层状含水页岩的抗拉强度特性试验研究

为分析层理和水对页岩的抗拉强度特性的影响，现场选取龙马溪组黑色页岩制备成4种含水状态含层理页岩，沿与层理呈0°、30°、60°和90°夹角加载进行巴西劈裂圆盘试验，试验过程同步进行声发射测试，并采用离散元软件3DEC对试验结果进行数值模拟验证。结果表明，相比于含层理页岩，同时考虑含水和层理的页岩在巴西劈裂试验中有其独特的破坏模式和力学特性。含层理页岩的巴西劈裂破坏模式和抗拉强度均与层理角度和含水率有关，破坏模式主要受控于层理与荷载的加载方向，水虽不会影响其破坏模式但能够导致次生裂纹的形成。抗拉强度则表现出随层理角度的增加而先减小后增大，随含水率的增加而减小的趋势。并且，在页岩同时受水和层理损伤作用时，受层理损伤程度越大，水对其损伤程度也越高。通过对含层理不同含水率页岩的微观结构分析得到了上述变化规律的内在机制，即页岩层理面处的内部矿物颗粒遇水膨胀，产生膨胀力作用，使页岩内部结构变得松散、破碎，微裂纹逐渐增多、变宽，宏观表现为次生裂纹的增多，矿物颗粒间的黏结力也在水的作用下降低从而使页岩的抗拉强度下降。

Experimental study on tensile strength of layered water-bearing shale

To analyze the effects of bedding and water on the tensile strength of shale, specimens with four water contents were prepared with Longmaxi Formation black shale. Brazilian disc splitting tests were carried out on prepared specimens along the angles of 0°, 30°, 60° and 90°. Acoustic emission tests were simultaneously performed during the experiments, and results were further simulated by the discrete element software 3DEC. The results show that, compared with the bedding shale, the shale with both water and bedding presents a unique failure mode and special mechanical properties. Both the fracture pattern and tensile strength of Brazil shale ae related to the bedding angle and water content. Particularly, the failure mode is mainly controlled by the loading direction of bedding. Although water do not affect the failure mode, it lead to the formation of secondary cracks. The tensile strength firstly decreases and then increases with increasing the bedding angle, while it decreases with increasing water content. Moreover, under the combined effects of water and bedding, the more the shale is damaged by the bedding, the higher it is damaged by the water. The mechanism of the above changes is obtained based on the analysis of the microstructure of the shale at different water contents. When the internal mineral particles are swollen with water at the surface of the shale, the expansion force is generated, and internal structure of the shale became loose and broken. Furthermore, microcracks gradually increased and broadened. The macroscopic performance accounted for the increase of secondary cracks. In addition, the bond strength between mineral particles is also reduced under the action of water, which further decreases the tensile strength of shale.