Prediction of the depth of excavation induced damage zone (EDZ) is essential for the design process of deep geological repositories (DGR). The general EDZ consists of three zones that are characterized by the degree of induced damage. The nearest zone to the excavation boundary is the highly damaged zone (HDZ) dominated by connected fractures. The inner EDZi undergoes small scale, discontinuous crack damage while outer EDZo consist of rock that is at or just beyond its damage initiation threshold. Rock beyond this zone undergoes decreasing amounts of elastic strain only.
Due to the natural uncertainty in geological phenomena, the prediction and understanding of the variability of EDZ depth is paramount in the design process to ensure long term stability of the DGRs. In hard rock under high stress, EDZ depth can be predicted using numerical simulation methods which employ an approach based on cohesion weakening and frictional strengthening (CWFS) with increasing inelastic deviatoric strain. While deterministic analyses of this type, based on conservative estimate of input parameters, are simple ways of dealing with uncertainty, they are not capable to capture the variability of the input properties which can lead to design deficiencies.
In Canada, the Cobourg limestone in Kincardine, ON, is currently the proposed rock unit to host low- to medium-level nuclear waste generated from the Ontario nuclear power plants. In this paper, First Order Second Moment reliability methods coupled with the CWFS approach are used to predict the variability of EDZ zones in numerical model. Explicit limit states are defined for each damage zone based on their characteristics and corresponding indicators. The accuracy of the methodology is investigated by analyzing EDZ depth variability attained from laboratory input data. Partial safety factors with confidence level are proposed for rock mass strength parameters which can be beneficial in conservative design.
The international consensus is that deep geological repositories (DGRs) are the best solution for safe, long-term nuclear waste disposal. The depth of excavation induced damage zone (EDZ) is an essential requirement for the design process of DGRs for nuclear waste facilities. The damage caused by the excavation process increases the permeability from the undamaged rock mass and represents a potential contaminate transport or leakage pathway. Hence, predicting and understanding the characteristics of EDZ is a crucial parameter to ensure long-term stability and safety of DGRs.
