Hydromechanical study of rock–mortar interfaces

Hydromechanical compression tests have been performed on rock–mortar interfaces representing the contact between a host rock and a concrete bulkhead within an underground nuclear waste repository. The rock used in the tests is a Toarcian argillite. Most published studies concerning rock–concrete interfaces involve concrete–concrete contacts in which rock replicas are used instead of real rock samples. As a result, the effect of rock features, such as bedding planes and changes of the rock interface zone, on the hydromechanical behaviour of the interface cannot be investigated. The tests discussed in this paper demonstrate that the mechanical response is not affected when changing the parameters of the samples even not mismatching both walls. On the contrary, an initial monitored lateral displacement modifies the hydromechanical behaviour by limiting the interface ability to be hydraulically closed. The latter ability has been quantified by a simple evolution law and the difference of behaviour between the two kinds of samples has been confirmed. The analysis led to determine the hydraulic aperture shows that the values obtained are much lower to the classical values available in the literature. Finally, the application of the experimental results to the confinement by a bulkhead showed the localization of the flow within the interface.