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针对干湿循环作用下填埋场封场覆盖系统压实黏土防渗失效等问题,系统开展了干湿循环作用下(室内模拟填埋场气候环境)压实黏土渗透特性及微观结构特征试验研究,探讨了干湿循环次数、压实度、试样尺寸对压实黏土渗透系数影响并从微观层次揭示其防渗失效内在本质。研究结果表明:干湿循环前,相同压实度的大、小两种尺寸渗透试样所测渗透系数基本相同,经3次干湿循环后,不同尺寸、不同压实度黏土渗透系数增加量却存在明显差异。干湿循环作用下,小尺寸高、低两压实黏土试样均只收缩不开裂,并且高压实黏土微观结构损伤大于低压缩黏土,其渗透系数的增加量也大于小尺寸低压实黏土。而大尺寸试样裂隙发育与现场压实黏土裂隙发育相似,高压实黏土内部裂隙体积小于低压实黏土,其渗透系数的增加量也小于低压实黏土。同时,大尺寸试样内部大量未闭合宏观裂隙致使其渗透系数增加量大于同等压实度条件下小尺寸试样渗透系数增加量。室内小尺寸试样无法体现干湿循环作用下压实黏土层内部干缩裂隙对其渗透性能的影响,因此,其渗透试验结果不宜作为评价压实黏土长期防渗性能的评价指标。
Aiming at the problems such as seepage control failure of compacted clay in the landfill cover system under the action of wet and dry cycles, the system has carried out experimental study on the infiltration characteristics and microstructure characteristics of compacted clay under the effect of the wetting and drying cycle (indoor simulated landfill climate environment) The effects of the number of wetting and drying cycles, compaction degree and sample size on the permeability coefficient of compacted clay were discussed. The intrinsic nature of seepage control failure was revealed from the microscopic level. The results show that before and after the wetting and drying cycle, the permeability coefficients measured by two kinds of large and small infiltration samples with the same compaction degree are basically the same. After three times of drying and wetting cycles, the permeability of clay with different sizes and compaction increases However, there are obvious differences. Under the action of the wetting and drying cycles, the small size high and low two compacted clay samples shrink only and do not crack, and the microstructural damage of the high pressure solid clay is greater than that of the low compressive clay, and the increase of the permeability coefficient is also larger than that of the small size low compacted clay . However, the fracture development of large-size specimens is similar to the development of on-site compacted clay fractures. The internal fracture volume of high-pressure clay is smaller than that of low-pressure clay, and the increase of permeability coefficient is also smaller than that of low-pressure clay. At the same time, a large amount of unclosed macroscopic fissures in the large-size specimen resulted in the increase of the permeability coefficient larger than the increase of the permeability coefficient of the small-size specimen under the same compaction condition. Therefore, the result of infiltration test should not be used as an evaluation index to evaluate the long-term seepage control performance of compacted clay.