Developing a generalized multiple-step loading damage model to predict rock behaviour during multiple-step loading triaxial compression test

Abstract

Multiple-step Loading Triaxial Compression Test (ML-TCT) method is a useful tool to evaluate strength parameters from a single specimen. However, because of accumulated damage in the specimen with repeated cycles of axial loading/unloading, the shear strength is prone to be underestimated. Therefore, considering two models which were previously developed for a siltstone and a mudstone, a generalized Multiple-step Loading Damage (MLD) model was developed to simulate ML-TCTs with various stress paths. Numerical simulations of generalized MLD model indicated that the margin between shear strength parameters determined by Single-step Loading Triaxial Compression Tests (SL-TCT) and ML-TCTs, increase with increasing rock strength. Moreover, the upper bound values for c′ and lower bound values for ф′ could be resulted for ML-TCTs with confining pressure in increasing manner. Whereas, the upper bound values for ф′ and lower bound values for c′ can be obtained for decreasing manner tests.