Stress-induced fracture and thermo-mechanical-hydraulic coupling in crustal rocks: influence on underground excavations

Engineering solutions for deep geological disposal of radioactive waste requires a challenging combination of knowledge: on one hand, how structures such as tunnels and caverns within a rock mass modify the local/regional stress state, and on the other hand, how these structures respond to in-situ stresses over century to millennium timescales. In all cases, pre-existing discontinuities (faults, fractures, interbedding and joints) and complex lithology (e.g. clay-rich zones and/or mudstone-halite interbeds) may significantly modify these responses which in turn are again modified by the presence of fluids and/or temperature.

To design structures with long-term stability this project will test a series of natural Mercia Mudstone samples using high force hydraulics to simulate real-world stress fields. Samples will be monitored via strain meters and microseismic sensors in the presence of temperature and fluids. Data from these calibrations will build a new understanding of the short-term (weeks to months) to long-term (centuries) stability of structures by integrating these new data into an initial geological model to incorporate the effect of destabilizing discontinuities and extrapolate to design scale and timescales. The project will also explore feedback(s) between rock mass damage evolution at elevated temperature/stress, and how water flows through the rock structure.