Water retention in unsaturated soils subjected to wetting and drying cycles

The suction is an essential parameter to describe and understand the behavior of unsaturated soils. The ability of unsaturated soils to retain water is quantified by determining the water retention curves (WRC), which express the hydraulic behavior of porous materials such as soil. These curves are determined by subjecting samples to several drying and wetting cycles. The curve during drying path is located above the wetting curve, developing a hysteresis phenomenon [1], and value of content water at a given suction value depends on the path used to reach this point. The aim of this paper is to present a study on the hydraulic behavior of soil, water retention capacity due to drying and wetting cycles, pointing out the hydro-mechanical behavior of unsaturated soils. In the first part, the effect of physical and mechanical properties of soil [32] (initial void ratio, particle size, cohesion, density...) on the water retention is presented. In the second part, a complete numerical model was developed, based on the empirical model of Van Genuchten [18], to model the two boundary curves, and the experimental scanning data were bestfitted using the same theory of Mualem model [13]. This complete model requires 4 parameters. This model has been validated with experimental data on different type of soils: sand [10], [34], U.S. Silica F-95 sand [30]

Discrete element models for grain breakage

International audienc

Micro-macro Approaches Coupled to An Iterative Process for Nonlinear Porous Media

An iterative homogenization approach is proposed in order to predict the nonlinear hydro-mechanical behaviour of porous media. This process is coupled to classical and modified secant extended methods and linear homogenization predictive schemes. At convergence of the iterative process, same equivalent behaviour is obtained for any secant method, any simplified homogenization used for the linear comparison material and for any initial porosity of the media. An application to the study of the nonlinear behaviour of clayey sediments is presented. The model parameters quantification is based on oedometric experimental results for different clays

Hydraulic behaviour of activated calcium bentonite mixed with polyionic charged polymers for landfill and earthwork applications

This paper aims to study the hydromechanical behaviour and the clay polymer interaction of amended Cabentonite.Samples were formed by mixing of Ca-bentonite with two soluble polyelectrolyte polymer powders.Some important parameters are studied: swelling, water adsorption and hydraulic performance for landfill andearthwork applications. Tests are performed with tap water and synthetized leachate (SL) in order to reproducethe hydrochemical phenomena. Hydraulic performance tests were performed with an oedopermeameter.Tests results show that polymers tend to reduce the permeability, in contact with the SL. Water adsorptionand free swell index tests confirmed that adsorption, swelling and permeability parameters depend on the clay polymer mixtures and polymers adding improve the clay properties. Each polymer’s charges have a different effect: the anionic polymer gives a low permeability to the mixture; the cationic polymer enhances the bentonite swell ability and water retention which can be used also as performance index

The effect of fluid streams in porous media on acoustic compression wave propagation, transmission, and reflection

International audienceno abstrac

2D numerical investigations of twin tunnel interaction

The development of transportation in large cities requires the construction of twin tunnels located at shallow depth. As far as twin tunnels excavated in parallel are concerned, most of the cases reported in literature focused on considering the effect of the ground condition, tunnel size, depth, surface loads, the relative position between two tunnels, and construction process on the structural lining forces. However, the effect of the segment joints was not taken into account. Numerical investigation performed in this study using the FLAC3D finite difference element program made it possible to include considerable influences of the segment joints and tunnel distance on the structural lining forces induced in twin tunnels. The structural lining forces induced in the first tunnel through various phases are considerably affected by the second tunnel construction process. Their values induced in a segmental lining are always lower than those obtained in a continuous lining. However, the influence of joint distribution in the second tunnel on the structural forces induced in the first tunnel is insignificant. The critical influence distance between two tunnels is about two tunnel diameter