Construction of a super-large prefabricated rectangular tunnel beneath a box culvert using pipe jacking: A case study.

Constructing large-section underground structures using the pipe jacking technique presents challenges, including the insufficient size of the rectangular pipe-jacking machine and the transportation and hoisting of large prefabricated ring structures. This paper introduces and investigates the construction, challenges, and key techniques involved in jacking a super-large rectangular prefabricated tunnel underpass a rainwater box culvert. The adoption of an assembly concept for manufacturing both the super-large rectangular pipe-jacking machine and ring structures, along with innovative in-shaft assembly and jacking techniques, effectively addresses issues in super-large section pipe-jacking engineering. The on-site monitoring data analysis reveals that the jacking force for the super-large rectangular tunnel significantly exceeds the estimated value. This is primarily attributed to excessive resistance during jacking in the reinforcement areas of the launching and receiving shafts, constituting 55 % of the total jacking force. Additionally, the jacking resistance from the soil chamber pressure accounts for approximately 22 % of the total force. The frictional resistance of the ring structures represents only 23 % of the total jacking force, with the average surface friction force approximately at 12.4 kPa. Vertical and horizontal relative deviations of the tunnel were controlled at 32 mm and 22 mm, respectively. The settlements of the ground surface and box culvert induced by pipe-jacking were vulnerable to the grouting pressure of lubricants, with maximum values of 35.9 mm and 39.1 mm, respectively. The experience learnt from this project can provide valuable insights for the application of large-section rectangular pipe-jacking technology in underground space development. [ABSTRACT FROM AUTHOR]