Construction Risks and Countermeasures of Super-large Diameter Mix-shield Machine with Accessible Cutting Wheel

Abstract

The accessible cutting wheel and cutter wear monitoring system for the super-large diameter mix-shield dramatically improves the safety and timeliness of cutter exchange in high pressure under water-crossing conditions, which potentially extends the adaptability of supersize Tunnel Boring Machine and accordingly enhances the performance as well as the economy of the project. However, through tracing and systematically analyzing dozens of mechanized tunneling using mix-shields with accessible cutting wheel in domestic and global projects, significant advantages, and time-related limitations were revealed, and corresponding risk are noticed, including: 1) The opening rate is zero at the center of the accessible cutting wheel and the isolation of slider pipe for disc cutter increase the probability of clogging on the cutting wheel panel and muck accumulation inside slide pipes; 2) Compared to the conventional cutting wheel, an incremental thickness of the accessible cutting wheel reduces the mobility of the slurry circulation and enlarges the distance between the slurry outlet and the tunnel face, favoring slurry stagnation since the discharge path of muck is increased; 3) The relatively large cutter spacing and low flexibility of cutter distribution result in weakening the rock-breaking ability, especially in very hard rock formation; 4) The timeliness and accuracy of cutter wear detection are insufficient, which easily gives rise to the formation of “rock ridges” on the tunnel face or secondary damage to other cutters as the “Domino Effect” if the firstly-broken cutter is not found in time. Given the limitations mentioned above, targeted countermeasures are proposed to address those problems, such as optimizing the flushing design, adopting auxiliary tunneling techniques, and strengthening the refined management based on relative geological conditions.