Freezing Temperature Field of FSPR under Different Pipe Configurations: A Case Study in Gongbei Tunnel, China

Abstract

As a new tunnel presupport construction technology, the freeze-sealing pipe roof method (FSPR) has been successfully applied to the Gongbei Tunnel Project for the first time in China. To overcome the practical difficulties of this new method in the freezing construction process, such as welding difficulties of the profiled freezing tube, refrigerant leakage, and long construction period, based on the principle of an equal cooling capacity, an improved design of freezing tube was proposed. By designing three different pipe configurations and using scaled model tests and numerical simulation, the feasibility of the improvement and the difference in the freezing temperature field were studied. The research results show that the improved design with double circular freezing tubes exhibited a lower temperature and a higher cooling rate during the test, and the time required to meet the freezing design requirements was significantly shortened. Finally, a composite structure of “pipe roof and frozen soil curtain” with a better carrying capacity and water sealing performance was formed. It was recommended to strengthen the temperature monitoring at the pipe wall in the preliminary stage of the freezing construction to ensure the water sealing effect between the pipes. In the later stage, attention should be paid to monitoring the thickness of the frozen curtain and reducing excessive frost heave through technical means such as cooling capacity control. The improvement and configurations proposed in this research could effectively replace profiled freezing tubes in the original project, better adapt to horizontal freezing projects of similar curved tunnels, achieve the freezing goal faster, and provide a reference for the promotion of the FSPR.

Numerical Analysis of the Effect of Groundwater Seepage on the Active Freezing and Forced Thawing Temperature Fields of a New Tube–Screen Freezing Method

“…The first p on the left side of the steel tube in the upstream area, starting and ending at c (1.9, 5, 16) and (4.9, 5, 16), with a total of four observation points set at 1 m int second path was set on the right side of the steel pipe in the upstream area, st stopping at coordinates (8.9, 5, 16) and (11.9, 5, 16), with a total of four observa set at 1 m intervals. The third path was set inside the top steel tube, starting an at coordinates (15,5,21) and (15,5,18), with four observation points set ever fourth path was set at the top of the steel tube. The starting and stopping coordi (15,5,28) and (15,5,15), with four observation points are set every 1 m. The fift set to the left of the steel pipe in the downstream region.…”

“…The starting and stopping coordinates were (15,5,28) and (15,5,15), with four observation points are set every 1 m. The fifth path was set to the left of the steel pipe in the downstream region. The starting and stopping coordinates were (18,5,16) and (21,5,16), with four observation points are set every 1 m. The sixth path was set on the right side of the steel tube in the downstream area, starting and stopping at coordinates (25,5,16) and (28,5,16), with a total of four observation points per 1 m. The observation path and observation points are shown in Figure 5.…”

“…The Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge used tube-curtain freezing technology for the first time in the world [10][11][12][13]; the process involved jacking the steel tube into the soil to improve the bearing capacity, and then allowing the freezing pipe to cool the soil, which improved the waterproofing and stability after freezing reinforcement, thereby forming the "frozen soil tube-curtain" composite support structure [14][15][16]. In recent years, relevant scholars have carried out in-depth studies and experimental demonstrations related to the construction of the tube-curtain freezing method [17][18][19][20], including control of the tube freezing limit [21,22], steel pipe jacking [23], and temperature monitoring [24]. These findings have played a positive role in promoting the popularization and application of the tube-curtain freezing method.…”

Model Test Study on Natural Thawing Temperature Field of Artificial Ground Frozen Wall

“…Hu et al [24] conducted a large physical model test of a freeze-sealing pipe roof and found that the method freezes faster and is more resistant to thermal weakening of excavation. Based on the principle of equivalent cooling capacity, Duan et al [25] designed the FSPR model test of double circular freezing pipes, which shows that the improved design can effectively replace the original design of the profiled freezing pipe by comparing the temperature field distribution.…”

Field Temperature Data Analysis of the Water Resistance Performance of Freeze-Sealing Pipe Roof Used in Tunnel through Water-Rich Strata

“…Zhou et al [10] presented a case study of this system on the mechanical responses in the construction process. Duan et al [11] studied the feasibility of the improvement and the diference in the freezing temperature feld by designing three diferent pipe confgurations and using scaled model tests and numerical simulation. Zhou et al [12] analyzed the vertical ground movement caused by frost heave and thawing based on the feld measurement.…”