Analysis Of Mechanical Characteristics And Deformation Law For Existing Metro Tunnel Upper Crossing By Close Range Excavation Passageway In Loess Region

With the construction of urban metro more and more, it will inevitably encounter newly constructed metro tunnel or excavation passageway crossing existing metro tunnel. Only the Xi’an area in recent years has completed many crossing existing metro tunnel projects. However, through the investigation and read a lot of literature to understand that the related research of existing metro tunnel upper crossing by close range in loess region is less, therefore, it is necessary to study it.Rely on Ⅲ-C toⅡ-B excavation passageway of Taibai road station of Xi’an metro line No.3, field tests and numerical simulation are conducted in this paper so as to analysis contacting pressure between initial supports and secondary linings, stress of secondary linings of existing metro tunnel, crown settlement, peripheral convergence and settlement of ground surface, the study results indicate as follows:The contacting pressure between initial supports and secondary linings of existing metro tunnel in later crossing line on the whole is larger than in earlier crossing line, and in one tunnel case the pressure on face construction surface side is greater than on the other side. Influenced by the change of upper crossing passageway height, the stress of the left side is pressure stress and the right side is first pressure stress after to pulling stress, the secondary linings of the earlier crossing line appears the trend twist to the left. The stress of secondary linings of later crossing line is basically symmetrical, which on the whole is larger than the earlier crossing line. The ground surface settlement process of the existing metro tunnel is shown to be the first uplift, then subside, and then gradually stabilized. Along the upper crossing passageway, the longitudinal distribution of ground surface settlement is the middle bigger than the value in both side. The vertical deformation of existing metro tunnel is shown as up floating, deformation curve is similar to normal distribution. The deformation of tunnel vault is performance as before upper crossing is subside, in the process of upper crossing is uplift, and after upper crossing is gradually stabilized. The horizontal deformation of the existing metro tunnel is mainly move to the left side, the horizontal deformation is less than vertical deformation, the main deformation of metro tunnel is vertical deformation. The peripheral convergence of the existing metro tunnel is shown to converge to the inner side, and is gradually stabilized at the end of the construction.The study results not only effectively guide the smooth implementation of the project, but also can provide reference for the design and construction of similar projects in loess region.