Mechanical Effects Under The Large-span Shallow Metro Station Construction With Center Drift Method

With the development of the urban railway system and the increasing of the shallow tunnel constructions, the excavation methods appear to be more and more diversiform.Center drift method is widely used in shallow tunnel engineering due to its special advantages. However, the study of the design and computing methods on this kind of complicated excavation methods is still not enough and should be improved further.Therefore, it is very important to balance the controlling of the deformation of the surrounding rocks and the construction speed on the condition that the stability of the tunnels is guaranteed. Meanwhile, it is also important to study the mechanical and deformation characteristics of the surrounding rocks and supporting structures under the same premise. Based on the analysis of the relevant research achievements both at home and abroad, relying on the excavation project at the Xinxingjie station of metro line 1 at Urumchi, Sinkiang, this paper investigates the mechanical and deformation characteristics of the surrounding rocks and supporting structures, the impact on the stability of the surrounding rocks caused by different excavation and supporting parameters, in the procedure of the pilot tunnel construction by using center drift method. The main research content:① Introduce the theoretical basis of the overlying layer’s sedimentation caused by the shallow tunnel construction. And propose the specific measures to control the sedimentation of the layer according to the regular distribution pattern of the sedimentation.② Aimed at the features of the support metro project, applying numerical analysis method to build two-dimensional model, compare and analyze the center drift method and both side heading method, including comparison the mechanical and deformation characteristics of the surrounding rocks and supporting structures within the two methods. The computing results show that the center drift method is better to keep the surrounding rocks stable.③ Considering the spatial effects of each pilot tunnels in the process of center drift method, on the basis of the geological conditions of the proposed project, applying the well designed excavation parameters and support parameters, build the three-dimensional numerical model of the center drift method; Simulate the whole process of the excavation and support according to the approach construction scheme, study the mechanical and deformation influence that the excavation had on the surrounding rocks and support structures, analyze its change rules, guide the construction, avoid risk.④ By tuning the excavation parameters and support parameters of the tunnel construction, compare and analyze the mechanical deformation characteristics of the surrounding rocks under different working conditions. For example, excavation step(1m, 2m, 3m), small pilot tunnel bench length(10m, 15 m, 20m), steel frame distance of the support structure(0.5m, 1.0m, 1.5m), reinforcing ring thickness of the surrounding rock(0m, 0.5m, 1.0m, 1.5m), and so on. After the comparison and analysis, considering the construction security and speed etc issues together, choose the optimal parameters.