This chapter considers the mechanics of the fracture process in rock, with emphasis on the engineering viewpoint. The development of a consistent fracture mechanics for rock is complicated by several factors, such as the extreme constitutive variability of rock. These factors are discussed in some detail. Next, empirical procedures for determining limiting states of stress are reviewed. In these procedures, the state of stress in the specimen is either homogeneous or inhomogeneous. However, the limiting states of stress, as determined in homogeneous and inhomogeneous tests, are often in disagreement, and possible reasons for differences are discussed. The coulomb-navier, mohr, and griffith theories of fracture are reviewed, and the merits and defects of each considered. Processes by which initial and branch fractures extend and ultimately produce terminal failure are examined. The chapter is concluded with a summary in which the state of the art is evaluated. Areas in which information regarding the fracture mechanism in rock is deficient or inconsistent are indicated, and topics for future research are suggested.
Fracture, an Adv. Treatise, Vol. VII, Fracture of Nonmet. & Comp. Academic Press, New York, Pp 93-155