Simulation of Slope Failure Distributions Due to Heavy Rain on an Island Composed of Highly Weathered Granodiorite Based on the Simple Seepage Analysis
Takatsugu Ozaki*1,, Akihiko Wakai*1, Go Sato*2, Takashi Kimura*3, Takanari Yamasaki*4, Kazunori Hayashi*5, and Akino Watanabe*1
*1Graduate School of Science and Technology, Gunma University
1-5-1 Tenjincho, Kiryu, Gunma 376-8515, Japan
*2Graduate School of Environmental Informations, Teikyo Heisei University, Tokyo, Japan
*3Graduate School of Agriculture, Ehime University, Ehime, Japan
*4Japan Conservation Engineers & Co., Ltd., Tokyo, Japan
*5Okuyama Boring Co., Ltd., Miyagi, Japan
To fully and rapidly develop a real-time early warning judgment system for slope failure at the time of heavy rains including overseas, it is necessary to predict water movement in the soil at the time of rainfall. In addition, to apply the system to a place where insufficient geotechnical and geological data have been amassed, it is necessary to evaluate the risk of slope failure based on physical properties obtained from a simple soil test. Therefore, in this study, the authors set Gogoshima Island in Ehime Prefecture as a study site and evaluated the water movement over time in the soil during heavy rain using a simple prediction equation of rainfall seepage process. Soil properties were determined through simple in-situ and laboratory tests. As a result, it was found that the factor of safety for slope failure in the head and wall of a valley dissecting the hillside slope composed of granodiorite in which weathering has progressed can be planarly evaluated using the simple prediction equation.
-  K. Okada, Y. Makihara, A. Shimpo, K. Nagata, M. Kunitsugu, and K. Saito, “Soil Water Index,” Tenki, Vol.48, No.5, pp. 349-356, 2001 (in Japanese).
-  Y. Ishihara and S. Kobatake, “Runoff Model for Flood Forecasting,” Bulletin of the Disaster Prevention Research Institute, Kyoto University, Vol.29, No.1, pp. 27-43, 1979.
-  T. Okimura, N. Torii, Y. Osaki, M. Nambu, and K. Haraguchi, “Construction of real-time type hazard system to predict landslides caused by heavy rainfalls,” J. of the Japan Society of Erosion Control Engineering, Vol.63, No.6, pp. 4-12, 2001 (in Japanese).
-  C. de Lima Neves Seefelder, S. Koide, and M. Mergili, “Does parameterization influence the performance of slope stability model results? A case study in Rio de Janeiro, Brazil,” Landslides, Vol.14, No.4, pp. 1389-1401, 2017.
-  Z. Shi, F. Wei, and V. Chandrasekar, “Radar-based quantitative precipitation estimation for the identification of debris flow occurrence over earthquake-affected regions in Sichuan, China,” Nat. Hazards Earth Syst. Sci., Vol.18, No.3, pp. 765-780, 2018.
-  A. Wakai, K. Hori, A. Watanabe, F. Cai, H. Fukazu, S. Goto, and T. Kimura, “A simple prediction model for shallow groundwater level rise in natural slopes based on finite element solutions,” J. of the Japan Landslide Society, Vol.56, No.Special_Issue, pp. 227-239, 2019 (in Japanese).
-  T. Ozaki, A. Wakai, A. Watanabe, F. Cai, G. Sato, and T. Kimura, “A simplified model for the infiltration of rainwater in natural slope consisting of fine sands,” J. of the Japan Landslide Society, Vol.58, No.2, pp. 57-64, 2021 (in Japanese).
-  G. Sato, T. Kimura, K. Hirota, T. Ching-Ying, and H. Tagi, “Distribution of shallow landslides and related mass movement processes induced by the heavy rain in July 2018 on Gogoshima Island, Ehime Prefecture, Japan,” J. of the Japan Landslide Society, Vol.56, No.3, pp. 129-134, 2019 (in Japanese).
-  Foresty Agency, Ministry of Agriculture, Forestry, and Fisheries, “Aerial laser measurement work in forest areas (Part 2) 2018,” https://www.maff.go.jp/j/budget/yosan_kansi/sikkou/tokutei_keihi/seika_H30/ippan/#190 (in Japanese) [accessed July 15, 2020]
-  K. Nagai, K. Horikoshi, M. Miyahisa, and T. Hiraoka, “1/50,000 Subsurface Geological Map and Explanatory Article of Mitsuhama Area,” Ehime Prefecture, 1975 (in Japanese).
-  Public Works Research Institute, “Investigation manual about soil site of slope using Soil Strength Probe,” Technical Note of Public Works Research Institute, Vol.4176, pp. 1-40, 2010 (in Japanese).
-  T. Tagawa, “Simple infiltration test of surface soil,” J. of Hydrological System, Vol.118, pp. 54-58, 2020 (in Japanese).
-  The Japanese Geotechnical Society, “Soil Testing (2nd Edition),” p. 17, Maruzen Publishing, 2010 (in Japanese).
-  M. Utada, “Alteration of Rokko Granites: Mineralogical and Magnetic Susceptibility Changes,” J. of Geography, Vol.112, No.3, pp. 360-371, 2003 (in Japanese).
-  T. Iida, “Knowledge of shallow landslide and deep-seated landslide for technicians,” p. 237, Kajima Institute Publishing, 2012 (in Japanese).
-  Y. Matsukura, “The Earth’s Changing Surface – Weathering and Erosion –,” p. 242, Asakura Publishing, 2008 (in Japanese).
-  Data Integration & Analysis System (DIAS), The University of Tokyo, “MLIT XRAIN dataset,” https://www.diasjp.net/service/xrain/ (in Japanese) [accessed September 18, 2020]
-  Geospatial Information Authority of Japan, MLIT of Japan, “Fundamental Geospatial Data (5m mesh DEM),” https://fgd.gsi.go.jp/download/mapGis.php?tab=dem (in Japanese) [accessed July 12, 2020]
-  Esri Japan Corporation, “Resample,” https://desktop.arcgis.com/ja/arcmap/latest/extensions/spatial-analyst/performing-analysis/cell-size-and-resampling-in-analysis.htm (in Japanese) [accessed November 1, 2020]
-  Esri Japan Corporation, “Slope,” https://desktop.arcgis.com/ja/arcmap/10.3/tools/3d-analyst-toolbox/how-slope-works.htm (in Japanese) [accessed November 1, 2020]
-  M. Nishigaki and Y. Takeshita, “Research on the Method of Determining Unsaturated Soil Hydraulic Properties by In-Situ or Laboratory Tests,” Okayama University, 1993 (in Japanese).
-  H. Hiyama, M. Takayama, and T. Noda, “Shear Strength Properties of Compacted Decomposed Granite Soil,” Trans. of the Japanese Society of Irrigation, Drainage and Reclamation Engineering (JSIDRE), No.205, pp. 109-117, 2000 (in Japanese).
-  S. Araki, M. Takeuchi, N. Torii, S. Shibuya, S. Kawajiri, and S. Kagamihara, “Strength Characteristics of Undisturbed Decomposed Granite Soil Focusing on Shear Modulus,” J. of Applied Mechanics, Vol.13, pp. 495-502, 2010 (in Japanese).