Experimental study on pore structure and freezing characteristics of graded soils based on NMR

The freezing characteristics of pore water is the basis for studying the moisture and heat transfer and frost heave of frozen roadbeds. Based on the nuclear magnetic resonance (NMR) technology, the effects of the fine-grained soil type, the fine-grained soil content and the maximum particle size on the freezing characteristics of graded soils are analyzed. The results show that the pore structure of the graded soils is highly related to the fine-grained soil type and content, and the pore distribution of the soil samples gradually changes from single peak to bimodal one as the clay content decreases. The influences of the maximum particle size on SFCC of the graded soils are relatively small, and the type and content of the fine particles are the important factors to control the unfrozen water content. The freezing of pore water gradually develops from large pores to small ones, while it is the opposite during thawing, and there is an obvious hysteresis between the freezing and thawing processes. After a freeze-thaw cycle, the pore structure of the soils changes slightly, the small and medium pores decrease and the large pores increase.