Effect of landfill leachate on the hydromechanical behavior of bentonite-geomaterials mixture

Abstract

The paper presents an experimental study on the compressibility, conductivity hydraulic (ksat) shear strength, unconfined compressive strength, and unconfined tensile strength and chemical characteristics of compacted bentonite- geomaterials mixtures for use as landfill bottom liners. To complete each experiment, MSW landfill leachate was used to determine the stress of strength under the effect of pollution on the mineralogy of the optimal mixture (the least permeable mixture). All three materials used in this study, including bentonite and two types of geomaterials (tuff and calcareous sand (crushed sand)) were obtained in the Laghouat, South Algeria, region. First, a study of the geotechnical properties of all selected materials and mixtures (under the effect of leachate) was carried out. A mineralogical survey was also conducted on these three materials to better understand the experimental results obtained. Measurements of the pH and EC of leachate-contaminated mixtures indicated a decrease in pH values and an increase in EC values. Interaction results of these mixtures with the MSW landfill leachate indicated that it reduces the compressibility behaviour, decrease the saturated hydraulic conductivity and increase the compressive strength and tensile strength. As for shear strength, an increase was observed in shear strength with an increase in calcareous sand content. The shear strength of the previously contaminated optimal mixture is shown an increase in the cohesion and a decrease in the friction angle. This observation was demonstrated by the Fang and Hirst (1973) method (Modified Mohr-Coulomb failure criterion). Finally, a consolidated drained study of the optimal mixture was carried out using a triaxial test. Results showed that the optimal mixture behavior is normally consolidated, and the internal friction angle value has attained 35°. It can be summarized that the 10% bentonite – 20% calcareous sand – 70% tuff mixture (named: B10CS20T70) meets the design requirements for landfill bottom liners.