To ensure the safe and efficient tunneling of the EPB/Slurry dual-mode shield before and after mode conversion, the Wu-Xin section of Nanning Metro Line 5 was considered. The principle of rational mode conversion point selection and relevant criteria were proposed with consideration to the mode conversion procedures. A numerical model was established with consideration to the effect of fluid-structure coupling, and the evolution of the tunneling face deformation and seepage flow during the tunneling process was comprehensively analyzed. A multi-objective optimization model for construction safety and cost optimization was established and the mode conversion point was obtained through the equivalent transformation. The distances between the rational mode conversion point and the stratum interface were compared and verified to the actual conversion point of the project. The research results reveal that the mode conversion point of the dual-mode shield should be selected in a relatively stable stratum, and the deformation of the tunneling face and the seepage flow are significantly different near the stratum interface. The critical value is three orders of magnitude difference of the permeability coefficient for the selection of different mode conversion points. When the difference in the permeability coefficient is less than three orders of magnitude, the mode conversion point should be 8 m away from the interface. The actual mode conversion point of the project is basically the same as the result obtained by this study, which can provide a reference to future studies on the selection and mode conversion of the EPB/Slurry dual-mode shield.
