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Abstract Based on the transferring stiffness principle，a settlement difference method is put forward to evaluate the influence of each construction step on adjacent shield，and the total effect on the existing tunnel can be obtained by synthesizing single-step increment. Based on an urban metro，simulation analysis for the shield moving-forward process of the metro excavated afterward is carried out. It is found that the arch foot of the slumping arch induced by the tunnel excavated afterward acts on upper-right of the existing tunnel. The maximum circumferential tensile stress in the existing metro caused by single construction step of right line is 0.13 MPa，and the maximum additional tensile stress is 0.857 MPa. Combined with the analysis of original stress state of existing tunnel considering segment joints，the important internal causes of crack are found out. The research enriches the simulation methods of adjacent tunnels and can provide valuable reference for study of crack control and even for tunnel design and construction.
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Received: 14 January 2009
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