Effect of pre-existing infilled fracture on characteristics of failure zones around circular opening

Understanding and predicting failure zones in fractured rocks around an underground opening is critical in designing excavation and support schemes. It is known that two symmetrical V-shaped failure zones of a circular opening occur in a homogeneous rock mass, but effect of infilled fractures on geometry of failure zone still remains poorly understood. In this study, biaxial compression tests were experimentally and numerically conducted on rock samples including an infilled fracture, and the effect of infilled fractures on the geometrical parameters (width, depth, and area) of failure zones around a circular hole were studied. Both the experimental and numerical results are in good agreement, and the results indicate that inclination angles and positions of infilled fractures can significantly affect the geometrical parameters of failure zones. Three characteristic stresses including crack initiation stress, crack damage stress and peak stress are defined and determined from the stress-strain and AE parameter-strain curves, and the ratios of crack initiation stress and crack damage stress over peak stress are comparable with the previous empirical formulars. In addition, stress distributions in the rock samples are compared to explain how infilled fractures affect geometrical parameters of failure zones.