2. Seismic/Geodetic Imaging Technologies
Estimation of Hydraulic Characteristics in Rock Mass by using Elastic Wave Dispersion
Ayumi Miyata(1), Yuzo Ohnishi(1), Satoshi Nshiyama(1), Takao Yano(1), Kenichi Ando(2) and Kimitaka Yoshimura(3)
(1) Graduate School of Engineering, Kyoto University, Japan. (2) Obayashi Co, Japan. (3) Radioactive Waste Management Funding and Research Center, Japan.
Abstract
Recently, underground space has been utilized for the purposes to dispose such as radioactive waste and CO2. In order to evaluate safety of geological disposal, it is important to know how ground water flow through rock masses. To measure underground hydrological characteristics, we develop the method to estimate permeability distribution in rock mass from elastic wave velocity. This method is based on dynamic poroelastic theory such as Biot and BISQ theory. These theories indicate that the elastic wave velocity through elastic solid saturated with pore water depends on its frequency and formulated with permeability with the characteristic frequency. Using these theories, we can estimate hydraulic characteristics from the characteristic frequency. First, in order to verify the applicability of these theories to rock mass, we performed laboratory tests. We measured P-wave velocity of rock specimens (shale, tuff, sandstone and granite) for various frequencies from 30kHz to 1100kHz. From these results, it was found that elastic wave dispersion for sedimentary rocks can be described by Biot theory and that for crystalline rocks can be described by BISQ theory. Next, in order to verify the applicability of this method to a real field, we performed in-situ experiment at Grimsel Rock Laboratory, Switzerland. We performed seismic exploration for several frequencies. As a frequency increased, elastic wave velocity increased in in-situ experiment. From the results, we made seismic tomograghy for each frequency using SIRT (Simultaneous Iterative Reconstruction Technique), calculated the change in velocity for each mesh The result will be introduced in full paper.
Last modified: Fri May 19 20:04:33 2006