Study On Strengthing Method And Effect Of Subway Tunnel Construction To The Upper Existing Building

Subway tunnel construction in the ground compact city will result in ground movement and deformation, which will lead to adverse influences to the perimeter and the upper buildings. Therefore, this paper research the subway tunnel excavation’s influences on the upper existing buildings and the reinforcement methods.This paper analyzes the deformation distribution of the upper soil after the tunnel excavation, put forward to use the preloading pile underpinning method to reinforce the settlement of the existing buildings caused by the excavation. Combined with a reinforcement project of a school dormitory settlement cracking in Xi’an, MIDAS GTS finite element software were used to analysis the force and the deformation of the dormitory after reinforcement. Four conclusions were drawn:(1) After the reinforcement of upper existing buildings, the settlement of the upper soil was normal distributed and the maximum settlement was occurred in the upper center of the tunnel.(2) When using preloading pile underpinning reinforcement, the settlement of the soil around the tunnel and the upper existing building foundation are obviously reduced, wherein the settlement of the upper building foundation can be reduced by 30%.(3) After using preloading pile underpinning reinforcement method, the stress and the deformation of the subway tunnel structure were changed lightly. Compressive stress was increased by 0.4% and tensile stress was reduced by3.6%-that will not cause security problems to the tunnel structure.(4) Based on the tests and analysis of the actual reinforcement construction, it was showed that after the use of preloading pile underpinning reinforcement method, the settlement of the dormitory was under control, the cracking did not continue on the wall. It suggested that the preloading pile underpinning reinforcement method was available. The short pile under the tunnel should be deep to 10 m, namely the distance from the bottom of the short pile to the top of the tunnel should be 3m-4m.The research results can provide reference to further study on the influence of the metrotunnel to the upper existing building and the reinforcement research. What’s more, it can be a reference of design and construction for similar reinforcement project.