This paper provides a brief summary of a continuous research programme by the authors since 2004, and highlights the research approach, achievements and outstanding issues for conceptual understanding, laboratory testing and mathematical modeling of the coupled stress-shear-fluid flow-solute transport processes of rock fractures. The focuses are put on stress and shear induced fluid flow anisotropy, transport pass channeling, and impact of considering different retardation mechanisms in single fractures of crystalline rocks, typically granites, due to its importance for the performance and safety assessments of geological radioactive waste disposal projects.
Rocks are natural geological materials containing fractures of different origins, sizes, mineral fillings, weathering degrees, orientations, termination patterns, thickness and shapes, and especially surface roughness features. In addition, rocks in-situ are under stress, caused by dynamicmovements in the upper crust of the Earth, such as tectonic plate movements, earthquakes, land uplifting/subsidence, glaciation cycles and tides, in addition to gravity. A rock mass is also a fractured porous medium containing fluids in either liquid or gas phases (e.g. water, oil, natural gases and air), under complex in-situ conditions of stresses, heating or cooling, freezing or thawing, fluid pressures, and complicated geochemical reactions, with connected fractures most often serve as the major energy and mass transport pathways and most active areas of geochemical reactions, especially for fractured hard crystalline rocks. This is the reason why the coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes is an issue of importance in the field of rock mechanics.
The terms "discontinuity" and "fracture" are used interchangeably in the rock mechanics literature. The term "fracture" is adopted throughout this paper as a collective term for all types of natural or artificial discontinuities such as faults, joints, dykes, fracture zones and other types of weakness surfaces or interfaces, unless specifically stated otherwise. The rock fractures are usually not just open voids with fresh and smooth surfaces. Their surfaces (or walls) are often rough, weathered and fully or partially filled with precipitated minerals, and their relative positions are often modified by geological history and loading conditions, such as opening, closing, faulting or shearing, with large or small relative displacements. The complexity in the surface topography makes understanding and quantitative representation of the physical-chemical behavior and rock fracture properties difficult issues.