Analytical solution of the shallowest overburden thickness of special-shaped shield tunnel in layered soil.

The water-rich shield tunnel plays a significant role in the rapid development of underground space construction. The use of various special-shaped shield tunnels is gradually emerging for the need of functional diversity. In this study, a shield tunnel shape coefficient was proposed, and the analytical solution for the shallowest overburden thickness of special-shaped shield tunnels in double-layered soil was derived using both linear and nonlinear soil resistance models. The variables influencing the shallowest overburden thickness of shield tunnels were analyzed, and the buoyancy of shield tunnels at different construction stages was discussed. Furthermore, the solution to determine the shallowest overburden thickness of shield tunnels in multi-layered soil was presented. It was observed that the shallowest overburden thickness of shield tunnels is negatively correlated with the tunnel shape coefficient, the longest length of the cross section, and the cohesion, internal friction angle, and submerged bulk density of the soil layer. The analytical solution for the shallowest overburden thickness, considering the shear force based on the nonlinear soil resistance model, is more conducive to ensuring the anti-floating stability of the shield tunnel without excessive anti-floating capacity. [ABSTRACT FROM AUTHOR]