当基坑需进行非截断条件下的承压含水层降水时，承压水抽降产生的影响范围远大于基坑开挖的影响范围，其对基坑外既有隧道的影响值得重视。进行了承压层减压降水对既有盾构隧道影响的有限元仿真模拟，考虑了既有隧道相对于承压含水层不同位置时，既有隧道周围土体应力场、既有隧道横断面内力和变形。研究结果表明，隧道全部或者大部分位于承压含水层中时，抽水除可引起隧道发生整体隆起或沉降外，还将导致隧道自身产生较大的竖向压缩变形；当隧道全部位于上、下部隔水层时，含水层抽水对其隧道的变形影响不大，但当隧道位于上部隔水层情况下，抽水将会引起隧道产生整体下沉。

Sometimes, at the condition that a confined aquifer is not completely cut off, its pressure-relief can occur when dewatering via pumping is conducted to prevent the heave failure of pit formation above. Such pressure-relief can have negative effect on ground settlement considerable larger than that due to pit excavation. Therefore, such effect on the existing shield tunnel adjacent to the pit has to be considered. The effect is simulated with finite element method in this paper. The stress field of surrounding soil, the deformation and internal forces of the cross-sections of tunnel at different locations relative to the confined aquifer are analyzed. The results show that, when either most part of tunnel or the whole tunnel is located in the confined aquifer, its pressure-relief can cause not only overall upheaval or settlement, but also vertical convergence deformation of the tunnel. When the tunnel is located in the aquiclude above or under the confined aquifer, the pressure-relief only produces little influence on the tunnel deformation. However, when it is located in the upper aquiclude, the tunnel would exhibit obvious settlement due to the pressure-relief in the confined aquifer.