Continuum-discontinuum analysis of failure mechanisms around unsupported circular excavations in anisotropic clay shales
Continuum-discontinuum analysis of failure mechanisms around unsupported circular excavations in anisotropic clay shales
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DOI：
10.1016/j.ijrmms.2013.10.006
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发表时间：
2014-01-01
影响因子：
7.2
通讯作者：
Vietor, T.
中科院分区：
文献类型：
--
作者：
Lisjak, A.;Grasselli, G.;Vietor, T.
粘土页岩中圆形开挖的稳定性是钻井和漏斗工程以及地质废物深储库中的关键问题。大量的实验证据表明，这些空洞周围的损伤区的影响，由层状材料结构引起的强力学各向异性。迄今为止，用于分析层状岩石中开口稳定性的绝大多数数值模型都是基于连续介质力学原理，采用经典的弹塑性材料剪切破坏理论。然而，一些实验观察表明，粘土页岩可能会在低限制条件下，如那些表征近场的挖掘，以脆性的方式尾巴。因此，一个替代的数值方法的基础上，非线性断裂力学原理和离散元方法被采用，以获得新的洞察这类岩土材料的破坏过程。为了解释粘土页岩微观结构对其力学行为的影响，提出了一种新的方法来捕捉强度的各向异性。通过这种数值方法，断裂模型的内聚强度参数被假定为单元键和分层方向之间的相对取向的函数。数值模拟技术的有效性定量地证明了标准的岩石力学试验上的硬化粘土岩，即蛋白石粘土。出现的强度和变形性能，连同模拟断裂机制，被证明是在良好的协议与实验观察。模拟技术，然后施加到模拟的开挖破坏区（EDZ）周围的圆形隧道水平层状蛋白石粘土。模拟压裂过程中，主要讨论的背景下观察到的损害机制在蒙特特里URL。此外，还分析了原地应力对EDZ几何形状的影响以及对地面支撑和隧道可施工性的可能影响。模拟结果突出了抗剪强度动员沿着层面在控制EDZ形成过程中的重要性。特别是，层面的滑动被证明是导致岩体decenclosure，这反过来又促进脆性破坏过程中的剥落的形式。数值技术目前仅限于二维分析，没有任何热-水-机械耦合。(C)2013爱思唯尔有限公司保留所有权利。
The stability of circular excavations in clay shales is a key issue in the drilling and funnelling industries as well as in the held of deep geological waste storage. A large body of experimental evidence indicates that the damaged zone around these cavities is influenced by strong mechanical anisotropy induced by the layered material structure. The vast majority of numerical models adopted to date to analyse the stability of openings in layered rocks have been based on continuum mechanics principles using classic shear failure theory for elasto-plastic materials. However, a number of experimental observations demonstrate that clay shales may tail in a brittle manner under low-confinement conditions such as those characterizing the near-field of the excavation. Therefore, an alternative numerical approach based on non-linear fracture mechanics principles and the discrete element method is adopted to gain new insight into the failure process of this class of geomaterials. In order to account for the influence of clay shale microstructure on its mechanical behaviour a newly developed approach to capture the anisotropy of strength is proposed. With this numerical approach, the cohesive strength parameters of the fracture model are assumed to be a function of the relative orientation between the element bonds and the layering orientation. The effectiveness of the numerical technique is quantitatively demonstrated by simulating standard rock mechanics tests on an indurated claystone, namely Opalinus Clay. Emergent strength and deformation properties, together with the simulated fracture mechanisms, are shown to be in good agreement with experimental observations. The modelling technique is then applied to the simulation of the Excavation Damaged Zone (EDZ) around a circular tunnel in horizontally bedded Opalinus Clay. The simulated fracturing process is mainly discussed in the context of the damage mechanisms observed at the Mont Terri URL. Furthermore, the influence of in situ stress on resulting EDZ geometry is analysed together with possible implications for ground support and tunnel constructability. Modelling results highlight the importance of shear strength mobilization along bedding planes in controlling the EDZ formation process. In particular, slippage of bedding planes is shown to cause rock mass deconfinement which in turn promotes brittle failure processes in the form of spalling. The numerical technique is currently limited to two-dimensional analyses without any thermo-hydro-mechanical coupling. (C) 2013 Elsevier Ltd. All rights reserved.