Abstract: In order to speed up the construction of double line subway tunnel,two shield machines are used in the excavation at the same time.Under the condition of invariable transverse spacing of the two shields,small longitudinal spacing will aggravate the disturbance of surrounding soil and affect the safety of surface building(structures).In this paper,with Wuhan Metro line 3 as engineering background,the characteristics of transverse and longitudinal surface deformations of shield tunnel excavation are analyzed through field monitoring and numerical simulation,and the regularity of longitudinal influence of double-line parallel tunnel excavated in the same direction is revealed.Results show that the numerical results accord with the field monitoring data;surface subsidence trough forms after the shield passes.The surface deformation above the tunnel vault remains the biggest,and the farther away from the axis of the tunnel,the smaller the surface deformation reaches.In the process of excavating,the surface uplift value above the front of shield reaches the maximum;the surface settling velocity increases rapidly after the shield passes and finally tends to be stable.In the process of shield excavating in same direction of double line metro tunnel,the secondary disturbance of shield contributes to the final surface deformation,but the longitudinal spacing of shields has no effect on the final surface deformation.With the increase of longitudinal spacing of shields,the total surface settling velocity slows down.It is safe and reliable when the longitudinal spacing of shields exceeds 50 m.The research result of this paper is expected to provide a basis for the safe and rapid construction of subway tunnels.

Key words: double line subway tunnel, field monitoring, numerical simulation, surface deformation, longitudinal spacing