Composed of heterogeneous mineral grains and microdefects at the microscopic scale, natural rocks are strongly heterogeneous. This typically results in macroscopically non-linear mechanical response under the action of external forces including thermomechanical and thermochemical effects. Classical macroscopic constitutive equations fail to describe the complex evolution of damage and its progress to failure. Recently, micromechanical damage models have been developed to address the complex macroscopic behavior of rock material. These models allow the evolution of real damage microstructures, including the initiation, growth and coalescence of defects with the result that this method links microscopic damage evolution to macroscopic mechanical response. We present a combined microscopic-macroscopic model that embeds the micromechanical model into a macroscale finite element model (FEM). The method is implemented in FEM with each grid block treated as a microscopic element (i.e. REV) of rock material. The evolution of both microcrack damage and of the macroscopic effective constitutive equation is then evaluated for each grid block. On this basis, the global stiffness matrix of the entire object is established and FEM used to solve practical rock engineering problems. A uniaxial tension experiment is simulated to validate the method. The stressstrain relations recovered for this numerical experiment replicate the experimental results including the evolution of damage and failure of the rock sample. This method provides an effective approach to study problems of rock damage and failure in engineering.
The past twenty years or more have witnessed unprecedented achievements in many large-scale rock engineering fields such as coal mining, petroleum and gas recovery, the development of geothermal reservoirs, the sequestration of radioactive wastes and CO2 among others. However, in all of these systems an important issue is how to reasonably model the evolution and impact of damage on the overall fracture behavior in rock [1].
