Cyclic Behavior and Pore Structure Deterioration of Cement-Stabilized Clay under Artificial Ground Freezing

Two-way tunneling offers an efficient approach for constructing long-distance underwater tunnels. To facilitate bidirectional shield docking in soft clay layers, the artificial ground freezing (AGF) technique, combined with low-dose cement grouting, is commonly used to enhance the soil strength and waterproofing capacity. However, grouting within fine-pored clay often results in nonhomogeneous cement-stabilized clay (CSC), which may induce uneven settlement under long-term traffic loading, particularly after freeze–thaw (F-T) action. This study investigates the effects of cement content and F-T conditions on the cyclic behavior of CSC through cyclic triaxial tests. Complementary nuclear magnetic resonance tests, interpreted using fractal theory, were conducted to quantify pore-scale deterioration. A cross-scale analysis was performed to establish the linkage between cyclic deformation and pore evolution. The results demonstrate that the F-T cycle leads to a higher accumulated plastic strain (APS), enlarged hysteresis loop areas, and reduced resilient modulus. These deterioration effects intensify further when the freezing temperature decreases. Increasing the cement content effectively mitigates the deterioration induced by F-T action, and a strong inverse correlation is observed between APS and pore fractal dimension. The proposed cross-scale damage model further reveals that the cyclic deformation induced by the F-T action is directly attributed to microstructural damage within the harmful pores. These findings offer valuable insights into the long-term performance of CSC in AGF-treated zones.