The creation of an excavation damaged zone (EDS) is expected around all man-made openings in civil engineering, in underground mining, and in petroleum engineering. The EDS may vary the physical, mechanical, and hydraulic properties of rock mass, and in turn dominate the evolution of EDS under coupled thermal, hydraulic and mechanical (THEM) environments. Understanding the development of EDS under coupled THEM conditions is of great importance for evaluating the engineering stability and safety, and for optimizing the supporting parameters. The work begins an introduction to the coupled THEM model for the rock damage, which is proposed when the damage variable is incorporated into the classic thermo hydro elastic model according to elastic damage theory. Next, the model is numerically implemented with finite element method by employing a numerical package called CONSOLE Multi physics (CM), and is also validated against some existing experimental observations. Finally, the model is used to simulate the formation and development of EDS under coupled THEM environments, and the effect of rock mass heterogeneity, potential THEM boundary conditions on the coupled THEM responses of rock mass is examined.
In enhanced geothermal systems, as in reservoirs for the sequestration of CO2, radioactive waste repositories, petroleum reservoirs, and other subsurface engineered facilities, the excavation damaged zone around the underground opening is influenced in both the short- and long-term by thermal-hydro-mechanical (THEM) behavior of fractured rock mass. The coupled THEM numerical models used in rock mechanics can be traced back to early 1980s, when many models were proposed based on the extension of Boot's theory of consolidations. Beginning from 1990s, under the form work of international cooperative project entitled DECO VALE, a number of benchmark tests (BIT) and test cases (TC) have been carried out in order to support development of computer simulators for THEM processes in geological systems [1–2]. Up to now, most numerical codes are still based on the assumption of elasticity and plasticity of rocks, or based on discrete approach where only a limited number of fractures are included to represent the fractured rock mass, thus the propagation of existing fractures, as well as the initiation of new fractures in rock mass, are usually ignored. However, both the hydraulic and thermal processes are sensitive to fracture initiation and propagation. Under the coupling of complex THEM processes the existing fractures may propagate and some new fractures may initiate, which in turn alters the thermal and hydraulic processes. Therefore, it's quite significant to incorporate the damage processes of rock in the numerical models in order to characterize the coupled THEM response of fractured rocks, especially during the formation and development of excavation damaged zone (EDS). In view of this, the authors have recently developed a damage-based THEM model to study the coupled THEM process during rock failure , which makes it a competitive candidate for characterizing the THEM response of the EDS around underground openings. To this end, it is to numerically study the development of EDS under coupled THEM condition that defines the objective of this work.