Exact satisfaction of uniaxial tensile and compressive strengths of rock in a new failure criterion considering Brittle-Ductile transition as an initial boundary condition

Abstract

Empirical rock failure criteria generally relates lateral stresses to axial strengths by a particular equation in which uniaxial tensile and/or compressive strengths are to be estimated from the failure criterion by applying the obtained parameters from triaxial datasets into the criterion equation. In order to satisfy the exact amounts of uniaxial tensile and compressive strengths in a failure criterion, a rational function is proposed as a failure criterion for isotropic, dry and intact rocks to be used in both tensile and compressive regions. The proposed criterion is validated by using 59 series of accurate triaxial test datasets which are belong to 20 different rock types selected from the literature. It has been shown that the proposed criterion is capable of predicting the triaxial behavior of rocks in both tensile and compressive regions. There are two coefficients for the proposed criterion ('c' and 'd') which have been estimated for used rock datasets by applying brittle-ductile transition as an initial boundary condition. The most proper brittle into ductile boundary, the confinement in which ∂τ/∂ σn=0 or in other words when ∂σ1/∂σ3=1, has been determined (σ3=ησc) in such a way that the best triaxial predictions have been obtained. Also, the values of the criterion coefficients are discussed in detail. © ISRM International Symposium on Rock Mechanics, SINOROCK 2009.