SUCTION-CONTROLLED EXPERIMENTS ON BOOM CLAY

The understanding of the thermo-hydro-mechanical behaviour of a clay b arrier is needed for the prediction of its final in situ properties af ter the hydration and thermal transient in a radioactive waste reposit ory. As part of the CEC 1990-1994 R&D programme on radioactive waste m anagement and storage, the CEA (Fr), CIEMAT (Sp), ENRESA (Sp), SCK.CEN (B), UPC (Sp) and UWCC (UK) have carried out a joint project on unsat urated clay behaviour (Volckaert et al., 1996). The aim of the study i s to analyse and model the behaviour of a clay-based engineered barrie r during its hydration phase under real repository conditions. The hyd ro-mechanical and thermo-hydraulic models developed in this project ha ve been coupled to describe stress/strain behaviour, moisture migratio n and heat transfer. A thermo-hydraulic model has also been coupled to a geochemical code to describe the migration and formation of chemica l species. In this project, suction-controlled experiments have been p erformed on Boom clay (B), FoCa clay (Fr) and Almeria bentonite (Sp). The aim of these experiments is to test the validity of the interpreti ve model developed by Alonso and Gens (Alonso et al., 1990), and to bu ild a database of unsaturated clay thermo-hydro-mechanical parameters. Such a database can then be used for validation exercises in which in situ experiments are simulated. The Boom clay is a moderately swellin g clay of Rupellian age. It is studied at the SCK.CEN in Belgium as a potential host rock for a radioactive waste repository. In this paper, suction-controlled experiments carried out on Boom clay by SCK.CEN ar e described. SCK.CEN has performed experiments to measure the relation between suction, water content and temperature and the relation betwe en suction, stress and deformation. The applied suction-control techni ques and experimental setups are detailed. The results of these experi ments are discussed in the perspective of the model of Alonso and Gens . The influence of temperature on water uptake was rather small. The m easured swelling-collapse behaviour can be explained by the Alonso and Gens model.