The factors controlling the engineering properties of bentonite-enhanced sand

Abstract

This paper considers the engineering behaviour of bentonite-enhanced sand (BES) mixtures in relation to their performance as environmental barriers. Data on the swelling and hydraulic conductivity are presented. At low effective stresses the bentonite within BES mixtures swells sufficiently to separate the sand particles. In such states two factors affect the void ratio reached by the bentonite after swelling, the ionic concentration of the pore solution and the bentonite fabric after compaction. Bentonite swelling is very sensitive to the pore solution concentration because increasing concentration suppresses the diffuse double layer component of swelling. Remoulding during compaction can result in a slight reduction in bentonite swelling, probably because of disruption to the cluster-based fabric of bentonite. At high effective stresses the bentonite has insufficient swelling capacity to force the sand particles apart, and the sand pore volume thus limits swelling.A model to predict the swelling and hydraulic conductivity of BES in distilled water and various salt solutions is described. This model requires the swelling behaviour and hydraulic conductivity of the bentonite in the relevant solution, and the compressibility and porosity of the sand component as input parameters. Soil tortuosity is used as a fitting parameter, and is estimated from Archie's equation. Application of this model to the swelling of compacted mixtures is shown to produce a good fit with the experimental data.

Characterization and hydraulic conductivity of tropical soils and bentonite mixtures for CCL purposes

“…(1992), Sivapullaiah et al (1998), Stewart et al (2003), Ebina et al (2004), Komine (2004) and others. A different approach investigates the improvements on the mechanical and chemical strength of bentonities with polymers (for instance, Bohnhoff and Shackelford 2013).…”

Performance of polymer-enhanced bentonite–sand mixture for covering arsenic-rich gold mine tailings for up to 4 years

“…It may differ from the final official version of record. Stewart et al 2003;Gueddouda et al 2008;Dimitrova and Yanful 2012). This combination of properties is achieved by using a mixture that contains enough appropriately graded sand to increase the strength of the compacted mixture and enough bentonite to seal the voids in the sand matrix.…”

Natural smectitic soils for protective liners in arid climate

“…The density should be high for providing best possible tightness, but the high swelling pressure that goes with it can displace and degrade the overburden that is required for erosion protection. Both the content of expandable minerals (commonly montmorillonite) and the density must therefore be balanced to give optimum performance (Stewart et al, 2003). The water uptake of initially air-dry CCL can take place as finger-like flow paths (loose structure) or by diffusive migration (dense structure).…”