HR: 1330h
AN: H42B-1077    [PDF]
TI: Measurement of Fracture Geometry for Accurate Computation of Hydraulic Conductivity
AU: Chae, B
EM: bgchae@kigam.re.kr
AF: Korea Institute of Geoscience and Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon, 305-350 Korea, Republic of
AU: Ichikawa, Y
EM: Ichikawa@mimi-erc.com
AF: Nagoya University, Surocho Chikusaku, Nagoya, 464-8603 Japan
AU: * Kim, Y
EM: yjkim@kigam.re.kr
AF: Korea Institute of Geoscience and Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon, 305-350 Korea, Republic of
AB: Fluid flow in rock mass is controlled by geometry of fractures which is mainly characterized by roughness, aperture and orientation. Fracture roughness and aperture was observed by a new confocal laser scanning microscope (CLSM; Olympus OLS1100). The wavelength of laser is 488nm, and the laser scanning is managed by a light polarization method using two galvano-meter scanner mirrors. The system improves resolution in the light axis (namely z) direction because of the confocal optics. The sampling is managed in a spacing 2.5 $\mu$m along x and y directions. The highest measurement resolution of z direction is 0.05 $\mu$m, which is the more accurate than other methods. For the roughness measurements, core specimens of coarse and fine grained granites were provided. Measurements were performed along three scan lines on each fracture surface. The measured data were represented as 2-D and 3-D digital images showing detailed features of roughness. Spectral analyses by the fast Fourier transform (FFT) were performed to characterize on the roughness data quantitatively and to identify influential frequency of roughness. The FFT results showed that components of low frequencies were dominant in the fracture roughness. This study also verifies that spectral analysis is a good approach to understand complicate characteristics of fracture roughness. For the aperture measurements, digital images of the aperture were acquired under applying five stages of uniaxial normal stresses. This method can characterize the response of aperture directly using the same specimen. Results of measurements show that reduction values of aperture are different at each part due to rough geometry of fracture walls. Laboratory permeability tests were also conducted to evaluate changes of hydraulic conductivities related to aperture variation due to different stress levels. The results showed non-uniform reduction of hydraulic conductivity under increase of the normal stress and different values of mechanical aperture from hydraulic aperture due to rough geometry of fracture walls. The hydraulic conductivity did not follow the cubic law. It verifies that a parallel plate model is not suitable to express the hydraulic conductivity including local fracture geometry. The measurement results are used to compute hydraulic conductivity along a rock fracture based on the homogenization theory.
DE: 1832 Groundwater transport
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2003 Fall Meeting