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。

This paper studies the anti-seepage failure of compacted clay layer (CCL) during wetting-drying cycles in a landfills cover system. The permeability and microstructure tests are conducted. The effects of wetting-drying cycles, degree of compaction and specimen size on permeability coefficient of CCL are discussed. The essence of anti-seepage failure is revealed at microscopic level. The research results show that the permeability coefficients of two size specimens are the same before wetting-drying cycles, but the increments of permeability coefficient of CCL with different degrees of compaction and specimen sizes are different after three times of wetting-drying cycles. The high-compacted and low-compacted small-size specimens both show shrinkage but no crack during wetting-drying cycles. For small-size specimens, the microscopic structural damage and the increment of permeability coefficient of high-compacted clay are larger than those of low-compacted clay. Unclosed cracks in large-size specimens result in larger increment of permeability coefficient than those in small-size specimens with the same degree of compaction. The small-size specimens can not reflect the influence of shrinkage cracks on the permeability of CCL. Therefore the permeability results of small-size specimens are not suitable for evaluating long-term seepage capacity of CCL.