Effect of water-proofing in Gongbei Tunnel by freeze-sealing pipe roof method with field temperature data

The actual water proofing effect between the pipes at different stages of the freeze-sealing pipe roof (FSPR) method is analyzed based on the field measured data. For the two different intersection patterns in the active freezing period, the thickness of the frozen soil between the steel pipes is calculated by the single-pipe formula. The results show that the frozen wall can form the intersection within the time allowed by the project, so that the frozen wall has initial water sealing performance. After the intersection, the thickness of the frozen soil between the pipes is calculated by the double-pipe formula. The results show that the development of the frozen soil wall is non-uniform. The development of the frozen soil near the middle in the longitudinal direction is better than that at the end, and the development of the frozen soil near the lower part in the lateral direction is better than that near the upper part. In addition, the impact of natural disasters such as typhoons on the near surface soil is proved controllable. During the excavation period, the measured data of the inter-tube temperature indicate that the strict and fine control of the construction schedule during the test excavation is beneficial to reduce the weakening of the frozen wall between the pipes, and the thermal disturbance during the official excavation has a significant impact on the frozen soil close to the excavation surface while the frozen soil slightly far from the excavation surface is almost unaffected. The frozen soil wall can still maintain enough frozen soil thickness to achieve the sealing effect considering the reduction of 20 cm. The study has verified the effect of water proofing between pipes and demonstrated the rationality of the FSPR method, which may provide reference and guidance for similar projects in the future.