Seismic response of bentonite enhanced soils to be used as fabricated liner in engineered landfills

Abstract

Earthquakes are one of the most severe natural disasters that are responsible for significant damage to structures causing vertical settlements, lateral spreads and tipping of buildings. Solid waste landfills can also be seriously affected by seismic activity. In landfills, liners of low permeability material are used to arrest the leachate. If the landfills are located in regions of high seismicity, the fabricated liners may be susceptible to damage. Generally, cohesionless soils are considered to be vulnerable to damage caused by earthquakes. Also, evidence of sandy soils with a substantial amount of fines being prone to liquefaction is available in the literature. If cracks develop in the liner, the whole purpose of engineered landfill gets defeated and all the investment incurred towards the landfill would go in vain. This paper aims at understanding the behaviour of landfill liner systems subjected to static and dynamic loading with emphasis laid on ascertaining the effect of adding plastic fines (bentonite) to the cyclic resistance of liquefiable sands and coal ash. The stress-controlled undrained cyclic triaxial tests were carried out at a frequency of 1 Hz and initial effective confining pressure of 150 kPa on soil specimens with 70 mm diameter and 140 mm height. It was observed that pore water pressure generated in sand-bentonite mixes with 10% bentonite is high and slowed down thereafter upon an increase in bentonite content up to 20% in the soil mix resulting in the increased cyclic resistance. The number of cycles required for initial liquefaction were quite less in coal ash, as compared to clean sand. It was found that coal ash is more susceptible to liquefy in comparison to sand.