Size effects in fracture of rock

The fracture of rock is influenced by the development of an intrinsic process zone in the form of a localized region of microcracking. This zone has a fundamental importance for defining the system behavior in terms of the post-peak instability and in terms of material strength such that size effects appear. This paper illustrates the change in the load-displacement response and presents evidence of the process-zone development with varying specimen size. It is demonstrated that fracture problems do not require geometric pr material nonlinearity to produce instability. The size of a structure that fails by fracture is an important factor. Furthermore, experiments suggest that an intrinsic zone develops in rock as a material characteristic. Because of this intrinsic length, two competing factors define the nominal strength-the positive contribution of the process zone and the depleting aspects of the undamaged volume, that is, the size.