Minimum cover depth estimation for underwater shield tunnels

In this note the authors demonstrate that simple application of the principles of effective stress and seepage laws leads to the perhaps surprising result that the long-term loads acting on linings below the water table are unaffected by whether the lining is watertight or not. This is only valid for cases where the original groundwater level is only little affected by the lining acting as a drain, and where the flownet is approximately radial, and is therefore of most relevance to relatively deep tunnels. The practical significance of this result is that it is erroneous to suppose that the total load on a watertight deep tunnel (or sewer lining or buried pipe) in soil would be reduced by allowing the lining to be permeable. By relieving the water pressure in the soil immediately outside the lining. a steady-state seepage would develop and the seepage stresses imposed on the soil grains (and therefore on the lining) would balance the relief of the water pressure.

Loads on leaking and watertight tunnel linings, sewers and buried pipes due to groundwater - discussion

A semi-empirical model for water inflow into a tunnel in fractured-rock aquifers considering non-Darcian flow

Support pressure for stability of circular tunnels driven in granular soil under water table

Observed performance of a 30.2 m deep-large basement excavation in Hangzhou soft clay

Semi-analytical solution for groundwater ingress into lined tunnel

Deep excavation in soft clay often causes additional deformations to surroundings. Then, if deformations cannot be predicted reasonably, the adjacent buildings may be threatened by the deep excavation. Based on the good field observations from ten deep excavations in Hangzhou, this paper aims to thoroughly investigate the characteristics of wall deflections and ground settlements induced by deep excavations.,On the basis of good field observation of ten deep excavations, the performances of excavations, supported by contiguous pile in Hangzhou, were studied, and also compared with other case histories.,The maximum wall deflections (dhm) rang mostly from 0.7 to 1.2 per cent He, where He is the final excavation depth, larger than those in Taipei and Shanghai. The observed maximum ground settlement in the Hangzhou cases generally ranges from 0.2 to 0.8 per cent He. Then, the settlement influence zone extends to a distance of 2.0-4.0 He from the excavation. The relatively large movements and influence zones in Hangzhou may be attributed to low stability numbers, large excavation widths and the creep effect. The excavation width is justified to have a significant influence on the wall deflection. Therefore, to establish a semi-empirical formula for predicting the maximum wall deflection, it is necessary to include the factor of excavation width.,The relevant literature concentrated on the characteristics of deep excavations supported by the contiguous pile wall in Hangzhou soft clay can rarely be found. Based on the ten deep excavations with good field observation in Hangzhou, the characteristics of wall deflection and ground settlements were comprehensively studied for the first time, which can provide some theoretical support for similar projects.

Evaluation of excavation-induced movements through case histories in Hangzhou

Analytical solutions for the steady-state seepage field in a finite seabed under homogeneous and isotropic conditions with a drained circular lined tunnel are developed. A numerical model is establ...

Analytical solutions for the steady-state seepage field in a finite seabed with a lined tunnel

In this study, analytical solutions for tide-induced pore pressure, seepage force and water inflow into a subaqueous drained tunnel are developed. The results are compared with numerical solutions from a commercial software. The effects of the soil permeability, shear modulus, lining thickness and buried depth of the tunnel on tide-induced pore pressure, seepage force and water inflow are discussed. Larger tide-induced pore pressure and seepage force are obtained for smaller tunnel depth and higher soil permeability. The phase lags of the maximal tide-induced pore pressure at different depths are determined and investigated.

Hongwei Ying

Papers

Semi-analytical solution for groundwater ingress into lined tunnel

Observed performance of a 30.2 m deep-large basement excavation in Hangzhou soft clay

Evaluation of excavation-induced movements through case histories in Hangzhou

Analytical solutions for the steady-state seepage field in a finite seabed with a lined tunnel

Tide-induced hydraulic response in a semi-infinite seabed with a subaqueous drained tunnel