Effects of compaction coefficients on microscopic pore structures and fractal properties of soft clay and freeze- thawed soft clay

Abstract

Abstract For subway connection channel projects built in coastal areas, freeze-thaw and compaction are two key factors that change the soil microstructure and affect engineering safety. Therefore, understanding the variation law of the microscopic pore structure of soft clay and freeze-thawed soft clay is crucial to the design and prediction of the serviceability of subway infrastructures. Considering this, to understand the effects of freeze-thaw and compaction coefficient on microscopic pore structures and fractal characteristics, a series of nuclear magnetic resonance (NMR) tests were performed on soft clay and freeze-thawed soft clay under different compaction coefficients. Based on the experimental data, a fractal theory was proposed to describe the fractal characteristics of the tested materials. Moreover, the effect of curing agents on the microscopic pore structure of soft clay was studied by adding two curing agents to the soft clay. The experimental results showed that compaction coefficients had a significant effect on the pore size distribution (PSD) of soft clay and freeze-thawed soft clay. As the compaction coefficient increased, the proportion of large pores decreased significantly, and the proportion of small and medium pores increased. Moreover, the compaction coefficient was found to have a significant effect on the fractal dimension (D) of soft clay and freeze-thawed soft clay whereby increases in compaction coefficients led to a trend of increased D and heterogeneity within soft clay and freeze-thawed soft clay. With the development of freezing front and the formation of ice lens, the pore structure of soft clay and the connection between soil particles are destroyed. The microscopic pore characteristics of the soil samples with an added solidifying agent were characterized by a significant increase in the number of small pores and a decrease in the number of large pores. This research can provide theoretical guidance for the construction of subway connection channel engineering projects.