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Monitoring of the progressive convergence of a tunnel shows that deformations occurring in the soil surrounding a tunnel exhibit a strong evolution with time. This time-dependent behaviour can be linked to three essential factors: the... more
Monitoring of the progressive convergence of a tunnel shows that deformations occurring in the soil surrounding a tunnel exhibit a strong evolution with time. This time-dependent behaviour can be linked to three essential factors: the distance from the point of interest to the working face over time, the distance of unsupported tunnel to the working face and the viscous properties of the soil.The objective of this paper is to propose a constitutive model of the time-dependent behaviour of soil which has been developed within the framework of elastoplasticity–viscoplasticity and critical state soil mechanics. The consideration of viscoplastic characteristic sets the current model apart from the CJS (Cambou, Jafari and Sidoroff) model as the basic elastoplastic model, and introduces an additional viscous mechanism. The evolution of the viscous yield surface is governed by a particular hardening called ‘viscous hardening’ with a bounding surface.The proposed constitutive model has been applied in the analysis of tunnelling. Two kinds of numerical calculations have been used in the analysis, axisymmetric analysis and plane strain analysis. Monitoring of the progressive convergence of a tunnel conducted in the railway tunnel of Tartaiguille (France), has been used to describe the calculation procedure proposed and the capability of the model.The finite difference software, fast Lagrangian analysis of continua (FLAC), has been used for the numerical simulation of the problems. The comparison of results shows that the observed deformations could have been reasonably predicted by using the constitutive model and calculation strategy proposed. Copyright © 2004 John Wiley & Sons, Ltd.
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A global constitutive model for granular material can be obtained from a change of scale using a statistical homogenization procedure. This kind of approach uses various operators for the change of scale. This paper presents the... more
A global constitutive model for granular material can be obtained from a change of scale using a statistical homogenization procedure. This kind of approach uses various operators for the change of scale. This paper presents the difficulties encountered to define all these operators and analyzes the validity of the relations proposed in the literature. These different analyses are based on the results obtained from a 2 D numerical simulation using the DEM.
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The homogenization techniques allow the macroscopic constitutive equations of a given material to be derived from its microscopic behaviour. The case of granular material is difficult because the microscopic level must be described in... more
The homogenization techniques allow the macroscopic constitutive equations of a given material to be derived from its microscopic behaviour. The case of granular material is difficult because the microscopic level must be described in discrete terms (contact forces and relative displacements). The present paper is devoted to a general discussion of this problem and to a presentation of different models of granular homogenization. Since we shall primarily be concerned with methodological issues and with comparison to the standard microcontinuous case, attention will be focussed on the simplest case of micro-elasticity assuming a linear contact law.
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In this paper a macroscopic elastic model is derived from a microscopic Hertz-Mindlin elastic contact law using an homogenisation technique. The results obtained in the case of an initially isotropic granular medium submitted to an... more
In this paper a macroscopic elastic model is derived from a microscopic Hertz-Mindlin elastic contact law using an homogenisation technique. The results obtained in the case of an initially isotropic granular medium submitted to an isotropic stress state are first presented. The influence of the static and kinematic internal variables defined in the homogenisation approach is then discussed. Extensions to
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... At present, the description of the behavior of cohesionless soil is not sufficiently realistic and accurate in complex loadings, especially with reorientation ... 11 ROWE PW (1969) "The relation between the shear strenght of... more
... At present, the description of the behavior of cohesionless soil is not sufficiently realistic and accurate in complex loadings, especially with reorientation ... 11 ROWE PW (1969) "The relation between the shear strenght of sands in triaxial compression, plane strain and direct shear ...
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This paper is dedicated to the analysis of the local phenomena which give rise to anisotropy in granular materials. This anisotropy can be observed for small strains (“elastic strains”) as well as large irreversible strains (“plastic... more
This paper is dedicated to the analysis of the local phenomena which give rise to anisotropy in granular materials. This anisotropy can be observed for small strains (“elastic strains”) as well as large irreversible strains (“plastic strains”). Elastic anisotropy appears to be due to the distribution of contacts, the shape of particles and the non-linear local contact law. Anisotropic non-reversible
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An elastoplastic-viscoplastic constitutive model for soils is presented in this study, based on an original approach concerning viscous modelling. In this approach, the viscous behaviour is defined by internal viscous variables and a... more
An elastoplastic-viscoplastic constitutive model for soils is presented in this study, based on an original approach concerning viscous modelling. In this approach, the viscous behaviour is defined by internal viscous variables and a viscous yield surface. The model has been developed from a basic elastoplastic model (CJS model) by considering an additional viscous mechanism. The evolution of the viscous yield
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This paper analyzes relationships allowing global variables to be deduced from local ones in granular materials. This change of scale is now clear for static variables but rather confusing for kinematic variables. This paper compares the... more
This paper analyzes relationships allowing global variables to be deduced from local ones in granular materials. This change of scale is now clear for static variables but rather confusing for kinematic variables. This paper compares the various established formulations for kinematic variables and also proposes original formulations. By running numerical simulations all the formulations in question are compared and the
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... i; and a' influence the first part of the response (Figure 6). Each load step was simulated using small time increment. ... The Authors are grateful for this support and thank Costaz J, L., Bufi G, and Catel P. for permission to... more
... i; and a' influence the first part of the response (Figure 6). Each load step was simulated using small time increment. ... The Authors are grateful for this support and thank Costaz J, L., Bufi G, and Catel P. for permission to publish the data. ...
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