• Title/Summary/Keyword: Continuum granular material

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Investigation of Subsurface Deformations for the Shallow Tunnel In A Granular Mass Using Two-Dimensional Laboratory Model Test and Numerical Analysis (2차원 실내모형실험과 수치해석을 이용한 사질토 지반의 얕은 터널에 대한 지중변형에 대한 규명)

  • Lee, Yong-Joo
    • Proceedings of the Korean Geotechical Society Conference
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    • 2006.03a
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    • pp.219-228
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    • 2006
  • In urban areas, tunnelling induced ground deformations, particularly ground settlements should be considered in order to minimize the damage of adjacent structures. Therefore, an appropriate monitoring system for the tunnel construction should be setup at the planning or design stage. A number of studies on ground settlements due to tunnelling in soft ground have been carried out so far. However, most studies have focused on clay soil rather than sand soil. In particular, a few studies on behaviour of subsurface deformations in granular material have been reported. In this study, two-dimensional laboratory model test with aluminium rods regarded as continuum granular material and close range photogrammetric technique, and numerical analysis were carried out in order to identify the behaviour of subsurface deformations due to shallow tunnelling. Direction and magnitude of displacement vectors from the model test was identical to the numerical analysis. In particular, the vector direction was appeared to be toward a point below the tunnel invert level. A narrow 'chimney or tulip like' pattern of vertical displacement was confirmed by both the model test and numerical analysis. This is consistent with the field data. In addition to the qualitative comparison, the quantitative comparison of subsurface settlements according to 2D volume loss showed good agreement between the model test and numerical analysis. Therefore, close range photogrammetric technique applied in the model test may be used to validate the result from the continuum numerical analysis.

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Behaviour of interfacial layer along granular soil-structure interfaces

  • Huang, Wenxiong;Bauer, Erich;Sloan, Scott W.
    • Structural Engineering and Mechanics
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    • v.15 no.3
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    • pp.315-329
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    • 2003
  • As shear occurs along a soil-structure interface, a localized zone with a thickness of several grain diameters will develop in soil along the interface, forming an interfacial layer. In this paper, the behaviour of a soil-structure interface is studied numerically by modelling the plane shear of a granular layer bounded by rigid plates. The mechanical behaviour of the granular material is described with a micro-polar hypoplastic continuum model. Numerical results are presented to show the development of shear localization along the interface for shearing under conditions of constant normal pressure and constant volume, respectively. Evolution of the resistance on the surface of the bounding plate is considered with respect to the influences of grain rotation.

A review on modelling and monitoring of railway ballast

  • Ngamkhanong, Chayut;Kaewunruen, Sakdirat;Baniotopoulos, Charalampos
    • Structural Monitoring and Maintenance
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    • v.4 no.3
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    • pp.195-220
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    • 2017
  • Nowadays, railway system plays a significant role in transportation, conveying cargo, passengers, minerals, grains, and so forth. Railway ballasted track is a conventional railway track as can be seen all over the world. Ballast, located underneath the sleepers, is the most important elements on ballasted track, which has many functions and requires routine maintenance. Ballast needs to be maintained frequently to prevent rail buckling, settlement, misalignment so that ballast has to be modelled accurately. Continuum model was introduced to model granular material and was extended in ballast. However, ballast is a heterogeneous material with highly nonlinear behaviour. Hence, ballast could not be modelled accurately in continuum model due to the discontinuities nature and material degradation of ballast. Discrete element modelling (DEM) is proposed as an alternative approach that provides insight into constitutive model, realistic particle, and contact algorithm between each particle. DEM has been studied in many recent decades. However, there are limitations due to the high computational time and memory consumption, which cause the lack of using in high range. This paper presents a review of recent ballast modelling with benefits and drawbacks. Ballast particles are illustrated either circular, circular crump, spherical, spherical crump, super-quadric, polygonal and polyhedral. Moreover, the gaps and limitations of previous studies are also summarized. The outcome of this study will help the understanding into different ballast modelling and particle. The insight information can be used to improve ballast modelling and monitoring for condition-based track maintenance.

Comparison of Shallow Model Tunnel Test Using Image Processing and Numerical Analysis (이미지 프로세싱을 이용한 얕은 터널 모형실험과 수치해석의 비교)

  • Lee, Yong-Joo
    • Journal of the Korean Geotechnical Society
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    • v.22 no.7
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    • pp.5-12
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    • 2006
  • In this study, 2D shallow tunnel model test using close range photogrammetric technique was conducted with aluminium rods simulating continuum granular material. Numerical analysis was also carried out in order to identify the behaviour of subsurface deformations caused by shallow tunnelling. Direction and magnitude of displacement vectors from the model test were identical to the result of numerical analysis based on the model data. In particular, it is shown that the vector direction was toward a point below the tunnel invert level. A narrow "chimney or tulip like" pattern of vertical displacement was confirmed by both the model test and numerical analysis. This behaviour is consistent with the field data. In addition to the qualitative comparison, the quantitative result of subsurface settlements according to 2D volume loss showed good agreement between the model test and numerical analysis. Therefore, close range photogrammetric technique applied in the model test may be used to validate the result from the continuum numerical analysis.

Dynamic Behaviour of Granular Meterial during the Rapid Motion (급속운동을 하는 입자물질의 동적거동)

  • Hwang, Hak
    • Geotechnical Engineering
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    • v.10 no.4
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    • pp.103-118
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    • 1994
  • The rapid motion of granular material is microscopically observed, and investigated by continuum theory. From the binary collision phenomenon two different times are introduced : flying time and contact time. The former says the non -stationary motion and at a same time the variation of bulk volume. The latter is operative by a delayed time during the contact and describes the elastic properties of granular material. With both times a dynamic constitutive equation is postulated for four state variables : dispersive pressure, viscosity, thermal diffusivity and energy annihilation rate. The balance laws of mass, momentum and energy which are represented through above four variabls, are applied to the model, in which due to the elastic property the relaxation and energy absorption are explained.

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