of multi-jointed rock models linearly decreases with the increase of the four geometrical parameters, while the elastic modulus nonlinearly varies with geometrical parameters. Compared with the joint spacing, the other three geometrical parameters affect the mechanical properties of jointed rock models more significantly. Three basic cracks on the surface of jointed specimens are observed in our tests, and six coalescence patterns are classified according to the combination of these basic cracks. Moreover, two failure modes of the jointed rock models occur in the present study, namely, the tensile failure mode and the tensile/shear mixed failure mode. In addition, the characteristics of microscopic energy evolution and the progressive failure behavior of multi-jointed rock models under uniaxial compression are numerically revealed using open-source DEM code ESyS-Particle. Our numerical results indicate that the total input energy is mainly restored as strain energy at the early stage, and then dissipated as friction energy and kinetic energy at the post-peak stage. The progressive failure processes of the multi-jointed rock models can be divided into five stages by characterizing the spatial development of micro-cracks and the maximum principal stress field.