Investigation of the fully coupled thermo-hydro-mechanical dual-medium model and the development of seepage mechanisms in fractured rock masses

Abstract

The seepage mechanism of fractured rock masses provides a basis for deep geothermal development, tunnel engineering, and nuclear waste disposal. This study developed a coupled thermal, hydraulic, and mechanical (THM) dual-medium model based on thermodynamic theory. The model derives constitutive relationships for saturated porous and fractured media, characterizing interactions through mass and heat exchange. Model accuracy was validated against analytical solutions for one-dimensional thermoelastic consolidation. Simulations reveal seepage evolution patterns: fracture flow velocity initially depends on aperture distribution, while pore flow follows pressure gradient; at steady-state, fracture flow is controlled by overall pressure gradient, and pore flow by fluid exchange. This transformation occurs as the fracture apertures adjust from thermo - mechanical coupling, where high-temperature injection causes thermal expansion and closure stress. The analysis shows that the mass flux creates preferential flow patterns, lateral stress causes pathway shifts, and temperature gradients lead to fracture-dominated patterns. A sensitivity analysis indicates that the fracture conductivity depends on the mechanical parameters, whereas temperature propagation relates to the convection intensity. This study explains the seepage transformation under multifield coupling for rock mass control and stability assessment.

Keywords

fractured rock mass / double-medium / thermo-hydro-mechanical coupling / numerical simulation / seepage mechanism / parameter sensitivity

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Central South University