Blowout control during EPB shield tunnelling in sandy pebble stratum with high groundwater pressure

Based on the earth pressure balance shield tunnelling of Shijidadao station to the ventilation shaft section of Lanzhou metro line 1, the blowout control of conditioned muck in sandy pebble stratum with high groundwater pressure is studied through field investigation, laboratory tests and three-dimensional numerical modelling. It is mainly concluded that: (1) A method is established for testing the anti-blowout of conditioned muck in laboratory; (2) The optimum concentration of sodium-based bentonite slurry and the optimum volume ratio of slurry to soil of the conditioned muck are determined, and the reliability of the anti-blowout of the conditioned muck is verified; (3) The volume ratio of foam to soil of the conditioned muck should be less than 1∶5 when using slurry and foam. The results of this study may guide shield tunneling at the section with the maximum longitudinal grade of -28‰ so as to effectively avoid shield-flooding risks due to blowout.