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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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