Experimental Study of the Mechanism of TBM Disk Cutter Penetration in Mixed-Faced Grounds under Confining Pressure

In this article, the effects of tunnel boring machine (TBM) disk cutter penetrations on rock fragmentation are experimentally investigated. In these tests, the tested sample is composed of Beishan granite and Chongqing sandstone. The effects of five sets of TBM disk cutter penetrations are investigated under confining pressure of 10 MPa, and 3-D forces acting on the rolling cutter and the forming rock chips are analyzed. It is found from the experimental results that in the mixed-faced ground, for granite, the boreability of the TBM disk cutter increases slowly with increasing penetration, while for sandstone, the boreability of the TBM disk cutter almost linearly decreases. At the same penetration, the average normal force and rolling force in granite are larger than those in sandstone, and cutter vibration becomes obvious when the disk cutter rolls through the interface of the composite rocks. Moreover, the optimizing penetration, which is equal to 2 mm in the mixed-faced ground composed of granite and sandstone under confining stress of 10 MPa, is provided to guide the TBM operation and to predict rock fragmentation in TBM tunneling.