Fracture mechanics of rocks : K. Kusunose, Journal of Physics of the Earth, 43(4), 1995, pp 479–504

Abstract

All forms of mining involve rock breaking of some description. Fracture mechanics aims to quantitatively describe the transition from an intact material to a broken one through crack propagation and growth. The main rock property used in fracture mechanics is fracture toughness. This property is compared to the estimated applied stresses and if the estimated applied stresses are greater, then catastrophic crack growth is expected. Currently fracture toughness testing is expensive as not many laboratories will conduct the tests. Also limited research has been conducted into the factors affecting fatigue fracture or cyclic loading. This thesis project looked at formulating an indirect way of calculating fracture toughness through relationships with other simpler rock properties. These rock properties are density, uniaxial compressive strength, Brazilian tensile strength, Schmidt hammer hardness and Shore scleroscope. This thesis also investigated the effects of frequency and amplitude on cyclic loading of the specimens. The results obtained are displayed and discussed in the report. Relationships were found between fracture toughness and all of the other rock properties. The cyclic loading tests could only be conducted at low frequencies due to unforeseen testing machine limitations. At these low frequencies (5Hz, 10Hz and 20Hz) no correlation exists between fracture toughness and frequency or fracture toughness and amplitude. For all of the relationships, limited data points were available. Thus one of the main recommendations is to conduct more tests to get a larger database. Also cyclic loading should be performed at higher frequencies to get a full understanding of the effects of frequency and amplitude. The research conducted in this thesis project has many industrial applications including blasting simulations and oscillating disc cutters. This project will provide a base from which to further investigate fracture mechanics.