چكيده لاتين
Leachate from waste landfill sites is generated as a result of water infiltration into solid waste, oxidation of waste materials, and gradual degradation of waste. Unengineered landfill sites allow leachate to easily permeate soil layers, potentially affecting engineering properties of the soil such as shear strength, volume change, compressibility, swelling, and chemical properties like heavy metal adsorption and retention. This thesis closely examines the impact of leachate from the household waste landfill in Isfahan on the mechanical and physical properties of the surrounding soil. For this study, nine soil samples were collected from the vicinity of the landfill, both superficially and at depth, and after conducting various tests, the effect of leachate pollution on the soil was assessed. ICP tests were carried out on the soil samples to investigate the transport and fate of heavy metals. The results indicated pollution in areas close to the landfill at the surface level, which significantly decreased with increasing distance and depth, resulting in negligible changes in the soil. Notably, the accumulation of heavy metals such as arsenic, zinc, lead, mercury, copper, manganese, and cobalt was higher in sample S1 compared to other samples, and it even exceeded the permissible standard values for soil in Canada. Analysis of the geotechnical test results revealed that the soil contaminated with leachate experienced a reduction in strength, an increase in porosity and permeability, and a decrease in the Atterberg limits and compressibility coefficient. Leachate caused a reduction in the liquid limit and plasticity index of the soil in sample S1, while no significant changes were observed in samples S2 to S9, which could be attributed to variations in the thickness of the double-layer water and its contraction. The results of the compaction tests indicated that with the increase and accumulation of pollutants, the optimum moisture content increased, which was due to the contraction of double-layer water. This change was observed in sample S1, while no changes were noted in samples S2 to S9, with the maximum specific weight of sample S1 being 1.84 g/cm³, while the other samples ranged from 1.95 g/cm³ - 1.97 g/cm³. The increase in soil pollution led to an increase in its permeability, attributed to corrosion and increased soil porosity, with the permeability of sample S1 being 7.43 × 10⁻⁶, while the other samples ranged from 3.09 × 10⁻⁶ to 3.78 × 10⁻⁶. Analyzing the pressure and swelling parameters in the consolidation test revealed that the cited values decreased with increasing pollution, attributable to the contraction of double-layer water; however, these changes were only observed in sample S1, where the pressure coefficient was 0.09, while other samples ranged from 0.13 to 0.17, and the swelling coefficient in sample S1 was 0.015, while other samples ranged from 0.021 to 0.026. The values of soil resistance parameters such as cohesion in sample S1 were approximately reduced by 30-40% compared to other samples, although no significant changes were observed in the angle of friction. Microscopic images indicated an increase in soil porosity, which itself is a reason for fundamental changes in physical properties.
Leachate from waste landfills is generated as a result of water infiltration into solid waste, oxidation of the waste, and gradual corrosion of the waste. Landfill sites that are not properly designed allow leachate to easily penetrate the soil layers, which may affect the engineering properties of the soil, such as shear strength, volume change, compressibility, swelling, and chemical properties like the absorption and retention of heavy metals.
