Thermo-hydro-mechanical coupling field-enriched finite element method for thermo-poroelastic fractured rock mass and its application

In this paper, a coupled thermo-hydro-mechanical field-enriched finite element method is developed to simulate the cracking behaviors in thermo-poroelastic fractured rock mass. The governing equations of displacement, fluid flow and temperature are based on the thermo-poroelastic theory, and the coupled relationships of these three physical fields are fully incorporated in the governing equations. The unified field variable is introduced to characterize the crack position, crack initiation and propagation, and to describe the damage-dependent physical parameters in the coupled governing equation system. The coupled multiphysics governing equations are solved by the staggered Newton-Raphson iterative algorithm. The accuracy of the proposed method is carefully validated by six problems in the aspects of analytical solutions, previous numerical solutions and FEM solutions. Additionally, the performance of the proposed method for simulating thermal-hydraulically induced crack initiation and propagation is validated and compared with the COMSOL results. Then, the proposed method is employed to predict the deformation of the tunnel surrounding rock under multiphysics coupling conditions. Finally, the application of the proposed method in geothermal extraction that considers different well patterns and fracture distributions has been realized. The numerical results have shown that the proposed method is capable of accurately simulating the crack initiation and propagation, predicting the deformation of tunnel surrounding rock, and simulating and optimizing the mining process of geothermal resources.