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Investigation on the THM Behaviour of a Heated Bentonite Barrier by Measurements and Numerical Calculations

The Temperature Buffer Test (TBT) was a common project between ANDRA and SKB performed in the Äspö Hard Rock Laboratory (HRL) in Sweden. DBE TECHNOLOGY GmbH joined the project by optical sensor instrumentation and numerical simulations. The TBT aims at investigating the behaviour of a bentonite buffer under a thermal load of up to 200 °C, during the water saturation process and over a period of 5 to 10 years. The thermal impact was recorded by a huge amount of geotechnical instrumentation as a basis for detailed evaluation. A full-scale deposition hole was used for the experiment. An important part of the work was to measure the thermal, hydraulic and mechanical processes in the bentonite during the saturation and afterwards. Thermophysical properties of MX-80 bentonite samples such as thermal conductivity, specific heat capacity, thermal diffusivity and thermal expansion have been analysed and applied for further modelling work. The empirical formulations indicate that the water content and temperature development have strong influence on these properties, especially on thermal expansion (shrinkage). The code TOUGH2 was applied to calculate the thermo-hydraulic coupled two-phase flow in bentonite. A good fit of calculated and measured temperature and suction values has been achieved and for hydraulic and thermal calculations plausible parameter sets have been obtained.