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• Studies on landslides

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Published Papers 【 display / non-display 】

• Estimation of soil moisture on volcanic ash slopes based on cosmic-ray neutron observations

  HIRASHIMA Yuta, TOKUMOTO Ieyasu, NAKAMURA Shinya, MIYAMOTO Hideki

  Journal of the Japanese Society of Soil Physics ( Japanese Society of Soil Physics )  160 ( 0 ) 29 - 41   2025.07 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  To assess the potential of the COsmic-ray Soil Moisture Observation System (COSMOS) for measuring soil moisture on the slope of volcanic ash soil, we analyzed the response of its epithermal neutron counts (N) to the volumetric water content (θ ) recorded by soil moisture sensors installed at five locations and three depths. By comparing θ across these locations and depths, we estimated the maximum effective observation depth of COSMOS is 17 cm. Based on this estimate, we constructed four datasets comprising the mean θ values from TDT sensors at a depth of 10 cm (θAvg) and the corresponding N values, along with their 3-hour, 12-hour, and 24-hour averages. In all combinations, the correlation between N and θAvg was low, suggesting that the presence or absence of vegetation cover significantly influences N. Consequently, we classified the data into periods with and without vegetation cover — determined using camera imagery — and applied distinct calibration equations for each period. This approach significantly improved the agreement between COSMOSestimated θ and θAvg. Our findings demonstrate the effectiveness of COSMOS for monitoring surface soil moisture on volcanic ash slopes characterized by exceptionally high porosity of volcanic ash soil.

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• N₂O emissions from controlled-release and conventional N-fertilizers applied to red-yellow soil in Okinawa, Japan

  Bandara W.B.M.A.C., Sakai Kazuhito, Anan Mitsumasa, Nakamura Shinya, Setouchi Hideki, Noborio Kosuke, Kai Takamitsu, Rathnappriya R.H.K.

  Soil & Tillage Research ( Elsevier )  248   1 - 16   2024.12 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  In Okinawa, Japan, controlled-release N fertilizers (CRFs) are promoted to reduce labor and to increase fertilizer use efficiency. However, N₂O emissions from N fertilizer applied to the widely prevalent Kunigami mahji (red-yellow soil), a local soil in the region, have not been examined so far. We conducted two laboratory experiments during winter and spring to compare N₂O emissions between CRF and standard fertilizer (ammonium sulfate: AS) in kunigami mahji. Two seasons were selected to explore the effects of moisture and temperature on N₂O emissions in relation to N fertilization. For each experiment, three soil chambers were used, each containing 1.4 kg of soil: one served as a control, and the other two received 1 g of nitrogen from either a linear-release-type CRF with 42 % N or AS with 21 % N. Over 9 weeks, N₂O emissions from the headspace of each chamber were measured every minute for 20 min, followed by 70 min of ventilation, in a continuous 90-minute cycle repeated throughout the study. Soil moisture, soil temperature, NO, and NO₃-N and NH₄-N in leachate were also analyzed. In Exp A (winter), nitrification was dominant, and N₂O emission from CRF (emission factor, EF, 0.4 %) was 88 % lower than that from AS (EF 3.9 %). In Exp B (spring), denitrification was dominant, and N₂O emission from CRF (EF 1.9 %) was 53 % lower than that from AS (EF 4 %). The frequently lower water-filled pore space (WFPS) in Exp A than in Exp B facilitated higher NO emission from AS than from CRF. Due to the consistently high WFPS in Exp B, most of the NO₃- in the soil was reduced to N₂O and N₂. N is more readily available in AS than in CRF, facilitating higher cumulative leaching of NH₄-N from AS. However, in both experiments, AS was denitrified more than CRF, producing more N₂O and resulting in lower leaching of NO₃-N. Our results highlight that choosing the appropriate form of fertilizer and good management of soil moisture content can reduce N₂O emissions and leaching of NO₃⁻ and NH₄⁺.

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• 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)

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  <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)

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  <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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Books 【 display / non-display 】

Books 【 display / non-display 】

• The Research Report on Slip Surface

  ( Part: Allotment Writing )

  2013.03

Other Papers 【 display / non-display 】

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

  Shinya NAKAMURA, Moe HATANAKA

    ( 70 )   2023.12

   

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

  Nakamura Shinya, Hatanaka Moe

    ( 70 ) 13 - 20   2023.12

   

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• 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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• Report of research activities and achievements (of Rural Environmental Conservation and Disaster Prevention Engineering)

  Kimura, Sho, Nakamura, Shinya

  THE SCIENCE BULLETIN OF THE FACULTY OF AGRICULTURE UNIVERSITY OF THE RYUKYUS   ( 67 ) 33 - 33   2020.12

   

• 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

   

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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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Academic Awards 【 display / non-display 】

• 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)

• Challenging research (sprout)

  Project Year: 2023.06  -  2026.03 

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

• Challenging research (sprout)

  Project Year: 2022.06  -  2025.03 

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

• Challenging research (sprout)

  Project Year: 2022.06  -  2025.03 

  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)

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• 2025.02

  -

  2026.03

  

• 2024.12

  　

  　

  

• 2024.11

  　

  　

  

• 2024.11

  　

  　

  

• 2024.10

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  2025.03

  

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