Effects of seepage in clay-sand composite strata on artificial ground freezing and surrounding engineering environment

With the emergence of more and more large-scale cross-sea and river-crossing projects in coastal areas, the artificial ground freezing (AGF) faces more complicated hydrogeological environmental problems and challenges. Based on the engineering background of the large seepage boundary near the frozen soft clay, a scale model is established through strict similarity design to analyze the effects of seepage on the freezing construction of overlying freeze-thaw sensitive soft clay and the surrounding engineering environment under the condition of soft clay with larger seepage sand layer. The temperature, frost-heave force and surface settlement in each affected area under different seepage velocities are measured. The results show that the excessive seepage velocity of the underlying sand layer will make it impossible to complete the freezing, and there is a critical seepage velocity. In addition, the freezing effects of the upper and lower freezing curtain edges of soft clay under seepage conditions are also completely different, especially the stable freezing temperature and the development mode of the frost-heave force. In the area directly affected by seepage, the latent heat effects of seepage on soft clay are significantly weakened, and the phase transition equilibrium time decreases linearly with the increase of seepage velocity. The whole comprehensive research results provide theoretical guidance and valuable advices for the optimization of freezing scheme and construction safety of AGF. The relevant predictions and suggestions are made for construction quality, tunnel safety and environmental management that may be encountered in engineering practice.