Evaluation of the Hydraulic Characteristics of Jointed Rock Mass based on Excavation-Induced Permeability of Single Rock Joint

Research Project , Research Report 2001

Hideyuki HORII Dept. of Environmental Engineering, the University of Tokyo
Junya INOUE Dept. of Environmental Engineering, the University of Tokyo(Research Partners)
H.H. Einstein Massachusetts Institute of Technology, USA
A.J.Whittle Massachusetts Institute of Technology, USA

Abstract

Geological disposal of high-level nuclear waste in deep underground rock mass has been greatly concerned with the hydraulic characteristics of the jointed rock mass, since groundwater flow is regarded as the only and the most likely means by which radionuclides are transported into biosphere. As intact rock blocks are almost impermeable due to its low permeability, the groundwater flow in the jointed rock mass mainly occurs through joints. The hydraulic characteristics of rock joints are mainly determined by the aperture distribution resulting from the geometric roughness of joint surfaces. The aperture distribution can be significantly altered due to in-situ stress conditions. The primary objective of the present study is to provide a method for estimation of excavation induced changes in the flow properties of jointed rock mass, especially in the excavation disturbed zone around tunnel opening. The strategy of the present study is as follows. First, the flow characteristics of single joint and their variation induced by the deformation are numerically examined. Then, the micromechanics based continuum model is employed to reveal the in-situ deformation of joints in the excavation disturbed zone. Finally, discrete network model was used for the flow analysis in the jointed rock mass. Using the present method, the changes in permeability and particle transport time of jointed rock mass, in which a circular tunnel was excavated, were estimated through the test simulation.

Keywords:

excavation damaged zone, jointed rock mass, joint permeability, high level nuclear waste, geological disposal