Comparative Analysis of Pit Foundation Excavation Schemes of Existing Shield Tunnels

In order to study the effect of three shield tunnel excavation on underlying shield tunnels in the loess area,by means of FLAC3 Dfinite difference numerical software and combining with the actual conditions of hydrogeology and engineering geology conditions,3D numerical model is established to compare the uplift displacement and stress of the existing shield tunnel structures caused by synchronous excavation and by-phase excavation.The results show that the excavation has a greater impact on the underlying of shield tunnel uplift displacement,and the tunnel uplift displacement decreases after structural construction of pit foundation,compared with synchronous excavation,phased excavation can reduce effect on the underlying shield tunnel,and the internal force of tunnel satisfy strength requirements,hence it is suggested that the excavation order should be firstly construct both sides and then in the middle.