Evaluation of Freezing Effect of Water-Rich Sand Layer Considering THM Coupling Effect

[Purposes] The artificial freezing method is often used in subway tunnel crossing the water-rich sand layer, and is subjected to the synergistic action of heat, flow, and force fields during soil freezing process. It is of great significance to study the multi-field coupling freezing effect for the application of artificial freezing method to ensure the effectiveness of soil water sealing and reinforcement. [Methods] Therefore, on the basis of the engineering background of artificial freezing method in Kunming Metro, a three-dimensional horizontal cup-type freezing thermal-fluid-force coupling field (THM) model was established, and the effects of cooling plan, groundwater seepage velocity, and formation saturation on freezing effect were investigated, and compared with measured results. [Findings] The results show that the higher the seepage velocity of groundwater, the more obvious the freezing effect is in the downstream frozen zone. The larger the seepage velocity, the larger the thickness difference between the upper and lower frozen walls. For different cooling schedule conditions, the freezing effect of -25℃ cooling schedule is the best. The vertical displacement and horizontal displacement caused by frost heave increase with the increase of saturation. The growth rate of vertical displacement is greater than that of horizontal displacement, the maximum vertical displacement is 8.43 mm, and the horizontal displacement is less than 1.80 mm. In practical engineering, the frost heave stress affects the adjacent structures, so the risk of instability, leakage, and shield axis deviation can be avoided by secondary grouting and melt sink grouting combined with pipe segments.