The Opalinus Clay shale formation is considered as a potential host geomaterial for the Swiss deep geological repository for radioactive waste. It presents different facies and it is characterised by a multi-scale heterogeneous composition, by a typical fissile structure with well-defined bedding planes and by anisotropic hydro-mechanical behaviour. This peculiar complexity makes it difficult to assign a unique set of geomechanical parameters to the material. This paper presents an experimental study aimed at characterising the lowest values of the shear strength parameters. In this sense, the shear behaviour was investigated on remoulded samples where the fabric and the diagenetic bonds of the intact material were eliminated. The results of a triaxial test campaign belonging to different facies of Opalinus Clay shale (“shaly” and “sandy” facies) are presented. Furthermore, with the aim to study the mechanical properties of fault zones in Opalinus Clay, the effect of large cumulated shear displacements on shear strength was also investigated. Ring shear tests were performed to determine the residual shear strength. The main geotechnical property which discriminates the different facies of Opalinus Clay is the grain-size distribution; in this sense, well-defined correlations between this intrinsic characteristic and shear strength angles of the remoulded material are presented.

Opalinus粘土页岩地层被认为是瑞士放射性废物深层地质处置库的潜在宿主土工材料。它表现出不同的相，其特征是多尺度的非均质组成，典型的易裂变结构，清晰的层理面以及各向异性的水力力学行为。这种特殊的复杂性使得很难为材料分配唯一的一组地质力学参数。本文提出了一项旨在表征抗剪强度参数最低值的实验研究。从这个意义上说，对重塑样品的剪切行为进行了研究，样品中的织物和完整材料的成岩键被消除了。属于不同相的三轴测试活动的结果介绍了Opalinus粘土页岩的“页岩”和“桑迪”相。此外，为了研究Opalinus粘土断层带的力学特性，还研究了大的累积剪切位移对剪切强度的影响。进行环剪切测试以确定残余剪切强度。区分Opalinus粘土不同相的主要岩土属性是粒度分布。从这个意义上讲，在此固有特性与重塑材料的抗剪强度角之间存在明确定义的相关性。