Experimental validation of block filtration mechanisms governing slurry penetration and filter cake formation in slurry shield TBM excavation

초록

The stabilization of the tunnel face in slurry shield tunnel boring machines (TBMs) is significantly influenced by the mechanisms of pressurized slurry penetration. This study employed infiltration column tests and modified fluid loss tests to investigate the characteristics of slurry penetration and filter cake formation under varying slurry concentrations and pressure levels. The transition point between two consecutive slurry penetration mechanisms was estimated by applying the blocking filtration laws and compared with predictions based on the Peclet number. The slurry permeability of sand and the infiltration distance during the slurry penetration stage were evaluated, both of which increased with higher pressure and lower slurry concentration. The hydraulic conductivities of the infiltration zone and the filter cake were estimated using the filtration equation and validated against experimental measurements. Additionally, the hydraulic conductivities of the filter cake obtained from the infiltration column tests were compared with those derived from the modified fluid loss tests. The results indicated that increased pressure and slurry concentration reduced the hydraulic conductivities of both the filter cake and the infiltration zone. Overall, the findings confirm that the blocking filtration laws provide a reliable framework, consistent with previously proposed methods for identifying transitions in pressurized slurry penetration mechanisms. Moreover, the filtration equation proved effective in evaluating the hydraulic conductivities of both the infiltration zone and the filter cake.

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