No abstract

No abstract

No abstract

Geosynthetic clay liners (GCLs) are used in landfill liner applications due primarily to their low hydraulic conductivity to water. The low hydraulic conductivity of GCLs comes from the structure of the clay in the bentonite. However, the interaction between clay and aggressive liquids may alter the structure of the clay and, thus, result in an increase in the hydraulic conductivity of the GCL. This paper presents the results of a project aimed at evaluating the impact of a synthetic leachate on the structure of four different bentonites used in the manufacturing of GCLs. The preparation of bentonite dispersions increased the interaction between the bentonites and the various liquids. The hydraulic properties of the dispersions also were tested using filter press tests to obtain flow curves. Results of these tests were correlated with the cationic concentration, electrical conductivity and pH of the 2 / 46 dispersions, swell indexes of the bentonite extracted from the GCLs, and permittivities of the intact GCLs determined in oedopermeameter tests. The results showed that one bentonite was more sensitive to the synthetic leachate than the other bentonites. For example, the permittivities of the more sensitive bentonite based on the oedopermeameter tests and filter press tests were respectively 2.11x10 -8 s -1 and 5.6x10 -8 s -1 , whereas the permittivities for other bentonites, including a natural sodium bentonite and two sodium activated calcium bentonites, were respectively 5.7 to 6.5x10 -9 s -1 and 3.2 to 3.5x10 -8 s -1 . The filter press test served as a quick and easy-to-use test to compare the performance of the various bentonites in containing a given liquid. However, the oedopermeameter test or direct permeation test is preferable to filter press tests or fluid loss tests for evaluating the long-term impact of a liquid on a bentonite.Keywords: bentonite, cation exchange, permittivity, synthetic leachate. INTRODUCTIONGeosynthetic clay liners (GCLs) generally consist of a layer of granular or powdered bentonite sandwiched between two geotextiles, linked by needle punching or stitch bonding.Bentonite has been widely studied, and consists of a mixture of minerals, with the predominant mineral being smectite (van Olphen, 1977;Patterson and Murray, 1983).However, the quality of bentonites used in GCLs for landfill applications may vary widely.The smectite mineral imparts to the bentonite its swelling properties and its low hydraulic conductivity. For landfill bottom liner applications in France, sodium bentonite is recommended for use in GCLs, meaning that sodium ions are the predominant exchangeable cations of the bentonite (MEEDDAT, 2008). The existence of sodium as the exchangeable cation may be the result of natural geological processes, as typically the case for Wyoming 3 / 46 sodium bentonites, or the result of an activation process whereby naturally occurring calcium bentonite is mixed with soda ash to force sodium-for-calcium cation exchange. These latter bentonites are often called sodium-activ...

No abstract

This paper focuses on the use of free–free resonance testing (FFR testing) applied to the characterization of stabilized silt and sand specimens treated in situ by deep soil mixing. The aim of FFR testing is to measure the natural frequencies of free vibration of the tested specimen. Compression and shear wave velocities, seismic moduli and Poisson’s ratio can be determined from these frequencies. Block samples were taken from soil–cement columns installed at a test site near Paris, France. Specimens of 100 by 50 mm (height to diameter ratio of 2) were cored from these blocks and submitted to FFR testing in the laboratory. The measured resonant frequencies were very repeatable for all specimens tested, validating the use of free–free resonance as a rapid testing method for the characterization of fairly heterogeneous stabilized soil specimens. It was found that both P-wave and S-wave velocities increase nonlinearly with unconfined compressive strength. A linear correlation between strength and dynamic stiffness was observed. Free–free resonance test results can be correlated with index parameters such as density and porosity and used for preliminary assessments of static stiffness as all these parameters varied linearly with measured wave velocities.

No abstract

Coastal erosion results from a combination of various factors, both natural and humaninduced, which have different time and space patterns. In addition, uncertainties still remain about the interactions of the forcing agents, as well as on the significance of non-local causes of erosion. We focused about the surface sediments in the Marennes Oléron bay, after a general description of the site that has many various activities. The superficial sediments show a mechanical behavior, mainly depends on the fine fraction for a composition that contains up to 60% of sandy material. Fine sediments fraction has a typical yield stress depending naturally of concentration or water content. This yield could be modified slightly or significantly by adding silt or sand. As a result, the rheological measurement sensitivity allows us to characterize five typical sediments that correlate with solid fraction and fine fraction.