In order to obtain the temperature field evolution in the mud silo during the freezing process for shield rescue

a model test of horizontal freezing inside the shield was designed based on similitude theory. This was applied to the tunneling project in the Yangtze River corridor of the Xinjizhou water supply pipeline in Jiangning District

Nanjing. The temperature evolution and distribution characteristics in the mud silo during freezing were studied

leading to the following conclusions. Firstly

using 20 freezing pipes arranged through geological exploration and grouting holes

the slurry chamber of the shield (diameter 6 480 mm) could be completely frozen within 75 days

with a maximum pipe spacing of 3.12 m. After 135 days of freezing

the average temperature of the frozen soil in the slurry chamber reached −13 ℃

with a longitudinal temperature difference of approximately 4.4 ℃. The overall freezing effect was uniform

meeting the water sealing and bearing requirements for shield chamber opening

thus facilitating shield rescue construction. Secondly

temporary suspension of freezing during construction led to temperature redistribution in the frozen soil of the slurry chamber. A 10-hour suspension caused the frozen wall temperature to rise to −14 ℃ to −10 ℃

but it returned to its pre-suspension state after 20 hours of resumed freezing. Thirdly

45 days post-freezing

the average temperature of the frozen soil in the shield slurry chamber rose to −4 ℃

meeting the requirements for shield re-pushing construction. It took about 20 days for the frozen soil temperature at the freezing pipe position to rise back to 0 ℃

remaining around 0 ℃ for approximately 125 days. During construction

auxiliary measures like forced thawing or circulating mud can accelerate the thawing of frozen soil in the shield’s slurry chamber. The horizontal freezing method in tunnels is an effective technique for improving formation to construct a maintenance environment in the shield chamber.