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1

Particle shape effect on macroscopic behaviour of underground structures: numerical and experimental study

Szarf K., Combe G., Villard P.

Studia Geotechnica et Mechanica

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2014

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Vol. 36, nr 3

67--74

EN

The mechanical performance of underground flexible structures such as buried pipes or culverts made of plastics depend not only on the properties of the structure, but also on the material surrounding it. Flexible drains can deflect by 30% with the joints staying tight, or even invert. Large deformations of the structure are difficult to model in the framework of Finite Element Method, but straightforward in Discrete Element Methods. Moreover, Discrete Element approach is able to provide information about the grain–grain and grain–structure interactions at the microscale. This paper presents numerical and experimental investigations of flexible buried pipe behaviour with focus placed on load transfer above the buried structure. Numerical modeling was able to reproduce the experimental results. Load repartition was observed, being affected by a number of factors such as particle shape, pipe friction and pipe stiffness.

2

FEM x DEM modelling of cohesive granular materials: numerical homogenization and multi-scale simulations

Nguyen T. K., Combe G., Caillerie D., Desrues J.

Acta Geophysica

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2014

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Vol. 62, no. 5

1109--1126

EN

The article presents a multi-scale modelling approach of cohesive granular materials, its numerical implementation and its results. At micro-scopic level, Discrete Element Method (DEM) is used to model dense grain spacking. At the macroscopic level, the numerical solution is obtained by a Finite Element Method (FEM). In order to bridge the micro- and macro-scales, the concept of Representative Elementary Volume (REV) is applied, in which the average REV stress and the consistent tangent operators are obtained in each macroscopic integration point as the results of DEM’s simulation. In this way, the numerical constitutive law is determined through the detailed modelling of the microstructure, taking into account the nature of granular materials. We first elaborate the principle of the computation homogenisation (FEMDEM), then demonstrate the features of our multi-scale computation in terms of a biaxial compression test. Macroscopic strain location is observed and discussed.

3

DEM numerical analysis of load transfers in granular soil layer

Chevalier B., Combe G., Villard P.

Studia Geotechnica et Mechanica

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2008

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Vol. 30, nr 1-2

147-163

EN

Load transfers and other arching effects are mechanisms frequently met in civil engineering, especially in areas subject to karstic subsidence or in geotechnical earth structures such as piled embankments. The study proposed focuses on the numerical discrete analysis of granular material response submitted to specific boundary conditions leading to load transfer (embankment built overa trench or over a network of piles). The influence of several parameters has been studied: granular layer thickness, friction behaviour and particle shapes. Various load transfer mechanisms are observed, depending on the boundaries and also on the granular layer properties. The comparison between three-dimensional Discrete Element Modelling and analytical calculation methods leads to a various agreement, depending on the case treated.