ABSTRACT
As discussed in Chapter 4, the dominant mode of failure of rock specimens under uniaxial compression is splitting where the fracture surface is approximately parallel to the direction of applied loading. This type of splitting failure normally involves a sequence of progressive micro-fracturing. The micro-cracking results from a high tensile stress concentrated at inhomogeneities, such as crack-like flaws, pore-like flaws, or soft or hard inclusions. For example, a circular hole, i.e. with zero elastic modulus, will create tensile stresses in the micro-structure above and below the hole potentially causing splitting parallel to the applied compressive load; whereas, a circular grain of high elastic modulus can be split in half similarly to the Brazilian test described in Chapter 3 but with the micro-fracture also parallel to the applied load. These initiated micro-cracks will propagate with increased loading, and eventually extend to the specimen surface to form a macroscopic splitting failure. Because of the importance of the coalescence of the developing fractures, in this Chapter, we analyse and describe further the growth of axial cracks from pre-existing flaws (including crack-like flaws and pore-like flaws) and their coalescence.
