Towards Understanding the Impact of an Excavation Damaged Zone in a Range of Illustrative Geological Environments and Implications for Backfill and Waste Package Evolution

In 2018, Radioactive Waste Management Ltd (RWM) established the Backfill Integrated Project (IP), aimed at providing the scientific, technological, and engineering underpinning for the development of backfill solutions for a future Geological Disposal Facility. The Backfill IP is complemented by a parallel workstream investigating the impact of void space on repository performance. One aspect of RWM's backfill development work has been to model the mechanical evolution of a proposed backfill material in a GDF. This work has also reviewed the potential effects of excavation within three illustrative host rock types, establishing a preliminary view of Excavation Damaged Zone (EDZ) development. The task has examined the possible impact of excavation activities and interactions with the developing EDZ over time, on both an illustrative backfill material and subsequent waste packages. Over the initial phases of these two projects, the approach to modelling has been to consider some key inputs such as geological boundary conditions, appropriate stress-strain ground models, and key methodologies. Outputs have aided a preliminary understanding of the development of an EDZ across the three potential categories of host geology and explored the potential implications for backfill selection criteria. Crucially, at this early stage, the projects have also identified gaps within which further work will be required. Ongoing development of analytical models across the next phases will further explore the interaction between the EDZ and the backfill material, examining key geotechnical properties that impact this relationship. Key aspects include backfill stability upon loading due to lining degradation over time and its ability to support the host rock. The impact of creep in relevant geologies will also be explored. Further work will also examine the evolution of crown space within the vaults and its impact on backfill stability and the EDZ over time. (author)