Investigation of the behaviour of bentonite by means of suction-controlled oedometer tests

In the context of an investigation of the near-field as a repository of high-level radioactive waste, the FEBEX Project, a set of laboratory tests has been designed to give a better understanding of the thermo-hydro-mechanical behaviour of unsaturated, expansive clays and to achieve an experimental corroboration of the constitutive models for these clays. Among these tests, several suction-controlled oedometer tests have been performed on a compacted, highly-expansive clay. Seven of them, in which combined paths of loading, wetting and drying have been followed, are presented in this paper. Suctions employed range from 0 to 500 MPa, and vertical loads from 0.1 to 9 MPa. The point of air entry has been identified for suctions around 120 MPa, beyond which the sample becomes very stiff. The influence of the stress path on the subsequent reversibility of the deformations has been highlighted. The swelling properties seem to be kept after intense drying. The behaviour observed, including collapse, agrees with models that relate the effects of the deformations in the microstructural level to those in the macrostructure.