Excavation Disturbance Zone in the UK Triassic and Jurassic Mudrocks - Implications for fluid flow in a nuclear waste repository

The safe geological disposal of high-level radioactive waste requires an in-depth understanding of how potential host rock formations respond to excavation-induced disturbances throughout the lifecycle of a Geological Disposal Facility (GDF). The Excavation Damaged Zone (EDZ) is a critical phenomenon, influencing fracture propagation, permeability evolution, fluid migration, and ultimately impacting radionuclide isolation and containment in the host rock.
The Mercia Mudstone Group (MMG) is being considered as candidate GDF host rock in the United Kingdom due to its low permeability and occurrence at the contextual depth of interest. However, research gaps exist in understanding how their microstructure, material heterogeneity and rock anisotropy control EDZ evolution and the implications for fluid migration, which could invariably impact the GDF’s long-term containment performance.
Extensive studies on European argillaceous formations, such as the Opalinus Clay at Mont Terri, Switzerland, Boom Clay at the HADES Underground Research Laboratory, Belgium and Callovo-Oxfordian Claystone in France, have established that excavation-induced fracturing initially increases permeability. However, time-dependent processes such as clay swelling, mechanical creep, and mineral precipitation gradually restore hydraulic properties closer to those of the undisturbed host rock. Existing models based on these European analogues often assume isotropy, minimising the role of mineralogical composition, bedding plane orientations, depositional fabrics, and diagenetic history in controlling fracture networks and preferential flow pathways. In contrast, UK mudrocks remain largely unexplored with respect to permeability evolution, microstructural features, the role of rock anisotropy, and its influence on fluid flow and geochemical dynamics within the EDZ.

The main aim of this PhD research is to generate a detailed process learning framework for investigating the macrostructural and microstructural evolution of disturbed and damaged UK mudrocks and develop into a conceptual model, the impact this will have on fluid flow in a nuclear waste repository in order to fulfil the safety requirement of long-term isolation and containment of radionuclides