Abstract
The stability analysis of the tunnel face is not only essential for guaranteeing the safe construction of urban shallow tunnels, but also directly affecting the influence degree of tunnel construction on nearby structures. The primary concerns in the stability analysis of the tunnel face are the instability mode of surrounding rocks and the limit support pressure on the tunnel face. In this paper, face stability of shallow tunnels in sands was conducted using a symmetrical model test. The ground surface settlement, support pressure on the tunnel face and progressive instability modes of sands at tunnel face are measured by using an LVDT (Linear Variable Differential Transformer) displacement sensor, high-precision pressure sensor and high-definition digital camera, respectively. The test results indicate that the shear failure band appears in sands in front of the tunnel face and develops from the tunnel invert to the tunnel crown. The upper sands undergo stress redistribution, and the pressure arch appears with initial form of “ellipsoid”, then of the “pyramid”. Moreover, the support pressure on the tunnel face experiences four stages, namely, rapid decline stage, the minimum stage, slowly raises stage and stable stage during tunnel excavation. The research results of this paper will provide theoretical support for the reasonable value of the support pressure on the tunnel face in practical engineering.
Highlights
Environment protection are attracting increasing attention with the ground traffic is becoming more and more busy, underground excavation has become the preferred method of tunnel construction instead of the cut-and-cover method
According to support condition at tunnel face, the tunnel construction method in urban areas is divided into two types, namely, the closed face tunneling method and open face tunneling methods
The tunnel face stability is a necessary condition to ensure the safety of shallow tunnel construction, and directly affects the impact of tunnel construction on nearby structures
Summary
Environment protection are attracting increasing attention with the ground traffic is becoming more and more busy, underground excavation has become the preferred method of tunnel construction instead of the cut-and-cover method. Chambon and Corté [3] developed the earliest centrifuge model test to study the stability of the tunnel face and obtain the failure mode of sands in front of the tunnel face. Mair [6] studied the different mechanisms of face instability of tunnels constructed in sands and clays by using a centrifugal model test. Chen et al [12] conducted centrifugal model tests to study the face failure of the earth pressure balance shield caused by steady seepage in saturated sandy silt. Their results indicated that the limit support pressure increases linearly with the increase in the water head difference between the ground and the chamber. The laws of development and evolution of the ground surface settlement are investigated and compared with the results of the support pressure on the tunnel face
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