Study On Deformation And Control Of Existing Metro Induced By Long-distance Adjacent Construction Of Utility Tunnel In Densely Urbanized Area

Utility tunnel was constructed on the densely urbanized area,which could induce many problems such as high environmental risk,tight safety control standard and limited construction period.In this study,the deformation of ground and adjacent existing tunnel induced by the long-distance utility tunnel excavation was investigated employing theoretical analysis,numerical simulation and experimental test.As a result,the technique for controlling excavation disturbance was proposed and then applied in the actual construction process.Therefore,the main findings were summarized as follows:(?)Based on the characteristics of long-distance excavation closing to the existing line,the analyzed model was simplified as a semi-infinite elastic plane with two circular holes under the specified boundary condition.According to the application of complex variable theory on analyzing the elastic half-plane problem,the conformal mapping and Schwarz alternation method were employed to investigate the analytical solution composed of complex variable when the boundary was of unloading condition,which could be adopted to calculate the deformation and stress of circular hole.The proposed analytical solution could guide the analysis on the displacement of the existing line with different approach distances under the worst condition.(?)During the unloading surface approaching to the existing line,the evolution of stress releasing region performed as a plane expansion and vertical development process in the surrounding soil.On the cross-section view,the deformation of existing line tended to the excavation surface under the effect of invert soil arching zone.The lateral soil arching zone developed to the deep soil layer with the increasing unloading ratio and unloading degree of foundation pit.The construction of utility tunnel and the backfill of overburden could further induce the uneven deformation of adjacent existing line.There was an exponential relationship between the displacement of the existing line crown and the unloading ratio or degree.The deformation of existing line increased obviously when the unloading ratio and the unloading degree exceeded 0.5 and 0.6,respectively.(?)It could be seen from the analysis on sensitivity of excavation parameters that the vertical distance between the pit bottom and the existing line was the main factor that determined the displacement of the existing line.When the unloading free face moved down to the pit bottom,the long axis of cross-sectional profile of the existing line where the elliptical deformation occurred gradually rotated and pointed to the pit bottom surface.The excavated parameters with large single unloading volume promoted the stable soil arching zone formed in the surrounding soil.Therefore,the disturbance to the stable arching zone should be decreased to prevent the side and the bottom loose region from connection,which could reduce the whole floating of the adjacent existing line.(?)Based on the requirement for reducing disturbance in the four-way joint section of utility tunnel,the island-reserved excavation method and the expanded grouting in bottom soil was adopted as the excavation disturbance control technology.The control technology has been applied in the construction process and the automatic real-time monitoring devices were installed on the existing line in operation.The monitoring data showed that the vertical displacement of the existing line met the admissible value.This suggested that the application of the proposed control technology on the adjacent excavation could reduce the risk of disturbance to the existing line under the premise of construction efficiency.