Faculty Profiles - NODA, Toshihiro

Presentations -

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A soil-water-air coupled finite deformation simulation on seepage failure of levee using the SYS Cam-clay model which can describe suction effect

Event date： 2018.6

Language：English Presentation type：Oral presentation (general)

Country：Japan

A seepage model test of a river levee on the ground having a highly permeable soil layer was simulated
using a soil-water-air coupled finite deformation analysis code incorporating the SYS Cam-clay model
which can describe suction effect. The simulated result showed that the levee body became normal
consolidation state due to decease in suction effect associated with increase in saturation degree and
thereby slip failure of the levee body could occur. In addition, the soil element on the slip surface showed
softening behavior with plastic volume expansion.

模型堤防の浸透破壊メカニズム解明のための空気～水～土骨格連成有限変形シミュレーション

吉川高広，野田利弘，内藤誠也，小高猛司，崔瑛

土木学会第72回年次学術講演会

Event date： 2017.9

Language：Japanese Presentation type：Oral presentation (general)

Venue：九州大学伊都キャンパス Country：Japan

平成24 年7 月の九州北部豪雨による矢部川堤防の被災は，局所的なパイピングをきっかけとして決壊した「越流なき破堤」として大きな衝撃を与え，複雑な地盤条件・水理条件においても合理的に河川堤防の安全性照査が可能な最新の地盤力学に基づく解析手法の構築が求められている．本稿では，粘土から砂，さらにはその中間土までの力学挙動を統一的な枠組みで記述可能な弾塑性構成式
SYS Cam-clay モデルを搭載した空気～水～土骨格連成有限変形解析コードを用いて，透水模型実験のシミュレーションを行い，浸透破壊する場合としない場合の違いを表現できることを示した（解析コードのValidation）．また，本解析コードを用いたケーススタディも実施して，基礎地盤と堤体の土質や境界／外力条件の違いが，浸透破壊発生の有無に与える影響を示した．

集排水機能を具備するマクロエレメント法の準静的問題における近似精度の検証

野中俊宏，山田正太郎，野田利弘

土木学会第72回年次学術講演会

Event date： 2017.9

Language：Japanese Presentation type：Oral presentation (general)

Venue：九州大学伊都キャンパス Country：Japan

バーチカルドレーンの排水効果を近似的に水～土連成解析に取り入れる手法としてマクロエレメント法と呼ばれる一種の均質化法がある．著者らはウェルレジスタンス現象の発生を合理的に扱えるよう，同手法にドレーンの排水機能を付加するなどして機能拡張を図った．本稿では，高機能化したマクロエレメント法の準静的問題における近似精度について検証した．この結果，著者らが高機能化を図ったマクロエレメント法は，計算コストを大幅に削減しつつ，複数本のドレーンを有する大規模でかつ盛土載荷を併用した真空圧密工法のように複雑な載荷履歴を受ける問題においても高い近似精度を発揮することが明らかになった．なお，同手法は動的問題においても高い近似精度を発揮する．

横ずれ断層におけるjogの存在を考慮したRiedelせん断帯の生成シミュレーション

豊田智大，野田利弘，山田正太郎，山田翔太

土木学会第72回年次学術講演会

Event date： 2017.9

Language：Japanese Presentation type：Oral presentation (general)

Venue：九州大学伊都キャンパス Country：Japan

本稿では，push-upおよびpull-apartを模擬した不連続な断層変位場（幾何学的初期不整）を境界条件として考慮した3 次元弾塑性有限変形解析を実施することで，横ずれ断層における局所的なjogの存在に起因した付随断層構造の形成プロセスを数値解析的に再現することを目指す．この結果、横ずれ断層におけるjog（幾何学的初期不整）を境界条件として考慮した弾塑性有限変形解析により，fractalなRiedel せん断やP-shear，低角・高角なせん断面といった特徴的な付随断層構造の形成過程を再現できた．

繰返し載荷による軟弱粘土の乱れの把握と骨格構造概念に基づく記述

中井健太郎，野田利弘，鈴木彩華，水上孔太

土木学会第72回年次学術講演会

Event date： 2017.9

Language：Japanese Presentation type：Oral presentation (general)

Venue：九州大学伊都キャンパス Country：Japan

従来の地震時被害／対策では砂質地盤の液状化現象が注目されることが多いが，メチオカン地震(1895)やトルコ地震(1999)など，軟弱粘土地盤が関与したと考えられる地震中～地震後被害も数多く報告され，近年研究も鋭意進められてきている．しかし，粘土地盤の実務・研究の多くは人工的な練返し正規圧密粘土を対象にした構成式が用いられており，骨格構造が発達した自然堆積地盤の動的挙動を把握するには十分と言えない．名古屋大学では土の骨格構造（構造，過圧密，異方性）とその働きを記述した弾塑性構成式（SYS カムクレイモデル）を提案している．本報では，繰返し載荷による軟弱粘土の乱れの影響を非排水三軸圧縮試験結果から把握するとともに，上記構成式の応答と対比することで，軟弱粘土の動的挙動の把握には構造概念が重要であることを示した．

Proposal of an estimation method for an incident wave to a bedrock by using a soil-water coupled elasto-plastic finite deformation analysis with viscous boundary

Event date： 2017.8

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

Records observed in bedrocks have been used to extrapolate seismic origin model. However, if non-linear response occurred in the surface ground, the influence of it on the records would not be negligible. In addition, multi-dimensional wave propagation can occur because most deposited grounds are neither horizontal nor even. Therefore, this study proposed a new estimation method for the incident wave to base rock from an observational record while taking into account non-linearity response of surface ground such as liquefaction phenomena and multi-dimensional wave propagation by using a soil-water coupled elasto-plastic finite deformation analysis code. In other words, through this achievement, a new utilization of the viscous boundary condition (VBC) will be proposed. In addition, the feasibility of the proposed method will be examined.

Extensive and localized subsurface damage caused by the interference between body waves and surface waves generated from the irregularly shaped bedrock

Event date： 2017.8

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

Most of the existing damage prediction methods not only do not substantially take account of the nonlinearity of the ground but also are based on one-dimensional vertical evaluations. Therefore, multi-dimensional effects due to an irregular stratigraphic and bedrock structure are not taken into consideration. In this paper, two-dimensional elasto-plastic effective stress analysis is carried out noticing the irregularity of the ground stratification. As a result, complex interference between the surface waves and body waves provides not only inhomogeneous deformation but also localized and extensive damage at the ground surface.

Simulation of Riedel shear bands formation considering the jog on strike-slip fault based on nonlinear geomechanics

Event date： 2017.8

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

A slip on strike-slip fault causes flower structures and Riedel shear bands within the overlying cover. In our former research, the Riedel shear bands formation process was simulated considering the material
imperfection in ground by utilizing the three-dimensional elasto-plastic finite deformation analysis code GEOASIA. On the other hand, it's known that the existence of jog (geometrical barrier) has an important
role on the formation process. This paper simulates a strike-slip faulting process considering jog as a
geometrical imperfection in ground on the strike-slip fault. As a result, the formation processes unique to
subsidiary fault such as fractal shear bands, P-shear, low and high angle shears appeared.

Geo-computational study on aftershock-induced expansion of liquefaction damage of sandy ground with groundwater-level rise due to main shock

Event date： 2017.8

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

In the 2011 off the Pacific coast of Tohoku Earthquake, extensive liquefaction damages were observed over a wide range of reclaimed coastal land. It is reported that, in Chiba prefecture, the big aftershock occurred 29 minutes after the main shock and it caused expanding the liquefaction damage. In this paper, using a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation 'SYS Cam-clay model,' it showed that groundwater level rise due to main shock expands liquefaction damage during aftershock.

1G shaking table tests of saturated fill slopes in terms of shift of resonance phenomena due to material-nonlinearity

Event date： 2017.8

Language：Japanese Presentation type：Oral presentation (general)

Country：Japan

Earthquake motions include waves of various frequency bands ranging from low to high frequency. Notably,
the difference in dominant frequencies affects the seismic stability of fill slopes. Hence, to analyze the
deformation/failure mechanism during an earthquake, 1G shaking-table tests were conducted on saturated fill
slopes considering the resonance phenomenon. Evaluating the seismic stability of the fill slopes depends on not only the magnitude of the acceleration but also the relationship between the natural frequency and the input frequency. Moreover, it is also important to grasp the change in the natural frequency associated with the progress of plastic deformation due to repeated loading.

1G shaking tests on saturated fill slopes focusing on relationship of input frequency and natural frequency

Difference between ceramic disc and micro-porous membrane on exhausted and drained triaxial compression test result of unsaturated silt

Soil-water-air coupled simulation with void ratio dependent SWCC model on exhausted and drained triaxial compression test of unsaturated soil

Simulation of immediate settlement of high permeable soil by using u-w-p formulation-based soil-water coupled analysis

Effect of stratum irregularity on ground surface damage during/after the occurrence of an earthquake

Seismic response analysis of ground improved by SCP method 2by using a soil-water coupled finite deformation analysis code that mounts the combined loading elasto-plastic constitutive model

A proposal of estimation method of incident wave to base rock considering effect of multidimensional wave propagation and nonlinearity of surface ground

A soil-water coupled analysis of a spherical gas holder on liquefiable ground during/after earthquake

A consideration of the seepage failure mechanism of a model river levee using a soil-water-air coupled finite deformation simulation

Numerical simulation of spike-shaped acceleration response in liquefied sandy ground

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