Research On Deformation Of Existing Underlying Shield Tunnel Caused By Excavation Construction

With the massive growth in urban traffic, subway become a good means to solve the trafficcongestion. At the same time, with the rapid development of urban construction, foundationconstruction will inevitably appear at the top of the subway tunnel. Excavation is bound toaffect the deformation of the subway tunnel below it. Currently the research on underlyingshield tunnel deformation effected by pit excavation is still not perfect, this paper used finiteelement software, and analyzed tunnel deformation factors, to study underlying shield tunneldeformation effected by excavation. This paper endeavored to do the following work:Firstly, this paper described the background, summarized the research situation aboutunderlying shield tunnel deformation effected by pit excavation at present, and it proposed theresearch questions to be addressed in this thesis.Secondly, it described the mechanism of soil deformation caused by excavation, thecalculation methods of earth pressure, pit uplift spring back and residual stress theory. It alsodescribed the calculation method of elastic foundation beam, calculated the analytical solutionsof the additional stress, vertical deformation, perturbation, moment, corner and shear in underlying tunnel.Thirdly, it used the software MIDAS/GTS with finite element analysis function andnumerical simulation method to study underlying shield tunnel deformation effected by pitexcavation. It analyzed tunnel deformation from the whole excavating process, the size of pit,the position between pit and tunnel. The results showed that: Vertical displacement is the maindisplacement of the tunnel. The tunnel deformation is as a linear increase with the space effectof excavation. Little effect on the position between the pit and tunnel of the horizontaldisplacement. The longitudinal length of excavation little affects the tunnel deformation. Thesupporting structure of excavation can reduce the deformation of the tunnel. Block excavationcan reduce the vertical deformation of the tunnel, and it also can shorten the exposure time ofthe maximum deformation of the tunnel. Engineering geological conditions have a significantimpact on the tunnel deformation, the deformation will increase with the poor geologicalconditions. At the end, it summarized the protective measures and monitoring techniques ofexcavation.