Abstract: 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.

Key words: underwater tunnel, tunnel lining, water pressure, water inflow, reduction coefficient