Hydromechanical Properties of a Leachate Contaminated Tuff/Sandy Soil/Bentonite Mixture

An empirical study on the chemical characteristics, swelling characteristics, mineralogical characteristics, hydraulic conductivity, shear strength and unconfined compressive strength of compacted tuff /sandy soil/bentonite mixtures used as landfill lining is presented in this paper. Landfill leachate was used to determine the effect of pollution on the parameters of these mixtures for each experiment. To carry out this study, three materials, including bentonite and two types of soils, namely tuff and sandy wastes (crushed sand), were collected in the Laghouat - South Algerian region. A study of the geotechnical properties of all selected materials and mixtures was initially performed. X-ray diffraction (XRD) results showed that the dissolution of minerals and montmorillonite content modified by landfill leachate decreased swelling characteristics and slightly increased saturated hydraulic conductivity. The pH and electrical conductivity measurements of leachate contaminated mixtures revealed a decrease in pH values and an increase in electrical conductivity values. In terms of shear strength, it increased with increased crushed sand content. The shear strength of the previously contaminated optimal mixture showed an increase in cohesion (C_uu) and a decrease in the friction angle (φ_uu). The results of unconfined compressive strength at the age of 90 days reached 1400 kPa for mixtures containing 70% and 80% tuff. This strength develops with increased deposition of cementitious materials (CaCO₃). In addition, the unconfined compressive strength of the contaminated mixture was increased. According to the results, the mixture of 10% bentonite/20% crushed sand/70% tuff responds to the structural criteria for compacted soil liners.