Investigation of methods for assessing the impact of adjacent
shield tunnels
Yasunori KOBAYASHI, Masayuki SAITOU
Nippon Civic Consulting Engineers Co., Ltd.
JSCE 57th Annual Conference, September 2002.
Key words: shield tunnel, large diameter, adjacent tunnel, segment lining,
stress relief ratio, elastic-plastic FEM analysis
Background
Shield tunneling for expressway tunnels normally involves two separate tunnels
being constructed side by side, one for each direction. The tunnels are usually
constructed in sequence; the first tunnel constructed is called a lead tunnel
and the second a following tunnel. In designing the linings for lead tunnels,
it is necessary to account for the change in stresses that will be caused by
the excavation of the following tunnel. This effect is particularly important
in large cross-section tunnels accommodating several vehicle lanes. The finite
element method (FEM) of numerical analysis has previously been used in the
design stage to investigate the effect of the adjacent tunnel. However, there
have been very few shield tunnels constructed with an external diameter of
10 m or more. Therefore, uncertainties remain regarding the accuracy of the
numerical analysis method for predicting the influence of adjacent large diameter
tunnels.
Research Summary
The objective was to
develop a practical predictive method for the effect of
the construction of the following tunnel on the lining of the leading tunnel
for large cross-section shield tunnels. The authors carried out elastic FEM
analysis and elastic-plastic FEM analysis and compared the results with actual
stresses measured in linings during construction of a large shield tunnel external
diameter (D 13 m, overburden 21.8 m, distance between tunnels 3.37 m (= 0.29D).
Practical information was obtained to enable more accurate selection of the
stress relief ratio, a numerical analysis parameter, for stress relief analysis.
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