Linear crack initiation analysis on rock surface under the combined action of sub-elevated temperature stress and fracture air-vapor pressure

Abstract

Near the surface of the Sichuan-Tibet line tunnel surrounding rock under construction is in a sub-hot and humid environment, and long-term accumulation will produce damp-heat diseases. The significant temperature difference leads to the thermal stress of the surrounding rock, and the surrounding rock fracture water vaporizes to create fracture air-vapor pressure, which induces crack initiation. The state equation of gases, thermoelastic mechanics, and the theory of linear elastic fracture mechanics are used to study the crack initiation law of rock under the joint action of sub-elevated temperature stress and fracture air-vapor pressure. The stress intensity factor's expression under the two joint actions is derived from the superposition principle. Then the initiation criterion considering both internal influencing factors (rock properties, crack geometry parameters (inclination angle)) and external influencing factors (far-field stress, temperature, humidity factors) is derived. The theory is used to quantitatively analyze the distribution law of tangential stress at the crack tip and the crack initiation form. The effects of each parameter on critical crack initiation angle and crack initiation strength are discussed. The theoretical results are further verified by numerical simulation. The results show that in the sub-elevated temperature range, the thermal stress and the fracture air-vapor pressure jointly affect the crack initiation law, and thermal stress is the dominant factor. With the temperature increase, KI >KII, the critical crack initiation angle increases gradually, the crack initiation form changes from shear to compression-shear, and finally tends to tension. The fracture air-vapor pressure promotes the tension part. The maximum tangential stress increases linearly with temperature. The maximum tangential stress and critical crack initiation angle increase first and then decrease with the rise of crack inclination angle and reach the maximum at 45°. The research results supply a theoretical basis for preventing and treating the rock crack propagation surrounding the tunnel under sub-elevated temperatures and high humidity.