LAUSR

In order to study the failure mechanism of fractured rock mass under different loading and unloading conditions, marble was used as the test material, which contained 45° double pre-existing cracks. The main processes, which initiation, propagation, coalescence of the cracks, were recorded by a high speed camera. To analyze the crack modes, it could be seen that shear stress played a main effect on the failure process of the uniaxial and biaxial loading of specimens. While shear stress played a significant role in the initial stage of unloading, tensile stress was dominated in the final stage of failure under unloading. At the same time, the numerical models under different loads have been established by ANSYS. It was found that the initiation and propagation characteristics of the main cracks in the experiment were basically consistent with the Mises stress distribution characteristics in the numerical simulation. Finally the effective shear stress ( τ e ) was defined by combining with the stress field theory and power function of Mohr-Coulomb failure criterion. The critical zones of the crack initiation were estimated. Compared with the experimental results, it could be proved that the angle between danger zone and pre-existing crack was about 40° and -140°.