Hydraulic conductivity of a dense prehydrated geosynthetic clay liner

Dense prehydrated geosynthetic clay liners (DPH-GCLs) are a particular type of GCL which, unlike conventional GCLs manufactured with dry bentonite, contain bentonite prehydrated during manufacturing. DPH-GCLs are produced by a patented process that includes bentonite prehydration with a polymer solution and vacuum extrusion. This paper describes the results of permeability tests that were carried out using flexible-wall permeameters to investigate the hydraulic conductivity of a DPH GCL to water, natural seawater and a 12.5mmol/L CaCl2 solution. Moreover, the efficiency of the 0.1 m overlap seams between DPH-GCL panels has been investigated by means of a medium-scale permeameter able to accommodate specimens 0.305 m in diameter. Test results showed that the DPH GCL has very low hydraulic conductivity to water (1

Hydraulic conductivity of a dense prehydrated GCL: impact of free swell and swelling pressure

Exposure to liquids with high electrolyte concentrations or high cation valence present in landfill leachates can cause significant increases in hydraulic conductivity of clays due to a reduction in the thickness of the double layer. Methods to prevent compression of the interlayer are: prehydration of the bentonite, compression with increasing the solids content and addition of polymers. The aim of this study is to evaluate the performance of a dense prehydrated GCL (DPH GCL) compressed during manufacturing and pre-hydrated with a polymeric solution. A series of hydraulic conductivity tests with deionised water, sea water and a 0.01 M CaCl 2 solution were performed on single sheet and overlapped DPH GCL samples. Free swell and swelling pressure tests have also been performed with this solutions and with a series of KCI and CaCl 2 solutions with a concentration varying from 0.001 M to 1 M. The overlapped samples were analysed in large scale laboratory permeameters at different effective stresses. In addition, swelling pressure tests on single sheet samples were conducted to analyse the swelling behaviour of the factory prehydrated GCL. The concomitant effect of prehydration, addition of polymeric compounds and densification increased the hydraulic performance of GCLs under aggressive conditions. The use of bentonite paste to seal the overlap in presence of seawater was shown to be crucial. The swelling pressure test may be proposed as an alternative to the swell index test to characterize the swelling behaviour of polymer prehydrated GCLs

Determination of consistency limits of clay by means of extrusion tests

The liquid limit of clay is commonly determined through the Casagrande test or the fall-cone test, while the plastic limit is determined through the hand rolling method. The greatest issue with some of these techniques is their low repeatability and operator dependency. In order to minimize those issues, an indirect-extrusion based technique was evaluated as an alternative method to determine both consistency limits. The experimental work was carried out on mixtures of kaolin and bentonite to cover a wide range of plasticity. The results suggested that there is a specific extrusion pressure linked to each consistency limit and that the results are repeatable. The liquid limit obtained through the extrusion method closely matches the results of the fall-cone test. Similarly, the plastic limit out of extrusion closely matches the results of the hand rolling method

Hydraulic conductivity and swelling pressure of GCLs using polymer treated clays to high concentration CaCl(2) solutions

A Geosynthetic Clay Liner (GCL) is a frequently used h ydraulic barrier system designed to impede the flow of contaminated leachate into the environment. The main objective of this barrier system is to maintain a low hydraulic conductivity that is determined by the bentonite fraction. In this study, calcium bentonite, natural sodium bentonites, and sodium activated bentonite were treated with the HYPER clay technique. This involves the adsorption of an anionic polymer, Sodium CarboxyMethylCellulose (Na-CMC) onto the surface of the clay material. The purpose of this research was to show the beneficial effect of the HYPER clay treatment on the swelling and hydraulic performance, while the bentonite is permeated with high concentration CaCl2 solutions. The test results showed that swelling and hydraulic performance increased with Na-CMC treatment, regardless of the type of bentonite that was used. Additionally, a powdered Na CMC configuration provided higher swelling and hydraulic performance compared to a granular configuration

Preliminary test on modified clays for seawater resistant drilling fluids

The quality of a drilling fluid declines in salt water conditions. An engineered clay (HYPER clay) was developed for geosynthetic clay liners with enhanced resistance to aggressive conditions. This study investigates the potential of this superior clay for drilling fluids applied in salt water conditions. A sodium bentonite was treated with a carboxymethyl cellulose (CMC) polymer following the HYPER clay process method. Preliminary tests were performed to investigate suitability of HYPER clay for seawater resistant drilling fluids. Fluid performance was characterized by its thixotropic behavior, rheological properties (gel strength, yield point and viscosity), swell and bleeding behavior. Drilling fluid performance was analyzed at various polymer dosages and electrolyte concentrations. Polymer treatment improved the gel strength and swelling ability of the fluid, especially in electrolyte solutions. Moreover, filter press tests (API 13B-1, 76% seawater) showed that filtrate loss decreased due to polymer treatment