Assessment of dune sand-bentonite mixtures for use as landfill liners

This study investigates the potential use of dune sand-bentonite mixtures as landfill liners. Bentonite was added in percentages of 5 to 20%. The suitability of the sand-bentonite mixtures was evaluated in terms of hydraulic conductivity, swelling/shrinkage, compressibility and shear strength. The hydraulic conductivity of the dune sand-bentonite mixtures decreases with the increase in bentonite content in a power form. Beyond 15% of bentonite the rate of decrease is small. Acceptable values of hydraulic conductivity (< 10^-7 cm/sec) were obtained for a bentonite content of 10% and more. The swelling pressure (and swelling percent) increases substantially with the increase in bentonite content specially when the bentonite content increased beyond 15%. The linear shrinkage of the sand-bentonite mixtures increases with the increase in bentonite content. Below 15% of bentonite the swelling and shrinkage potentials are small. The compressibility parameters (i.e. the compression index (c_c) the recompression index (c_r) and the coefficient of consolidation (c_v) are practically constant with the bentonite content and are within the range reported in the literature for clays. The compressibility of sand-bentonite mixtures is generally small. The sand-bentonite mixtures possess both cohesion and angle of internal friction. The shear strength increases with the increase in bentonite content at low normal stresses and independent of bentonite content at higher normal stresses. The results of scanning electron microscope (SEM) were used to explain the mechanisms behind the variation of the above engineering parameters.