Study On The Mechanism Of Ground Surface Settlement Induced By Shield Construction In Xi'an

Xi'an is of the most major metropolis in west development of China. The congested traffic has become a serious problem for loess area such as Xi'an, and the construction of subway is viewed as an effective solution to the problem. The shield driving method has been one of the main construction methods in the urban tunnel in our country. Meanwhile, due to collapsible loess, some special engineering problems would be faced .The soil property has an influence on ground settlement to some extent during the tunnel construction. So it would make practical sense to study surface settlement while building tunnel in loess area.The paper summarizes ground settlements influencing factors, characteristic of ground settlements in Xi'an tunnel. The mechanics of surface settlement induced by shied construction is generalized systematically. Build tunnel in the loess area is rarely involved, because of the complex environment in Xi'an and probabilistic loess mechanics parameters. The disturbance of soil caused by shield tunnel construction results in the soil movement, mainly the ground settlement, which is one of the problem highly concerned in the design and construction process of shield tunneling. Shield tunneling is simulated by a finite difference code FLAC3D according to survey information. Then, the characteristic of ground settlement is studied on the basis of combination of the measured data of Xi'an No.2 Subway Line and the result of numerical analysis. It generally analyzes the characteristic of ground settlement with respect to the depth, the characteristic of ground settlement on lateral section of the tunnel and the lateral extension of settlement as well as ground settlement on longitudinal section of the tunnel. With calculation complexion of loess area, the regularity is studied from the characteristics of loess. The author attaches great importance to the relative displacement between the structure of subways and the surrounding soils in condition of soaked and unsoak -ed different capacity of containing water. So it is useful and practical to Xi'an tunnel's construction in the future that studied the soil sedimentations.