The Callovo-Oxfordian (COx) claystone is selected as the host rock in the French project for geological disposal of radioactive waste. In its initial state, the host rock is fully saturated. Due to the low permeability, the pore fluid pressure can locally evolve in a quasi undrained condition due to subsequent mechanical and thermal loading, and then significantly affects deformation and cracking process of geological barrier. Most previous studies were carried out in quasi drained conditions or with constant pore pressure. Poromechanical behavior of COx claystone in undrained condition has been so far rarely investigated. In the present work, we carry out a new series of laboratory tests. Two representative loading paths are considered: triaxial compression with constant confining pressure and triaxial extension with constant mean stress. The variations of strain and pore pressure are measured during the tests. It is found that the poromechanical behavior of the claystone is clearly affected by loading path. The failure strength is higher in triaxial compression than in extension. The evolution of pore fluid pressure is correlated with volumetric strain. Compared with the results obtained in drained tests, it seems that the Terzaghi effective stress can be used for the description of pore fluid pressure effect on failure strength.

中文翻译：

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Callovo-Oxford系粘土岩不排水三轴压缩和拉伸试验孔隙力学行为试验研究


法国放射性废物地质处置项目选择 Callovo-Oxfordian (COx) 粘土岩作为主岩。在其初始状态下，主岩完全饱和。由于渗透率低，后续的机械和热载荷作用下，孔隙流体压力会在准不排水条件下局部演化，进而显着影响地质屏障的变形和破裂过程。以前的大多数研究都是在准排水条件或恒定孔隙压力下进行的。迄今为止，在不排水条件下COx粘土岩的孔隙力学行为很少被研究。在目前的工作中，我们进行了一系列新的实验室测试。考虑两个代表性的加载路径：具有恒定围压的三轴压缩和具有恒定平均应力的三轴延伸。在测试过程中测量应变和孔隙压力的变化。研究发现，粘土岩的孔隙力学行为明显受到加载路径的影响。三轴压缩的破坏强度高于拉伸的破坏强度。孔隙流体压力的演变与体积应变相关。与排水试验结果相比，太沙吉有效应力似乎可以用来描述孔隙流体压力对破坏强度的影响。