Analysis Of Pore Distribution And Soil-Water Characteristic Curve Of Malan Loess Under Different Depositional Environments

Loess is widely distributed,and its structural characteristics vary greatly in different regions due to different sedimentary environments.In order to study the relationship among the pore distribution(PSD),the soil-water characteristic curve(SWCC)of loess and its depositional environment,intact Malan loess samples were taken from the upper parts of the Loess Plateau in Heifangtai,Hepingzhen,Zhengning of Gansu Province and Jingyang of Shaanxi Province.Moreover,the undisturbed S₁ paleosoil samples were taken from Jingyang as a control.On the basis of measuring physical indexes of specimens,mercury intrusion method was used to measure PSD curves of soil samples,filter paper method was adopted to measure SWCCs and the microstructure images of the soil samples were obtained by scanning electron microscope.Based on the climatic data of study areas in the past ten years,the causes of the differences between the pore distribution and soil-water characteristics of loess are explained from the perspective of climate,and the following results are obtained:(1)The PSD curves of Malan loess in Heifangtai and Hepingzhen are unimodal;for Malan loess in Jingyang,the PSD curve is bimodal;the PSD curve of Zhengning is trimodal;that of S₁ paleosol in Jingyang is uniform while soil-water characteristic curve of each soil sample has the morphological characteristics corresponding to its pore distribution.(2)The comparative analysis between pore distribution and soil-water characteristics shows that the shape of soil-water characteristic curve is controlled by pore distribution,and the control mechanism is explained.Besides,combined with the microstructure images obtained by SEM,the control relationship is further verified from the perspective of microstructure.(3)According to the climatic data of the past decade,the modern climatic characteristics of the study areas are described.The analysis shows that the difference among pore distribution of loess is mainly determined by the strength of pedogenesis.The weaker the pedogenesis is,the more concentrated the pore distribution is,the stronger the pedogenesis is,the pore distribution is uniform,and the precipitation is the key factor affecting the pedogenesis.(4)The ratio of precipitation to evaporation is defined as the coefficient of evaporation and infiltration(C_EI),which is used as an index to describe the strength of pedogenesis.According to the C_EI,the model of PSD is classified as follows:when C_EI?0.3,PSD is unimodal;when 0.3<C_EI?0.4,it is bimodal;when 0.4<C_EI?0.5,it is trimodal;when C_EI>0.5,it is even,and the corresponding SWCCs are single inflection point,double inflection point,three inflection point mode and linear mode respectively.