Effects of Confining pressure on stress intensity factors in underground cracked rock masses

Many underground rock masses are usually subjected to multiaxial states of stress. Moreover, cracks are known as candidate locations for fracture extension. Therefore, it is important to investigate the fracture behavior of cracked rock masses under such multiaxial stress states. However, most of the previous investigations have focused on the ambient conditions and ignored the effects of confining pressure, which in reality exists for in-situ stress conditions. In this paper, to investigate the effects of confining pressure on the mode I and II stress intensity factors (KI and KII), a large number of 3D finite element models have been used for simulating two test specimens, a circular and a semi-circular disc with a center crack. The specimens are subjected to diametral compression load F. For simulating the confining pressure, a uniformly distributed pressure (Pm) is applied to all of the external faces of the specimens. By analyzing the created models for various crack lengths, crack angles and confining pressure values, the effect of Pm on the stress intensity factors is studied. The results show that the presence of confining pressure has a significant influence on the mode I stress intensity factor but it has little effect on the mode II stress intensity factor.