ABSTRACT
The external water pressure acting on tunnel lining is discussed in the paper. The load due to ground water on tunnel is generally seepage body force. In condition that normal stress on the interface of lining and rock is tensile, the lining is under the action of surface load due to ground water, so called external water pressure, p 0 =β 1 β 2 β 3 γh 0, where γ is specific weight of water, h 0 is the height of water column between ground water table and axis of tunnel, β 1 is the correction coefficient considering the initial seepage field of groundwater,β 2 is a reduction coefficient, ranging from 0 to 1.0, considering the permeability difference of surrounding rocks and lining in condition of β 1 = 1.0 and β 3 is a coefficient considering the effectiveness of drainage system, specially designed for reducing the external water pressure on tunnel lining in condition of β 1 = β 2 =1.0. Detailed theoretical and practical discussions and suggestion of the ranging values of β 1,β 2and β 3 are given. The proposed approach can help tunnel designer avoid the subjective estimation of external water pressure on lining and therefore to make the design more safe and reasonable.
