UNDERGROUND FLOW THROUGH PIPES AND ITS INFLUENCE TO LANDSLIDES

Research Project

Project/Area Number	03454074
Research Category	Grant-in-Aid for General Scientific Research (B)
Allocation Type	Single-year Grants
Research Field	林学
Research Institution	KYOTO UNIVERSITY
Principal Investigator	MIZUYAMA Takahisa KYOTO UNIV., AGRICULTURE, ASSOC.PROF, 農学部, 助教授 (00229717)
Co-Investigator(Kenkyū-buntansha)	FUKUSHIMA Y. NAGAOYA UNIV., PROFESSOR, 大気水圏研究所, 教授 (00026402) KOBASHI S. KYOTO UNIV., AGRICULTURE, PROFESSOR, 農学部, 教授 (40026604) 鈴木雅一東京大学, 農学部, 助教授 (10144346)
Project Period (FY)	1991 – 1993
Project Status	Completed (Fiscal Year 1993)
Budget Amount *help	¥6,500,000 (Direct Cost: ¥6,500,000) Fiscal Year 1993: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1992: ¥1,200,000 (Direct Cost: ¥1,200,000) Fiscal Year 1991: ¥4,700,000 (Direct Cost: ¥4,700,000)
Keywords	pipe flow / landslide / field observation / forest hydrology / 流出機構 / 斜面崩壊 / パイプフロ-
Research Abstract	A two-year observation of the discharge from underground pipes made the following things cclear. First, ten natural pipes were found in a small hollow. Three pipes of the seven pipes, which are located at the downstream end of the hollow, always discharge water. The others drain only during heavy rains. Most of the volume of the direct discharge is covered by the pipe water flow. Second, the pipe water flow can only be seen when the antecedent rain and rainfall intensity is enough. Third, the patterns of the pipe flow rate correstpond well to rainfall patterns. Forth, the discharge rates from the pipes have the upper limits. The limits may be controlled by the dimensions of the pipes. Fifth, two pipes were dug out. They last only 50 cm long and lead to a layr if gravel. This means that the flow that comes out of these pipes should in this case not be called pipe flow but rather gravel layr flow. Sixth, the outflow rates from pipes are will explained with a tank model. These facts could possibly explain the coincidence between the peak time of rainfalls and the time of the occurrence of debris flows and/or landslides that have not been able to be explained by theories developed assuming homogeneous soil layrs. Smooth outflow through pipes, however, does not explain the occrrence of debris flow. Pipe collapse can happened and yhis was observed once during the observation period, these collapses increase the hydraulic pressure and may trigger landslides.