| Due to the low permeability,the soil-bentonite barrier shows a good application prospect in water and soil pollution prevention project in China.For soil-bentonite barrier,it is very important to select soil samples that have high fine particles content and are easy to be mixed with bentonite slurry as base soils.The waste soil is a kind of loose and homogeneous material with high fine particles content,which can be reused as backfilling material.However,oweing to the complex composition of waste soil,it is necessary to test and evaluate the water permeability of waste soil-bentonite barrier.In this paper,three kinds of waste soils(Huainan waste soil,Lvnong 1 waste soil and Lvnong 2 waste soil)were selected as base soils,and two kinds of bentonites(Wyoming bentonite and Gaomiaozi bentonite)were used as the research object.The water permeability of waste soil-bentonite backfill was tested and studied by means of laboratory scale test,field scale test and numerical simulation.The following research results were obtained:(1)Results of the backfill materials environmental geotechnical characteristics tests showed that the three kinds of waste soil were poor graded sand,and the heavy metals content didn't exceed risk control standard for soil contamination of development land,which meaned that the secondary contamination of heavy metals in waste soil can be neglected;Both Gaomiaozi bentonite and Wyoming bentonite were sodium-based bentonite,while the montmorillonite content(67.1%),CEC value(70.73cmol/kg)and swell index(8 mL/2g)of Gaomiaozi bentonite were significantly lower than Wyoming bentonite.(2)The effects of base soils type,bentonite content,type and mixing process on soil-bentonite permeability coefficient were studied by consolidation test and flexible wall permeability test.The test results indicated that when the content of Gaomiaozi bentonite reached 20%and the waste soils were pre-wetted,the waste soil-bentonite permeability coefficient was 1.1 × 10-7cm/s under 50 kPa consolidation stress;Reducing the particle size of base soil and utilizing base soil wetting process can improve the backfill water permeability:the permeability coefficient of soil-bentonite under base soil wetting process can reach 1/2 of that treated by traditional mixing method;When the content of Gaomiaozi bentonite was higher than 20%,the improvement effect on permeability coefficient of base soil wetting process was equivalent to that of increasing the content of bentonite under low consolidation pressure.However,when the consolidation pressure was high,increasing the content of bentonite was still better than that of base soil wetting process.(3)The microscale pore structure of backfilling under different mixing process was revealed by CT test,which determined the air-induced porosity of backfill.The air-induced porosity of backfill under base soil wetting process was the smallest(4.28%),while the mixing base soil directly with bentonite slurry process was the largest(6.73%),and the base soil and bentonite dry mixing process was centered(5.22%).(4)A field scale test of the waste soil-bentonite vertical barrier(length × width × height:8 m× 0.6 m × 9 m)was carried out in a simple landfill at Huainan.The construction process of waste soil-bentonite barrier for simple landfill was discussed and the performance was evaluated by numerical simulation:When waterhead was 8.7m and the wall embedding depth was 9m,the breakthrough time of waste soil-bentonite barrier was 9.25 years,in which the top part of barrier was breaked-through;When the waterhead decreased from 8.7m to 0.5m,the breakthrough time was prolonged for 153 years;Under 0.5m waterhead,the breakthrough time of soil-bentonite under base soil wetting process was prolonged for 23 years compared with that under direct mixing of base soil and bentonite slurry process. |
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