In situ field measurements of air permeability in eroded loess formations

Loess is an unsaturated soil and is widely distributed in arid and semi-arid areas in northwest China. Air permeability is a key parameter for determining the permeation performance of unsaturated soil. At present, the air permeability of loess is mostly determined by laboratory measurements with few studies using in situ measurements. In this paper, an improved loess air permeameter was used to measure the air permeability of in situ loess and undisturbed loess samples in three typical loess regions. The in situ air permeability measurement results obtained with the improved air permeameter were compared with laboratory (in-lab) permeameter measurements of undisturbed loess samples since the in-lab-based method is relatively mature. Experiments were conducted to investigate the influence of the void ratio, the water content and other parameters of the eroded loess formation on the air permeability of the in situ loess samples. The results showed that the in situ air permeability measurements obtained from the improved air permeameter are highly reliable. The air permeability of loess in different regions was highly correlated with the particle size distribution. The higher the clay content, the lower the number of effective permeation pores and the lower the air permeability of the loess. Increasing depth is positively associated with the water content and the dry density, but negatively related to the void ratio and air permeability. The air permeability was the highest near sinkholes, fissures, and trenches; it initially decreased with increasing distance from these features and stabilized eventually. The results of this study successfully provide technical information and support for engineering applications in loess areas.