Abstract
This paper presents a numerical study on the rock fragmentation process induced by a tunnel boring machine disk cutter under different free face conditions. A grain-based discrete element method is incorporated into the particle flow code to synthesize appropriate rock samples, considering macroscopic mechanical properties and fracturing mechanisms. The influences of free face structures (height H, spacing S, and direction) on rock breaking mode, normal force, and penetration specific energy are investigated via numerical simulations. Results show that the rock breaking force and PSE of the side free face (STFF) model are significantly lower than those of the top free face (TFF) model. Based on the rock fragmentation analyses in rock breaking mode, four critical values were obtained, which can be used as the basis to design free face structures considering the rock breaking performance. The normal force significantly improves with free face spacing while the PSE is primarily influenced by free face height and rock breaking mode. These findings may be useful to understand the rock breaking mechanism of a disk cutter under free face conditions and can be used as guidance for the design of free face structures.
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