ELASTOPLASTIC ANALYTICAL STUDY ON THERMAL FRACTURING OF HIGH-LEVEL RADIOACTIVE WASTE DISPOSAL

In low-permeability rock masses, the difference in thermal expansion coefficients between the solid skeleton and pore fluid can lead to a significant increase in pore pressure under high-temperature conditions (i.e., thermal pressurization), which readily induces tensile failure. Focusing on the stability of host rocks surrounding a deep geological disposal system for high-level radioactive waste (HLW) under thermal loadings, this study establishes a coupled Thermo-hydro-mechanical (THM) elastoplastic analytical model. In the constitutive modelling, the Mohr-Coulomb elastoplastic constitutive model is employed to characterize the stress-strain relationship of claystone, while Fourier's law and Darcy's law are adopted to represent heat conduction and fluid flow, respectively. Analytical (or approximate analytical) expressions for the distributions of temperature, pore pressure, stress, and displacement in the host rock are derived, revealing the mechanical control mechanisms governing thermally induced rock failure. The solutions show good agreement with results obtained from COMSOL finite element simulations and laboratory tests, thereby validating the high accuracy and engineering applicability of the proposed model. Parametric analyses indicate that the thermal pressurization effect significantly elevates near-field pore pressure, leading to a transition of the hoop effective stress from compression to tension, which readily induces tensile failure (thermal fracturing) in the host rock. Furthermore, the influences of key factors such as the solid skeleton thermal expansion coefficient and tunnel wall temperature on the host rock responses are systematically investigated. The analytical model developed in this study features a concise mathematical form, well-defined parameters, and high computational efficiency, making it suitable for rapid risk assessment of thermal fracturing and optimization of key parameters during the preliminary design phase of nuclear waste disposal systems.