Directory of Researchers

SONODA Yusuke
Graduate School of Agricultural Science / Department of Agricultural Engineering and Socio-Economics
Assistant Professor
Agricultural Engneering
Last Updated :2023/12/12

Researcher Profile and Settings

Affiliation

  • <Faculty / Graduate School / Others>

    Graduate School of Agricultural Science / Department of Agricultural Engineering and Socio-Economics
  • <Related Faculty / Graduate School / Others>

    Faculty of Agriculture / Department of Agricultural Engineering and Economics

Research Activities

Research Interests

  • 土質力学
  • 地盤工学
  • パイプライン
  • ため池
  • 廃止ため池
  • 農業農村
  • 災害

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Geotechnical engineering
  • Environmental science/Agricultural science / Rural environmental engineering and planning

Committee Memberships

  • Jun. 2023 - Present, 公益社団法人 地盤工学会, 「地盤工学会誌」編集委員会 委員

Awards

  • Mar. 2023 六篠会学術奨励賞 神戸大学農学研究科

  • Mar. 2014 神戸大学農学研究科, 六篠賞学術奨励賞

  • Nov. 2013 地盤工学会, 第48回地盤工学発表会 優秀論文発表者賞

  • Nov. 2013 農業農村工学会 京都支部, 第69回農業農村工学会 京都支部研究発表会 研究奨励賞

  • Mar. 2012 神戸大学農学研究科, 六篠賞学生賞

Published Papers

  • Small-sized Buried Model Tests on Effectiveness of EPS Pipe Foundation

    Sonoda, Y, Kawamura, M, Sawada, Y, Kudo, H, Kawabata, T

    Nov. 2022, Proceedings of the 7th Asian Regional Conference on Geosynthetic on Hazard’s Risk Management, Innovation, and Sustainability, (N-009), English

    [Refereed]

    International conference proceedings

  • SONODA Yusuke, SAWADA Yutaka, IKAWA Chihaya, TAKAHARA Gentaro, KAWABATA Toshinori

    It is difficult to backfill and compact the narrow space in the bottom side of the pipe and ensure sufficient quality. Insufficient backfilling may cause unexpected deformation and stress concentration in the pipe. In this study, a method of installing EPS as a pipe foundation was proposed, and its effectiveness was examined through a model experiment using 300 polyethylene pipes. The results showed that, when EPS is installed, depending on its geometry, slightly larger strains may occur at the bottom of the pipe or at the contact point between the pipe and EPS, but these strains are significantly smaller than the strain concentrations caused by insufficient backfilling and are not large enough to cause pipe failure, indicating the effectiveness of the EPS as a pipe foundation.

    Japan Chapter of International Geosynthetics Society, 07 Oct. 2022, Geosynthetics Engineering Journal, 37, 85 - 92, Japanese

  • Yusuke Sonoda, Yutaka Sawada, Kohei Ono, Yoko Ohta, Toshinori Kawabata

    The safety of buried flexible pipes is often discussed separately in terms of cross-sectional and longitudinal deformations, which can be clarified based on the circumferential and pipe axial strains, respectively. However, in modes of localized longitudinal deformation, such as differential settlement subjected to external pressure, principal strains (i.e., maximum tensile and compressive strains) on the pipe may occur in the directions different from the circumferential and axial directions. In this study, a model experiment to reproduce differential settlement was conducted using a pipe with a diameter of 300 mm, focusing on the actual damage caused by soil runoff around a buried pipe joint. In the experiment, the principal strains exerting on the pipe were calculated by measuring the strains in three directions: circumferential, axial, and intermediate. The results indicated that the principal strains in the pipe changed in the directions different from the circumferential and axial directions of the pipe owing to differential settlement, and they were approximately 1.5 times greater than the circumferential and axial strains. These results indicated the possibility of a new risk of pipe failure that cannot be captured through the strain only in a single direction (i.e., circumferential and axial pipe strains) as measured in previous studies. The results of this study are useful not only as a method to consider the behavior of a pipe deformed in cross-sectional and longitudinal directions combined, but also as a benchmark for the three-dimensional numerical analysis of buried pipes subjected to localized differential settlement.

    2022, Transportation Infrastructure Geotechnology

    Scientific journal

  • SONODA Yusuke, TOKUMASU Mizuki, SAWADA Yutaka, KAWABATA Toshinori

    It has been reported that a buried flexible pipe excessively deformed due to the sheet-pile extraction after backfilling. Many studies have been conducted on the design method in consideration of the influence of sheet-pile extraction. However, studies for the aim of establishing methods of reducing pipe deformation are scarce. In this study, a sheet pile pullout tests were conducted to verify the effect of the backfill material integrated using geogrids to prevent the horizontal earth pressure from rapid decreasing, thus suppressing the pipe deformation during sheet-pile extraction. In addition, the separate integration of the base and upper area of the pipe was more effective in suppressing pipe deformation.

    Japan Chapter of International Geosynthetics Society, 19 Oct. 2021, Geosynthetics Engineering Journal, 36, 37 - 44, Japanese

  • SONODA Yusuke, TOKUMASU Mizuki, SAWADA Yutaka, KAWABATA Toshinori

    Sheet pile construction has often been adopted for installations of pipelines in cases such as limited worksites or high ground water level. However, the sheet-pile extraction is likely to cause significant damage to buried flexible pipe. In the Japanese current design standard for irrigation pipeline, the influence of the sheet-pile extraction is empirically considered only by reducing the coefficient of subgrade reaction e´0. Thus, the difference in construction conditions is not accurately reflected in the design. In this study, the model tests on the sheet-pile extraction were conducted under the difference conditions of breadth of sheet-pile, using the flexible pipe in which the 20 biaxial load cells were installed circumferentially. As a result, the significant decrease in the earth pressure acting on the pipe and most of the pipe deformation occurred before the lower end of sheet-pile was extracted to the top of pipe. In addition, the wider the breadth between sheet-piles in this study was, the smaller the pipe deflection was, because the reduction of horizontal earth pressure was suppressed and vertical one was decreased.

    The Japanese Society of Irrigation, Drainage and Rural Engineering, 2021, Transactions of The Japanese Society of Irrigation, Drainage and Rural Engineering, 89 (2), I_379 - I_386, Japanese

  • Kohei Ono, Yusuke Sonoda, Yutaka Sawada, Hoe I. Ling, Toshinori Kawabata

    In Japan, a trenchless rehabilitation method has often been used for replacing aging irrigation pipes because of the economical reason. With the method, damaged host pipes are repaired with new pipes. Namely, the rehabilitated pipeline system comprises two pipes: a damaged host pipe and a liner. The mechanical behavior of liners is influenced by host pipes. In the present study, in order to reveal the mechanical behaviors, centrifuge model tests were carried out under various conditions including the damage levels of the host pipe, the positions of surcharge load, the ring stiffness of the liner, and the stiffness of the backfill. Test results indicate that the deflection of the liner increases with the damage level of the host pipe, and the influence of the host pipe on the liner is negligible when the host pipe reaches the ultimate damaged state. In addition, the strain concentration occurs at the crown of the inner due to the contact between the edge of the damaged host pipe and the liner. The strain concentration is reduced by 20 % with the increase of the ring stiffness of the liner. It is also revealed that the strain concentration appears even if the stiffness of backfills increases.

    01 Sep. 2015, Transportation Infrastructure Geotechnology, 2 (3), 139 - 154

    Scientific journal

  • SAWADA Yutaka, SONODA Yusuke, ONO Kohei, INOUE Kazuya, MOHRI Yoshiyuki, ARIYOSHI Mitsuru, KAWABATA Toshinori

    Recently, trenchless rehabilitation methods for aging irrigation pipes are often used. In this method, a new pipe is inserted into an aging pipe. Therefore, the rehabilitated pipeline consists of the outer aging pipe and the inner rehabilitated pipe. However, the mechanical influences of the damaged outer pipes on the inner rehabilitated pipes are not clear. In the present study, in order to reveal the influences, model experiments were conducted under the different damage levels of the aging pipe and loading positions. Experimental results indicate that the deflection of the rehabilitated pipe increases according to the damage level of the aging pipe. In addition, the strain concentration occurs at the top and the bottom of the rehabilitated pipe due to the point contact of the edge of the aging pipe. It is also found that the deflection and the strain distribution of the rehabilitated pipe under the eccentric load are significantly affected by the damage level of the aging pipe.

    The Japanese Society of Irrigation, Drainage and Rural Engineering, 2014, Journal of the Agricultural Engineering Society, Japan, 82 (3), 157 - 163, Japanese

  • Finite element analyses on mechanical behavior of inner rehabilitated pipes affected by outer aging pipes

    Kohei Ono, Yutaka Sawada, Akira Izumi, Taiki Miki, Yusuke Sonoda, Kazuya Inoue, Toshinori Kawabata, Hoe I. Ling, Liming Li, Johji Hinobayashi

    This paper discusses an analytical study on the pipe rehabilitation method for the purpose of establishing a fundamental design standard. In this method, as the new pipe is directly inserted into the aging pipe, there are several possibilities for construction in terms of cost reduction. Prior to the current study, it was not clear how the damaged outer pipe mechanically influenced the inner pipe when an external force was applied to the ground. In the present study, centrifuge model tests and finite element analyses for the buried pipe are carried out in an effort to evaluate interaction problem. Results of the testing and analyses indicate that the deformation mode of the new pipe is largely dependent on the damage level of the outer pipe. Additionally, the concentration of stress within the inner pipe occurs at the position where there is cracking of the outer pipe in a certain damaged condition. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).

    2014, Proceedings of the International Offshore and Polar Engineering Conference, 709 - 714

    International conference proceedings

  • K. Ono, K. Inoue, Y. Sawada, A. Izumi, Y. Sonoda, T. Miki, Y. Mohri, H. I. Ling, L. Li, J. Hinobayashi, T. Kawabata

    This paper discusses an experimental study on the pipe rehabilitation method for the purpose of establishing a fundamental design standard. In this method, as the new pipe is directly inserted into the aging pipe, there are several possibilities in terms of cost reduction. It is not clear how the damaged outer pipe mechanically influences the inner pipe through interaction with the surrounding soil when an external force is applied to the ground. In this study, centrifuge model tests for the buried pipe are carried out. The test results indicated that deformation mode of the new pipe largely depends on the damage level of the outer pipe. When the damage state is not serious, the outer pipe protects the inner pipe from deforming and behaves positively. However, the outer pipe, if at ultimate limit state, has almost no influence on the mechanical behavior of the inner pipe. Additionally, the concentration of stress within the inner pipe tends to occur at the position where there is cracking of the outer pipe in a certain damaged condition. © 2014 American Society of Civil Engineers.

    2014, Pipelines 2014: From Underground to the Forefront of Innovation and Sustainability - Proceedings of the Pipelines 2014 Conference, 1040 - 1048

    International conference proceedings

  • SONODA Yusuke, KAWABATA Toshinori, MORIKAMI Hironobu, DODO Hiroaki, ASAO Hitomi

    In order to clarify the behavior of buried pipe on the non-uniform bedding, experiments and 3-dimentional finite element analyses were conducted. By removing the soil from the valves of the bottom of test pit after backfilling uniformly, loose area was made in the ground. In the analysis, different input parameters made it possible to simulate the non-uniform ground. The pipe behavior was monitored at the three cross sections. Two sections are surrounded by the loosened ground locally. Another is between former two sections. From the results, it was clear that circumferential tensile strain acted on the part of the pipe by local swelling at the sections surrounded by the loosened ground. On the other hand, even circumferential tensile strain did not act but maximum shear strain increased at the middle section because of a kind of twisting force.

    Japan Society of Civil Engineers, 2013, Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM)), 69 (2), I_779 - I_786, Japanese

  • Experiments for buried flexible pipe supported by non-uniform bedding

    Toshinori Kawabata, Yusuke Sonoda, Hitomi Asao, Hironobu Morikami, Hirohumi Nakashima

    There are many earthquakes and torrential rain in Japan. By these reasons, the soil around the buried pipe is lost and the bed can become non-uniform. To clarify the behavior of buried pipe on the non-uniform bedding, the model experiments and rosette analysis were conducted. As a result, the concentration of stress and shear stress like a "twist" occurred at the buried pipe. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).

    2013, Proceedings of the International Offshore and Polar Engineering Conference, 260 - 265

    International conference proceedings

  • Mechanical behavior of buried inner rehabilitated pipes affected by aging pipes with different damage level

    Toshinori Kawabata, Yusuke Sonoda, Kohei Ono, Yoshiyuki Mohri, Mitsuru Ariyoshi, Hoe I. Ling

    The purpose of this study is to clarify how the damaged old pipe affects the inner rehabilitated pipe in the ground. Using some model pipes which have several damage levels, vertical loading test for buried pipe was conducted. As a result of this experiment, it was found that the stress concentration was occurred on the rehabilitated pipe by the edge of damaged old pipe. In addition, it was clarified that the inner circumferential strains occurred on the rehabilitated pipe was noticeably different depending on the damage level of the deteriorating old pipe. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).

    2013, Proceedings of the International Offshore and Polar Engineering Conference, 710 - 715

    International conference proceedings

  • The influence of non-uniform bedding on the mechanical behavior of buried flexible pipe

    Y. Sonoda, T. Kawabata, H. Asao, H. Morikami, H. I. Ling

    The soil around the buried pipe may become loose locally because of large earthquake and torrential rain, and the bedding may become non-uniform. However, the effect of non-uniform bedding on buried pipe remains to be clarified. In this study, experiments were conducted in order to clarify the behavior of buried pipe on the non-uniform bedding. The experimental pit has 64 holes (100 mm×100 mm) with valves at the bottom to create the non-uniform bedding. Polyvinyl chloride pipe, having a diameter of 600 mm and 3 measuring sections (Section-A, B, and C), was used. The distance between sections was 200 mm. The test showed that, when the sand was removed from the pipe bottom level around Section-A and Section-C, the pipe moved asymmetrically. As a result, when the ground becomes loose locally, large tensile strain acted on a Section-A (C) of the pipe closest to loosened ground, but maximum shear strain decreased. On the other hand, at the mid-section (Section-B) between the sections, which was close to loosened ground, circumferential tensile strain hardly occurred, but principal tensile strain acted almost in a pipe axial direction. Maximum shear strain at the mid-section increased to have a risk of yield failure. © 2013 American Society of Civil Engineers.

    2013, Pipelines 2013: Pipelines and Trenchless Construction and Renewals - A Global Perspective - Proceedings of the Pipelines 2013 Conference, 1321 - 1329

    International conference proceedings

  • Dynamic behavior for buried flexible pipe subjected to ground shear deformation

    Toshinori Kawabata, Yoshiyuki Iwasaki, Yusuke Sonoda, Yoshiyuki Mohri

    The purpose of this study is to clarify the deformation mechanism of buried flexible pipes subjected to simple shear deformation. As a result of the experiment and the analysis (2-dimensional discrete element method; DEM), it was clarified that large bending strains are generated at the position of 45 degrees from the spring line by ground shear deformation. In addition, bending strains of the pipes are shown to depend on the shear strain of the ground. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE).

    2012, Proceedings of the International Offshore and Polar Engineering Conference, 337 - 342

    International conference proceedings

  • T. Kawabata, Y. Sonoda, Y. Mohri, M. Ariyoshi, Y. Iwasaki

    In designing a pipeline, deflection and stress of the pipe are calculated through structural analysis based on bending ring stiffness EI/D3. The pipes with equivalent bending ring stiffness would have the same behavior in design. However, it is easily understandable that the behavior of pipe may be influenced not only by EI/D3, but also by the relationships between E and I. In this paper, shaking table test for buried flexible pipes were conducted to evaluate the effects of pipe thickness on the dynamic behavior. Some pipes having approximately equivalent bending ring stiffness and different thickness were used. In this experiment, these pipes were buried in the laminar box and shaken by horizontal sine wave. As a result, it was found that the larger bending strain and radial stress of the pipe occurred with the thinner wall. This result suggests that the probability of the buckling of the pipe is higher on thinner pipes. It is evident that the pipelines for irrigation should be designed in consideration of this fact. © 2012 American Society of Civil Engineering.

    2012, Pipelines 2012: Innovations in Design, Construction, Operations, and Maintenance - Doing More with Less - Proceedings of the Pipelines 2012 Conference, 1015 - 1024

    International conference proceedings

MISC

  • コロナ禍での学生・研究生活

    園田悠介

    Jul. 2022, ジオシンセティックス技術情報, 38 (2), 51 - 51, Japanese

Presentations

  • Flume model test on granular materials flowing into a small fill dam

    Sonoda Y, Tsujimoto, K, Matsumoto, T, Sawada, Y

    6th World Landslide Forum 2023, 17 Nov. 2023

  • スラスト力を受ける二条埋設管路の模型実験

    井上優佑, 太田遥子, 澤田豊, 園田悠介, 河端俊典

    第80回農業農村工学会京都支部研究発表会, Nov. 2023, Japanese

  • Centrifuge model test on the risk of insufficient compaction and the effect of EPS foundation at the pipe bottom side

    Yusuke SONODA, Yutaka SAWADA, Hoe I. LING, Liming LI, Toshinori KAWABATA

    第58回地盤工学研究発表会, 11 Jul. 2023, Japanese

    Oral presentation

  • 貯留水に流入する粒状体の流動性に関する一考察

    園田悠介, 松本赳, 澤田豊

    第79回農業農村工学会京都支部研究発表会, Nov. 2022, Japanese

  • 管底側部に設置したEPS基礎がたわみ性埋設管の力学挙動に与える影響に関する埋設模型実験

    園田悠介, 伊川千颯, 辻本琴音, 永谷太志, 工藤秀穂, 澤田豊, 河端俊典

    第71回農業農村工学会大会講演会, Aug. 2022, Japanese

  • 矢板施工における矢板厚と根入れ長がたわみ性埋設管の土圧に与える影響

    徳増美月, 池端瑠香, 園田悠介, 澤田豊, 河端俊典

    第71回農業農村工学会大会講演会, Aug. 2022, Japanese

  • 貯留状態のため池に流入する土石流に関する基礎的実験

    園田悠介, 松本赳, 井上優佑, 澤田豊, 河端俊典

    第71回農業農村工学会大会講演会, Aug. 2022, Japanese

  • 矢板引抜き時の埋設たわみ性管に作用する土圧について

    徳増美月, 園田悠介, 戸田茉優, 澤田豊, 河端俊典

    第70回農業農村工学会大会講演会, Aug. 2021, Japanese

  • たわみ性埋設管の管底側部の締固め不足に対する対策工に関する実験的検討

    河村未奈, 青木達也, 伊川千颯, 園田悠介, 日野林譲二, 澤田豊, 河端俊典

    第70回農業農村工学会大会講演会, Aug. 2021, Japanese

  • 損傷レベルの異なる既設管が更生管変形特性に与える影響に関する遠心力模型実験

    澤田豊, 井上一哉, 園田悠介, 小野耕平, 三木太貴, 高原祥, 泉明良, 毛利栄征, Ling H.I, 河端俊典

    平成26年度農業農村工学会大会講演会, Aug. 2014, Japanese

  • 老朽既設管の影響を受ける更生管力学挙動に関する遠心力模型実験

    澤田豊, 園田悠介, 小野耕平, 三木太貴, 高原祥, 毛利栄征, 河端俊典

    第49回地盤工学研究発表会, Jul. 2014, Japanese

  • 損傷レベルの異なる老朽 既設管の影響を受ける更生管の力学挙動

    小野耕平, 園田悠介, 三木太貴, 河端俊典, 澤田豊, 毛利 栄征, 有吉充

    平成25年度農業農村工学大会講演会, Sep. 2013, Japanese

  • 老朽既設管の影響を受ける更生管力学挙動に関する偏心載荷実験

    小野耕平, 園田悠介, 河端俊典, 三木太貴, 毛利栄征, 有吉充

    第48回地盤工学研究発表会, Jul. 2013, Japanese

  • 不均一な地盤条件における埋設管力学挙動に関する模型実験―ロゼット解析法による実験的検討―

    園田悠介, 浅尾瞳, 百々宏晶, 河端俊典

    第48回地盤工学研究発表会, Jul. 2013, Japanese

  • 不均一な地盤条件における埋設管力学挙動に関する検討―長軸大口径管を対象とした3次元有限要素法解析

    百々宏晶, 園田悠介, 河端俊典, 村井和樹

    第48回地盤工学研究発表会, Jul. 2013, Japanese

  • 周辺地盤密度を考慮した不均一地盤における埋設管力学挙動に関する模型実験

    園田悠介, 河端俊典, 浅尾瞳, 森上浩伸, 中島博文

    農業農村工学会京都支部第69回研究発表会, Nov. 2012, Japanese

  • 埋設管周辺部グリッド補強効果に関する単純せん断実験

    園田悠介, 百々宏晶, 河端俊典, 小野耕平, 真木貴也

    農業農村工学会京都支部第69回研究発表会, Nov. 2012, Japanese

  • Experiments for Influence by Non-uniform Bedding on Pipe Behavior

    園田悠介, 河端俊典, 森上浩伸, 中島博文, 浅尾瞳

    平成23年度農業農村工学会大会, Sep. 2012, Japanese

  • Dynamic Behavior of Flexible Buried Pipe with Rigid Bedding

    甲賀洋輔, 園田悠介, 小野耕平, 河端俊典, 毛利栄征, 有吉充

    平成23年度農業農村工学会大会講演会, Sep. 2012, Japanese

  • せん断土槽を用いた同一環剛性を有するたわみ性埋設管の振動台実験に関する一考察

    岩﨑善之, 河端俊典, 毛利栄征, 有吉 充, 甲賀洋輔, 園田悠介, 小野耕平

    第47回地盤工学研究発表会, Jul. 2012, Japanese

  • 管厚が地盤のせん断変形を受けるたわみ性埋設管の変形挙動に及ぼす影

    園田悠介, 河端俊典, 岩崎善之, 真木貴也

    第47回地盤工学研究発表会, Jul. 2012, Japanese

  • 不均一な地盤条件における埋設管力学挙動に関する模型実験

    園田悠介, 河端俊典, 森上浩伸, 中島博文, 浅尾瞳, 小野耕平, 久保京子, 真木貴也

    第47回地盤工学研究発表会, Jul. 2012, Japanese

  • 地盤のせん断変形を受けるたわみ性埋設パイプの変形挙動に関する模型実験

    岩崎善之, 河端俊典, 園田悠介, 甲賀洋輔

    農業農村工学会京都支部第68回研究発表会, Nov. 2011, Japanese

  • 管剛性が地盤のせん断変形を受ける埋設管の挙動に与える影響

    岩崎善之, 河端俊典, 園田悠介, 甲賀洋輔

    農業農村工学会京都支部第68回研究発表会, Nov. 2011, Japanese

  • 管口径が地盤のせん断変形を受ける埋設管の挙動に及ぼす影響

    岩崎善之, 河端俊典, 園田悠介, 甲賀洋輔

    平成23年度農業農村工学会大会講演会, Sep. 2011, Japanese

  • Experimental Verification for Buried Flexible Pipe Subjected to Shear Deformation

    岩﨑善之, 河端俊典, 甲賀洋輔, 園田悠介

    平成23年度農業農村工学会大会講演会, Sep. 2011, Japanese

  • 地盤のせん断変形を受けるたわみ性埋設パイプの変形挙動に関する一考察

    岩崎善之, 河端俊典, 園田悠介, 甲賀洋輔

    第46回地盤工学研究発表会, Jul. 2011, Japanese

  • 神戸地盤のせん断変形を剛性埋設パイプの浮上に関するDEM解析

    岩崎善之, 河端俊典, 園田悠介, 甲賀洋輔

    第46回地盤工学研究発表会, Jul. 2011, Japanese

Association Memberships

  • 国際ジオシンセティックス学会 日本支部

    Apr. 2020 - Present
  • The Japanese Geotechnical Society

    Apr. 2020 - Present
  • The Japanese Society of Irrigation, Drainage and Rural Engineering

    Oct. 2010 - Present

Research Projects

  • セル補強された土のせん断力学挙動の解明と省力的液状化緩和工法の開発

    園田 悠介

    日本学術振興会, 科学研究費助成事業, 研究活動スタート支援, 神戸大学, Aug. 2023 - Mar. 2025

  • 廃止する溜池の治水施設としての活用に関する研究

    園田 悠介

    日本学術振興会, 科学研究費助成事業 特別研究員奨励費, 特別研究員奨励費, 神戸大学, 28 Apr. 2021 - 31 Mar. 2024

    本研究は,溜池の「廃止手法」を確立し,土砂災害の被害を軽減し得る治水施設としての価値を見出そうとするものである.しかし,土石流等の流入に対する溜池堤防の安定性や堰止め効果は全くの未知数である.そのため,本年度は,溜池に土石流が流入した場合の基本的挙動やため池堤体に及ぼす衝突荷重について,特に貯水の影響も考慮した検討を行うことを目的に土石流模型実験を行った. 実験は,幅30cm,傾斜角45°の実験水路を用いて実施した.土石流を模擬した砕石やセラミックビーズを上流から流下させ,下流の貯水状態を模擬した堤体模型に衝突させた.その際,堤体模型に取り付けた荷重計で衝突荷重を計測するとともに,高速度カメラによる撮影を行い,画像解析から土石流の流入挙動を評価した.また,レーザー変位計を用いて流下速度の計測も行った.実験条件としては,貯留水による影響を考慮するため,貯留水の水位を0cm,2cm,5cm,10cm,15cmに変化させたケースのほか,斜面下端からの距離や流下速度が異なるケースを実施した. 実験の結果,土石流は,潜り込むように貯留水に流入し,急激な水位変動を引き起こすことが明らかとなった.そのため,当初期待していたような,貯留水があることで土石流が減勢する効果よりも,水位変動による影響の方が大きく,貯留水が多い場合には,堤体に作用する荷重が増大する可能性が明らかとなった.一方で,堤体模型が無い状態で土石流材料を流下させた場合に,低い水位でも土石流の流出長さが短くなる傾向があり,定性的ではあるが貯留水による土石流の減勢効果を評価することができた. これら実験結果から明らかとなった衝突荷重や急激な水位変動に関する知見は,溜池堤体に大きな影響をおよぼすファクターであると考えられ,今後の土石流に対する堤体の安定性や破壊メカニズムの解明に極めて重要なものである.

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