Robust Design Method of Large-diameter Shield Tunnels through Multiple Strata
Since the large-diameter shield tunnel usually goes through multiple strata, the variation of ground condition may have a very significant impact on the tunnel performance. Unfortunately, the conventional design method cannot consider the effect of uncertainty of the multiple strata. Thus, the robustness design method of large-diameter shield tunnelling through multiple strata is proposed. The design parameters of structural parameters and uncertain parameters of ground parameters are defined as design parameter sets and uncertain parameter sets respectively. Then each design parameter set is combined with an uncertain parameter set, and then the safety factor can be calculated. Following, the reliability index, robustness index, as well as the cost index of the design set, can be obtained through the mean and standard deviation of these safety factors. The constraint conditions with target reliability are provided to sort out the design sets that do meet the constraint conditions to be defined as the potential design. Finally, the multi-objective optimization of the robustness index is carried out through the genetic algorithm NSGA-II to solve the Pareto Front, and the key points are found on the Pareto Front to complete the robust design. A case of a large-diameter shield tunnel through multiple strata is presented, which proved the feasibility of the robust design method.