Coupled THMC simulator that can describe the long-term evolution in rock permeability and stiffness due to mineral reactions within rock fractures generated by cavity excavation. The developed simulator was applied to perform the long-term prediction by assuming the subsurface environments near the radioactive waste repository. Analysis results show that although generated fractures during excavation of disposal cavity result in the permeability increase and the elastic modulus decrease, after the excavation, the permeability and the elastic modulus of the damaged zone decreased to that of the intact zone and increased to 30 % of the initial state, respectively. These changes of rock permeability and stiffness after excavation were driven by pressure dissolution within rock fractures. Overall, analysis results indicate that pressure dissolution within the fractures has significant influence on the evolution of hydro-mechanical damage of rock generated by cavity excavation.

1. Introduction

It is important to predict the evolution of the hydraulic and mechanical properties of rocks surrounding the disposal facility for evaluating the performance of geological disposal system of high level radioactive wastes (HLW). The change of material properties of surrounding rocks should be caused by influence of multi-physics phenomena including the heat transfer from waste package, the transport of groundwater, fracture generation during cavity excavation, and chemical reactions between rock minerals and pore water. Thus, coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) numerical simulation considering above-mentioned multi-physics phenomena should be required. Among the processes of HLW geological disposal, fracture generation during cavity excavation exerts significant influence on the change of hydraulic and mechanical properties of surrounding rocks (Aoyagi et al., 2019). In addition, after cavity excavation, mineral reactions such as pressure dissolution within generated fractures may control the long-term evolution of rock permeability and stiffness (Yasuhara et al., 2011). However, existing coupled THMC simulators cannot evaluate the above long-term evolution of rock permeability and stiffness due to mineral reactions.

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2019. Japanese Society for Rock Mechanics. Permission to distribute - International Society for Rock Mechanics and Rock Engineering
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