The engineering application of geomechanical and hydrogeologic models for fractured rock masses requires confidence in the underlying concepts and assumptions used, and the characterization data that provides the basis for parametrization and boundary conditions. This is particularly critical for design and safety analysis of radioactive waste repositories in fractured rock, which require isolation for extended periods. Although much is known about the engineering performance of fractured rock masses, there is still considerable uncertainty and variability in performance predictions, particularly when considering the heterogeneity and “channeling” of flow and transport in fractures and interactions with fracture infillings, coatings, and other immobile zones.
This paper describes the development of a Pragmatic Validation Approach for models of fractured rock mass flow, solute transport and geomechanics considering the limitations of fractured rock site characterization. Because the intended applications include safe isolation of radioactive waste, the validation approach must consider the IAEA definition of validation (IAEA 2018). However, the validation approach must also be practical given the very real conceptual and characterization uncertainties involved.
This paper describes the development of a Pragmatic Validation Approach for models of fractured rock mass flow, solute transport and geomechanics. The approach is being developed within the SKB Task Force on Groundwater Flow and Transport of Solutes (TF GWFTS www.skb.se/taskforce) which has recently commenced a new task considering how best to validate and build confidence in models.
The SKB GWFTS Task Force is a forum for the international organisations supporting the Äspö Hard rock laboratory. In this setting these organisations can collaborate and interact in the area of conceptual and numerical modelling of groundwater flow and solute transport in fractured rock. The overall objective of the Task Force is “to increase the understanding of the processes that govern retention (retention here refers to both reversible and irreversible immobilisation processes) of radionuclides transported in crystalline rock and to increase the credibility in the computer models used for groundwater flow and radionuclide transport” (Gustafson et al., 2009).
