Abstract:

Due to the shallow overburden near the working shaft, tunnel floating often occurs when a largediameter slurry shield bores adjacent to the working shaft. In this paper, the physical environment and operation techniques of slurry shield that affect the floating of shieldbored tunnels are analyzed, with considering the design experience of slurry shieldbored tunnels in soft soil area. The study results show that the main factors that affect the tunnel floating include ground water, simultaneous grouting, shield attitude control, ground reaction and grout backflowing; the main factors that have indirect influence on the tunnel floating include overburden thickness, ground water level, tunnel dimension, material density, overburden compression characteristics, shield boring speed and segment joint stiffness; main countermeasures for tunnel floating include installing artificial overburden, optimizing the shield boring parameters and shield attitude control, installing floatingresistant portal structures, improving the grouting techniques and the grout performance, carrying out secondary grouting and strengthening the longitudinal connections between segments.

Key words: soft soil, large diameter slurry shield, tunnel floating, influence factor, countermeasure