The design of large-diameter shield tunnels is challenging due to the complex stratigraphy.Conventional design methods relied on borehole data to identify favorable stratigraphic sections or averaged stratigraphy.However,these methods failed to depict accurately during the tunnel excavation.To address the issue,this study first proposes a new approach by constructing a coupled Markov chain model using existing borehole data to determine the most possibly crossed dominant strata during shield tunneling.Subsequently,numerical simulations with various design parameters are conducted,the standard deviation related to convergence deformation of large-diameter shield tunnels is used as the robustness index,and a robust design of large-diameter shield tunnels based on stratigraphic variability.Study results show that the dominant strata of the coupled Markov chain model provide a more precise assessment of stratigraphy for shield tunnels.Moreover,the robust design based on the refined stratigraphic condition is more suitable for practical implementation.The commonly used strata design approaches at present are optimized to guarantee that the strata chosen are close to the actual situation during tunneling,which can effectively reduce the tunnel construction cost and enable the tunnel to have better robustness.
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