Study on the rock breaking mechanism of double disc cutters under confining stress based on CDEM

This study focuses on the critical issues of tunnel boring machine (TBM) rock-breaking efficiency and mechanisms under deep high-stress environments. Double disc cutters indentation tests were conducted at varying confining stress levels. Combined with continuous-discontinuous element method (CDEM) simulations, the influence mechanism of confining stress on the combined rock-breaking mechanical behavior and fragmentation characteristics of double disc cutters was analyzed. A post-processing program was designed to extract rock fragmentation size distribution, enabling quantitative analysis of cuttings size distribution and identification of the critical penetration depth where rock transitioned from ductile to brittle failure. The study demonstrates that confining stress exerts a significant mechanical effect on double-cutter rock breaking. On one hand, it enhances the synergistic effect between cutters, promoting rock fragmentation. On the other hand, it dominates the transition of failure modes from brittle spalling to plastic shearing and compaction, resulting in reduced large-sized rock fragments and increased critical cutting depth. Concurrently, a critical confining stress range exists where the inhibitory effect on cutter rock breaking is most pronounced, leading to the lowest rock breaking efficiency. These findings provide theoretical foundations and data support for optimizing TBM cutterhead design and excavation parameters under varying stress conditions.