Exploring Chemical Enhancement of Subcritical Fractures in Geomaterials

Abstract

Propagation of subcritical cracks is studied in a geomaterial subject to weakening by the presence of water, which dissolves a mineral component of it. Such weakening is common when tensile micro-cracks develop, constituting sites of an enhanced mineral dissolution. Meanwhile, the dissolution process at each active site of the inter-surface is affected by the chemical properties of the environment, e.g. the PH value. In this research, a previous concept of reactive chemo-plasticity is adopted with the yield limit depending on the mineral mass dissolved and causing a chemical softening. The dissolution is described by a rate equation and is a function of a variable internal specific surface area, which in turn is assumed to be a function of the dilative plastic deformation. Two loading modes are adopted to investigate the chemical enhancement of propagation of a single crack. The behavior of the material is rigid-plastic with a chemical softening. The extended Johnson approximation is adopted, meaning that all the fields involved are axisymmetric around the crack tip with a small, unstressed cavity around it. An 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 calibration against available data will be performed in the future, followed by a series of experiments to simulate the real case.