Experimental study on TBM cutter penetration damage process of highly abrasive hard rock pre-cut by high-pressure water jet

When highly abrasive hard rock strata are encountered during the TBM boring process, severe problems, such as low TBM boring efficiency and severe tool wear, emerge. High-pressure water jet-assisted TBM rock breaking technique has been developed and applied in steps. In this study, the effect of confining pressure and precutting slits on the penetration damage in highly abrasive hard rock is studied through TBM cutter penetration tests. Some main conclusions are drawn as follows: (1) For intact rock samples, the increase in confining pressure leading to a reduction in the unloading effect after the initial crack emerges when the confining pressure is higher than 15 MPa. Meanwhile, the boreability of the highly abrasive hard rock also significantly decreases, making it more difficult for rock breaking. (2) When examining the penetration damage process of intact and pre-cutting rock samples, a similar contact compaction stage (stage I) and microcrack initiation stage (stage II) can be found, while the crack propagation-penetration damage stage (stage III) shows significant differences in rock fragmentation patterns and force-penetration depth curve characteristics. (3) Under high confining pressure, precutting slits can enhance the initial decrease of the force by increasing the unloading effect of the TBM cutter on the rock sample after the initial crack is produced. Meanwhile, the reduction in peak strength index (PSI) and mean load index (MLI) values indicates that the penetration difficulty is significantly reduced. Hence, this contributes to the improvement of the boreability while the TBM is digging in highly abrasive hard rock.