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To study the crack propagation mechanism of jointed rock mass under pre-split blasting, LS-DYNA software was used to carry out numerical simulation of rock mass blasting with vertical single joint, horizontal single joint and vertical parallel joint. The influence of in-situ stress was discussed. The results show that when there is a vertical single joint in the center of the blastholes, the cracks between holes can be penetrated. The joints have a tendency to close, and the joint is conducive to improving the degree of rock fragmentation between holes. When there is a vertical parallel joint in the center of the blastholes, the wing crack at the joint tip can be penetrated, but good fragmentation effect of rock cannot be achieved between parallel joints. When the horizontal joint is close to the blast hole, more tensile cracks will occur when the stress wave transmits to the back burst side of the joint surface. When the horizontal joint is far from the blasthole, the blocking effect of the joint is obvious. Under the action of hydrostatic in-situ stress, the initiation and propagation of radial tensile cracks and tip wing cracks are restrained. Under the action of non-hydrostatic in-situ stress, the crack growth is more restrained in the direction of the minimum principal stress, and the restraining effect increases with the increase of the maximum principal stress. [ABSTRACT FROM AUTHOR]

The strain-softening process of rock media after peak-load was simplified into a series of plastic flows and brittle falls. The plastic deformation region caused by the excavation of a spherical cavity was divided into several concentric spherical rings. Assumed that in each spherical ring the rock masses were infinitely homogeneous and isotropic. Based on Mohr-Coulomb criterion and non-associated flow rule, the closed-form solutions of stresses and displacements around the spherical cavity subjected to hydrostatic initial stresses were obtained. Through the characteristic point of material properties in each spherical ring, supplementary equations of rock media to be destroyed were presented and the iterative formulas of plastic radii were also obtained. Considering that deformation parameters of the surrounding rock mass deteriorate after peak-load, this paper respectively discussed the effects of the linear degradation of the elastic modulus and Poisson's ratio on the displacement of free surface, softening radius and rupture radius. [ABSTRACT FROM AUTHOR]