Selection Method and Application of Dual‐Mode TBM in Composite Strata: A Case Study of Shenzhen Metro Line 14

With the continuous development of urban railway construction, metro tunnels tend to cross complex geological formations. Single‐mode tunnel boring machines (TBMs), typically designed to accommodate a specific type of rock mass, often encounter severe eccentric cutter wear and attitude deflection, when tunneling in composite strata. The inadequate support pressure exerted by the TBM under a single excavation mode that fails to balance the soil and water pressure of the weak strata may result in collapse of the tunnel face. The dual‐mode tunneling equipment, which has flexible adaptability in complex environment could be the potential solution to the problems of tunneling in longitudinal composite strata. However, traditional selection methods mainly focus on the influence of parameters of an individual stratum, according to empirical analysis. While dual‐mode TBM selection requires comprehensive consideration of the combined effects of efficiency, duration, and cost related to the distribution of different strata. Based on the comparison of tunnel projects using dual‐mode tunneling equipment worldwide and their strata parameters, the fundamental principles of dual‐mode TBM selection were proposed in this research. A fuzzy comprehensive evaluation model was developed for the earth pressure balanced (EPB) mode and open cutting mode to determine the limit length of each section for mode adjustment. Finally, a case study in Shenzhen Metro Line 14 was presented to verify the innovative selection method of dual‐mode TBM. The results show that the adaptability evaluation results are consistent with the actual project, based on the field‐obtained operational parameters.