Experimental study on air permeability and microscopic mechanism of intact and remolded Malan loess, Loess Plateau, China

As a natural foundation and fill material for construction in loess areas, there exists a significant impact on the stability of the engineering construction due to the permeation characteristics of the eolic sediment Malan loess. In this study, a series of air permeability tests were conducted for intact loess and remolded loess by using an improved air permeameter. We determined the influence of the water content, wetting and drying, dry density on the air permeability k_a, and the use of microstructure models, scanning electron microscope (SEM) micrographs, and 3D super depth of field microscope micrographs to elucidate the microscopic mechanism of the air permeation. The results show that the air permeability k_a of the remolded loess increased with the initial water content of remolding loess at dry density of ρ_d ≦ 1.6 g/cm³ increase, which is because of the formation of aggregates, and menisci water effect in loess; however, at dry density of ρ_d > 1.6 g/cm³, the air permeability started to decrease. The k_a reduced remarkably as the water content of the intact and remolded loess increased during wetting process, and the air permeability during the drying process was always higher than the air permeability in the wetting process at the same water content. With the increase in the dry density, the air permeability of the remolded loess decreased; from a microstructural perspective, large and round pores tend to be small and elongated and irregular pores at high dry density. This paper will contribute to elucidating air permeability characteristics of loess and reducing the permeation risk in stability of the engineering construction in the Loess Plateau.