Stability of an open dumpsite with ageing

Abstract

Open dumping is the most commonly used method adopted in Sri Lanka as solid waste management. However, slope failures of open dump sites lead to environmental pollution as most of the open dumps are located near water bodies. Therefore, analysing the stability of open dumps is important in implementing mitigatory measures where required. Abandoned Udapalatha open dump site which is located near Gampola, Sri Lanka was considered as a case study to analyse the stability of its slopes consisting of old and new waste representing different degrees of decomposition. Shear strength parameters of the waste samples of the old and new waste sites were determined using box samples at different depths with particle size less than 9.5 mm. Specific gravity test, Oedometer test and Standard Proctor compaction test were performed to obtain Gs, primary and secondary consolidation parameters, maximum dry density and the optimum moisture content. In addition, direct shear test was carried out to determine the shear strength parameters of the fill. Slope stability analysis was carried out using Slope/W and Plaxis-2D software considering Mohr Coulomb and soft soil creep models respectively for waste material. Consideration of primary and secondary consolidation settlement within the landfill in the Plaxis-2D analysis resulted in an increase in the Factor of safety (FOS). Therefore, FOS values obtained from the slope stability analysis of the old site, was higher than that in the new waste site.