Research On The Influence Of Deep Excavation To Adjacent Existing Tunnel

With the rapid development of city, in order to meet the residents daily travel convenience, in the center of a second-tier cities crowd gatherd, and the use of underground space becomes more and more popular, thus emerged a large number of deep foundation pit engineering in the center of the city. And this kind of foundation pit engineering in the construction process will impact on the surrounding existing buildings, underground pipelines and adjacent subway tunnel. Therefore, how to accurately calculation the horizontal and vertical displacement of soil and metro tunnel in the design and construction of deep foundation pit, and guarantee the safety of the foundation pit supporting structure itself and the supporting structure and to ensure the safety and mormal use of adiacent buildings and subwav tunnel, is a urgent need to solve the problem in the process of construction of foundation pit.In this paper, combined with the two stage deep foundation pit engineering of Xi’an international center for DK-2, using ANSYS finite element software to establish three-dimensional finite element model of the excavation of foundation pit, in the process of excavation, has been analyzed quantitatively the deformation of retaining structure of foundation pit,the heave of pit bottom soil, the settlement of the surrounding soil and the horizontal displacement and vertical displacement of the adjacent to the existing subway tunnel; studied on the subway tunnel in different depth,subway tunnel and excavation in different horizontal spaceing, subway tunnel in different soil conditions under the influence factors on both the horizontal displacementand vertical displacement effect of subway tunnel structure. The main conclusions are as follows:(1) In the foundation of pit excavation, the soil pressure on both side of foundation pit is smaller, less effect on the deformation of retaining structure of foundation pit,with the increasing of excavation depth, the horizontal and vertical displacement of the retaining structure of foundation pit is also increasing, but the increase amplitude of the vertical displacement showed a gradually decreasing trend.(2) In the process of pit excavation, with the pit at the end of the release of soil stress, the soil heave of pit bottom also unceasingly increases, the maximum displacement is 28.8 cm.(3) In the excavation of shallow soil, the deformation of soil around the foundation pit is expressed as a linear change, but with the increase of excavation depth, there will be some nonlinear variation.(4) In the process of foundation pit excavation, subway tunnel deformation mainly focus on horizontal displacement, and the horizontal displacement is much larger than the vertical displacement.(5) Based on the simulated of different buried depth of subway tunnel,the results show that: with the increasing of the subway embeded depth, the subway tunnel deformation shows gradually decreasing trends. When the embedment depth is less than 20 m, the tunnel displacement greatly influenced by the change of the buried depth of tunnel; When more than 20 m, less affected.(6) By means of simulated of metro tunnel from the foundation pit supporting structure with different horizontal distance, the results show that 7.5 m is a critical point.Horizontal distance increase from 7.5 m to 10 m,in this process, the decreases amplitude of the horizontal displacement of subway tunnel is maximum, reaching42.2%. While increased from 10 m to 15 m, the decrease amplitude of the vertical displacement of subway tunnel is 25.7%.