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• Studies on landslides

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Published Papers 【 display / non-display 】

• Hydraulic conductivity and its relationship to grain-size distribution in the Tomigusuku Formation, Shimajiri Group, central-southern Okinawa Island : The process of rainwater infiltration into slope ground

  ITO Takuma, KIMURA Sho, NAKAMURA Shinya

  Journal of the Japan Landslide Society ( The Japan Landslide Society )  61 ( 6 ) 220 - 224   2024.11 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

  　View Summary

  <p>  The Shimajiri Group is widely distributed in the central and southern regions of Okinawa Island, an area prone to frequent landslides. To elucidate the rainfall infiltration processes that trigger rainfall-induced landslides, this study examined the relationship between hydraulic conductivity and grain-size distribution. The target strata primarily comprise alternating layers of sandstone, originating from sediment gravity flow deposits, and mudstone, derived from hemipelagic mud. X-ray CT imaging was performed on specimens used for hydraulic conductivity measurements to observe the presence of cracks. The hydraulic conductivity of specimens without cracks demonstrated a power-law relationship with the median grain size. Conversely, specimens with cracks exhibited increased hydraulic conductivity. The hydraulic conductivity of remolded specimens without cracks closely followed the power-law approximation curve, underscoring the impact of cracks on increasing hydraulic conductivity. These findings suggest that the presence of micro-cracks within the Shimajiri Group may significantly influence the groundwater supply mechanism, thereby contributing to the occurrence of rainfall-induced landslides.</p>

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• Influence of Effective Normal Stress on the Relationship between Shear Displacement and Hydraulic Conductivity in Strongly Weathered Granite Soil : Insights form Landslide Hazards induced by the 2017 Northern Kyushu Heavy Rainfall

  KIMURA Sho, ITO Takuma, NAKAMURA Shinya

  Journal of the Japan Landslide Society ( The Japan Landslide Society )  61 ( 6 ) 209 - 219   2024 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

  　View Summary

  <p>  The 2017 Northern Kyushu meteorological disasters consequently resulted in several landslides in areas of strongly weathered granite sand. Therefore, this study aimed to examine the relationship between water conductivity changes and the shear displacement of strongly weathered granite sand collected from the aforementioned landslides using a ring-shear experiment. We identified a notable influence of effective normal stress on the reduction of the hydraulic conductivity and total porosity of the sand. Plotting water conductivity as a function of shear displacement generated three patterns-no change, linear reduction, and rapid-gradual reduction in hydraulic conductivity-at each effective normal stress level. When the effective normal stress was 200 kN/m², the hydraulic conductivity at approximately 1,000 mm and 6,000 mm post-shear was decreased by two and three orders of magnitude compared to that before shear, respectively. Contrarily, there was no change in hydraulic conductivity when the effective normal stress was 50 kN/m². Particle size distribution post-shearing varied from coarse sand― and coble-sized particles to fine sand― and silt-sized particles, with particle size subsequently decreasing with effective normal stress. This particle size reduction is in accordance with post-shear porosity reduction. These results indicate that the minimum strength along the slip surface is fully softened strength in landslide occurrence. Fully softened strength is defined as no effect of previous stress histories due to weathering. The higher residual strength is applicable in the slip surface after small shear displacement. The furtherance of landslide movement in strongly weathered granite sand are induced in large and deep sliding surface zones because of low hydraulic conductivity following heavy rainfall.</p>

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• Global Optimization of Cultivar Trait Parameters in the Simulation of Sugarcane Phenology Using Gaussian Process Emulation

  W B M A C Bandara, Kazuhito Sakai, Tamotsu Nakandakari, Preecha Kapetch, Mitsumasa Anan, Shinya Nakamura, Himasha Rathnappriya

  Agronomy   11 ( 7 ) 1379   2021.07 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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• Development of a Rapid Evaluation Method for Cane Deterioration Using Near-infrared Spectroscopy

    82 ( 4 ) 354 - 361   2020.07 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

• Development of sugarcane and trash identification system in sugar production using hyperspectral imaging

  Kittipon Aparatana, Khwantri Saengprachatanarug, Yoshinari Izumikawa, Shinya Nakamura, Eizo Taira

  Journal of Near Infrared Spectroscopy ( SAGE Publications )  28 ( 3 ) 133 - 139   2020.06 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

  　View Summary

  Classification and differentiation of clean sugarcane from trash (green sugarcane leaf, dry sugarcane leaf, stone, and soil) are important for the sugar payment system at a sugar mill. Currently, the methods used to do this are manual and subjective. Therefore, this study is aimed at accurately differentiating clean sugarcane from trash by using hyperspectral imaging with multivariate analyses. Samples containing sugarcane billets and trash mixed in a ratio of 18:38 were analyzed in this study. The reflectance data of the samples were analyzed in the wavelength range of 400–1000 nm via principal component analysis (PCA). The PCA model was capable of identifying all of the clean sugarcane and trash samples. The spectral loadings of the PCA model show that the sugarcane and trash samples are easily identifiable based on the color (visible light) of each class, water absorption (approximately 970 nm), and chlorophyll absorption (approximately 680 nm). Based on the characteristic wavelengths of the PCA loading peaks, over 90% of the sugarcane and trash samples were differentiated using a multiple linear regression model. Sugarcane and trash are classified by using partial least-squares discriminant analysis and support vector machine models. For all wavelengths, the classification rate is 92.9% and 98.2%, respectively. This shows that sugarcane and trash can be accurately classified and differentiated by using hyperspectral imaging and multivariate analyses.

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• Research on weed control and management of cut slope in Okinawa

  Shinya NAKAMURA, Moe HATANAKA

    ( 70 )   2023.12

   

• Integrated IoT platform designed for field monitoring and environmental control

  MIYAMOTO Hideki, NAKAMURA Shinya, HIRASHIMA Yuta, OYAMA Masami, OHKITA Shoji

  Journal of the Japanese Society of Soil Physics ( Japanese Society of Soil Physics )  148 ( 0 ) 39 - 43   2021  [Refereed]

   

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• Consciousness and behavior for typhoon events and related phenomena in Okinawa, Japan : A resident consciousness survey

  Saito Sayaka, Nakamura Shinya

    65 ( 65 ) 19 - 82   2018.12

   

• Landslide stability analysis utilizing shear strength of slip surface soil:Asato and Tyunjun landslides, Okinawa, Japan

  Kimura, S., Gibo, S., Nakamura, S. and Vithana, S. B.

  Proceedings of International Conference on Advances in Analysis, Modeling & Design 2010 ( ASCE )    1246 - 1254   2010.02  [Refereed]

   

• Application of recovered strength in stability analysis of reactivated landslide, Xuechengzhen, China

  Nakamura, S., Gibo, S., Yasumoto, J., Kimura, S. and Vithana, S. B.

  Proceedings of International Conference on Advances in Analysis, Modeling & Design 2010 ( ASCE )    3149 - 3154   2010.02  [Refereed]

   

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Presentations 【 display / non-display 】

Presentations 【 display / non-display 】

• Estimation of surface frictional resistance of Shimajiri-mudstone layers

  2022.12  -  2022.12 

• Soil Properties of Takano-dai Landslides in Minami-Aso Village

  2022.12  -  2022.12 

• Metal corrosion and oil discoloration of the head part of slope reinforcement works in the island environment

  2021.12  -  2021.12 

• Current status of regional agriculture after the construction of underground dams

  2021.12  -  2021.12 

• Responses of ground water level and soil moisture to rainfall in landslides with different geology

  2021.12  -  2021.12 

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• Ground anchor

  Industrial Property No 特願2016-22295  (2016.02.08)

  Patent No 特許第6037253号  (2016.11.11)

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• E. B. Burwell Jr. Award, Geological Society of America

  2012.11.05   Geological Society of America  

• Incentive Award, The Japan Landslide Society

  2004.09.01   The Japan Landslide Society  

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• Challenging research (sprout)

  Project Year: 2023.06  -  2026.03 

  Direct: 4,800,000 (YEN)  Overheads: 6,240,000 (YEN)  Total: 1,440,000 (YEN)

• Grant-in-Aid for Scientific Research(B)

  Project Year: 2022.04  -  2026.03 

  Direct: 13,700,000 (YEN)  Overheads: 17,810,000 (YEN)  Total: 4,110,000 (YEN)

• Landslide risk characterization using integrated wireless sensor network system for point and area-averaged measurements

  Grant-in-Aid for Scientific Research(C)

  Project Year: 2020.04  -  2023.03 

  Direct: 3,400,000 (YEN)  Overheads: 4,420,000 (YEN)  Total: 1,020,000 (YEN)

• Innovative Landslide Warning System for New Evolution of Disaster Mitigation Science

  Challenging research (sprout)

  Project Year: 2017.06  -  2019.03 

  Investigator(s): MIYAMOTO HIDEKI 

  Direct: 4,900,000 (YEN)  Overheads: 6,370,000 (YEN)  Total: 1,470,000 (YEN)

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  Cosmic-ray soil moisture observing system (COSMOS), a method of measuring cosmic-ray neutrons (φ) near soil surface, was installed on a volcanic ash soil slope and examined to establish an innovative landslide warning system. Although the determination of near-surface soil moisture content (θ) based on φ-value was difficult due to the heterogeneity and uncertainty of water balance within sensing slope area, response of φ to soil water index (SWI) and/or θ was observed during the rainy season. We believe that the COSMOS presented here would be a unique method to monitor near surface soil moisture content of whole slope area if compatible soil moisture model considering the growth of plant communities and 3-dimentional topographic data are proposed.

• Study on Risk Evaluation and Growth of Farm Crops by the Irrigation of Rural Sewerage Treatment Water and Digested Slurry

  Grant-in-Aid for Scientific Research(C)

  Project Year: 2016.04  -  2019.03 

  Investigator(s): NAKANO Takuji 

  Direct: 3,600,000 (YEN)  Overheads: 4,680,000 (YEN)  Total: 1,080,000 (YEN)

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  It was lowly possible for the treatment water of rural sewerage facilities to exert adverse influences including nourishment inhibition of root upon the crops. It was clear that the treated water gave good effect to crops without damaging the growth of the crops. Among elements contained in the treated water, it is nitrogen and boron to be more likely to make good use. It is important that effective use be made of these element effects on irrigation. It was found that BOD and SS in treated water of submerged biological filters were assumed to depend on influent concentration and aeration intensity of contact aeration tank. It was considered that treated water in anaerobic and aerobic filter tanks was suitable for the irrigation use than treated water in sedimentation storage tank and aerobic filter. It was suggested that the operation in aeration intensity and MLSS of aeration tank was importance to use treated water of intermittent aerobic suspended-growth processes for irrigation.

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Social Activity 【 display / non-display 】

• 2025.02

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  2026.03

  

• 2024.12

  　

  　

  

• 2024.11

  　

  　

  

• 2024.11

  　

  　

  

• 2024.10

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  2025.03

  

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