盾构下穿时既有隧道变形机理及遮帘效应研究

Research on Deformation Mechanism and Shadowing Effect of Existing Tunnel when Shield Tunnel Underpasses

采用三维有限元数值分析,研究了不同竖向间距盾构下穿施工时既有隧道和地层的变形机理,及既有隧道的遮帘效应。结果表明:下穿工况中,既有隧道的竖向沉降小于基准工况(无既有隧道)中相同位置处的地层沉降,且间距越小差距越大;不同下穿间距下既有隧道横截面变形差异明显,当间距小于2D(D为隧道直径)时,既有隧道横截面最终变形为斜“鸭蛋”型;当间距大于2D时,既有隧道横截面变形为竖“鸭蛋”型;由于既有隧道的刚度远大于地层,对隧道上方一定范围内的地层产生遮帘作用,导致该范围内地层沉降较小,且随埋深增加沉降先增大后减小;遮帘效应影响范围随新旧隧道竖向间距的增大而减小。

By use of the three-dimensional numerical simulation,this paper investigated the deformation mechanism of the existing tunnel and stratum and the shadowing effect of the existing tunnel caused by different vertical spacing shield during under-crossing construction.The results show that:In the underpass condition,the vertical settlement of the existing tunnel is less than the ground settlement at the same position in the reference condition(without existing tunnel),and with the smaller distance the settlement is larger.The cross-section deformation of the existing tunnel is obviously different under different underpass spacing.When the spacing is less than 2D(D is tunnel diameter),the existing tunnel cross-section will eventually deform into inclined“duck egg”type.When the spacing is more than 2D,the cross section of the existing tunnel deforms into vertical“duck egg”type.Because the stiffness of the existing tunnel is much greater than the ground,the existing tunnel yields the shadowing effect to the ground.Thus,the ground settlement in this range is small,and the settlement above the existing tunnel first increases and then decreases with the increasing depth.The influence range of the shadowing effect decreases with the increase of the vertical space between the new and old tunnels.