Abstract: 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.

Key words: compacted clay, drying-wetting cycles, mechanical property, pore size distribution, micromechanism