Research Of Optimizing Construction Scheme Of The Accessory Structure Mined Tunnel Passing Over The Existing Tunnel Project Nearly In Loess Area

With the development of Xi’an metro network planning and the increase of metro lines, there will be more and more problems of the cross over among metro lines. Xi’an is located in the loess deposit in the middle of Weihe basin, and the engineering geology is complex, so the engineering geological condition is complicated. In addition, the control requirements of deformation and atress are higher when passing through the existing metro tunnel, which puts forward severe challenges to propose the construction scheme of the cross over among metro lines. Furthermore, there is no ready-made construction technology and research results can be used for reference. Therefore, it is urgent to study to use which construction scheme of the cross over among metro lines to ensure the safety of existing subway structure.This paper Relying on Xi’an metro line three station affiliated South Taibai Road Underpass structure cross cover existing subway engineering. The main research work is as follows.(1) In this paper, based on the existing subway two lining casting time and the reinforcement effect of the interlayer soil, the paper puts forward four kinds of the construction scheme of the cross over among metro lines. Scheme one: the existing subway both carry on the secondary lining and grouting for interlayer soil, and then carried on the construction of the passageway. Scheme two: the existing subway carry on the secondary lining but do not grouting for interlayer soil, and carried on the construction of the passageway directly. Scheme three: existing subway before pouring the second lining instead of using temporary steel reinforcement, and the interlayer soil grouting reinforcement, and then across the tunneling channel construction, finally pouring both secondary lining of subway. Scheme four: existing subway before pouring the second lining instead of using temporary steel reinforcement, but no interlayer soil grouting reinforcement, directly construct the passageway, finally pouring both secondary lining of subway. Analysis the four construction scheme deformation and stress of existing subway in during the passageway construction process of the most unfavorable case. Through the comparative analysis, we select scheme one.(2) The scheme should be used to relying on engineering. During the construction, we survey the pressure between primary support and secondary lining, the internal force of secondary lining, crown settlement, peripheral convergence in existing subway and surface subsidence. By analyzing the data, it can be known that the overall deformation of the scheme is small. For the initial support and secondary lining pressure, existing subway left line due to avoid water pipe caused biasing. Left pressure is greater than the right side. But the overall pressure in numerical partial small. Existing subway right line pressure left and right symmetry. For secondary lining internal force, existing subway left line left compressed but right tensioned. Existing subway right line left and right symmetry. Vault is pulled and the rest of the parts are pressed, the scene of the secondary lining structure does not crack, the overall structure is in a safe state.