A three-dimensional strength criterion based on true triaxial testing of rocks
Perhaps the most important mechanical property of rock is its compressive strength. Strength criteria such as the Coulomb, Mohr, or Hoek-Brown, are strictly correct only when the intermediate and least principal stresses are equal (σ2 = σ3). At the University of Wisconsin we employ a new true triaxial testing apparatus that enables the application of three unequal principal stresses to rectangular prismatic specimens. Comprehensive series of tests on several rock types have demonstrated that, contrary to common criteria, the compressive strength (peak σ1) for a given 3 increases significantly with the magnitude of σ2, reaching levels of up to 10-100％ higher than the peak σ1 when σ2 = σ3. The true triaxial strength criterion is obtained by plotting all test results in a modified Nadai (1950) domain, in which the data points are best fit by a power function in which the octahedral shear stress, τoct, at failure is related to the mean stress acting on the plane of failure, σm,2; τoct = A σm,2 B, which in some cases can be reasonably linearized to τoct = C σm,2 . True triaxial tests reveal that for a constant 3 the onset of dilatancy also increases with the magnitude of 2, thus retarding the onset of the failure process. Moreover, the dip angle of the fault at failure rises monotonically with 2 for fixed σ3, again contrasting commonly used criteria.
Bezalel Haimson
University of Wisconsin. USA
国际会议
香港
英文
1-8
2009-05-19（万方平台首次上网日期，不代表论文的发表时间）