Deformation and hydraulic conductivity of compacted clay under waste differential settlement

Abstract

Landfill is still the most important process to dispose of municipal solid waste in China, while landfill closure aims for pollution control, security control, and better land reuse. However, uneven settlement of landfill cover system is very likely to cause deformation and cracking. The objective of this paper is to examine the effects of geogrid reinforcement on the deformation behaviour and hydraulic conductivity of the bentonite-sand mixtures that are subjected to differential settlement. The laboratory model tests were performed on bentonite-sand mixtures with and without the inclusion of geogrid reinforcement. By maintaining the type and location of the geogrid within the liner systems as constant, the thickness of the bentonite-sand mixtures is varied. The performation of the liner systems with and without the inclusion of geogrid reinforcement was assessed by using jack to control differential settlement. Un-reinforced bentonite-sand mixtures of 100 mm and 200 mm thickness were observed to begin cracking at settlement levels of 2.5 mm and 7 mm, respectively. When settlement reached 25 and 42.5 mm, cracks for 100 mm and 200 mm thick bentonite-sand mixtures without geogrid penetrated completely. The settlement levels for bentonite-sand mixtures of 100 mm thickness with and without geogrid reinforcement was found to be 10 mm and 15 mm, respectively, when its hydraulic conductivity was around 5 * 10-7 cm/s. In comparison, geogrid reinforced bentonite-sand mixtures was found to sustain large deformation with an enhanced imperviousness. The results from the present study can provide theory evidence of predicting deformation and hydraulic conductivity of the landfill cover system.