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Volume 45 (2004 - 200･･･
- Issue 6 Pages 281-
- Issue 5 Pages 224-
- Issue 4 Pages 174-
- Issue 3 Pages 118-
- Issue 2 Pages 60-
- Issue 1 Pages 2-
Volume 45, Issue 2
Displaying 1-4 of 4 articles from this issue
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Hisafumi ASAUE, Katsuaki KOIKE, Shinichi TAKAKURA, Tohru YOSHINAGA, Mi ...2004 Volume 45 Issue 2 Pages 60-70
Published: June 10, 2004
Released on J-STAGE: March 25, 2010
JOURNAL FREE ACCESSMT (magnetotelluric) method has been widely used to clarify resistivity distribution for exploring deep geological structures and reservoir locations of geothermal and petroleum resources. This method was applied to structural analysis of fracture zones in deep parts of the Futagawa fault zone, an active fault striking east-northeast and west-southwest along the southern edge of Kumamoto plain, central Kyushu, southwest Japan. Three lines were set perpendicular to the fault and the MT measurements were carried out at 32 points. Average distance between adjacent two points is about 1km. To reduce the artificial noises that have effect on electric and magnetic fields at the measurement points, a remote reference technique was adopted. The original measurement data were coupled with the MT data that were acquired concurrently with this study at the two sites located 100-150km apart from the fault. Resultant apparent resistivity and phase data were applied to a smoothness-constrained 2D inversion analysis under ABIC minimization criterion for DC resistivity data. The resistivity distributions estimated by this inversion analysis show clearly the low resistivity zones smaller than 10Ω·m at all the lines, which imply that the Futagawa fault zone is accompanied with largely fractured zones by repetitive tectonic events. These zones are found to be located from the 1- to 7-km depths with 200- to 1000-m widths and deepened toward the southwest at the angle of 35°. By tracing the fracture zones, the fault can be considered to dip steeply toward the north. This deep structure corresponds to the characteristics detected by the electric sounding and radon prospecting data on the MT lines.View full abstractDownload PDF (4133K) -
Eiji NAKATA, Takahiro OYAMA, Yasunori MAHARA, Yoshihisa ICHIHARA, Hiro ...2004 Volume 45 Issue 2 Pages 71-82
Published: June 10, 2004
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSIn a coal mine tunnel excavated at the below the sea floor, we investigated the slaking properties of sedimentary rocks, coarse sandstone, fine sandstone and sandy mudstone. Rock samples, which were calcite-free rocks, disintegrated on steeping in distilled water, following an initial drying phase. On the other hand, samples maintained their integrity in contact with brackish water (NaCl: 3.3wt%).
Strongly slaking rocks were generally collected in the excavated tunnel below the sea-floor. These rocks contained more than 1.5wt% Na-type smectite.
Non-slaking rocks were collected at ground surface exposures of the coal-bearing formation and in an oxidization zone associated with a fault in the tunnel. These rocks contained less than 5wt% mixed ion-type smectite. The uniaxial compressive and tensile strength of coarse sandstone saturated with brackish water was significantly larger than that of the rock saturated with distilled water. Coarse sandstone showed a higher permeability for brackish water (with higher viscosity) than for distilled water. Coarse sandstone saturated with distilled water in rock permeability tests disintegrated when seeped in distilled water after drying. In contrast, coarse sandstone saturated with CaCl2 solution did not disintegrate during similar contact with distilled water after drying.
The chemical composition of original porewater, thickness of the diffusion double-layer and drying process thus have a clear influence on the slaking, strength, and permeability properties of these sedimentary rocks.View full abstractDownload PDF (3519K) -
Michinao TERADA, Seiji EBISU, Takashi NISHIYAMA, Hiromu KUSUDA, Yasuno ...2004 Volume 45 Issue 2 Pages 83-89
Published: June 10, 2004
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSObservation of micro cracks occurred in a rock anchor, which was recovered from the underground after in-situ pullout test was performed to make clear the failure mechanizm of rock anchors. A clear distinction between micro cracks and other component is usually difficult because micro cracks don't have very distinctive feature optically. To attempt to solve this major difficulty, micro cracks were coated with cyanoacrylate mixed with fluorescent dye, and then visualized under ultraviolet light. Various patterns of micro cracks, which were not detected under natural light, were identified clearly under ultraviolet light in the specimen collected from over 2 meters under the ground.
Micro cracks were also represented realistically by several methods of image processing, and then length and direction of micro cracks were measured. Based on the micro cracks direction, the angle from the direction of pull-out load become greater gradually from about 45 deg. to 90 deg. when the depth of rock anchor increased. Moreover, many micro cracks parallel to the direction of pull-out load were identified at the maximum depth in rock anchors.
Observational results indicate that the failure of rock anchors may progress over the depth which was considered previously by the pull-out test.View full abstractDownload PDF (1696K) -
Kouki KASHIWAYA, Tetsuro YONEDA2004 Volume 45 Issue 2 Pages 90-100
Published: June 10, 2004
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSCrack patterns occurring in mudstones and granites at various degrees of weathering intensity were characterized by multifractal analysis. In addition, physical property measurements, optical microscopic observations, particle analysis, and XRD analysis were carried out to determine textural and compositional features of the samples. By a comparison of the generalized dimension spectra derived from the analysis, the applicability of multifractal theory to crack pattern analysis was considered. Furthermore the relationships between crack patterns and textural and compositional features are discussed. The results may be summarized as follows:
1) Homogeneous crack patterns developed in mudstone samples weathered in a cyclic drying and wetting process. In weathered granite which underwent chemical weathering process, inhomogeneity of crack distribution increased with weathering intensity.
2) The homogeneous crack pattern in the mudstone samples can be attributed to the high effective porosity and fine, homogeneous mineral distribution in the matrix. The heterogeneous pattern of the granite may be due to selective weathering-durability of the constituents of the weathered granite and its holocrystalline-granular texture.
3) The generalized dimension spectra obtained by multifractal analysis reflects the complexity and homogeneity of crack pattern. And, it precisely illustrates the nature of crack patterns better than conventional fractal analysis.
4) Multifractal analysis can be effectively applied to characterize the intensity and the progress of rock weathering, and to predict the engineering properties and the weathering behavior of rock.View full abstractDownload PDF (2904K)
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