Advanced excavation damage zone behaviour prediction for immediate and delayed construction response during deep tunneling and deep geological repository development

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Disposal of high-level nuclear waste is a critical engineering challenge for all countries that generate nuclear power. The expert consensus is that underground disposal is the only viable long-term option. Canada, along with numerous countries, is moving forward with research and advanced plans for high-level (spent fuel) waste disposal and is currently in the site selection process for its own underground repository. The ultimate cost to Canadians, of such a repository, will be 10's of $Billions and the long-term viability and safety relies on management of the Excavation Damage Zone (EDZ) induced around repository infrastructure. Safety assessment is primarily concerned with maximum extent of EDZ and the gradient of increased fluid mobility within this damaged halo. Within the EDZ is the more fractured highly damaged zone (HDZ) near the excavation boundary. The staged, time-dependent and dynamic response of the EDZ/HDZ is also a critical issue in deep tunnelling with comparably high economic value at stake. In Canada and around the world, tunnels are being developed at increasing depths in brittle rockmasses for civil infrastructure or mine access. While generally considered in mining, brittle response of the HDZ due to construction has often been overlooked at the design stage in many recent world-class tunnelling projects, with serious impacts on worker safety, delays and increased costs. In nuclear waste repositories, detectable HDZ in shafts is typically removed at the end of service life prior to backfilling and is therefore not considered in shaft safety assessment. The nature and time-dependent response of the HDZ during and after construction, will nevertheless impact the subsequent EDZ behaviour. It will also be an engineering challenge in terms of sequencing, safety and support. Different candidate sites will have different predicted levels of brittle HDZ, and degrees of dynamic rupture, which must be recognized prior to construction to enable adjustments in design. Proposed research funded by this Discovery Grant builds on previous NSERC-funded progress (characterizing the general nature of damage initiation), focusing now on evolving damage controlled by stress path, geometry, lithology and geostructure, and on the time-dependent nature and dynamic response of EDZ/HDZ during the 4D tunnel construction sequence. The end result will be major improvements in behavioural prediction and risk management for deep construction in brittle rock, improving worker safety, support reliability and monitoring effectiveness. This work will create a step change in reliability of preliminary engineering assessments and designs, significantly reducing risk costs and improving project viability for Canadian underground infrastructure worth $Billions. 5 PhD's, 7MSc's and 3 USRA's will trained during this DG research program and gain significant national and international exposure.