Research on rock breaking behaviors of different TBM hobs under grooving condition produced by water jet

Abstract

The water-jet-assisted method is very promising to improve the cutting performance of the TBM hob. The current researches are mainly focused on flat-blade hob (FB hob), but the researches on the rock breaking behaviors of spherical-tooth hob (ST hob) and pyramidal-tooth hob (PT hob) under grooving condition produced with water jet are very limited. To investigate the rock breaking behaviors of FB, ST, and PT hobs under the grooving condition, the penetration experiments and simulations of the three types of hobs are conducted. Then the penetration process, penetration force, and penetration efficiency of three types of hobs are compared and discussed. The results denote that the elastic deformation of the rock first is presented, then a dense nucleus is produced, and finally, a huge rock chip is formed with the growth of the penetration depth, regardless of the hob types. During this penetration process, the penetration force first rises steadily and then reaches its peak value, and finally drops and fluctuates. The increasing speed of penetration force for the FB hob is larger than that of the ST and PT hob during the increasing phase of the penetration force. Meanwhile, the peak penetration force and penetration difficulty coefficient of the FB hob are also larger compared with that of the ST and PT for the same cutting width. To effectively use the cutting groove to promote macro crack propagation and break rock, the cutting width should be controlled within the critical cutting width, 40, 40, and 30 mm, respectively for the FB, ST, and PT hob. At such critical cutting width, namely the optimal cutting width, the highest penetration efficiency can also be achieved. Besides, as the cutting width ranges within the optimal cutting width, the three types of hobs' breaking efficiency could be evidently enhanced with the assistance of the cutting groove. The ST hob presents better adaptability in breaking rock under the grooving condition simulating water-jet-assisted method compared with the FB and PT hob, considering the hob's breaking force, breaking efficiency and wear life.