Analysis of Stratum Deformation Rules Induced by the Construction of Double-Tube Parallel Shield Tunnels for Metro

With No.202 bid section of Dalian Metro double-tube parallel shield tunneling as engineering background,considering the layers of soil mass as well as the process of tunnel construction:shield driving,grouting and lining assembling,the successive construction process of double-tube parallel shield tunnels in the same direction was simulated with FLAC3D and the simulated results were compared with in-situ values.Results show that,after the completion of the right line tunnel driving,the soil layers above tunnel are closer to the surface,the vertical deformation caused by shield construction is smaller.The width of ground settlement trough is bigger.The width parameter of ground settlement trough is 0.56.When short-distance double tunnels are successively excavated,mutual disturbance occurs in soil mass.The characteristics of asymmetricaltwo-peakof the vertical stratum deformation are more obvious when the distance between the soil layer and tunnel axis is shorter.The distances between rock strata and tunnel axis are different when the characteristics of two peaks disappear owing to the layered property of rock strata.There is horizontal displacement of different directions on the surface near both sides of center line and the axis of two tunnels.The pile foundation and shear wall within this range will bear additional shear action during tunnel driving,and is liable to crack.Therefore,protective measures should be considered in construction.Monitoring results have validated the correctness of the numerical simulation method.Ground settlement develops rapidly within the range of 12m from shield tunnel face to monitoring point.