Air permeability variation of compacted loess: effects of soil basic properties and dry-wet cycles

Loess, featured by its low permeability and cost-effectiveness, has become an increasingly popular material for landfill cover systems. However, the occurrence of cracks in loess caused by rainfall and evaporation poses challenges to the performance and durability of these cover systems. This study aims to comprehensively investigate variations in air permeability of compacted loess under normal and dry-wet cycle conditions. The conventional triaxial instrument was modified to meet the requirements of the air permeability test of loess. The influence of factors such as permeability pathway, water infiltration time, dry density, and water content as well as dry-wet cycles on the air permeability was thoroughly explored. And the applicability of established models in describing loess air permeability was assessed. The results confirmed that the airflow in compacted loess followed Darcy's law, and there was a clear correlation between air permeability and these influencing factors. Loess samples with a diameter of 38 mm and a height of 76 mm were found to be more suitable for air permeability testing. Cracking in loess significantly increases air permeability, with longitudinal cracking having a greater effect than transverse cracking. Lower-density samples exhibit more pronounced cracking than higher-density samples. Both initial water content and humidification water content were identified as influential factors during dry-wet cycling and have a substantial impact on the variation of air permeability. These findings contribute to a better understanding of the air permeability characteristics of compacted loess in landfill cover systems, enabling improved design and performance evaluation for sustainable waste management practices.