Effect of salt permeants on the consolidation and hydraulic behaviour of fibre treated black cotton soil for landfill application

Abstract

Clay liner functions as an impermeable barrier between leachate and groundwater in landfills. In this work, naturally available black cotton (BC) soil is adopted as a liner material due to its high swelling and low hydraulic conductivity, which helps to eliminate the risk of groundwater pollution by preventing pollutant mobility. The liner's potential is threatened by two issues: shrinkage cracks and chemical attacks. BC soil induces desiccation cracks and high compressibility due to its high shrinkage potential upon drying, which severely impacts its hydraulic conductivity behaviour. In recent years, fibres have been used as reinforcing materials to control compressibility and shrinkage cracks of the liner. In this investigation, waste tire fibres, which were used as a reinforcing material, mixed with BC soil in the proportion of 5, 10 and 15% by their dry weight. Since the essential parameters of liner would change due to the interaction of chemicals in leachate, hence, this study examined the consolidation and hydraulic properties of fibre mixed BC soil in the presence of two inorganic salt permeants (NaCl and CaCl2) of two concentrations (0.1 and 1N) to mimic the leachate effect. The results revealed that when salt solutions were utilised as saturating pore liquids, the time to achieve the 90% of consolidation (t90) of fibre-treated BC soil was decreased, thereby increasing the coefficient of consolidation (cv). These changes were more significant at higher concentrations of pore liquids. The t90 value for 15% fibre-treated soil with DI water is 27.0 min, and it decreased drastically to 0.8 min (97.0% reduction) for 1N NaCl solution and 0.6 min (97.8% reduction) for 1N CaCl2 solution at the higher consolidation pressure of 784.5 kPa. Compression index (Cc) and void ratio (e) were reduced with the salt permeants irrespective of the fibre content. Finally, it was shown that salts substantially impact the hydraulic conductivity values of fibre-treated soil and that up to 10% fibre content is appropriate for landfill liner application.