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  • Petrology—Handbooks, manuals, etc.

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  • 5104 Physical Properties of Rocks: Fracture and flow


AGU REFERENCE SHELF, VOL. 3, PP. 127-147, 1995

Rock failure

D. A. Lockner

Analysis of a wide range of problems in the geosciences requires knowledge of the failure process in rock. This includes tunnel design and other engineering applications as well as geophysical problems such as earthquake prediction. The empirical Coulomb failure criterion |τ|=C+μi′σn where C is cohesion, τ is shear strength and δn is normal stress, was proposed in the late 18th century and continues to be of great practical use. In the 1920's, Griffith [48] demonstrated the importance of flaws, which act as stress concentrators, in controlling the strength of brittle materials. Using this approach, fracture mechanics (e.g. [5, 17]) has been highly successful in relating defect structures to fracture strength and related properties. Through the 1960's, many of the advances in the theory of fracture and friction in rock have had their origins in metallurgy; a fact that has mixed blessings since plastic yielding, commonly involved in the deformation of metals, may be completely absent in room-temperature brittle deformation of common silicates such as quartz [154]. Thus, in contrast to plastic yielding which has little or no pressure sensitivity, a material obeying the Coulomb equation (1) shows significant strengthening with pressure. Although a Coulombic material may deform in a manner described as plastic flow, the microscopic mechanisms of grain rolling or crushing and associated dilatancy, are quite different than those responsible for plasticity in metals. The same processes are likely to occur during shearing across a fault surface.

Citation: Lockner, D. A. (1995), Rock failure, in Rock Physics & Phase Relations: A Handbook of Physical Constants, AGU Ref. Shelf, vol. 3, edited by T. J. Ahrens, pp. 127–147, AGU, Washington, D. C., doi:10.1029/RF003p0127.

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