Study of thermal field of soil freezing in shallow covered tunnel with subsurface excavation passing through ground with thin aquifer under complex conduction

Artificial freezing water sealing reinforcement method for water-enriching layers of Shang-Xin tunnel of Nanjing metro Line No. 2 is proposed. Numerical model of freezing temperature field is built for the water inflowing tunnel by ADINA software. The effects of distance of freezing pipes, brine temperature and diameter of freezing pipes on development of freezing walls, thickness of freezing wall and average temperature are studied. On the basis of this study optimization design is implemented. And the freezing method is successfully applied to the construction. The study demonstrates that the application of artificial freezing can solve this special geotechnical problem. The distance of freezing pipes should less than 1 meter so as to get effective freezing wall. Using brine temperature of -30 degrees C may not only meet the need of cooling capacity but also meet the economical requirement. There is no significant effect on the thickness of freezing wall and the average temperature by using freezing pipes of large diameter.