Mechanical Characteristics of Mud-Water Balance Steel Pipe Jacking in Deep-Buried High-Hydrostatic Pressure Strata

To investigate the mechanical characteristics of mud-water balance steel pipe jacking under deep-buried high-hydrostatic pressure strata, field monitoring was conducted on the pipe-soil contact pressure, pore water pressure, and pipe strain in the advanced drainage pipe jacking project at Wangjiazai Tunnel in Yunnan Province. The monitoring contact pressures were systematically compared with the design values in domestic and international standards. Additionally, numerical simulations were used to study the influence of secondary grouting pressure on the pipe. The results show that: (1) By comparing the monitoring contact pressure values under non-operational conditions with the calculated values in the standards, the earth pressure calculated using the calculation model and calculation parameters specified in the Japanese super large diameter PC method and Chinese T/CECS 246-2020 demonstrated superior agreement with the monitoring values. (2) During the jacking process, secondary grouting pressure significantly affected the contact pressure of the pipe, especially after entering the strong water-rich zone, where a rapid increase in grouting pressure led to sharp changes in the contact pressure on the grouting side. (3) Circumferential strain monitoring showed an alternating tension-compression pattern between opposite sides of the pipe, and axial strain deviated from the zero point due to the Poisson's effect and negative frictional forces, indicating an eccentric compression state during the jacking process. (4) After validation, numerical simulations were used to study the impact of secondary grouting pressure on the pipe. As the grouting pressure increased, the horizontal position yielded first in unilateral grouting, while in the bilateral grouting, the top and bottom of the pipe yielded first. The pressure control boundaries for unilateral and bilateral grouting were found to be 2.5 MPa and 0.6 MPa, respectively.