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Volume 48 (2007 - 200･･･
- Issue 6 Pages 285-
- Issue 5 Pages 232-
- Issue 4 Pages 162-
- Issue 3 Pages 116-
- Issue 2 Pages 66-
- Issue 1 Pages 2-
Volume 48, Issue 2
Displaying 1-4 of 4 articles from this issue
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Hayato TOBE, Masahiro CHIGIRA, Shoji DOSHIDA2007 Volume 48 Issue 2 Pages 66-79
Published: June 10, 2007
Released on J-STAGE: March 26, 2010
JOURNAL FREE ACCESSIn 1972, numerous numbers of shallow landslides were induced in granite and granodiorite areas by a heavy rainstorm in Obara village, Aichi prefecture, central Japan. We examined quantitatively the effects of petrologic types and precipitation amounts on the landslide distribution and densities in the disaster area. The landslide density in granite area was 293/km2 and was larger than ten times of that in granodiorite area (13/km2), even though both the areas had experienced a strong precipitation of about 200mm per 5 hours. Landslide densities increased with the amounts of precipitation in the granite area, but did not in the granodiorite area. Investigation with airborne laser scanner and aero photographs was successively applied to detect landslides by the 1972 rainstorm and also preceding landslides in an area of 3km2, which indicated that the above contrast of landslide densities had already existed before the 1972 disaster. The differences in landslide densities and in increase of landslide density according to the amount of precipitation between granite and granodiorite areas could result from the difference in weathering profiles of these two rocks. The most widely distributed granite in the surveyed area is weathered granite with grade DH, (decomposed granitoid) and/or DM (moderately weathered gruss), which likely is loosened with a well defined front and provides preferable conditions for landslide. In addition, a certain type of granite is micro-sheeted in the surveyed area, also providing a preferable condition for landslide occurrence. On the other hand, the most widely distributed granodiorite is of grade DL (strongly weathered saprolite), of which granodiorite is not likely loosened with a well-defined front. This may be the reason why fewer landslides occurred in the granodiorite area.View full abstractDownload PDF (5109K) -
Eiji TAMURA, Akira JYONAI, Shin-ichi MATSUZAKI, Syuichi HASEGAWA2007 Volume 48 Issue 2 Pages 80-89
Published: June 10, 2007
Released on J-STAGE: March 26, 2010
JOURNAL FREE ACCESSThe concrete foundation set up on the cut ground has upheaved by 66mm in seven years after unloading of ground which is 25m in thickness. The upheaval of the foundation has been caused only at smectite-bearing crush zone in unweathered crystalline schists. The smectite content in the fault gauge is 10-15%, and the smectite was generated by the hydrothermal alteration. In this paper, the swelling characteristic of the crush zone is shown by the in-situ investigation and the laboratory test. The upheaval of crush zone is estimated to have swelled gradually from the surface to in the ground. The observed swelling depth is coincident with overburden load. The upheaval model was made by the geological structure and using the relation between the load and the swelling rate of the smectite bearing crush zone. The upheaval convergence by the FEM analysis roughly coincides with that by the level observation.View full abstractDownload PDF (1885K) -
Yukiyasu FUJII, Takato TAKEMURA, Manabu TAKAHASHI2007 Volume 48 Issue 2 Pages 90-96
Published: June 10, 2007
Released on J-STAGE: March 26, 2010
JOURNAL FREE ACCESSIn Yakushima, granitic and sedimentary boulders are cracked polygonally on their surface. They are called “Kikkouboulders”, which mean polygonal pattern in Japan. The size of the polygonal pattern is proportional to the size of the Kikkou-boulder, therefore bigger boulder has bigger polygonal pattern. The Kikkou-boulders show a concentric crust and core structure. The depth of the polygonal cracking reaches the boundary between the crust and core structure. The characteristics of the Kikkou-boulders indicate that they are core-stones, which are ellipsoidal blocks separated from bedrock by the cause of weathering. It is also suggested that the polygonal cracking is generated from the weathering of the rock.View full abstractDownload PDF (5694K) -
A Case of Notoro Argillaceous RockKouki KASHIWAYA, Satoru KAWASAKI, Katsuhiko KANEKO, Tetsuro YONEDA2007 Volume 48 Issue 2 Pages 97-102
Published: June 10, 2007
Released on J-STAGE: March 26, 2010
JOURNAL FREE ACCESSTo clarify factors causing uneven heaving on a cutting plane of Tertiary Miocene Notoro formation, mineralogy, chemistry, and rock texture were examined. Samples are four argillaceous rocks collected from the cores of noticeably or slightly heaving points. Results showed that the samples of the noticeably and slightly heaving points have similar mineral and chemical compositions, but their rock textures are different. The samples of the noticeably heaving point have coarser granular variations than those of the slightly heaving point, and the matrix of the former was more widely impregnated with fluorescent resin than it of the latter. When it is assumed that the heaving occurred from the influence of water, the uneven heaving may result from difference in void structures which developed closely correlating with the granular variations.View full abstractDownload PDF (1653K)
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