岩石不等长裂纹应力强度因子及起裂规律研究

天然岩体中含有数量众多的裂隙且绝大多数为不等长裂隙,而那些具有一定尺度和规模的主控裂隙对岩体稳定性起决定作用。为研究不等长裂纹相互作用规律及主控裂纹起裂规律,基于Kachanov法,推导了远场受力的两条拉剪不等长共线裂纹的尖端应力强度因子表达式并从理论上分析了裂纹间距对裂纹相互作用的影响;通过最大周向应力准则,计算了单轴受拉时不同裂纹倾角的主控裂纹起裂角,绘出理论断裂准则曲线;推算滑动裂纹的应力强度因子,对含不等长裂纹的类岩试件进行单轴压缩试验。结果表明:当裂纹间距大于等于小裂纹长度时,小裂纹对主控裂纹的起裂几乎无影响;主控裂纹起裂角只与裂纹角有关,单轴受拉时,起裂角随裂纹角增大而减小,单轴受压时,起裂角随裂纹角增大而增大;当裂纹倾角小于30°时,起裂临界荷载急剧增大。

Stress intensity factors and initiation of unequal collinear cracks in rock

There are many cracks in the natural rock mass and the majority of the cracks are unequal. The main control crack with a certain scale decides the stability of the rock mass. In order to study the interaction rules of the cracks with unequal length and the initiation rules of the main control crack, based on the Kachanov method, the expressions for the stress intensity factors of two collinear cracks with unequal length loaded by uniaxial tractions at infinity are derived, and the influence of the crack distance on the interaction is theoretically analyzed. The initiation angle of the main crack under uniaxial tension is calculated by the maximum circumferential stress criteria and the theoretical fracture criteria curves are drawn. The stress intensity factors of sliding close cracks are derived and the compression tests on rock-like specimens with two unequal collinear cracks are performed. The results show that the small crack almost has no effect on the initiation of the main control crack when the crack distance reaches the length of the small crack. The initiation angle of the main control crack is only related to the crack incline angle, and it decreases with the increase of the crack angle when the cracks are loaded by uniaxial tension and it increases with the increase of the crack angle when the cracks are loaded by uniaxial compression. The initial critical load increases rapidly when the crack incline angle is less than 30°.