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Abstract:Pressurized bentonite slurry is applied on a tunnel face to form a filter cake to stabilize the tunnel face when the slurry shield excavates through the sandy soil. Failure of the tunnel face may be caused by a high permeable filter cake, which commonly has a long penetration distance of slurry in sands. A column system with a height of 680 mm and a diameter of 300 mm was developed to model pressurized slurry infiltration in sands. Pressure transducers were installed to estimate the hydraulic conductivity of the filter cake during slurry infiltration. The electrical conductivity of the leachate of collected samples was measured. Results show that the majority of fine particles in slurry are within the range 100-300 mm into the sand specimen. The time for forming an impermeable filter cake is about 300 s, which indicates the impermeable filter cake is hard to form during the excavation.

Purpose The shield tunnels closely constructed near the foundations have an inevitable influence on the structures, even results in the large settlement or uplift of the structures. Design/methodology/approach The comparison of structural deformation of three different foundations is presented based on the field monitoring data. Findings Shield tunnelling parameters vary for the different types of foundations. For the long pile foundations, the recommended speed is 3 to 4 cm/min, the grouting pressure is about 0.3 MPa and the grouting rate ranges from 150 to 180. Originality/value The study based on the field monitoring data is rarely reported, especially the topic about the structural deformation of different types of the foundations.

Purpose This paper aims to analyse the effect of soft soil grouting on the deformation of the closed shield tunnel with the measured data. Design/methodology/approach Combining the measured data of vertical, horizontal and convergence deformation of the adjacent tunnel during the grouting construction in foundation pit engineering, the influence of grouting on metro tunnel in soft soil area is analyzed. Findings The researches indicate that early grouting has the main effect on the horizontal displacement of the tunnel; Due to the disturbing effect of the uninterrupted grouting construction on the soil and the transfer pressure of the rheological soil to the bottom of the tunnel, the tunnel is obviously lifted; And the convergence deformation of the tunnel increases caused by the overburden pressure in the vertical direction, so that the tunnel appears the phenomenon of staggered seam, large opening of bolted joint, damaged segment even leakage of water. Originality/value The study based on the field monitoring data is rarely reported, especially the topic about inadvertent grouting in soft soil area is likely to cause severe deformation of adjacent metro tunnel.