Mode analysis of pore distribution and soil -water characteristic curve of Malan loess under different depositional environments

In order to examine the relationship between pore size distribution (PSD) and soil -water characteristic curve (SWCC) of loess and its depositional environment, intact Malan loess samples were taken from the upper parts of Loess Plateau in Hepingzhen in Zhengning county of Gansu Province and Jingyang county of Shaanxi Province. On the basis of measuring physical indexes of specimens，mercury intrusion method was used to measure PSD curves of soil samples, and filter paper method was adopted to measure SWCC. The result shows that the PSD curve of Hepingzhen is unimodal; for Jingyang, the PSD curve is bimodal; the PSD curve of Zhengning sample is trimodal while the corresponding SWCC of each soil sample has a stepped shape. The relationship between SWCC and PSD indicates that pore distribution controls the mode of the soil -water characteristic curve. Scanning electron microscope (SEM) photographs of three samples were obtained and the microstructure also showed this phenomenon of regional differentiation. Climatic analysis for each sampling point shows that the difference of PSD curves of the Malan loess in different regions is determined by the strength of pedogenesis. In this paper, the ratio of precipitation to evaporation is defined as the coefficient of evaporation and infiltration (CEI), which is used as an index to describe the strength of pedogenesis. According to the CEI, the model of PSD is classified as follows: when CEI≤0.3, PSD is unimodal; when 0.3＜CEI≤0.4, it is bimodal; when 0.4＜CEI≤0.5, it is trimodal, and the corresponding SWCC is single inflection point, double inflection point and three inflection point mode.