2004 Fiscal Year Final Research Report Summary
Study on the formative processes of a weathering profile of granite and the prediction of its landslides induced by rainstorms
| Project/Area Number |
15340169
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geology
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| Research Institution | Kyoto University |
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Principal Investigator |
CHIGIRA Masahiro Kyoto University, Disaster Prevention Research Institute, Professor, 防災研究所, 教授 (00293960)
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| Co-Investigator(Kenkyū-buntansha) |
SIDLE Roy C. Kyoto University, Disaster Prevention Research Institute, Professor, 防災研究所, 教授 (30359781)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Granite / Landslide / Filtration / In-situ measurement / Water-rock interaction / Weathering |
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| Research Abstract |
Continuous monitoring of the flux, the electrical conductivity, and the chemistry of water from just beneath the groundwater table clarified the filtration behavior of rainwater through decomposed granite in combination with the pore pressure measurements of soil water Heavy rainfall first reaches the groundwater table through express ways like cracks, temporarily reducing the electrical conductivity of the groundwater at a rainfall event. Then, a wetting front descends and pushes the water in the capillary fringe by propagating the air pressure in the vadoze zone, gradually increasing the electric conductivity of the groundwater. The water in the capillary fringe is rich in Ca supplied from plagioclase of the decomposed granite and its silica concentration is controlled by the precipitation of cristobalite. After pushing down of the capillary water, rainwater itself reaches to the groundwater table, decreasing the electrical conductivity of the water. Cation concentrations in the soil water are controlled by ion exchange. The measurement of pore pressure of soil water in multiple depths in the vadoze zone, indicated that the wetting front descends at a rate of 1 m/(30 h). Surface loosened soil layer creeps by the iteration of drying and wetting ; it occurred even pore pressure is still negative.
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