Mapping the state of fracture around cavities

Abstract

The state of stress around cavities is heterogeneous. Consequently, the state of fracture may also vary from point to point. Under compressive loading, cavity may be in one of four possible states: pre-fracture (pre-microfracture initiation), microfracture propagation (initiation to the onset of dilata dilatancy to failure) and post-failure. These four states are separated by the crack initiation stress, the crack damage stress and the failure stress. fracture events with confining pressure is examined with reference to three intact rocks: a brittle granite, a semi-brittle limestone and a ductile sal The maximum principal stress (σ 1) at crack initiation, crack damage (onset of dilatancy), yielding and failure are established as a function stress (σ 3). For a single intact rock, all four fracture events can be represented using one function (the Rocker function) with a single fac various fracture states. The proposed fracture criteria, based on the experimental data, are combined with the existing state of stress to prepare a fracture map around an elli intact Lac du Bonnet granite. The state of stability is expressed through a newly defined stability factor, the unconfined strength ratio (USR), wh to the traditional safety factor. In contrast to the conventional safety factor in rock mechanics (SF strength/σ 1), which is σ 3 <tensile strength space, the USR is defined for any point in the σ 3–σ 1, space of the stability diagram.