Mechanical behavior of rocks subjected to true triaxial stresses: are Mohr-type criteria adequate?

摘要

An extensive series of true triaxial tests in Westerly granite and KTB amphibolite has been conducted using the new University of Wisconsin polyaxial loading system. Results demonstrate the significant effect of the intermediate principal stress on both strength and deformability. The commonly used Mohr -type criteria, which neglect that effect, yield overly conservative strength estimates. A new strength criterion which invokes all three principal stresses, and which is supported by the reported tests, is proposed. The larger the intermediate principal stress, the higher the dilatancy onset, i.e. the wider the elastic range. Microme-chanical studies show that brittle failure under true triaxial loading is reached when a through-going steeply inclined fracture is produced from the coalescence of localized microcracks aligned with the plane that contains the least and largest principal stresses.