Clay Behaviour Around Tunnels

QPAC is being used to model coupled Thermal-Hydraulic-Mechanical and Chemical (THMC) processes in clay in support of the geological disposal of radioactive waste.

For example, QPAC has been used in the international DECOVALEX-2011 research project with the objective of developing scientific methodologies for modelling Thermal-Hydraulic-Mechanical and Chemical (THMC) processes and demonstrating how these can be applied to both detailed and performance assessment calculations.

In DECOVALEX-2011, Quintessa contributed to Task A (one of three Tasks) on behalf of the Radioactive Waste Management Limited (RWM) of the UK Nuclear Decommissioning Authority (NDA). This task was concerned with the evaluation of numerical modelling approaches for coupled THMC processes in Opalinus Clay. More specifically, Task A attempted to model and better understand the results of the Mont Terri Rock Laboratory micro-tunnel Ventilation Experiment (VE) and associated experiments. The experiment itself comprised a sealed tunnel into which defined air-flow rates and relative humidities were applied.  These tunnel inputs were cycled and the response in terms of hydraulic behaviour in the tunnel (relative humidity) and host rock (relative humidity, water pressure, mechanical displacements and geochemical changes) were measured.

Significant progress was made in understanding the coupled Hydro-Mechanical behaviour of the VE and underpinning laboratory experiments, such that the fundamental process set for tunnel-scale drying and wetting appears to be relatively well understood. Further improvements to the predictive power of the models have been gained by coupling the porous medium model with a new model of the distribution of water vapour and air flow in the tunnel itself. Also, the QPAC model was augmented to include reactive and non-reactive tracer transport of key chemical species, which in conjunction with available field data, further constrained the THMC coupled process system.  The QPAC model was then used to make successful blind predictions of the hydro-mechanical behaviour of the tunnel and host-rock against data that were withheld from the modelling teams.

The above figures show the relative humidity in the VE tunnel (top) and water saturation in the host-rock (bottom) using fully coupled Hydro-Mechanical calculations in QPAC.