Responses of Cross-River Tunnel due to Overlying Shield Tunnel Construction (Ⅱ):Influence of Distance

摘要

Construction of shield tunnel will inevitably change the stress field and displacement field of soil mass.Consequently,adjacent existing underground structures will be affected by construction of new projects.As a typical example,the responses of cross-river tunnel due to overlying subway tunnel construction are presented and the influence of the vertical distance between two tunnels is particularly focused on.Considering the difference of discount coefficients between transverse rigidity and longitudinal rigidity of shield tunnel,the change of stress field in soil mass,and so on,the writers conducted numerical analyses via 3D finite element program for four values of vertical distance (2 m,5m,8 m,and 11.4 m).Displacements,curvatures,and inner forces of cross-river tunnel were selected to investigate the responses of cross-river tunnel due to new subway tunnel excavation with different distances.The results show that the rebound pattern and amplitude of cross-river tunnel depend on the distance between the two tunnels.The increase of distance induces decreases of rebound amplitude and maximum lateral displacement.Compared with the rebound values,the lateral displacement values are comparatively smaller and even can be ignored in engineering.In addition,the cross-river tunnel is almost unaffected beyond the distance of 2.5D (D represents the external diameter of cross-river tunnel) to the symmetric plane.Furthermore,the internal forces in symmetric plane of cross-river tunnel are close to the initial values and the internal forces in longitudinal direction decrease with the increase of the distance between two tunnels.Finally,the minimum curvature radii can't achieve the critical value in the four cases and the maximum rebound values exceed the critical value in some cases according to the criteria of metro protection in Shanghai.