Responding of soil-water characteristics of compacted loess soil to its pore structure

Dry density and moulding water content are two key factors affecting the soil-water characteristic curve of compacted loess. This paper aims to study the influence of the dry density and the moulding water content on the macroscopic soil-water characteristics of compacted loess from microscopic perspective. For this purpose,the filled loess of Yan'an was collected,and two sets of samples were made by static pressure method. The moulding water content of group A with different dry densities of 1.40 g/cm3,1.60 g/cm3 and 1.80 g/cm3 is 10%,and the dry density of group B with different moulding water contents of 10%,16%(optimal water content) and 18% is the maximum(equal to 1.79 g/cm3). In the study,the contact filter paper method was used to measure the full range of wetting soil-water characteristic curves,the SEM images were obtained using polished slices of epoxy-filling soil samples,and the pore distribution curves were measured by the mercury intrusion method. The test results show that the soil-water characteristic curves of the soil samples with different dry densities in group A basically overlap in the residual stage but present regular changes in the near saturated stage and the transition stage. The soil-water characteristic curves of group B also basically overlap in the residual stage,but that,with increasing the moulding water content,the air occlusion value decreases and the suction range of the transition zone widens,resulting in a change from a single wetting mode to a dual wetting mode in the transition stage. Through micro-structure analysis,it is found that the soil-water characteristics of the two sets of samples are essentially controlled by the pore size distribution and that there is a corresponding relationship between the coincident point and the intersection point of soil-water characteristic curves and pore distribution curves. The distribution range of the dominant pores determines the suction range of the transition stage,and the size of the dominant pores determines the wetting rate in the transition stage. The number of peaks(single or double peak) of the pore distribution curve determines the wetting mode(single or double dual wetting mode) of soil-water characteristics,and the coincident pore area curves determine the similar soil-water characteristic curves. © 2022, Science Press. All right reserved.