Abstract
The construction of urban cross-river tunnels usually requires passing under river embankments, which inevitably disturbs the embankment substratum and causes ground deformation. Previous engineering cases have shown that embankment settlement is greater than ordinary surface settlement and that uneven settlement results in cracks of in the embankment, reducing the embankment stability. Based on a cross-river tunnel project in China, the construction risks caused by the additional stress on the embankment substratum, asymmetrical embankment load, and shield tunneling in saturated fine sand are analyzed during a large-diameter slurry shield tunneling below an urban river embankment diagonally. Additionally, relevant risk control measures, such as slurry pressure, jacking thrust setting, and driving velocity in the saturated fine sand stratum, are evaluated. The results show that during shield tunneling under a diagonal urban river embankment, the additional stress and asymmetrical load effects should be considered, and the shield slurry pressure and jacking thrust should be adjusted according to the distance between the cutter head and the embankment. Furthermore, based on settlement monitoring data, the driving velocity of the shield should be reasonably adjusted in a timely manner to avoid disturbing the fine sand stratum below the embankment.
Highlights
With rapid urban development, methods for quickly crossing a river and linking the two sides of a city have become the main concerns for modern society, and the utilization of cross-river shield tunnels has become an inevitable choice for its excellent tunneling speed, lower environmental impact, and good seismic performance. e Channel Tunnel (1994), the Tokyo Bay cross-sea tunnel (1997, Japan), the Elbe River fourth highway tunnel (2003, Germany), the “Green Heart” railway tunnel (2007, Netherlands), the Port Miami road tunnel (2003, USA), the Orlovsky River road tunnel, and the new Suez Canal tunnel are examples of famous cross-river shield projects with large diameters around the world
Based on a typical crossriver shield tunnel project, the construction risk caused by the effects of additional stress, asymmetrical load of the embankment, and the strata underlying the embankment during the process of a large-diameter slurry shield tunneling diagonally under the river embankment are analyzed
When the large-diameter slurry shield passed under the embankment diagonally, the effects of the additional stress on the underlying stratum, the asymmetrical load of the embankment, and the comprehensive properties of the fine sand stratum can all contribute to cracking of the embankment, thereby threatening the stability of the embankment and causing severe construction risks, if the shield tunneling parameters are not reasonably controlled
Summary
Methods for quickly crossing a river and linking the two sides of a city have become the main concerns for modern society, and the utilization of cross-river shield tunnels has become an inevitable choice for its excellent tunneling speed, lower environmental impact, and good seismic performance. e Channel Tunnel (1994), the Tokyo Bay cross-sea tunnel (1997, Japan), the Elbe River fourth highway tunnel (2003, Germany), the “Green Heart” railway tunnel (2007, Netherlands), the Port Miami road tunnel (2003, USA), the Orlovsky River road tunnel (under construction, Russia), and the new Suez Canal tunnel (under construction, Egypt) are examples of famous cross-river shield projects with large diameters around the world. Is paper analyzed the construction risk caused by a large-diameter slurry shield (with a diameter of 11.3 m) passing under a river embankment at an angle while considering the embankment factors mentioned above, and an adjustment scheme is put forward for use during tunneling under a river embankment in a saturated fine sand stratum. Based on a typical crossriver shield tunnel project, the construction risk caused by the effects of additional stress, asymmetrical load of the embankment, and the strata underlying the embankment during the process of a large-diameter slurry shield tunneling diagonally under the river embankment are analyzed. Under the action of the semitrapezoidal distributed load ABCD, the calculation results of vertical additional stress σz at the buried depth of the tunnel axis (z 16.1 m) is shown in Figure 3 (x represents the distance between the shield cutter head and the embankment foot and is positive in the driving direction).
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