Study on the macro-mechanical behavior and micro-structure evolution law of broken rock mass under triaxial compression

Under the joint action of anchoring force and high in situ stress, the broken rock mass (BRM) in deep metal mines is actually under three-dimensional (3D) compressive stress, and its triaxial compression mechanical behavior is the key factor to control the stability of the surrounding rock. Therefore, it is necessary to perform research on the macro-mechanical behavior and micro-structural evolution of BRM under such similar stress state. In this work, based on 2D images, we propose a high-efficiency and low-cost method to reconstruct the 3D topographic features of the BRM. The particle flow code is used to study the effects of confining pressures and particle sizes on the mechanical properties, porosity, coordination number, acoustic emission characteristics, and fragmentation characteristics of the BRM. The results show that as the confining pressure increases, the compressive capacity and volume shrinkage of the BRM increase. The compressive capacity of the BRM reduces, and the secondary fragmentation become more violent with the increasing of particle sizes. At lower confining pressure, the rotation and translation of the BRM are main reasons for the change in the porosity. At higher confining pressure, the secondary fragmentation of the BRM as well as the migration of the small volume of rock are responsible to the change in the porosity. Secondary fragmentation of the BRM is mainly induced by tensile failure. The ratio between shear and tensile cracks in number decreases with increasing particle size of BRM. The results can provide some guides for the support design of the BRM in deep metal mines.