A new hydro-mechanical model for bentonite resaturation applied to the SEALEX experiments

Abstract

Bentonite barriers perform safety critical functions in many radioactive waste disposal concepts, but it is challenging to accurately predict bentonite resaturation behaviour in repository settings. Coupled models of the hydro-mechanical (HM) response of bentonite are used to demonstrate understanding of bentonite behaviour in experiments and to predict the response of bentonite in a repository environment. Following trials of a range of numerical approaches, a new model is presented, referred to as the Internal Limit Model, which makes use of key observations on limiting stresses supported in bentonite samples in experimental data. This model is based on the Modified Cam Clay model, and uses the observation that for a given dry density of bentonite, there is a limiting stress that the sample can support, be that stress due to swelling, compaction or suction, to explicitly couple the hydraulic and mechanical models. The model is applied to experimental data from the SEALEX experiments, involving a 70/30 by mass mixture of MX80 bentonite and sand. The model is able to reproduce the experimental data using a single set of parameters for all the experiments considered. This builds confidence that the model will be useful in the future for predictive modelling given appropriate data to characterise the bentonite material being used.

Comparative modelling of laboratory experiments for the hydro-mechanical behaviour of a compacted bentonite–sand mixture

“…where is the bulk modulus, ′ is effective mean stress, is deviatoric stress, is the pre-consolidation pressure and 0 , , , are all constant parameters. The virgin consolidation line is based on an original relationship, called ILC (Internal Limit Curve, Thatcher et al, 2016) that is based on relationships derived from published data (Wang et al, 2012) and on a conceptual understanding of energy balances in the bentonite. It is used to parametrize both the water retention curve and the plastic failure of the material.…”

Properties of Bentonite-Based Sealing Materials during Hydration

“…Examples include the Tunnel Sealing Experiment (TSX) at Manitoba, Canada [15]; the Full-Scale Engineered Barriers Experiment (FEBEX) at Grimsel, Switzerland [16]; RE-SEAL at Mol, Belgium [17,18]; and the Engineered Barriers (EB) test at the Mont Terri URL [19]. These experiments have provided data to evaluate the response of the multibarrier system of the DGR, improving the conceptual understanding of coupled processes affecting bentonite behavior and allowing the development of numerical models [20]. In parallel to the full-scale testing, several mock-up tests have been performed on the hydration process of BBSM.…”

“…The numerical studies of the mock-up and in situ experiments of the SEALEX project, in general, performed well and could often predict the endpoints of the experiment, such as swelling pressure and the amount of injected water. The details of the transient effects, however, were much more difficult to predict [13,20,[22][23][24].…”

DECOVALEX-2015: an international collaboration for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems

“…investigated Excavation Damage Zone (EDZ) sealing during a water injection test at the Tournemire URL. In a second paper(Thatcher et al 2016b), the same group developed a new hydro-mechanical model for bentonite resaturation and applied it to the SEALEX experiments. FraserHarris et al (2016) developed a nonlinear elastic approach for modelling HM behavior of the SEALEX experiments on compacted MX-80 bentonite Mokni (2016).…”