Research on the relationship between saturated permeability and pore distribution characteristics of loess-paleosol

Due to differences in sedimentary environments, the paleosol is denser than the overlying loess, and its saturated permeability coefficients should be lower than that of the loess. This intuitive understanding has been challenged by the experimental results of several permeability tests which indicate that paleosol and loess have similar saturated permeability. In order to reveal the mechanism behind this phenomenon, we focused on the loess-paleosol strata of the loess tableland located in Jingyang County, Shaanxi Province. Undisturbed loess and paleosol specimens were extracted at equal intervals of 1 m from a 33 m exploratory well. Variable head permeability (VHP) tests were then conducted to determine their saturated permeability coefficients. Concurrently, mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) tests were conducted to obtain the pore distribution curves and microstructure images of typical samples, respectively. The analysis of the relationship between saturated permeability and pore distribution characteristics in loess-paleosol was analyzed based on the aforementioned experimental results. VHP test results illustrated that the saturated permeability coefficients of loess and paleosol decrease regularly with increasing burying depth, and the values of the saturated permeability coefficients of adjacent loess and paleosol samples are very close. MIP and SEM test results demonstrated a consistent pore structure in loess, whereas paleosol exhibited an irregular clump-fissure structure characterized by the presence of fissures in dense clay clumps. Saturated permeability coefficients were found to be contingent on the content of permeable pores, with loess primarily featuring large pores (pore diameter > 2 μm), and paleosol predominantly consisting of micro-cracks between clumps. Despite their similar permeability coefficients, the permeability mechanism were fundamentally different. This study establishes a theoretical foundation for studying the pore distribution characteristics of loess and paleosol, as well as addressing engineering challenges in loess areas.