A mechanistic view of some aspects of jointing in rocks

Abstract On the assumption that joints are tensile fractures, the origin of jointing is examined by using the concept of the microscopic Griffith crack of fracture mechanics. Most joints are expected to form through nucleation at tensile stress concentrations of Griffith cracks during a period of rising compressive stress and low confining pressure. The process of stable fracture propagation from numerous Griffith cracks is aided by porewater pressure and stress corrosion. Joints may also form during unloading through a residual stress effect. A mechanism of fracture through residual stress connected with failure at compressive stress concentrations of Griffith cracks is proposed and its implications examined.