Mechanisms of coupled mode I-II fracture initiation in rocks subjected to heat flow-induced fracture gas-steam pressure and heat flow stress

Abstract

The construction of tunnel projects in the Sichuan-Tibet region has led to the occurrence of rock fractures caused by high temperature and high humidity, which are inevitable challenges. When there is fracture water in rock fractures and it encounters a heat flow, the water vaporizes into fracture steam, which undergoes thermal expansion to generate fracture gas-steam pressure. The heat flow direction is at an angle to the crack, causing heat flow stress in the rock. To understand the mechanism of crack initiation and propagation in rocks under the joint action of uniform heat flow-induced fracture gas-steam pressure and heat flow stress, the control equation for fracture gas-steam pressure is derived and expressions for stress intensity factor, crack temperature field, stress field, and crack initiation strength criterion are established based on the theory of complex variable functions. The key parameters are analyzed and discussed, finding that under low heat flux density, small incidence angles, and large crack inclination angles, KI values are higher, and the crack initiation is mainly in tension. Under high heat flow density, large incidence angles, and crack inclination angles near 45°, KII values are higher, and the crack initiation is mainly in shear. The coupling effect of KI and KII is more sensitive to heat flow density and inclination angle. The critical initiation angle and initiation strength increase with the increase of heat flow density and incidence angle, with heat flow density being the determining factor.