Abstract: Shield type selection is critical for tunneling efficiency in complex geological conditions. In the Shenzhen metro line 12, an EPB/TBM dual-mode shield was used in the Huaide-Fuyong section, whereas a composite shield was applied in the Cuigang Industrial Park-Huaide and Yonghe-Fuyong sections. A comparative analysis is performed on the tunneling performance differences between these two shield types in rock strata, focusing on operating parameters, construction progress, machine utilization, cutter wear, and rock muck conditions. The results reveal the following. (1) In rock strata, the dual-mode shield in TBM mode uses a central belt conveyor for mucking and operates with an empty soil chamber under atmospheric pressure. The cutterhead thrust and torque are the primary factors affecting rock-breaking efficiency. This results in a high cutterhead rotation speed, a low disc cutter wear rate, and good rock muck integrity. (2) The screw conveyor on the dual-mode shield in EPB mode and the composite shield results in low mucking efficiency. The soil chamber fills with muck, requiring higher thrust and torque to transport it. As a result, the cutterhead rotation speed and penetration rate are low, and the cutters experience severe wear, leading to low equipment utilization and overall tunneling efficiency. (3) In long-distance rock strata, the advance rate of the dual-mode shield in TBM mode is four times faster than that of the dual-mode shield in EPB mode and three to six times faster than that of the composite shield.

Key words: shield type selection, tunneling performance, dual-mode shield, composite shield, rock strata