Risk assessment method for subway-crossing shield tunnel based on ground loss ratio

Abstract

With the accelerating urbanization and development of increasing underground space in China, shield tunnels have been widely applied to underground roads in central urban areas. However, there are many subways, bridge pile foundations, pipelines, and other buildings (structures) in the central urban areas with complex surroundings. Therefore, it will be an unavoidable engineering difficulty for the construction of shield tunnels in the central urban area to cross existing buildings (structures) at a close range, such as tunnels, underground pipelines, and basements. There are few studies on the shield tunnel with an outer diameter of 15 m and above crossing existing buildings (structures). The core concept of numerical simulation of a subway-crossing shield tunnel is an idealized assumption of main factors and an omission of secondary factors. Consequently, the accuracy of the risk assessment method based on numerical simulation is over-dependent on the experience of engineers. In practical engineering applications, people often have great disputes about numerical simulation results. To solve the above problems, this paper uses the Midas_GTS finite element analysis software to study the risk assessment method for shield tunneling in Shanghai by taking the Shanghai Beiheng shield tunnel with an outer diameter of 15.0 m as an example. As the soil layers in Shanghai are evenly distributed with little difference, construction quality is the main control factor for the risk difference in the construction of the shield tunnel in Shanghai. In this context, this paper proposes to assess construction quality using the ground loss ratio index obtained through the back analysis of the measured data. Meanwhile, the simulation method adopted for back analysis and the ground loss ratio index are also used to assess the risks in shield tunneling. The settlement results of the Shanghai Beiheng shield tunnel under-passing the M11 shield tunnel predicted by the above risk assessment method are consistent with the actual results.