Residual Properties Estimated from Post-Peak Triaxial Unloading: Case Study of a Hard Rock Mine Site Available to Purchase

Physical and mechanical properties of rock material determined from laboratory testing are an integral part of the geological characterization and engineering design process for underground works. Typical intact rock properties derived from a laboratory testing program consist of peak strength and elastic properties (Young's modulus and Poisson's ratio), as measured through unconfined or confined (triaxial) testing. However, with the advent of stiff, servo-controlled loading frames able to collect accurate post-peak data during triaxial tests, it is also possible to estimate residual properties, including strength, friction angle and cohesion. The current study presents the results of residual properties estimated from over 300 triaxial tests completed between 2005 and 2018 on core samples collected from a hard rock mine site. Testing was completed on a variety of heterogeneous rock types ranging in diameter from 36 to 84 mm, under confinement up to 70 MPa. Residual properties are estimated from the triaxial unloading curve using the continuous state failure approach and compared to the Mohr-Coulomb residual strength constants derived from bi-linear fit to raw residual strength and confinement data. It was observed that the Mohr-Coulomb residual fit consistently under estimated residual friction angle and overestimated the residual cohesion values determined through analysis of the triaxial unloading curves.