Quantifying Multifactor Effects on Mud Cake Formation Risk for a Tunnel Boring Machine with the Analytical Hierarchy Process

Tunnel boring machines often encounter clogging during excavation in strata with rich clay content. The clogging can damage the cutterhead and interrupt excavation. Cutting tool clogging, also known as mud cake formation, has a strong effect on excavation work efficiency. While current studies are focusing on the mechanism of clogging, engineering practice still heavily relies on qualitative empirical judgement. To quantitatively assess the risk of mud cake formation, we carefully selected 22 influential parameters to reflect the effect of geological, machinal, and operational risk factors in the tunneling process and established a rubric for risk factor contributions using the analytical hierarchy process (AHP). The results imply the liquidity index, plasticity index, cutterhead torque, and total thrust force contribute to around 45% of the total influence on mud cake formation, while machinal factors are less influential than geological and operational factors. We verified the framework with a tunnel section from the Guangzhou Metro Line 22 that had mud cake formation reported. Rings labelled as high risk for mud cake formation by our framework concurred with those rings with mud cake actually observed. Project log and operational parameter variations were incorporated to explore the connection between mud cake formation and treatment.

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