ABSTRACT
ABSTRACT: The three-dimensional failure criterion for concrete proposed by Lade (1982) and used for rocks by Kim and Lade (1984) is expressed in terms of the first and the third invariants of the stress tensor and it requires three parameters for characterization of the strength. One parameter is slightly higher than the uniaxial tensile strength of the rock and is used to capture the cohesion and the tensile strength. Another parameter is used to describe the opening angle of the failure surface, i.e. similar to the friction angle, while the third parameter is employed to describe the curvature of the failure surface in meridian planes that contain the hydrostatic axis. Typically, the results of three triaxial compression tests and the tensile strength from a Brazilian test or from an estimate are required for determination of these three parameters. The failure surface has a smooth continuously curved, triangular cross-section in the octahedral plane and it has curved traces in the meridian planes. Careful inspection of parameters determined from a number of high quality tests on rocks presented in the literature reveals that two of the parameters relate to each other for rocks. It is therefore possible to obtain the two parameters from the results of a single triaxial compression test. The third parameter may be obtained from an estimate based on the compressive strength of the rock. The relation between the two parameters is demonstrated for rocks, and it is shown how the results from a single test are used to determine the parameters to describe the threedimensional failure surface for rocks.
