Abstract:

As metro lines keep increasing in large cities, shield tunnel crossing liquefied foundation may appear. The potential risk of floating damage exists in shield tunnels once earthquake occurs. In order to study the seismic response of the liquefied stratum around shield tunnel, several shaking table tests were carried out under three different peak accelerations. The developing characteristics of the excess pore pressure as well as the floating laws of the shield tunnel were analyzed. The experimental results indicates that: (1) The liquefied appears at the surface and in the shallow area of the saturated sand firstly, The degree of liquefaction decreased along with the increment of buried depth of the shield tunnel, which means increasing the depth of the tunnel can reduce the liquefaction; (2) The floating mechanism of shield tunnel can be revealed by the model experiment. Even if the foundation is not fully liquefied, the tunnel floating movement appears when the buoyancy caused by the excess pore water pressure is larger than the summation of the residual overburden pressure and tunnel gravity. The antifloating ability of shield tunnel can be improved by eliminating liquefaction foundation and increasing tunnel weight, which ensure the tunnel safety during the earthquake.

Key words: shield tunnel, sand liquefaction, tunnel uplift, floating mechanism, antifloating design