The Effect Of Shielding Construction On The Upper Existing Tunnel For Perpendicularly Crossing Tunnels

With the increase of mileage of subway construction in our country,the distance tunnel is increasing,and new problems are put forward for researchers.Based on previous study,this paper uses the method of indoor experiment and numerical analysis to simulate the construction process with Hangzhou Metro Line 2 under Yuhuangtang tunnel project,which is close to the ancient pier intersection.At the same time,influence of tunnel spacing,internal force on the bending moment,soil displacement and surface subsidence of the existing tunnels in process of excavation is carried out.And have been made an intensive study of the changing behavior of the surrounding soil and the existing tunnels in excavation process of new tunnel.The research work and achievements are as follows:(1)Based on results of unloading and recompression triaxial tests of silty clay based on GDS dynamic and static triaxial instrument,it is found that the stress-strain curve of Hangzhou soft soil is basically hyperbolic curve,and it has good normalization characteristics and conforms to Duncan-Chang model.(2)The subsidence of the lower subway tunnel has the greatest impact on existing tunnels in the upper part of overlapping area.The maximum settlement of ground is located on the surface above midpointof center line of the two subway tunnels.The settlement in vertical lower shield tunnel is in accordance with the Peck formula,The influence of tunnel,the settlement within overlapping range is smaller;in the direction of subway tunnel axis,the displacement of overlapping parts is smaller than two sides.(3)The maximum value of the shear force is mainly in the upper and lower surface of tunnel and near the center line of long axis.The results show that reinforcement of soil in the overlapping area can effectively reduce influence of the lower tunnel construction on upper tunnel and the surface of tunnel.(4)Through analysis of data and engineering analogy,it is suggested that the cumulative total displacement of tunnel structure,the longitudinal displacement caused by under construction,the longitudinal deformation of existing tunnel structure and the control value of the stress increase of existing tunnel lining structure are recommended.