Application of the Extension Strain Criterion for Sandstone Failure Evaluation under Tension and Shear Stress Conditions

The article discusses the possibility of analysing, in geomechanical terms, the applicability of the extension strain criterion to assessing the fracture and failure process of sandstone samples. The results of laboratory tests of indirect tension, as well as uniaxial and triaxial compression were used to identify various forms of the criterion. The criterion parameters for fracture initiation and advanced failure processes were presented, and the results in both cases are different. The possible ways of applying this criterion to assess crack initiation in a tension test and failure in a shear test were also presented. Digital image correlation (DIC) analyses were used to determine the deformations of sandstone samples in both test types. The results of these studies show the possibilities to use this condition, e.g., to assess the stability of large-diameter boreholes (for disposal of radioactive waste) and wellbore stability, and to monitor and track the behaviour of tunnels drilled in strong rocks.