Strain localisation and seepage characteristics of rock under triaxial compression by 3D digital image correlation

Abstract

The rock mass can be unstable due to the coupling effect of stress and seepage field, adversely affected by the geological field conditions. In this regard, this study implemented a 3D digital image correlation (3D-DIC) technique to conduct triaxial compression tests on sandstone samples under different seepage pressures. We analysed the evolution of strength and permeability during the rock failure process and space-time evolution of the surface radial strain. The results show that the strength and brittleness of the rock decrease with increasing seepage pressure. Further, the mechanical properties of the rock sensitive to were highly dependent on the seepage pressure. We also established a function model of permeability and axial strain consistent with the test results. By analysing the radial-strain-field of the rock surface at specific time points, we observed a gradual process of strain localisation instead of a sudden occurrence before failure. We extracted the spatial coordinates of the first 5% radial strain and subsequently conducted the spatial relation analysis by average-nearest-neighbour-analysis (ANNA). In addition, the approximate failure surface was fitted using the first 5% radial strain points in space, and the distance between the radial strain points and the fitted failure surface in space was analysed. This study shows that points with large strain values gradually converged towards the location of the fracture surface during the gradual failure process of the rock. Finally, this study provides a new method for predicting the failure zones of rock.