Compacted clay is an effective and economical engineering barrier for seepage prevention and gas blocking in landfills (including tailings pond, landfill, etc.). In addition to the lack of durability such as desiccation cracks of compacted clay modified by clinoptilolite and sodium polyacrylate, it is also necessary to consider the changes of engineering properties such as water holding capacity, water and gas resistance, and strength of compacted clay. Therefore, through oven evaporation test, flexible wall permeability test and unconfined compressive strength test, this paper studies the water retention, permeability and strength characteristics of compacted clay with different amounts of clinoptilolite and sodium polyacrylate. Orthogonal experiment L16(45) was used to optimize the amount of clinoptilolite and sodium polyacrylate and the compaction conditions, and further combined with the analytic hierarchy process (AHP), the factors affecting the water retention, permeability and strength of the compacted clay before and after the modification of clinoptilolite and sodium polyacrylate were discussed simply and quickly, and the applicability of the orthogonal experiment traditional analysis method and the analytic hierarchy process in the modified compacted clay of clinoptilolite and sodium polyacrylate was studied.
The gas diffusion/permeation and solution permeation dominant channels formed by desiccation cracks in compacted clay have become a significant hidden danger of environmental pollution. This study used clinoptilolite and sodium polyacrylate(Na-PAA) as a new water-retaining agent to enhance the water-holding capacity and impermeability. The primary and secondary order and optimal combination of all influencing factors, such as the replacement content of clinoptilolite (A), the content of Na-PAA (B), mixing moisture content(C), dry density(D) and curing age(E), were studied by orthogonal experimental. The results reveal that (1) The traditional analytical method and the Analytic Hierarchy Process (AHP) to obtain the optimal combination of unified A4B4C4D4E3, that is, replacement content of clinoptilolite, the content of Na-PAA, the mixing moisture content, dry density and curing age was 25%, 1.2%, 23%, 1.8g/cm3, and 14d, respectively. (2) For the multi-index test, the traditional analytical method just can obtain the factors order of a single index. And it is difficult to determine the comprehensive degree of each factor to multi-index. (3) The AHP to the quantitative calculation of each factor level index weights, the influence of all the factors on the multi-index integrated primary and secondary order. (4) the verification results show that we need to adjust the best combination of dry density ρd≥0.90×ρdmax, moisture content w=OMC+(0-4%).
Clinoptilolite and sodium polyacrylate (Na-PAA) were used as water-retaining agents to improve the water-holding capacity of compacted clay cover (CCC). The optimum moisture content and Atterberg limits of the CCC modified by clinoptilolite and Na-PAA were studied. The soil–water characteristic curve (SWCC) of the CCC modified by clinoptilolite and Na-PAA was studied. The mesostructure of the CCC was analyzed by polarized light microscopy. The test results show that: (1) the optimum moisture content and liquid limit of the CCC modified by clinoptilolite and Na-PAA increased, while the maximum dry density decreased; (2) the SWCC of the CCC modified by clinoptilolite and Na-PAA shifts to the upper right, and the volume moisture content of modified CCC is higher than that of unmodified CCC under the same matrix suction; (3) the air−entry value (AEV) of the clinoptilolite-modified CCC increased by 45.92%, and the Na-PAA increased the AEV of the clinoptilolite-modified CCC by about two times; and (4) the flocculation structure and porosity of modified CCC decreased, and the porosity was distributed uniformly.
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