Faculty Profiles - NODA, Toshihiro

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不飽和シルトの体積圧縮時の水分特性に関する実験的研究

吉川高広，野田利弘，北折陽一

土木学会第74回年次学術講演会

Event date： 2019.9

Language：Japanese Presentation type：Oral presentation (general)

Venue：香川大学幸町キャンパス Country：Japan

近年，豪雨による斜面や盛土等の不飽和地盤・土構造物の崩壊が相次いで発生し，その被災メカニズムの解明が強く求められている．不飽和土の力学挙動を把握するためには，水分特性を把握することが必要である．不飽和土の水分特性の主な特徴としては，吸排水時のヒステリシス性と間隙比依存性が挙げられる．本研究では，間隙比依存性（体積圧縮時）の水分特性に注目して，不飽和シルトの排水条件および非排水条件の三軸試験を実施した．

The mechanical properties and stiffening of short fiber-reinforced sands with several relative densities

Jakhongirbek Ganiev, Yamada Shotaro, Nakano Masaki, Sakai Takayuki, Noda Toshihiro

Event date： 2019.9

Language：English Presentation type：Oral presentation (general)

Country：Japan

Reinforcement of soils using tension resisting elements is an actual and alternative solution for ground improvement and stabilization issues both for engineering and economic purposes. It is well-known that discrete flexible fibers act like plant roots and give the possibility to increase the strength and stability of soils. Prevalence of effectiveness of soil reinforcement with fibers started almost 15 years ago. However, there are not enough studies for describing the effect of fibers on soil behaviour and techniques of application of fiber-reinforcement in practice. This study was targeted on obtaining the behaviour of fiber-reinforcement of sandy materials with different relative densities and find out a more suitable method for specimens' preparation with the vision of future application on construction site.

海底地すべりによる正断層群の形成過程に関する数値解析的検討

山田英司，河村精一，野田利弘，中井健太郎，浅岡顕

土木学会第74回年次学術講演会

Event date： 2019.9

Language：Japanese Presentation type：Oral presentation (general)

Venue：香川大学幸町キャンパス Country：Japan

地すべり移動体の内部では，複数のリストリック正断層が平行に形成されて断層群を成すことも多い．本報告では，海底地すべり移動体内に存在する正断層群形成過程に関する数値解析的検討結果について述べる．解析には骨格構造概念に基づく土の弾塑性構成式SYS Cam-clay modelを搭載した水～土骨格連成有限変形解析コードGEOASIAを用い，固結状況が異なる３つの水平堆積した海底地盤（地盤１：堆積直後の状態，地盤２：未固結～半固結状態，地盤３：固結状態）を対象として，地盤傾斜時の挙動を調べた．ここでは，地盤は堆積後，続成作用により固結が進行して強度が増加する点に注目した．すなわち，堆積完了時の状態を基準とし，続成作用が進行すると，土粒子実質部分（間隙比）は変わらないが，セメンテーション等により土の骨格構造が発達すると考え，固結状況の違いを土の骨格構造の発達度や発展速度の違いとして表現した．

L2地震下で顕著になる河川堤防直下の軟弱粘性土の揺すりこみ沈下挙動

中井健太郎，野田利弘，黒口拳四朗

土木学会第74回年次学術講演会

Event date： 2019.9

Language：Japanese Presentation type：Oral presentation (general)

Venue：香川大学幸町キャンパス Country：Japan

日本の国土は起伏に富んでいるため，可住地が狭く，都市機能が沖積平野に集中している．平野部は一般的に地下水位が高いことに加えて，堆積年代が若いことから地盤が軟弱であることが多く，地震時に液状化をはじめとする地盤災害が発生する危険性が高い．人口・資産が集中した区域で河川堤防が被災し，決壊すると，甚大な浸水被害につながってしまうため，河川堤防の耐震性照査および適切な対策が重要である．しかし，従来の地震に対する耐震性能照査や設計は，静的照査法に基づき，砂質基礎地盤の液状化に伴う沈下量が外水位を超えないかどうかの判定のみであった．東日本大震災の被害調査を受けて，粘性土基礎地盤上の堤体の液状化が注目され，基礎地盤の液状化に加えて，堤体の液状化による沈下・変形も照査の対象事象に含めることが検討されているが，それでもなお不十分で，あくまで堤体材料（砂質土）の液状化であり，粘性土自体の地震変状や不安定化は考慮されてはいない．本報では，砂質土が卓越する断面および軟弱な粘性土が厚く堆積する断面上の河川堤防に対して，L1地震動およびL2地震動を入力した時の地震応答解析を実施し，軟弱粘性土地盤の地震時挙動の把握を試みた．使用した解析コードは，土の骨格構造とその働きの差異によって砂から粘土，両者が混在した中間土を同じ理論的枠組みで記述する土骨格の弾塑性構成式SYSカムクレイモデルを搭載した水～土骨格連成有限変形解析コードGEOASIAである．

Experimental attempt to produce soft clayey specimen by adding hydration reaction controlled cement

Event date： 2019.7

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

Soft clay foundation often shows long-term large settlement under embankment loading as the compressibility is large. On the other hand, the clay foundation has been considered to be safe for dynamic problem. However, the recently investigated results showed that clay foundation showed remarkable loss of rigidity due to earthquake, which leads to tremendous seismic damages, as seen in the 1957, 1985 Mexico earthquakes and the 2015 Nepal earthquakes. These areas possess the soft lakedeposits consisting of soil types with extremely high water contents, namely, soft and sensitive clays. Therefore, it is important to grasp both static and dynamic mechanical properties of naturally deposited clayey materials. To this aim, it is indispensable to carry out various systematic experiments using the undisturbed soil samples. However, it is difficult to prepare a number of homogeneous soft clay samples, due to the problems of variability of quantities during sedimentation, sampling disturbance and high expense of boring survey. Therefore, in this study we focused on cementation reaction, in order to artificially produce the soil sample having similar characteristics to those of naturally deposited soft clay. By doing so, while maintaining the reproducibility of the specimen, it might be possible to perform a large amount of systematic experiments, and also to conduct such model experiments as impossible in the past. Although numerous experimental studies have been conducted to reproduce the natural soft clay with cement, the cement was directly added to soil in most cases. As the result, the solidification effect was so strong that localized failure occurred in the soil specimen due to cracking followed by sudden decrease of shear stress with no increase in excess pore water pressure. So, in terms of the necessity to reduce the solidification effect, we newly attempted "addition of hydration reaction controlled cement" and "calcium leaching" to represent similar characteristics to soft clay material. In this report, we discuss the influence on mechanical properties when hydration reaction controlled cement is added to clayey soil.

Experimental attempt to produce soft clayey specimen by leaching of calcium followed by cement solidification

Localized seismic damage induced by the complicated wave propagation, amplification and interference occurring in the Aso caldera

Study on the mechanical properties and stiffening effect of short fiber-reinforced geomaterials

Event date： 2019.7

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

Reinforcement of soils using tension resisting elements is an actual and alternative solution for ground improvement and stabilization issues both for engineering and economic purposes. It is well-known that discrete flexible fibers act like plant roots and give the possibility to increase the strength and stability of soils. Prevalence of effectiveness of soil reinforcement with fibers started almost 15 years ago. However, there are not enough studies for describing the effect of fibers on soil behaviour and techniques of application of fiber-reinforcement in practice.
This study was targeted on obtaining the tendency for fiber-reinforcement of sandy materials and find out a more suitable method for specimens' preparation with the vision of future application on construction site.

Installation and validation of a new evolution rule for induced anisotropy into the combined loading elasto-plastic constitutive model

Evaluation of eigen vibration characteristics around soil structure by the localized participation factor

Experimental simulation of internal erosion using water-soluble chemical fertilizer

The effects of slight change of grain size distribution on the shear behavior of sandy soil

Triaxial tests on cyclic water absorption-drainage history of unsaturated silt

Description of water absorption-drainage hysteresis of unsaturated silt based on SWC model taking trapped air into consideration

Expansion of liquefaction damage during aftershock induced by groundwater-level rise due to main shock: soil-water-air coupled elasto-plastic finite deformation analysis approach International conference

Noda Toshihiro, Yoshikawa Takahiro

VIII International Conference on Coupled Problems in Science and Engineering (COUPLED 2019)

Event date： 2019.6

Language：English Presentation type：Oral presentation (general)

Venue：Sitges(Barcelona), Spain Country：Spain

In the 2011 off the Pacific coast of Tohoku Earthquake, it is reported that, in Chiba prefecture, the big aftershock occurring 29 minutes after the main shock caused expanding the liquefaction damage in the sandy ground. In this study, using a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation SYS Cam-clay model, it is shown that groundwater level rise due to main shock may expand liquefaction damage during aftershock.

Dynamic Soil-Water Coupled Finite Deformation Analysis of a Highly-Permeable Soil Specimen on an Undrained Plane-Strain Compression Test International conference

Toyoda Tomohiro, Noda Toshihiro

VIII International Conference on Coupled Problems in Science and Engineering (COUPLED 2019)

Numerical simulation of unsaturated soil triaxial test based on a soil-water-air coupled analysis incorporating a void ratio-dependent SWC model International conference

Noda Toshihiro, Yoshikawa Takahiro

VIII International Conference on Coupled Problems in Science and Engineering (COUPLED 2019)

Event date： 2019.6

Language：English Presentation type：Oral presentation (general)

Venue：Sitges(Barcelona), Spain Country：Spain

In this study, to examine mechanical behavior of unsaturated soil, a series of triaxial tests was conducted and the soil-water-air coupled finite deformation simulation was performed. The simulation made use of a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation, SYS Cam-clay model, in which suction effect is newly taken into account, and a soil water characteristic (SWC) model which is dependent on void ratio. The simulation treated a triaxial test as the solution for an initial and boundary value problem. A series of processes of suction decreasing, isotropic consolidation, and exhausted-drained shearing was simulated from a single initial condition using a single set of material constants.

Numerical simulation of cyclic water absorption-drainage triaxial test using a soil water characteristic model taking trapped air into consideration

Event date： 2019.5

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

Numerical simulations of cyclic water absorption-drainage triaxial tests were performed using a soil water characteristic (SWC) model taking trapped air into consideration. It was demonstrated that a mere
consideration of transition between trapped air and continuous air in the SWC model allowed us to express
the hysteresis of the saturation degree during water absorption-drainage. In addition, unexhausted and
undrained triaxial compression tests of two specimens with the same zero suction but with different
saturation degree due to difference in water absorption-drainage history were well simulated.

Proposal of combined loading elasto-plastic model

Event date： 2019.5

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

This paper proposed a new framework in elasto-plastic theory for soils called "combined elasto-plastic constitutive model." This framework allows the SYS Cam-clay model, which can describe the mechanical behavior of naturally deposited clayey soils, and the non-associated Drucker-Prager model, which has mainly simulated the undrained shear behavior of sandy soils, to simultaneously work within a single model. This paper introduced the basic formulation of this new framework and demonstrated that the proposed model could produce typical sand and clay behaviors.

2008年岩手・宮城内陸地震時に見られた荒砥沢ダム堤体の強い非線形応答の弾塑性地盤力学による再現と入力地震動の推定

山田正太郎，野田利弘，浅岡顕，澤田義博

第15回日本地震工学シンポジウム

Event date： 2018.12

Language：Japanese Presentation type：Oral presentation (general)

Venue：仙台国際センター Country：Japan

2008年岩手宮城内陸地震時に荒砥沢ダムでは，底部監査廊で最大加速度1024Gal，中段コア部と最上部天端ではそれぞれ，535Gal，525Galの記録が得られた．ダム基礎で1000Galを超える記録は異例であり，基盤に対する堤体の応答倍率が1を大きく下回るのも異例である．論文では，堤体材料の動的変形特性を広範なひずみ領域で説明できる弾塑性構成式を用いて水～土連成の有限変形解析を実施し，①応答倍率が0.5倍にまでも低下する現象は堤体材料の履歴減衰が原因で，②ダム基礎での1024Galの観測記録（E+F）は，強い非線形応答時のダム内部での反射・屈折現象を反映しており，入力地震動（E）は最大500Gal程度であったことを明らかにした．

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