Environmentally enhanced crack propagation in a chemically degrading isotropic shale

Abstract

Crack propagation is studied in a geomaterial subject to weakening by the presence of water, which dissolves a mineral component. Such weakening is common when tensile microcracks develop, constituting sites of enhanced mineral dissolution. A previous concept is adopted of reactive chemo-plasticity, with the yield limit depending on the mineral mass dissolved, causing chemical softening. The dissolution is described by a rate equation and is a function of variable internal specific surface area, which in turn is assumed to be a function of dilative plastic deformation. The crack vicinity in plane strain is subject to a constant subcritical all-round uniform radial tensile traction. The behaviour of the material is rigid-plastic with chemical softening. The extended Johnson approximation is adopted, meaning that all fields involved are axisymmetric around the crack tip, with a small, unstressed cavity around it. Initial dissolution proportional to the initial porosity activates the plastic yielding. The total dissolved mass diffuses out from the process zone and the exiting mineral mass flux can be correlated with the displacement of the crack tip. A simplified semi-analytical solution for this model is presented.