Chemically- and mechanically-mediated influences on rock fractures and their implications on thermomechanical loading cycle

Abstract

A model is presented to represent changes in the mechanical and transport characteristics of fractured rock that result from coupled mechanical and chemical effects. The specific influence is the elevation of dissolution rates on contacting asperities which result in a stress- and temperature-dependent permanent closure. A model representing this pressure-dissolutionlike behavior is adapted to define the threshold and resulting response in terms of fundamental thermodynamic properties of a contacting fracture. These relations are incorporated into a stress-stiffening model of fracture closure to define the stress- and temperature-dependency of aperture loss, and behavior during stress and temperature cycling. These models compare well with laboratory and field experiments, representing both decoupled isobaric and isothermal responses. The model was applied to explore the impact of these responses on heated structures in rock. The result showed a reduction in ultimate induced stresses over the case where chemical effects were not incorporated, with permanent reduction in final stresses after cooling to ambient conditions. Similarly, permeabilities may be reduced over the case where chemical effects are not considered, with a net reduction apparent even after cooling to ambient temperatures. These heretofore neglected effects may have correspondingly a significant impact on the performance of heated structures in rock, such as repositories for the containment of radioactive wastes.