Study On Barrier Mechanism And Function Enhancement Of Covering System For Organic Industrial Polluted Sites

This paper aims to address the limitations of traditional compacted clay covers,such as water loss and cracking in high temperatures during summer and insufficient gas pollution barrier performance.The study explores innovative barrier materials,construction techniques,and field demonstrations to overcome these drawbacks.Detailed investigations were carried out on water retention properties,barrier and crack inhibition mechanisms of the new materials,and their performance was confirmed through on-site experiments.Additionally,a construction process was established.The main research findings are summarized as follows:（1）This study aimed to identify the factors controlling the gas barrier performance of compacted clay through on-site experiments.Results revealed that water content,compaction,and vegetation type significantly influenced the gas barrier performance of compacted clay.The gas diffusion coefficient of compacted clay exceeded 10^-6 m²/s,failing to meet the required standard,when the water content was below 20.5%.Additionally,cracks appeared in the compacted clay cover when the compaction was less than 87%,with Conyza Canadensis and Paspalum being the corresponding vegetation distribution,and the maximum crack depth was10 times greater than that of the Bermuda grass site.（2）Four types of polyacrylamides,namely cationic,anionic,zwitterionic,and nonionic,were screened for improving the water retention performance of compacted clay through laboratory experiments.The results showed that the anionic polyacrylamide was the most effective at a dosage of 1.0%,with a water content increase of 1.1-1.2 times compared to other modified compacted clays.Additionally,the gas permeability test indicated that the addition of1.0%anionic polyacrylamide resulted in the lowest gas permeability of compacted clay,which was 0.6-0.9 times lower than that of other modified compacted clays.Furthermore,the anionic type had the most significant effect on the liquid limit of the soil,which was 1.03-1.3 times higher than that of other modified compacted clays.（3）This study aimed to investigate the mechanism by which anionic polyacrylamide enhances the water retention performance of compacted clay.Water holding capacity tests,soil cracking tests,and microscopic analyses were conducted.The results indicated that the addition of polyacrylamide increased the geometric shrinkage factor of the soil beyond 3,leading to anisotropy during soil shrinkage.However,the improved water retention performance mitigated soil shrinkage cracking.The intercalation effect of polyacrylamide was observed to increase the interlayer spacing of compacted clay,thereby enhancing its water retention performance.（4）The gas barrier performance of compacted clay improved with anionic polyacrylamide was further investigated by modifying it with activated carbon powder.The composite material was tested for its gas barrier performance through indoor experiments.The results indicated that bamboo activated carbon showed the highest adsorption capacity for phenol and improved the water retention performance of the soil.At a bamboo activated carbon dosage of 10%,the modified compacted clay no longer demonstrated significant increases in liquid limit and water holding capacity.Additionally,the gas permeability decreased by 1.67 times,while the gas diffusion coefficient decreased by 5 times.（5）Thermal insulation layer technology was proposed to enhance the water loss cracking resistance of compacted clay covers through material selection and thickness optimization.Numerical simulations indicated that using thermal insulation materials could effectively reduce soil temperature,with extruded polystyrene displaying the best thermal insulation performance.The temperature of the soil with the thermal insulation layer was reduced by 30%,and the moisture content increased by 1.0-1.5%,resulting in a five-fold decrease in water loss rate compared to compacted clay without a thermal insulation layer.The thermal insulation efficiency of the material increased initially and then decreased with increasing thickness,with extruded polystyrene insulation boards showing the highest thermal insulation efficiency at a thickness of 30 mm.（6）After conducting field demonstration research,a construction procedure was developed to improve the performance of compacted clay cover.In-situ testing and indoor sampling revealed that incorporating composite materials in the modified compacted clay resulted in a two-order-of-magnitude reduction in the saturation permeability coefficient and gas diffusion coefficient,measuring 5.8×10^-10 m/s and 7.8×10^-8 m²/s,respectively,compared to conventional materials.Furthermore,the use of a thermal insulation layer was found to effectively attenuate temperature variations of the compacted clay.The insulating effect of the compacted clay was ten times better than without a thermal insulation layer.The study also employed a long short-term memory network prediction method to accurately forecast the moisture content and temperature of the compacted clay with satisfactory precision and consistency.