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Volume 41 (2000 - 200･･･
- Issue 6 Pages 323-
- Issue 5 Pages 256-
- Issue 4 Pages 200-
- Issue 3 Pages 126-
- Issue 2 Pages 70-
- Issue 1 Pages 2-
Volume 41, Issue 2
Displaying 1-4 of 4 articles from this issue
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Tomochika TOKUNAGA2000 Volume 41 Issue 2 Pages 70-76
Published: June 10, 2000
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSA complete set of anisotropic poroelastic parameters for Berea sandstone at low TERZAGHI effective stress (confining stress minus pore fluid pressure) was obtained for a series of drained, undrained and unjacketed tests using a triaxial vessel. Thirty-six stress-strain and stress-pore pressure slopes were obtained from hydrostatic and uniaxial experiments on three samples whose orientations were parallel, perpendicular, and forty-five degrees to the bedding plane. Stressstrain slopes during hydrostatic experiments indicated that the sandstone's poroelastic behavior was transversely isotropic. A non-linear least-square fitting technique was applied to obtain the complete set of poroelastic parameters. Results show that the sandstone is poroelastically anisotropic at low TERZAGHI effective stress conditions but it is reasonable to assume micro-isotropy. Volumetric compliances obtained from this result with that from previous measurements, which assumed that the sandstone was isotropic, were consistent between each other.
This technique gives us internal consistency checks and a measure of the reliability of the values, and it yields a more reliable set of poroelastic constants.View full abstractDownload PDF (1762K) -
Emergence of Water Film in Layered Sand due to Seismic Liquefaction and Its Effect on Soil StabilityTakaji KOKUSHO2000 Volume 41 Issue 2 Pages 77-86
Published: June 10, 2000
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSIn order to investigate the effect of heterogeneously stratified structure of loose sand during seismic liquefaction, two types of model test have been carried out. In a simple one-dimensional model test, it is found that a water film is easily formed beneath a less permeable sublayer in a liquefied loose sand and sustained still after the resedimentation of sand. The mechanism for formation of a stable water film may be explained by a upward seepage force exerted by water flow from liquefied sand acting against an overlying reaction layer. 1G shake table tests are then carried out for twodimensional slope models with seams of silt within a saturated sand. Water films formed beneath silt seams enables soil mass above them to laterally flow along water films not only during but also after shaking as sometimes witnessed in past earthquakes. While, in the case without silt, the soil deforms mostly during shaking and almost stops after that. If the silt seam breaks due to excessive hydraulic gradient, it may trigger re-liquefaction in the upper sand sublayer and lead to farther instability. Thus, the emergence of water film in layered sand during seismic liquefaction have been clarified together with its significant effect on the soil instability in terms of failure mode, timing, etc.View full abstractDownload PDF (1947K) -
Long Term Tritium Concentration Records in the Metropolis of TokyoMasayuki IMAIZUMI, Takami KOMAE, Satoshi NIHIRA2000 Volume 41 Issue 2 Pages 87-102
Published: June 10, 2000
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSLong-term tritium concentration records for 1969 to 1997 were used to evaluate the recharge mechanism of confined groundwater in the Metropolis of Tokyo. Fluctuation patterns of time series of tritium concentrations are classified into the following four types: 1) Gently-sloping peak type (type A), 2) Sharp peak with irregularly decreasing curve type (type B), 3) Simple decreasing without peak type (type C), and 4) Low concentration with an average tritium concentration of 5 TU or less and monotonous changing type (type D). Type D is seemed to be the fluctuation pattern of pre-bomb tritium.
Analysis of time series of tritium concentrations of types A, B and C by theconvolution integral model using the normal distribution function as a simple transit time distribution function shows that the difference of dispersion causes three types of fluctuation pattern. The depth of penetration of bomb tritiuminto aquifers was used to calculate the rate of groundwater recharge on the assumption of vertical downward infiltration of precipitation and groundwater. The rate of recharge of the unconfined groundwater was estimated to range from 75 mm/year to 140 mm/year, and that of confined groundwater to range from 493 mm/year to 1, 752 mm/year. However, the vertical distribution of the fluctuation patterns under the upland of Tama district suggests that the confined groundwater is not recharged from the unconfined groundwater with a vertical downward flow, and that the recharge of the confined groundwater is supplied from groundwater with a lateral flow recharged in the area where the confined aquifers outcrop near the surface of the earth. Therefore the rate of recharge of the confined groundwater appears to indicate the apparent rate of recharge.View full abstractDownload PDF (3500K) -
Hideki INAGAKI2000 Volume 41 Issue 2 Pages 103-112
Published: June 10, 2000
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSMany slope surface failures occurred on weathering granite in Suzuka range.
These slope surface failures are characterized as follows. Thickness of slope failures is very thin such as less 1m and the sliding mass contains many roots of plants. However, weathering granite as underlying basement rocks does not contain roots of plants caused by no existence of crack in itself.
These slope failure has been named slope failure along roots of plants by author. In the other hand, there is ancient forest around Tagami peak in Tanagami mountains near Suzuka range. Slope surface failures are not located in this area due to vegetate many big trees having strongly their roots into underground. This paper describes features of slope failure along roots of plants and reinforcing effects of roots of plants in soil against slope failure based on comparison of the both cases.View full abstractDownload PDF (2661K)
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