Optimal pipeline position of annular freezing reinforcement during the replacement of shield tail brush

How to prevent and control the leakage at shield tail during the replacement of shield tail brush is critical for shield tunnel construction. Herein, an annular freezing reinforcement method during the replacement of shield tail brush was proposed, and the optimal position for one annular freezing pipeline, if adopted, was analysed through numerical modelling. In addition, the development law of the temperature field of the annular freezing soil curtain was also studied. The results show that the drilling method is flexible for annular freezing reinforcement during the replacement of the shield tail brush. Besides, it also has little effect on the durability of segments and strong construction practicability, as well as good, safe and reliable reinforcement effect, particularly good water-stop effect. Specifically, the best pipeline position is 0.3 m over the shield tail, where the best freezing effect can be provided, satisfying the design requirements. The final soil temperature at the gap between the shield tails will rise about 9 ℃ if the radius of the annular freezing pipeline increases by 0.3 m. Moreover, the －1 ℃ isotherm reaches the shield tail gap after 6-day freezing at the optimal pipeline position, with the water sealed initially by the freezing soil curtain, and the －10 ℃ isotherm reaches the shield tail gap after 10-day freezing, so that the freezing effect of the freezing soil curtain is strengthened. Therefore, arranging an annular freezing pipeline at the optimal position can greatly improve the water sealing performance and safety, which could provide some reference for the development of related projects in the future.