2017 Fiscal Year Annual Research Report
地形発達効果および気候変動を考慮した斜面危険度の広域評価
| Project/Area Number |
16F16378
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| Research Institution | Kyoto University |
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Principal Investigator |
中北 英一 京都大学, 防災研究所, 教授 (70183506)
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| Co-Investigator(Kenkyū-buntansha) |
WU YING-HSIN 京都大学, 防災研究所, 外国人特別研究員
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| Project Period (FY) |
2016-11-07 – 2019-03-31
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| Keywords | vegetation / groundwater / Poroelasticity / Mohr-Coulomb theory / Numerical simulation / hillslope stability / landscape evolution / extreme climate |
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| Outline of Annual Research Achievements |
It is universally accepted that the extreme climate becomes more frequent. Our environment becomes warmer, and rainstorms tend to be intense. Global warming directly or indirectly influences hillslope vegetation, landform and stability, which are the dominant factors for slopeland hazard occurrence. As being the origin of slopeland hazards, landslide is our analysis target. We aim to propose a new model coupling among landform evolution, hillslope vegetation, and hillslope stability for more precisely assessing landslide susceptibility trend under climate change influence. In FY2017, it has successfully finished our planned objectives, including developing a three-dimensional landslide model and preliminary development of hillslope groundwater model. To identify unstable zones prone to landslide on steep and vegetated hillslopes, our developed landslide model adopts the mechanical approach to consider transient vegetation surcharge and root-reinforcement and groundwater motion. Tree-growth allometric equations are used for quantitative modelling of transient tree surcharge and root-reinforcement. Poroelasticity is used for evaluating stress equilibrium in hillslope under given groundwater flow and vegetation forcing. Then, Mohr-Coulomb failure theory is applied to find the unstable zones. The three parts above are numerically calculated by using the finite element method. We have performed case study of the 2014 Hiroshima debris flow event. The results has been presented in several domestic and international conferences.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In FY2017, we have finished developing a three-dimensional landslide model, and performed case study of the 2014 Hiroshima debris flow event. On the other hand, the development of groundwater model has been smoothly in the progress. Particularly, for more precise landslide hazard assessment, we focus on modeling groundwater motion in a thin soil layer on a hillslope, which is different from the over-simplified assumption of parallel groundwater motion in a two-dimensional soil later on a hillslope. So, regarding the concern above, we adopts Dupuit-Boussinesq (DB) theory for modeling the groundwater flow in our target soil layer. In our development, we have discovered a new insight of DB theory, and rigorously derived a novel formula to distinguish if a groundwater table exists or not at the upstream of a steep hillslope. This result has been submitted to an international journal for review. Besides, we are developing a three-dimensional groundwater model using a Godunov-based finite-volume-scheme. As a pioneering attempt of using finite-volume-method, our groundwater model can not only simulate groundwater flow in a thin soil layer over irregular bedrock on a hillslope, but can also achieve precise and robust computation for a wider simulation domain. Some of analysis using this three-dimensional groundwater model has been presented in some conferences. Using the groundwater model, we are working on verification by some experiments or field measurement, and re-analyzing the 2014 Hiroshima debris flow event.
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| Strategy for Future Research Activity |
This research has three phases, including development of models of landslide, groundwater and landscape evolution, integration of all models, and analyses of some cases. In the last two fiscal years, we have finished the development of the three-dimensional landslide model and preliminary development of groundwater model. In FY2018, we would like to continue and finish groundwater model development, and to perform case analysis of the 2014 Hiroshima debris flow event. Then, the landscape evolution model will be readily developed by directly utilizing the numerical scheme of groundwater model. Finally, we shall take a few months for integration of three models of landslide, groundwater, and landscape, and perform case study of past events, i.e., 2014 Hiroshima debris flow disaster and another similar extreme-rainfall-triggered event in Japan or other country. The expected research productions will be a complete high-resolution model for landslide hazard assessment considering extreme climate, and some analyses of past landslide disasters triggered by extreme climate. Each component model and case analysis will be prepared for several conference presentations and paper publications in international journals.
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Research Products
(4 results)
