Study on the Support Pressure of Tunnel Face for the Construction of Pipe-Jacking Across Thin Overburden River Channel Based on Mud-Water Balance

Pipe-jacking construction technology is favored in urban construction due to its advantages of non-excavation and high safety. However, the instability of the tunnel face often occurs due to unfavorable conditions such as pipe-jacking across river channel, shallow soil cover, and improper control of support pressure. In this paper, combined with the limit balance method, the general mathematical expressions of the tunnel face support pressure (lower limit value Pmin and upper limit value Pmax) were derived when passive damage and proactive destruction occurred in the tunnel face of the pipe-jacking; the optimal value Po of the support pressure in the tunnel face based on the mud-water balance principle was given. Then relying on the project of Y25-Y26 pipe-jacking across the Chu River channel in Hefei North District, a numerical simulation method was used for further discussion. The results indicated that: when the river overburden was 3m, the ultimate support pressure calculated by numerical simulation was 881.786kN, and the optimal support ratio "λ" was taken in the interval of 1.0~1.5; The upper limit value Pmax, lower limit value Pmin and optimum value Po calculated by theoretical equations were 2669.977kN, 309.910kN and 1044.870kN respectively; The support pressure of the tunnel face should be set in a reasonable range between the upper limit value Pmax and the lower limit value Pmin, so as to ensure that the support pressure of the tunnel face of the pipe-jacking construction and the resistance always keep a balanced state. The relevant research results of the paper provided an important technical guarantee for the successful implementation of the dependent project, and at the same time can serve as a reference example for similar projects.