Hydro-mechanical numerical modelling of geotechnical problems using local second gradient models

peer reviewedThe paper presents some applications of a local second gradient theory used to describe the mechanical behavior of a continua. This theory has been developed in order to avoid some well known drawbacks of classical theories, when softening and/or localization occur in a computation. This theory is extended and then applied in a hydromechanical coupled problem, in the case of fully saturated geomaterials. The corresponding finite element method taking into account the geometrical non linearities is detailed. Preliminary results using the finite element code developed in this context are then discussed and allow to study post localization behavior

A finite element method for poro mechanical modelling of geotechnical problems using local second gradient models

In this paper, a new finite element method is described and applied. It is based on a theory developed to model poromechanical problems where the mechanical part is obeying a second gradient theory. The aim of such a work is to properly model the post localized behaviour of soils and rocks saturated with a pore fluid. Beside the development of this new Coupled theory, a corresponding finite element method has been developed. The elements used are based on a weak form of the relation between the deformation gradient and the second gradient, using a field of Lagrange multipliers. The global problem is solved by a system of equations where the kinematic variables are fully coupled with the pore pressure. Some numerical experiments showing the effectiveness of the method ends the paper. Copyright (c) 2005 John Wile

Permeability evolution and water transfer in the excavation damaged zone of a ventilated gallery

peer reviewedThe fluid transfers occurring around underground galleries are of paramount importance when envisaging the long-term sustainability of underground structures for nuclear waste disposal. These transfers are mainly conditioned by the behaviour of the surrounding material and by its interaction with the gallery air. The hydro-mechanical behaviour of the excavation damaged zone, which develops around galleries due to the drilling process, is thenceforward critical because it is composed of fractures having a significant irreversible impact on flow characteristics and transfer kinetics. Besides, the material interaction with the gallery air may engender water drainage and desaturation. Thus, a gallery air ventilation experiment, preceded by its excavation, is numerically modelled in an unsaturated argillaceous rock to study its influence on hydraulic transfers. The fractures are numerically represented with shear strain localisation bands by means of a microstructure enriched model including a regularisation method. The impact of fracturing on the transport properties is addressed by associating the intrinsic permeability increase with mechanical deformation which is amplified in the strain localisation discontinuities. Such dependence permits us to reproduce a significant permeability increase of several orders of magnitude in the excavation damaged zone, in agreement with available experimental measurements. After the excavation, the hydraulic transfers are studied through the reproduction of a gallery air ventilation experiment that implies drainage and desaturation of the surrounding rock. These transfers depend on liquid water and water vapour exchanges at gallery wall that are introduced through a non-classical boundary condition. The model prediction successfully captures the drainage and desaturation kinetics of undisturbed and damaged rock

Implementation of path following techniques into the finite element code LAGAMINE. Part II: Material non linearity

This short report concerns the second part of the work performed in ArGEnCo in order to implement advanced incremental-iterative solution techniques into the finite element code LAGAMINE for geometrical and phys- ical non-linear problems. More specifically, it deals with the implementation of a convergence criterion suitable for material non linearity and the validation of the approach on a Brazilian test on a concrete specimen

Memory and feeling of pastness

The aim of this paper is to provide an answer to the following question: How is it that content that is produced in the present can be attributed to the past? According to behavioral data and the active inference framework, we have developed the idea that the feeling of pastness is rooted in both an attribution process and an inference that originates from the phenomenological feeling accompanying any cognitive processing. More precisely, we propose that the feeling of pastness arises from an inference made to resolve the perception of a change in the phenomenological experience or fluency associated with the ongoing process, even when this process is not directly related to the stimulus being judged

Numerical modeling of 3 point bending test of a reinforced concrete beam using a second gradient theory

Being a quasi-brittle material, concrete exhibits a strain softening behavior that cannot be reproduced with classical continuum mechanics models. To regularize the problem, an internal length should be introduced. Several ways to do so have been proposed in the literature. One way is the so called local second gradient model. It is a local theory as it introduces the internal length by enriching the kinematical description of the continuum adding higher order gradients of the displacement according to the work of Cosserat [8], Toupin [18], Mindlin [19] and Germain [9,10]. The model has been developed by Chambon et al. [11,12] and has this far been used mainly to reproduce the behavior of soils. It is here applied for the first time to a reinforced concrete beam subjected to a 3 point bending test

Bending tests on reinforced concrete beams: numerical modelling using a second gradient theory

Being a quasi-brittle material, concrete exhibits a strain softening behavior that cannot be reproduced with classical continuum mechanics models. To regularize the problem, an internal length should be introduced. Several ways to do so have been proposed in the literature. One way is the so called local second gradient model. It is a local theory as it introduces the internal length by enriching the kinematical description of the continuum, adding higher order gradients of the displacement according to the work of Cosserat [1], Toupin [2], Mindlin [3] and Germain [4,5]. The model has been developed by Chambon et al. [6,7] and has this far been used mainly to reproduce the behavior of soils. It is here applied to two bending tests of reinforced concrete beams