A vanishing diffusion process in unsaturated soils

A model for simulating water flow and air flow in unsaturated soils is presented herein. Drainage from a one-dimensional soil column is specifically investigated. A mathematical analysis of the equations reveals that, due to a vanishing diffusion process, the gradient of the water degree of saturation is infinite at the water table. Moreover, this discontinuity propagates at a velocity that satisfies a local non-linear equation involving only the properties of the material. A numerical simulation of this problem serves to confirm the results obtained.     

Macroscopic and Micromechanical Approaches to the Modelling of the Osmotic Swelling in Clays

The osmotic swelling in clays has been extensively studied at the physico-chemical scale. The present paper addresses the question of the modelling of this phenomenon from the mechanical point of view. First, the classical macroscopic thermodynamic framework for saturated porous continua is extended in order to take into account the solid-salt interaction through the concept of macroscopic activity coefficient of the salt. The micromechanical approach then incorporates this interaction through the concept of swelling pressure which is used for describing the internal forces in the fluid phase at the microscopic scale. The results of a physico-chemical theory for the solid-salt interaction, such as the e.d.l. theory, can be introduced in both approaches. Each of them leads to the identification of a deviation, of chemical origin, to Terzaghi's effective stress principle. Besides, the micromechanical approach allows us to clearly differentiate the mechanical and the chemical parts of clay materials elasticity.     

Determination of liquid water content and dielectric constant in porous media by the capacitive methodDétermination,par la méthode capacitive,de la teneur en eau liquide et de la constante diélectrique dans un milieu poreux

A capacitive sensor-based apparatus has been settled to determine the liquid water amount and dielectric constant in consolidated porous media. This technique relies on the dielectric properties of water, air, and mineral substrate. The experimental procedure is described for successively oven-dried samples at 323 K. It allows us to determine the sample dielectric constant as a function of the sample water amount. For limestones from Caen region, an affine relationship is found at 293 K. This is then compared with other empirical soils data and with existing homogeneisation techniques applied to undeformable heterogeneous dielectrics. To cite this article: T. Fen-Chong et al., C. R. Mecanique 332 (2004).     

Adsorption and strain: The CO2-induced swelling of coal

Enhanced coal bed methane recovery (ECBM) consists in injecting carbon dioxide in coal bed methane reservoirs in order to facilitate the recovery of the methane. The injected carbon dioxide gets adsorbed at the surface of the coal pores, which causes the coal to swell. This swelling in confined conditions leads to a closure of the coal reservoir cleat system, which hinders further injection. In this work we provide a comprehensive framework to calculate the macroscopic strains induced by adsorption in a porous medium from the molecular level. Using a thermodynamic approach we extend the realm of poromechanics to surface energy and surface stress. We then focus on how the surface stress is modified by adsorption and on how to estimate adsorption behavior with molecular simulations. The developed framework is here applied to the specific case of the swelling of CO₂-injected coal, although it is relevant to any problem in which adsorption in a porous medium causes strains.     

Effects of surface irregularities upon the dynamic response of bridges under suspended moving loads

The effects of surface irregularities upon the dynamic response of bridges under suspended moving loads is analyzed by means of a theoretical study. The paper deals with geometrical imperfections of two types, global and local ones. The former may represent irregularities due to permanent loads, creep process or deflections produced by prestressing forces acting on young concrete. The local ones may represent the initial joint or local defects. The vehicle dynamics model is a simple degree of freedom oscillator and the method of analysis used is a Rayleigh-Ritz one. In some cases the amplification factors are found to be much greater than those given by current international design codes and the dynamic effects can no longer be neglected.     

A general theory of thermoporoelastoplasticity for saturated porous materials

A general theory of thermoporoelastoplasticity for saturated porous materials is presented. The theory is derived from the thermodynamics of open systems and irreversible processes. The thermal effects, due to the saturating fluid, are taken into account through a latent heat associated with the increase of fluid mass content. The theory does not assume incompressibility nor infinitesimal displacements for the saturating fluid. To take into account the plastic compressibility of the skeleton, the notion of plastic porosity is introduced. This plastic porosity is different from the overall plastic dilatation. The usual isothermal phenomenological theories appear to be particular cases of the proposed general theory.     

Crystallization,pore relaxation and micro-cryosuction in cohesive porous materials

A poro-elastic analysis is undertaken to account for the pressure time history of water-infiltrated pores within a material subjected to freezing. The thermodynamic-mechanical equilibrium of undercooled water and ice crystal, and Poiseuille-like flow through the connection channels, combine to reveal three successive mechanisms: in-pore crystallization, in-pore partial melting and a micro-cryosuction process, driving liquid water from the yet unfrozen pores to the frozen sites. The model turns out to be apt to predict the macroscopic relaxation process observed at the onset of crystallization as reported in the literature for cement-based materials. To cite this article: O. Coussy, T. Fen-Chong, C. R. Mecanique 333 (2005).     

Scattering of elastic waves by an inclusion with an interface crack

A method of perturbation is used to derive an integral representation of the displacement field for the scattering of a plane wave from an inclusion with an interface crack. In the long-wave approximation it is shown that the solution of only an associated static problem is required and formal expressions are derived for the scattered far field amplitudes and scattering cross section. In the case of a cylindrical inclusion the solution of the associated static problem is then used to find in a closed form the corresponding expressions for plane incident P- and S-waves.     

Non-Linear Binding and the Diffusion–Migration Test

In this paper we investigate the non-linear binding effects upon the diffusion–migration test. For the diffusion test we derive the conditions required for the non-linear binding isotherm to produce an actual penetration front. When more than two ion species are present we show that the diffusion coefficient associated with a particular ion cannot be extracted from the diffusion test on account of multi-species electrical effects. In the migration test where an external electrical field is applied to the sample, we give the conditions required for the propagation of a stable travelling wave. In addition new explicit expressions of the time-lag are obtained for both tests, allowing the determination of the properties of the unknown binding isotherm whatever its physical nature. Throughout the paper the results and the method are illustrated by the diffusion of the Cl^– ion within cement-based materials, using experimental data extracted from literature. The theoretical predictions compare well to these experimental data.