不同地连墙插入深度下承压含水层减压降水对既有隧道的影响

当基坑需进行未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，并分析了采用地下连续墙插入承压含水层时，不同插入深度对隧道变形的影响，结果表明：随着地下连续墙插入承压含水层深度的增加，直至完全截断承压含水层，既有隧道沉降逐渐减小，但受地下连续墙变形的影响，隧道在水平方向仍存在较大位移。因此，当既有隧道与减压井净距较小时，即使承压含水层被完全截断，也应重视减压降水对隧道水平方向变形造成的影响。此外，长期减压降水将会引起隧道产生可观的沉降。因此，应尽量避免承压含水层未被完全截断条件下进行长期减压降水。

Influence of pressure-relief of confined aquifer on existing tunnel under conditions of different inserted lengths of diaphragm wall

If the confined aquifer is not completely cut off by the diaphragm wall during the pressure-relief process which is used for preventing the heave failure of deep excavation, the sphere of influence of ground settlement caused by pressure-relief of confined aquifer is much larger than that caused by the excavation. Therefore, the deformation characteristics of the existing shield tunnels caused by pressure-relief of confined aquifer are simulated by finite element method; and then the diaphragm wall is inserted into the confined aquifer, the effect of the length of diaphragm wall into the confined aquifer on the deformation of tunnel is analyzed. The results show that, as the length of diaphragm wall inserted into the confined aquifer increases, the settlement of tunnel decreases. But because of the deformation of wall, horizontal movement of the tunnel is considerable during the pressure-relief process. So it should be pointed out that when the tunnel is close to the dewatering well, even there is a diaphragm wall cutting off the confined aquifer, the influence of dewatering on the horizontal deformation should be paid attention to. Besides, the long-term pressure-relief process will cause severe settlement of the tunnel; so it should be avoided when the confined aquifer is not completely cut off.