Application of Full-Scale Experimental Cutterhead System to Study Penetration Performance of Tunnel Boring Machines (TBMs)

Rock penetration is the most important function of tunnel boring machines (TBMs). Based on a detailed review of TBM rock penetration research, this study introduces a rarely reported full-scale experimental cutterhead system that combines the advantages of in situ penetration tests and laboratory rock-breaking tests. The main focus of this study is to investigate TBM penetration performance using this experimental cutterhead system. Nine groups of penetration tests were conducted on an integral concrete specimen with cutterhead rotational speed and net penetration varying from 1.9 to 5.9 r/min and 2.5 to 8.8 mm/r, respectively. The cutting force and chipping performance of each cutter were monitored, examined, and analyzed considering boreability and mechanical efficiency. The results indicate that the cutter normal force is unaffected by the cutter installment radius and cutterhead rotational speed. However, the muck weight and specific excavation rate increase in perfectly fitted exponential functions with increasing cutter position number, indicating that the cutting efficiency increases with cutter position number. Muck sieving results show that face cutters produce larger and more elongated chips than center cutters, as the extent of cutter side sliding declines with increasing cutter installation radius. The boreability index decreases in a perfectly fitted power function with increasing net penetration, indicating that the critical threshold for cutterhead net penetration is approximately 5 mms/rev. The proposed models predicting the cutter normal force and boreability index were compared with 13 sets of in situ penetration test data. This study can guide TBM excavations encountering rocks with equivalent strength and intactness.