水底隧道衬砌水压力是衬砌结构设计的关键参数之一，根据对衬砌水压力作用机制的探讨，“全堵型”隧道衬砌承担全部静水压力，而对于“排水型”隧道，衬砌只承受部分水压力，作用在衬砌上的水压力应该进行折减。根据渗流理论，推导了轴对称条件下衬砌水压力折减系数的理论公式及利用隧道衬砌前与衬砌后涌水量的反分析简化公式，并通过数值方法验证了其可靠性。计算结果表明： 1）隧道涌水量随着衬砌渗透系数的减小而减少，当kl/ks=0.001时，涌水量几乎为0，而水压力折减系数近似等于1； 2）对于不同的kl/ks值，水压力折减系数与涌水量存在一个公共点，这个交点范围为kl/ks=(0.02 ~ 0.03)，对应的水压力折减系数约为0.5； 3）对围岩进行注浆可以有效减少涌水量，但仍会有较大的水压力作用在注浆圈上，对注浆圈的长期耐久性提出了较高的要求； 〖ＪＰ＋１〗4）利用隧道衬砌前后涌水量推导的衬砌水压力折减系数反分析公式，其计算结果可靠、有效，可以在以后隧道结构设计中应用。

The water pressure on the tunnel lining is one of the key parameters of tunnel structure design. The waterprooftype lining bears hydrostatic pressure. However, the drainagetype lining usually partially responds to the hydrostatic pressure. The hydrostatic pressure exerted on the lining should be reduced. The water pressure reduction coefficient of the lining under the conditions of axial symmetry is deduced, and its reliability is verified by means of numerical method, on basis of waterseepage theory. The calculation results show: 1) The water inflow decreases as the lining permeability reduces. When the value of kl/ks is 0.001, there is almost no water inflow and the water pressure reduction coefficient is nearly equal to 1. 2) There is a public intersection between the water inflow and the water pressure reduction coefficient for different values of kl/ks, and the range of kl/ks is from 0.02 to 0.03, meanwhile, the water pressure reduction coefficient is about 0.5. 3) The water inflow can be effectively stopped by means of grouting. 4) The calculation results are reliable and effective.