Experimental investigation on failure behaviors and mechanism of an anisotropic shale in direct tension
Experimental investigation on failure behaviors and mechanism of an anisotropic shale in direct tension
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各向异性页岩直接拉伸破坏行为及机理实验研究
DOI：
10.1007/s40948-021-00294-x
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发表时间：
2021-10
影响因子：
5
通讯作者：
Wang Jun
中科院分区：
文献类型：
--
作者：
Li Cunbao;Zou Bingbing;Zhou Hongwei;Wang Jun
纹层发育的页岩具有明显的物理力学各向异性，导致在不同应力条件下的破坏模式复杂;然而，关于海相页岩直接拉伸行为的相关研究却很少报道。对龙马溪页岩进行了7种不同层理方向的直接拉伸试验。在考虑层状效应的情况下，对比分析了各向异性泥页岩试件的极限强度、破坏模式和声发射演化特征。进一步探讨了层状岩体直接拉伸破坏的内在机理。结果表明，页岩在直接拉伸条件下的极限强度在1.5 ~ 9.5MPa之间，具有明显的结构依赖性各向异性，并与不同层位的破坏模式有关。具体而言，可以观察到四种不同的失效模式，而不是纯拉伸断裂：锥形头失效（THF），平面拉伸失效（PTF），层活化失效（LAF），以及跨层面的混合模式失效（MMF）。AE监测有助于揭示页岩样品的渐进破坏演化，记录与最终破坏模式完全一致的各种空间信号簇。为了解释层状岩石在直接拉伸条件下的复杂破坏行为，基于单弱面理论（SPW），提出了一种考虑拉伸和剪切破坏的组合准则，该准则能够预测层状岩石的各向异性表观抗拉强度并再现其破坏模式。根据该准则估算出龙马溪页岩的层理抗拉强度为2.21 MPa，基质抗拉强度为6.62 MPa。横观各向同性岩石的各向异性抗拉强度评价需要进一步探索新的实验方法，因为在多层结构的冲击作用下，岩石往往经历拉剪混合模式的应力状态，而不是单纯的拉伸。
Shales with well-developed laminations show remarkable physical and mechanical anisotropy, resulting in complicated failure patterns under different stress conditions; However, relevant studies on the direct tensile behaviors of marine shales are rarely reported. In this study, a series of direct tensile tests were conducted on Longmaxi shale specimens at seven different bedding orientations. The characteristics of the ultimate strengths, failure patterns and acoustic emission evolution of anisotropic shale samples are comparatively analyzed by considering the layer effect. The underlying failure mechanism of layered rocks in direct tension is further discussed. The results show that the ultimate strength of shale under direct tensile conditions, varying between 1.5 MPa and 9.5 MPa, has apparent structure-dependent anisotropy and is associated with the failure patterns at various layer orientations. Specifically, four different failure patterns instead of a pure tensile fracture can be observed: tapered head failure (THF), planar tensile failure (PTF), layer activation failure (LAF), and mixed-mode failure (MMF) across the bedding planes. AE monitoring helps to reveal the progressive failure evolution of shale samples, recording various spatial signal clusters in good accordance with the ultimate failure patterns. To interpret such complex failure behaviors of layered rocks in direct tension, a combined criterion considering both tensile and shear failures was formulated based on the single plane of weakness theory (SPW), which enables one to predict the anisotropic apparent tensile strengths and reproduce the failure patterns. According to the proposed criterion, the bedding and matrix tensile strengths of Longmaxi shale are estimated to be 2.21 MPa and 6.62 MPa, respectively. Novel experimental methods should be further explored to assess the anisotropic tensile strengths of transversely isotropic rocks, as the samples often experience a tensile-shear mixed-mode stress state instead of pure tension under the impact of multi-layer structures.
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影响因子：
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