Growth of geologic fractures into large-strain populations: review of nomenclature, subcritical crack growth, and some implications for rock engineering

• Published in: International journal of rock mechanics and mining sciences (Oxford, England : 1997) Vol. 37; no. 1; pp. 403 - 411
• Main Author: Schultz, R.A
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2000
• ISSN: 1365-1609; 1873-4545
• DOI: 10.1016/S1365-1609(99)00115-X

Several aspects of fracture arrays are reviewed briefly and discussed. The terminology applied to progressive or multi-stage brittle deformation in rock masses is improved by noting fundamental mechanical differences in fracture type and the kinematic coupling between dilatant mixed-mode crack displacements and wing cracks developed at the fracture tips. An array of initially mixed-mode (I–II) cracks will evolve under remote tensile least principal stress and with increasing strain to a dilatant, mode-I crack array oriented approximately perpendicular to the remote tensile stress. This progressive fracture growth thus defeats predictions of fracture-set orientation and displacement based only on a Mohr circle estimate of initial elastic stress (valid in the rock mass only at the earliest stages of fracture nucleation). Slow, subcritical crack growth in rock is associated with distinctive changes in fracture population geometry, as shown by published numerical simulations of fracture–network evolution. An increase in the stress corrosion index promotes joint clustering and significant changes in joint length–frequency that may lead to characteristic differences in the statistics of large-strain fracture populations. These geometric clues can be used to refine estimates of strength and deformability of rock masses and to infer classes of physico-chemical processes acting at the fracture tips during the development of the fracture population.