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利用RMT–150C岩石力学测试系统,对重庆彭水含天然裂隙脆性页岩在单轴循环荷载作用下的变形及破裂特征进行了试验研究。研究结果表明:(1)在循环加卸载和裂隙的共同影响下页岩所含天然裂隙使页岩性质局部劣化、加剧裂隙扩展和破坏提前,导致屈服应力、破裂压力和峰值强度等减小,其中峰值强度降低了13.7%~58.3%;(2)轴向应变形成封闭的“尖叶”状滞回环,并呈疏—密—疏排列,而横向应变形成上开口“8”字形滞回环,并呈密—疏排列,横向应变-循环次数曲线可分为初始变形阶段、小速率等速变形阶段、大速率等速变形阶段和失稳破坏阶段等四阶段演化规律,前期横向应变突变现象可作为天然裂隙和新裂隙扩展、交汇完成,进入大速率等速变形阶段的标志,后期突变可作为整体失稳破坏的前兆;(3)含天然裂隙页岩的破坏模式主要呈拉剪贯通模式和拉贯通模式,两种贯通模式均至少包含一条贯通天然裂隙的拉裂隙;(4)在弹性阶段,有效弹性模量与损伤面积系数呈线性关系,损伤面积系数越大,有效弹性模量越小;(5)在低应力水平内循环,不可逆变形缓慢增加,轴向应变-循环次数曲线始终处于初始变形阶段,试样不发生破坏;在高应力水平内循环,经历3个变形阶段后试样发生破坏;在接近峰值应力的应力水平内循环,曲线直接进入加速变形阶段,几次循环后试样发生破坏。该研究为认清页岩的裂隙扩展形成复杂裂隙网的发展机制提供了有益参考。
Using the RMT-150C rock mechanics test system, the deformation and rupture characteristics of natural fissured brittle shale in Pengshui, Chongqing under uniaxial cyclic loading were studied. The results show that: (1) Natural fractures in shales under the common influence of cyclic loading and unloading and fractures cause local degradation of shale properties and aggravate fracture expansion and failure ahead of time, resulting in decrease of yield stress, fracture pressure and peak intensity, The peak strength decreased by 13.7% -58.3%. (2) The axial strain formed a closed “cusp ” hysteretic ring and was sparse - dense - sparse arrangement, while the lateral strain formed on the opening Shaped hysteresis loop with dense-sparse arrangement and horizontal strain-cyclic curve can be divided into four stages of evolution such as initial deformation phase, small velocity constant velocity deformation phase, large velocity constant velocity deformation phase and failure failure phase, Strain catastrophe phenomenon can be used as a sign that the natural fractures and new fractures expand and converge to enter the stage of large velocity constant velocity deformation, and the late catastrophe can be used as a precursor of the overall instability damage. (3) The failure modes of natural fractures include shales (4) In the elastic phase, the effective modulus of elasticity has a linear relationship with the damage area coefficient, and the larger the damage area coefficient , The smaller the effective elastic modulus; (5) The cycle at low stress level, the irreversible deformation increases slowly, the curve of axial strain - cycle number is always in the initial deformation stage, the sample does not occur damage; cycle in high stress level, experienced After 3 deformation stages, the sample was destroyed. The stress was cycled near the peak stress, and the curve directly entered the stage of accelerated deformation. After several cycles, the sample was damaged. This study provides a useful reference for understanding the development mechanism of shale fracture expansion and forming complex fracture network.