A Reconsideration of the Extension Strain Criterion for Fracture and Failure of Rock

• Published in: Rock mechanics and rock engineering Vol. 49; no. 12; pp. 4667 - 4679
• Main Authors: Wesseloo, J., Stacey, T. R.
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.12.2016; Springer Nature B.V
• Subjects: Civil Engineering; Earth and Environmental Science; Earth Sciences; Excavation; Failure analysis; Fractures; Geophysics/Geodesy; Original Paper; Rocks; Strain; Extension strain criterion; Failure criterion; Polyaxial strength; Extension fracturing; Fracture initiation criterion
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-016-1059-0

The complex behaviours of rocks and rock masses have presented paradoxes to the rock engineer, including the fracturing of seemingly strong rock under low stress conditions, which often occurs near excavation boundaries. The extension strain criterion was presented as a fracture initiation criterion under these conditions (Stacey in Int J Rock Mech Min Sci 18:469–474, 1981 ). This criterion has been used successfully by some and criticised by others. In this paper, we review the literature on the extension strain criterion and present a case for the correct interpretation of the criterion and the conditions suitable for its use. We argue that the extension strain criterion can also be used to provide an indication of damage level under conditions of relatively low confining stress. We also present an augmentation of the criterion, the ultimate extension strain, which is applicable under extensional loading conditions when σ 2 is similar in magnitude to σ 1 .