Abstract: Many popular models have been proposed to study the fractal properties of the pores of porous materials based on mercury intrusion porosimetry (MIP). However, most of these models do not directly apply to the small-micro pores of loess, which have a significant impact on the throat pores and tunnels for fluid flow. Therefore, in this study we used a combination of techniques, including routine physical examination, MIP analysis, and scanning electron microscope (SEM) image analysis, to study these small-micro pores and their saturated water permeability properties. The techniques were used to determine whether the fractal dimensions of six MIP fractal models could be used to evaluate the microstructure types and permeability properties of loess. The results showed that the Neimark model is suitable for analysis of small-micro pores. When applied to saturated water permeability, the results from this model satisfied the correlation significance test and were consistent with those from SEM analysis. A high clay content and density cause an increase in the number of small-micro pores, leading to more roughness and heterogeneity of the pore structure, and an increase in the fractal dimensions. This process further leads to a decrease in the content of macro-meso pores and saturated water permeability. Furthermore, we propose new parameters: the ^*Ellipse and its area ratios (^*EAR). These parameters, coupled with 2D-SEM and 3D-MIP fractal dimensions, can effectively and quantitatively be used to evaluate the types of loess microstructures (from type I to type III) and the saturated water permeability (magnitude from 1×10^-4 cm/s to 1×10^-5 cm/s).

Key words: Malan loess; Fractal models; Small-micro pores; Mercury intrusion porosimetry (MIP); Microstructure; Saturated water permeability

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