Study On The Effects Of New Metro Station Crossing Under The Existing Metro Station In Small Distance

At present, it is an inevitable problem that the newly built station of metros crossing the existing in the planning and construction of metropolis traffic network. The interaction of the close-spaced construction is very complex. How to make these influences into minimum and grip exactly for deformation characteristics and rules of the ambient soil layer and adjacent underground existed structure through metro construction course becomes an important task. Thus, it can not only pledge the construction to go on wheels, but also the existing lines to secure, normal operation and to seek a safe, economic, reasonable construction method.That Beijing XuanWumen No.4 Line crosses under the existed line is the first project that station crossing under exiting station, According to this one practical project this paper has made an overall and systemic analytical study on influence of urban metro tunnel construction by shallow excavation upon the overlying existed structure, by long-distance automation monitors and numerically simulated. specifically as follows.Firstly, this article key point is to apply long-distance automation monitors to the exiting station structure and the track, including the settlement and the incline and so on, with the static level, the beam plate clinometer, the dislodgement to count and so on. At the same time, a lot of information on-site monitoring, in the course of excavation and construction of the subway station, the reason of the existed structure settlement was analyzed, the settlement in the first excavation occupy 42 percent of the total settlement of existed structure. The soil for grouting between the new subway station and the existed subway station can effectively reduce the impact of the construction of new lines on the existed structure.Secondly, the whole process of the excavation was numerically simulated by FLAC3D, and the impact of the construction process on the existed structure was predicted and analyzed, and the results were consistent with the measured results. Numerical simulation of the existing structure for the maximum settlement -8.4 mm than the real value of -6.24 mm larger 2.16 mm, an increase of 34.6%. Although the simulation results too large in the actual monitoring results, but the simulation results accurately reflect the construction process of displacement trends.Thirdly the numerical model for the new subway station crossing the existed subway station is established by FLAC3D, and the effects of different factors on the behaviors of existed station structure settlement are investigated. The sidestep excavation is superior to that level of full-face, short footage is better than long footage, under the conditions of a certain rock layer, The increase of thickness between new station and existed station would increase the settlement of the existed station structure.