Computational Limit Analysis of Shield Tunnel Face with a Consideration of Permeability Anisotropy

Abstract:

The shield method is widely applied in the construction of subways and instability of the excavated surface of shield tunnels will be induced if insufficient support pressure is exerted， resulting in significant economic losses and casualties. The hydraulic states will be changed by the excavation and the induced water flow not only introduces the seepage force but also deteriorates the mechanical behavior of the surrounding soils. Therefore， more attention should be paid to the stability of the tunnel face under seepage conditions. The permeability of the surrounding soils is mostly simplified to be isotropic， which is in fact anisotropic due to the effect of the depositional environments. Based on the bounding theory， a three-dimensional computational limit analysis method is established by the combination of the simplex strain finite element method and the semi-definite programming. Through the incorporation of seepage analysis， the effect of permeability anisotropy on the seepage field， the limit supporting pressure and the collapse mechanism of the shield tunnel face is discussed. The present paper can provide important guidance to the construction of shield tunnels.

Key words:stability of excavation face;anisotropy of permeability;limit analysis;seepage force