Cutterhead failure analysis during EPB shield excavation in urban metro tunnels: a case study of the Shenyang metro

This study investigates an unprecedented cutterhead failure, characterized by a 900 mm diameter reduction due to severe wear, encountered during earth pressure balance (EPB) shield tunneling in the gravel strata of a Shenyang metro tunnel, China. To elucidate the underlying causes and mechanisms, a comprehensive analysis of the wear patterns on the failed cutterhead was performed. Additionally, a cutterhead model test was designed to assess the influence of soil conditioning and cutting tool failure on wear and operational parameters. The primary findings revealed that the failure was predominantly attributable to inadequate wear resistance at the cutterhead’s outer periphery, compounded by the detachment of external cutters. Based on these insights, two optimization strategies were developed and implemented in a subsequent tunnel excavation: enhancing the wear-resistant configuration of the outer periphery and refining soil conditioning techniques. Post-optimization analysis demonstrated substantial improvements, with average cutting tool wear, torque, and thrust reductions of 73.68%, 12.35%, and 57.80%, respectively. These enhancements not only stabilized the excavation rate but also preserved cutter integrity. This research highlights the efficacy of targeted solutions in mitigating abnormal wear, offering critical insights for future cutterhead design and EPB shield tunneling practices in abrasive ground conditions.