亚高温裂隙气-汽压作用下岩石近表Ⅰ-Ⅱ复合型裂纹起裂研究

Initiation of near-surfaceⅠ-Ⅱmixed mode cracks in fractured rocks subjected to hypo-high temperature and air-vapor pressure

我国西南地区隧道近表围岩长期处于亚高温、高湿环境,易产生湿热病害。围岩裂隙水汽化会产生裂隙气-汽压,影响裂纹起裂强度及扩展路径。为研究亚高温裂隙气-汽压岩石裂纹起裂机制,基于裂隙气体状态方程及线弹性断裂力学理论,推演了远场压剪应力和裂隙气-汽压共同作用下岩石裂纹起裂模型及应力强度因子计算公式,提出压剪复合应力状态下的起裂准则及起裂强度和临界起裂角的计算方程,分析裂纹尖端周向应力分布规律及起裂特征,讨论各参数对起裂强度及临界起裂角的影响。结果表明:裂隙气-汽压受温度和气体饱和度共同控制,温度占主导因素;在低、高裂纹倾角时,K_(Ⅰ)远大于K_(Ⅱ),裂纹以张拉起裂为主,裂隙气-汽压起促进作用;裂纹倾角处于15°~75°范围,K_(Ⅰ)和K_(Ⅱ)较为接近,裂纹以压剪复合起裂为主,裂隙气-汽压起抑制作用;裂纹尖端周向应力呈正弦式分布,最大周向应力随裂隙气-汽压增大而减小,临界起裂角随裂隙气-汽压增大而增加;随温度增加或气体饱和度增加,起裂强度减小,临界起裂角增加;理论计算与室内试验结果吻合较好。研究结果为亚高温高湿环境下隧道近表围岩裂纹扩展分析提供理论依据。

The near-surface surrounding rock of tunnels in southwestern China has been in a hypo-high temperature and high humidity environment for a long time,which is prone to thermal and humid diseases.The water vaporization of surrounding rock cracks produces crack air-vapor pressure,which affects the crack initiation strength and propagation path.In order to study the crack initiation mechanism of hypo-high temperature fractured air-vapor compression rock,based on the fracture gas state equation and linear elastic fracture mechanics theory,the rock crack initiation model and the calculation formula of stress intensity factor under the combined action of far-field compressive shear stress and fracture air-vapor compression are deduced.The crack initiation criterion and the equation of crack initiation strength and critical crack initiation angle under the combined stress state of compressive-shear are proposed.The circumferential stress distribution law and crack initiation characteristics at the crack tip are analyzed,and the influence of various parameters on the crack initiation strength and critical crack initiation angle are discussed.The results show that the fracture air-vapor pressure is jointly controlled by temperature and gas saturation,and temperature is the dominant factor.At low and high crack inclination angles,K_(Ⅰ)is much larger than K_(Ⅱ),and the crack initiation is mainly tensile,and the air-vapor pressure plays a promoting role.The crack inclination angle is between 15°and 75°,the value of K_(Ⅰ)and K_(Ⅱ)are close.The crack initiation is mainly compression-shear,and the crack air-vapor pressure inhibits the crack initiation.The circumferential stress at the crack tip is sinusoidally distributed with the change of polar angle,and the maximum circumferential stress decreases with the increase of fracture air-vapor pressure,and the critical crack initiation angle increases with the increase of fracture air-vapor pressure.With the increase of temperature and gas saturation,the initiation strength decreases and the critical initiation angle increases.The theoretical calculation is in good agreement with the laboratory test results.The research results provide a theoretical basis for crack propagation analysis of tunnel near surface surrounding rock under hypo-high temperature and high humidity environment.