The Influence Of Foundation Pit Excavation On Adjacent Existing Tunnel

With the growing development of city Tunnel vigorously,More and more excavation inevitably adjacent or intersecting to existing tunnel. Excavation cause varying degrees of soil stress release around the pit, Resulting in the displacement of supporting structures and stratum around pit,and then caused additional stress and additional tunnel deformation,great deformation may caused a risk of leakage and cracking of tunnel,thus affecting the structural safety and running of the tunnel,Therefore it is necessary to analyze the influence of excavation on adjacent tunnel.Combined with the actual project that high-rise building foundation pit near the terminal of Jiaozhou Bay tunnel in Qingdao,use finite element analysis software MIDAS/GTS to study the influence of deformation and stress of whole process of excavation on adjacent existing tunnel.Quantitative given the reference of proper excavation distance and depths for Qingdao similar excavation. The main research of this paper can be summarized as follows:1. The statistics cases have been collected in which the foundation pits are adjacent to the existing tunnel. By using data statistical method, the influential factors are classified, such as the overview of foundation pit engineering, relative distance between the foundation pit and tunnel, supporting structure, reinforcement, space-time effect, underground water, etc. Then, according to the statistics chart and data, the deformation characteristics of the nearby tunnel caused by excavation of deep foundation pit can be analyzed and summarized systematically.2. The displacement effect due to the surrounding wall soil unloading of adjacent excavation is not considered by the theoretical analysis method. Based on the principle of equivalent stiffness of continuous model, the horizontal and vertical additional stress is calculated by the Mindlin solutions. Furthermore, the tunnel structure is considered as the beam with infinite length. The additional stress is imposed on the Winkler model and the governing equation is built up on the adjacent tunnel structure. So the influence of foundation pit excavation of subway tunnel will be estimated.3. The actual excavation near the existing tunnel under the unique geological conditions in Qingdao,Using MIDAS / GTS software to establish the impact analysis calculation model of the Influence of the Foundation Pit Construction on the Adjacent Tunnel Structure,Consider the process of tunnel deformation,Dynamic analysis of the impact on the existing tunnel,calculated results were compared with the actual monitoring results,Verify the rationality and validity of the finite element mode,Provides the basis for the next simulation of different conditions of the tunnel influence.4. On the basis of the analysis of the engineering example, by changing the thickness of the excavation, the depth, and the level of excavation, Under the conditions of different pit excavation depth,spacing,dimensions,Thickness,analysis of the deformation and stress of the tunnel structure.