岩石的劈裂和卸载破坏机制

MECHANISM OF SPLITTING AND UNLOADING FAILURE OF ROCK

概括含缺陷的岩体结构模型,并利用其研究岩石在加载和卸载时内部出现的拉应力及其对岩石破坏模式的影响。为模拟深部岩体的赋存环境,研究3种受力条件下的岩石应力状态:单轴无侧限压缩、具有初始静水压力时的加载和初始静水压力作用下岩石的卸载。分析表明,无论是加载还是卸载,岩体中均将出现局部拉应力。在加载情况下,岩体中出现的拉应力有可能导致平行于加载方向的劈裂;而在卸载情况下,岩石中将在缺陷处形成平行于卸载方向的拉应力。岩石中出现的拉应力主要与岩体内缺陷的物理参数、初始应力大小和卸载速率有关。对卸载时初始应力和卸载速率对缺陷应力集中的影响进行分析,结果表明:卸载速率越快,缺陷处的应力集中越大,若缺陷尺寸较大,岩体中的局部拉应力和初始应力近似成正比。根据得到的局部应力表达式,在深地下工程中,快速卸载将必然导致岩体的拉伸破坏。

After the introducing of rock structure model with nonuniformities, the influence of stress concentration on the failure mode of rock are analyzed based on stress concentrates during deformation on nonuniformities. In order to investigate the behavior of rock in depth, three cases of stress conditions are studied. They are unconfined uniaxial compression, the loading and unloading of hydrostatic stressed rock in axial direction. Analysis shows that both in loading and unloading process, tension stresses appear in rock. In the loading case, the tension stress may result in splitting which is parallel to the loading direction. In the unloading case, the tension stress is parallel to the unloading direction. The main influential factors of tension stress are physical parameters of nonuniformities, initial stress of rock and unloading speed. The influence of unloading duration and initial stress on the stress concentrations of nonuniformities is analyzed in detail. Results show that the shorter the unloading duration is, the greater the stress concentration is. And if the scale ofnonuniformities is large enough, the local tension stress will be approximately proportional to the initial stress. According to the expressions of local tension stress, rock mass will be destructed by tension during rapid unloading in deep rock engineering.