Abstract: Indoor test, on-site measurement, and simulation calculation are performed to investigate the effects of heat preservation process and form, freezing hole spacing, length of unfreezing section, and freezing time on surface frost heaving in the aim of researching the form of freezing pipes and surface frost heaving in subway tunnel freezing project. The freezing process of the airport segment tunnel of the north extension line of Guangzhou Rail Transit Line 13 is taken as the research background. Results show that partial freezing can be effectively achieved by using thermal insulation materials for freezing pipes, and the insulation materials should be waterproofed to prevent the thermal conductivity from increasing induced by groundwater. The frost heave on the surface is inversely proportional to the length of the insulation, and the proportional coefficient decreases with the increase of the hole spacing but increases with the extension of the active freezing time. The predictive equation of frost heave is presented. In addition, the distance of the freezing pipe can be reduced to cut the construction period and energy consumption under the premise of ensuring the surface frost heave.

Key words: subway tunnel, form of freezing pipes, surface frost heave, partial freezing, prediction of frost heave