Investigation of rock breaking mechanism with TBM hob under traditional and free-face condition

Abstract

To compare the rock breaking mechanism of the tunnel boring machine (TBM) hob under traditional condition and free-face condition, a series of rock cutting tests and rock cutting simulations of the TBM hob under two cutting conditions are conducted. The rock chip, rock breaking forces and rock breaking efficiency etc. are investigated in this study. The research results denote that the rock chip size under the free-face is far larger than that under the traditional condition. Both the rock breaking forces and the rock breaking efficiency under the free-face condition could be reduced and be enhanced respectively compared with that under the traditional condition when the value of St and Sf ranges from 20 mm to 80 mm. Furthermore, the numerical and theoretical results also confirm the cutting rock under the free-face condition is promising, which can be applied to the water-jet TBM and the two-stage cutterhead TBM to improve the rock breaking performance of the TBM hob significantly.