Numerical Exploration of Residual Stress Mechanisms in Rock

Abstract

Residual stresses are known to exist within the microstructure of crystalline materials as a result of material formation processes and exists in a state of equilibrium with their own internal forces. Research has proven their existence, and engineering applications have been derived for glass and metal to achieve desirable material properties. In the field of rock mechanics and rock engineering, the existence of residual stress has been acknowledged, but beyond that, little research has been performed to investigate their behaviour and implications and they are often omitted from design considerations due to their state of equilibrium. Using numerical modelling techniques such as grain-based modelling, insights on the effects of residual stress in rock can be explored. Grain-based models were created in 2D with RS2, and in 3D with 3DEC, to explore potential implications for residual stress in the field of rock mechanics and rock engineering. Methods to implement residual stress in numerical models were developed and used to explore the effects of residual stress on modelling outcomes. In RS2, three main implications were investigated. The first examines a relationship between residual stress and crack closure strains in compression tests. The second investigates the influence of residual stresses on the formation and propagation of damage (microcracks) within rock specimens. The final simulation relates to the stresses and displacements associated with a mobilized residual stress field due to the addition of a circular excavation in a rock block. In 3DEC, the formation of damage due to unloading a specimen containing residual stresses was examined. Compression tests were performed on the unloaded specimens to investigate for crack closure strains as a result of the damaged formed through residual stress redistribution during unloading. The investigations undertaken in this study suggest that residual stresses have a real and non-negligible influence on rock behaviour and their omission may not be a valid approach when performing design in rock that contains these stresses.