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Volume 49 (2008 - 200･･･
- Issue 6 Pages 318-
- Issue 5 Pages 256-
- Issue 4 Pages 204-
- Issue 3 Pages 126-
- Issue 2 Pages 64-
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Volume 49, Issue 4
Displaying 1-4 of 4 articles from this issue
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Examination in the Northern Kitakami MountainsTakehiro OHTA, Atsushi HASEGAWA, Tomoyuki TAKAMI, Akihiro KAWAMURA2008 Volume 49 Issue 4 Pages 204-216
Published: October 10, 2008
Released on J-STAGE: November 04, 2011
JOURNAL FREE ACCESSThe changes of disaster topography and vegetation in northern Kitakami mountains area were investigated by aerial photograph on six periods during 1970 to 2001. The hard sedimentary rocks considered in homogeneous conditions are distributed in this area. The climate conditions of this area were constant from 1970 to 2001. The geomorphometric study was performed using detailed digital elevation model that was obtained by aerial laser measurement at late autumn in 2000.
As the results of these investigations, it is explained that both of geomorphological conditions and vegetation changes influence the generation and the reduction of disaster topography. For example, the number of collapse increases, as the average value of slope angle in drainage basin becomes large. In proportion to decrease of the distribution area of Quercus serrata/chestnut/deciduous broadleaf forest community, the number of collapse increases. However, if the average of slope angle in the drainage basin is small, the basin has no slope collapse even after the deforestation. When the average of slope angle and the ratio of surface area to drainage basin area in the basin become large, many disaster topographies occur in the basin. Therefore, it is assumed that we can assess the possibility of disaster topography developments by the numerical value of vegetation and geomorphology.View full abstractDownload PDF (4041K) -
Youqing CHEN, Tsunehiro KOBAYASHI, Yuichiro KURIKI, Hiromu KUSUDA, Mam ...2008 Volume 49 Issue 4 Pages 217-226
Published: October 10, 2008
Released on J-STAGE: November 04, 2011
JOURNAL FREE ACCESSIn order to gain further insight into changes in the properties and microstructures of granite due to temperature changes, two typical granites with different granularities, Westerly and Fujioka granite, were subjected to a onecycle heating and cooling test under various conditions: two maximum maintenance temperatures, 300 and 500°C, and two heating rates. Properties reflecting the internal microstructures, such as size, weight, effective porosity, and P-wave velocity, were measured before and after the thermal cycle and microstructures were visualized and observed using the fluorescent approach.
No significant differences in sample size and weight were identified. However, an increase in the effective porosity and gradual decrease in P-wave velocity were clearly identified after the test. This suggests that changes in microstructure occur within granites. Marked differences due to the heating rate were not identified in our examination. Microcracks along grain boundaries developed and widened in the tested samples, and this tendency was pronounced in more strongly heated samples. These microscopic observations agree well with the observed changes in properties. Furthermore, a difference in the crack growth pattern between the two granites was observed. In fine-grained Westerly granite, few new cracks formed in quartz grains and crack development was mainly along grain boundaries, while in coarse-grained Fujioka granite, many cracks developed in a network pattern in quartz grains in addition to the grain boundary cracks. It was inferred that one of the causes of the different crack growth patterns was the variation in grain size and shape. In both granites, nearly identical characteristic crack development patterns were observed in other major constituent minerals, feldspar and biotite. In feldspar, with increasing temperature, cracks grew straight and wide along the weak planes such as cleavages and twin planes. Cracks in biotite grains mainly developed along cleavages in the samples heated up to 500°C.View full abstractDownload PDF (4332K) -
Comparison of Methods of Asbestos Measurement in Natural RocksKinya KATO, Takayuki KATOH, Satoshi OKAMURA, Tetsu WADA2008 Volume 49 Issue 4 Pages 227-235
Published: October 10, 2008
Released on J-STAGE: November 04, 2011
JOURNAL FREE ACCESSWe examined several methods of measurement of chrysotile, one of several fibroid forms of asbestos under various environmental conditions, and evaluated those methods using modal analysis by polarized microscope, X-ray diffraction (XRD) analysis, and the phase contrast and dispersion microscope (PCDM) analysis. In comparison between modal and the PCDM analysis indicated that the fibroid asbestos contents in the almost completely ground powder samples are very low, which is less than the standard of the work environment concentration. However, the cross fiber vein type chrysotile associated with a granitic body is not broken to unfibroid grains by the grinding process. This means that different degrees of crystallinity of the chrysotile may cause several fibroid forms of asbestos. Examination of asbestos dispersal during the grinding of samples in the draft chamber indicates that moist conditions tend to diminish the dispersal of asbestos compared to dry conditions.View full abstractDownload PDF (2303K) -
Junichi YORITA, Mitsumasa OKAMURA, Kazuaki ISHIGAKI, Toshihiro ASAKURA2008 Volume 49 Issue 4 Pages 236-245
Published: October 10, 2008
Released on J-STAGE: November 04, 2011
JOURNAL FREE ACCESSCohesive soil of Quaternary age, in particular of middle Pleistocene or later age, may be due to significant deformation and surface settlement in response to tunneling. In the excavation of a tunnel of about 900m long through this type of soil, tunnel deformation and surface settlement were strongly controlled by the soil strength properties, which were correlated with the N-value of the standard penetration test obtained during test drilling. This confirms that these soil properties can be used for the prediction of deformation and the control of measurement at site.
During the excavation, a prominent fold zone, presumably caused by horizontal compression, and an associated shear zone involving a right-lateral strike-slip fault movement of 80 m were encountered. This kind of observation is rare in Quaternary formations. In the studied soil, fine cracks developed by deformation further increased deformation and surface settlement. As a result, the deformation properties of the soil could not be predicted only from the N-value and strength properties. The modulus of deformation decreased with rock quality designation (RQD), a parameter used in core boring. This implies that the deformation properties of cracked soil can be predicted by using RQD together with the N-value.View full abstractDownload PDF (2882K)
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