Abstract
With the rapid development of the tunnels constructed under the rivers and seas, the research on face stability of shield tunnel in water-rich sand has important theoretical value and engineering application significance. In addition to the loads exerted by overlaying strata, the tunnels constructed in water-rich strata are usually subjected to high hydrostatic pressure or seepage forces, which are apt to cause the ground collapse of the shield tunnel face. The distribution of hydraulic head field around the tunnel face is critical to assess the impacts of the seepage forces on the tunnel face stability. This paper investigates the axisymmetric problem of the face stability of the shield tunnel under a seepage condition within the framework of limit equilibrium analysis. First, numerical simulations are carried out in this paper to analyze the distribution rules of total hydraulic head and pore water pressure near the tunnel face of the shield tunnel under the condition of stable seepage with different cover depths. Then, based on the distribution rules of total hydraulic head, new formulas for predicting the total hydraulic head along the horizontal and vertical directions are proposed and compared with the numerical simulations in this paper and existing approximate analytical solutions. Second, the classical axisymmetric limit equilibrium model is revised by incorporating the new approximate analytical solutions of hydraulic head field to determine the failure modes and the limit support pressures with a numerical optimization procedure. Lastly, the comparisons of the results obtained from the theoretical analysis model in this paper and the existing approaches are conducted, which shows that the failure mechanism proposed in this paper could provide relatively satisfactory results for the limit support pressures applied to the tunnel face.
Highlights
When the shield tunnel locates under the water table line, the soil or rock excavation often induces underground water seepage
Lü [3] conducted a series of 1 g model tests to analyze the influences of tunnel depth, seepage, and water level on the limit support pressure of the shield tunnel face and their experimental results were compared with the theoretical predictions
The classical limit equilibrium model is revised by incorporating the new approximate analytical solutions of the hydraulic head field to determine the failure modes and the limit support pressures with a numerical optimization procedure
Summary
When the shield tunnel locates under the water table line, the soil or rock excavation often induces underground water seepage. Lü [3] conducted a series of 1 g model tests to analyze the influences of tunnel depth, seepage, and water level on the limit support pressure of the shield tunnel face and their experimental results were compared with the theoretical predictions. Chen et al (2018) [4] carried out centrifugal model tests to investigate the face failure of earth pressure balance shield induced by steady state seepage in saturated sandy silt ground Their results indicated that the limit effective support pressure approximately increases linearly with the increase of the difference of hydraulic head between the ground and the chamber. Numerical simulations are carried out to analyze the distribution rules of total hydraulic head and pore water pressure near the shield tunnel face under the condition of stable seepage with different cover depths. Numerical Simulation of the Distribution Rules of the Seepage Field Near the Tunnel Face
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