Optimization and Field Validation of Soil Conditioning Scheme for EPB Shield Tunneling in Cobble–Boulder Stratum: Case Study on Beijing Metro Line 16

As laboratory experiments evaluating soil strata conditioning schemes for earth pressure balance shield (EPBS) tunneling are limited by the size of the test equipment, large pebbles and boulders are typically replaced by an equal mass of smaller pebbles (≦40 mm), resulting in behaviors that differ significantly from those of the in situ soil and causing the obtained conditioning scheme to perform poorly during actual tunnel construction. This study applied a laboratory-obtained conditioning scheme during EPBS tunneling in the boulder- and pebble-rich soil strata between Yushuzhuang and Wanpingcheng on Beijing Metro Line 16 to determine the optimal soil conditioning scheme using the upper soil chamber pressure, cutterhead torque, tunneling speed, and total thrust tunneling parameters as evaluation indices. The optimized soil conditioning scheme provided a better soil conditioning effect than the laboratory-obtained scheme and confirmed that the considered parameters reflected the soil conditioning effects. Finally, the correlations between these three soil conditioning factors and the four tunneling parameters were analyzed using a full factorial experimental design to obtain contour plots of their quantitative relationships for use in similar tunneling projects.