干湿循环作用下压实黏土力学特性与微观机制研究

针对干湿循环作用下填埋场封场覆盖系统压实黏土防渗结构损伤等问题，系统开展了干湿循环作用下（室内模拟填埋场气候环境）压实黏土力学特性及微观结构特征试验研究，从微观层次揭示了压实黏土在干湿循环作用下变形特性和强度衰减内在本质。研究结果表明：随着干湿循环次数的增加，压实黏土初始变形段区间割线模量增加，末段区间割线模量大幅度降低，变化幅度随初始压实度的增加而增加；同时，压实黏土剪切强度呈减小趋势，但减小幅度随初始压实度和围压的增加而减小。经过3次干湿循环后，压实黏土发生不可逆的体积收缩，体积收缩比例随压实度的增加而减小，低压实黏土和高压实黏土的体积收缩20.5%和11.5%。同时，低压实黏土和高压实黏土的大孔体积增加25.7%和53.9%，微裂隙体积增加3.1%和41.7%，增加幅度随初始压实度的增加而增加。压实黏土不可逆的体积收缩致使土体更加密实，从而导致压实黏土初始切线模量和强度增加。同时，大孔体积增多和微裂隙的发育，导致压实黏土剪切强度和末端切线模量降低，干湿循环对不同压实度黏土力学特性影响是二者的综合表现。

Mechanical properties and micromechanisms of compacted clay during drying-wetting cycles

To investigate the problems such as the failure of compacted clay liners as the anti-seepage structure in the landfills cover system under the action of drying-wetting cycles, experiments under the simulated climatic environment of landfills have been conducted to determine the mechanical properties of compacted clay and its microstructure characteristics during the drying-wetting cycles and hence to reveals the intrinsic nature of the damage of compacted clay from the micro level. The experimental results show that as the number of drying-wetting cycle increases, all the secant moduli of low-, medium- and high-compacted clays increase at initial stage, while they decrease significantly at later stage, and the magnitude of secant modulus variation increases with the increase of initial compactness. Meanwhile, the shear strengths of above-mentioned three compacted clays decrease, and the magnitude of variation decreases with the increase of initial compactness or confining pressure. After three drying-wetting cycles, the total pore volume of compacted clay shows irreversible shrinkage, resulting in the increase of initial tangent modulus and shear strength. The shrinkage ratio decreases with the increase of compactness, and the shrinkage ratios of low- and high-compacted clays are 20.5% and 11.5%, respectively. The large pore volumes of low- and high-compacted clays increase 25.7% and 53.9% and the microcrack volumes increase 3.1% and 41.7%, respectively, resulting in a decrease in the shear strength and tangent modulus at later stage. The effect of drying-wetting cycles on the mechanical property of compacted clay with different compactness is controlled by two factors, i.e. the decrease of total pore volume and the increase of big-pore and microcracks.