Analysing the volume change behaviour of compacted bentonites upon THM processes based on the framework of BExM model

Compacted bentonite is often considered as a possible buffer/backfill material for deep geological disposal of high-level radioactive waste. During the long-term lifespan, the bentonite barriers will undergo coupled thermo-hydro-mechanical (THM) progresses, which induce complex volume changes. In this work, the volume change behavior of compacted bentonites undergoing THM interactions was analyzed based on the framework of Barcelona Expansive Model, in which the thermal volume changes were taken into account by adopting the approach of Tang and Cui (Geotechnique 59:185–195, 2009). After analyzing the published experimental results of wetting/drying and heating/cooling cycles, new fI and fD functions were put forward for describing the interaction between micro- and macro-structures, while a thermal loading yield function curve was established for describing the TM behavior under unsaturated conditions. Some cyclic wetting/drying and thermal loading tests reported and modelled in literature were simulated to verify the relevance of the improvements undertaken. Comparisons among the original model, the modified model as well as the test results clearly showed a satisfactory performance of the model in describing the volume changes of compacted swelling clays upon THM processes.