Ground Settlement Law, Jacking Force Prediction, and Control Countermeasures for Large-Section Rectangular Pipe Jacking of National Highway Underpass

The rectangular pipe jacking method is an efficient, green, trenchless technology for constructing urban underground space. However, some problems, including the high jacking resistance, the instability of the tunneling face, and excessive ground settlement during the large-section rectangular pipe jacking for the underpass of national highways, seriously affect construction safety and traffic. Based on the engineering background of the large-section rectangular pipe jacking in constructing the subway entrance tunnel of Guangzhou Metro Line 7, this work adopts the methods of theoretical calculation, numerical simulation, and engineering application. Five kinds of mechanical models for pipe soil slurry interactions in rectangular pipe jacking are analyzed. An evaluation of the applicability of the jacking force prediction of the different models is conducted. Moreover, the ground settlement law for the large-section rectangular pipe jacking for the underpass of national highways under different influencing factors, including slurry sleeve thickness, grouting pressure, and earth chamber pressure, is revealed. The control countermeasures of the ground settlements, such as installing a waterproof rubber curtain for the tunnel portal, pipe jacking machine receiving techniques, thixotropic slurry for reducing friction resistance, and soil stability at the tunneling face, are carried out. The results show that there is no need to install an intermediate jacking station in the large-section rectangular pipe jacking project with a jacking distance of 63 m. The most reasonable thickness of the thixotropic slurry sleeve is about 150 mm. The most reasonable grouting pressure range is 600-700 kPa. An earth chamber pressure of about 153 kPa is more reasonable to control the soil stability of the tunneling face. The engineering practice shows that the maximum ground settlement of the national highway during jacking is 10 mm. The maintenance effect is excellent, and the traffic operates normally.