Abstract

It is important to understand the long-term migration of radionuclides considering carious rock engineering projects such as the geological disposal of radioactive wastes. The network of fractures and pores in a rock mass can play important roles as the pathway of the fluid flow of rock. The geometry of the network can change due to sealing of a material in the long term. The result of laboratory measurements shows that the permeability of a fractured igneous rock decreased by the sealing of the fracture by the fine-grained materials.

The above results have been obtained by the permeability test using distilled water. Usually groundwater contains fine-grained minerals such as clays. It is probable that the accumulation of the fine-grained minerals occurs in a fracture if the groundwater flows in a fracture in a rock. In addition, the aperture of the fracture can decrease if the fine-grained materials accumulate, which decreases the permeability. Therefore, it is essential to conduct the permeability measurement using water including fine-grained materials to understand the characteristics of the permeability of a rock. However, none has conducted the permeability measurement using water containing fine-grained materials.

In this study, we have conducted the permeability measurement using water including clays. Specifically, we used a macro-fractured granite as a rock sample, and investigated the change of the permeability under the flow of the water including clays. It was shown that the hydraulic conductivity decreased with elapsed time. The accumulation of the clays was observed in the fracture of the granite sample. It is concluded that the accumulation of fine-grained minerals in the fracture decreases the permeability of fractured rock. In addition, it is concluded that the sealing and the healing of the fractures in rock are possible under the flow of the groundwater including clays.

1. Introduction

It is important to understand the long-term migration of radionuclides considering carious rock engineering projects, such as the extraction of petroleum, carbon capture and storage, and the geological disposal of radioactive wastes. The network of fractures and pores in a rock mass can play important roles as the pathway of the fluid flow of rock (Nara et al., 2011a). The geometry of the network can change due to sealing of a material in the long term. The result of laboratory measurements shows that the permeability of a fractured igneous rock decreased by the sealing of the fracture by the fine-grained materials (Wang et al., 2016; Perez-Flores et al., 2017).

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