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.
