Optimum spacing and rock breaking efficiency of TBM double disc cutters penetrating in water-soaked mudstone with FDEM

Cutter spacing is one of the key factors affecting the rock breaking efficiency of Tunnel Boring Machine (TBM). In the excavation of deep soft rock tunnels, the water content can change the fragmentation behavior by TBM cutters, and further influence rock breaking efficiency. This study takes mudstone as an example to study the influence mechanism of water content on the optimum cutter spacing and rock breaking efficiency when TBM disc cutters penetrate soft rock. Firstly, the FDEM water migration-fracture coupled model considers the water weakening effect based on existing experimental fitting results. Secondly, several numerical experiments are conducted to calibrate the microscopic parameters input in FDEM. Finally, a series of numerical experiments of TBM double disc cutters penetrating in water-soaked mudstones are carried out using the coupling model. The crushing characteristics, cutter force, acoustic emission (AE), and crack pattern with different water content and cutter spacing are discussed in detail. Moreover, a novel recognition algorithm is proposed to calculate the rock chip distribution and area. The crack number, work done by the cutters, and specific energy (SE) are quantitatively analyzed. The results indicate that the water content of 2%–3% and the cutter spacing of 60–80 mm can lead to the lowest SE and highest rock breaking efficiency. Overall, the optimum cutter spacing decreases with the increase of water content. The modeling results can supply guidance for the optimization of cutter spacing during TBM tunneling in water-rich soft rock ground.