Fracture in rock

Abstract

Fracture is perhaps the most important topic in rock mechanics today, primarily because it is the dominant mechanism of rock failure at the relatively low pressures and temperatures at shallow depths in the earth's crust and because existing fractures strongly influence the physical and mechanical behavior of the rock mass. Fracture considerations therefore pervade all of man's interests dealing with exploration and production of natural resources, engineering projects under or on the earth's surface, and the prediction, modification, and control of earthquakes. For example, (1) estimates indicate that about 5% of the energy generated in the United States is consumed in fracturing rocks [Lewis, 1966]; (2) in the petroleum industry an understanding of fracture is essential in relation to ‘fracture porosity’ reservoirs, hydraulic fracturing, secondary recovery programs, structural inferences from existing fractures, underground storage of gas, and drilling technology; (3) in certain geothermal projects, fractures serve both as subsurface permeability channels and as surfaces to heat circulating waters; (4) the in situ ‘mining’ of oil shale or of the gasification of coal is primarily a matter of man's ability to fracture the rock mass under controlled conditions; (5) in mining and tunneling operations, fractures influence the stability of the openings as well as the extraction of rock or ore; and (6) recent developments in earthquake research have focused attention on fracture (dilatancy) as the source of a host of premonitory events from which it may someday be possible to predict earthquakes [Nur, 1972; Whitcomb et al., 1973; Scholz et al., 1973]. Accordingly, there is ample mission orientation for even the most basic research designed to gain a better understanding of fracture processes in rock and of the mechanical behavior of rock masses containing fractures.