Artificial ground freezing (AGF), widely employed in subway tunnel construction, significantly alters the microstructure of surrounding soils through freeze-thaw processes. These changes become critical under subway operation, where traffic-induced dynamic loading can lead to progressive soil deformation. Understanding the dynamic behavior of freeze-thaw-affected soils is therefore essential for predicting and mitigating deformation risks. This study investigates the microstructural evolution of soil subjected to a single freeze-thaw cycle-representative of AGF practice-and subsequent dynamic loading. Dynamic triaxial tests were conducted under a fixed dynamic stress amplitude of 10 kPa and loading frequencies of 0.5 Hz, 1.5 Hz, and 2.5 Hz, simulating typical subway traffic conditions. Microstructural analyses were performed using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Results show that the freeze-thaw cycle leads to a denser yet more disordered particle arrangement, with sharper and more angular particles, as reflected by increased probability entropy and reductions in surface porosity, form factor, and uniformity coefficient. Dynamic loading further causes particles to flatten and align in a more directional manner, accompanied by decreased surface porosity and form factor, and an increased uniformity coefficient. Pore structures become more uniform and less complex. Among various microstructural indicators, total intrusion volume from MIP displays a strong correlation with cumulative plastic strain, suggesting its potential as a micro-scale predictor of soil deformation. These findings enhance our understanding of the coupled effects of freeze-thaw and dynamic loading on soil behavior and offer valuable insights for improving the safety and durability of subway tunnel systems constructed using AGF.

This study investigates the Strain characteristics of reinforced soft clay surrounding a tunnel subjected to cyclic loading, employing the Global Digital Systems cyclic triaxial test on the saturated reinforced clay near Shanghai Metro Line 4's Hailun Road station. Initially, the study examines the impacts of frequency, dynamic stress amplitude (DSA), and loading cycles on cumulative plastic strain. Following this, the orthogonal design method was employed to organize tests, and an evaluation method for assessing soil strain was developed through mathematical statistical analysis. The results indicate at the constant vibration frequency, cumulative plastic strain increases with an increase in DSA and decreases with as load frequency increases. DSA is the primary factor influencing the axial deformation of subway tunnels, whereas the interaction between load frequency and vibration frequency is negligible. The findings suggest that measures to prevent and control subway tunnel settlement should concentrate on DSA during the early stages of subway operation. A novel concept and calculation method for the influence rate of axial deformation of clay mass under cyclic loads were introduced, enabling the determination of a parameter's significant influence on deformation. The early stage of subway operation is the focus for preventing engineering geological disasters. Dynamic stress amplitude (DSA) is the primary factor influencing the axis deformation of subway tunnels, while the interaction between load frequency and vibration frequency is negligible.