Evaluation of the effect of TBM disc cutter wear on rock cutting efficiency

The geometry of the disc cutter is one of the most important factors in the rock cutting process of mechanized tunnel boring machines (TBMs). However, during excavation, the optimal conditions of the disc cutter are not constant due to disc cutter wear. One of the most significant consequences of cutter wear is the increase in the contact area of the disc cutter with the rock so when the wear of the cutter exceeds its maximum limits, it should be replaced. Therefore, this study will examine the effect of disc cutter wear on TBM operational parameters such as thrust force, net penetration rate, and specific energy. In order to achieve this, six types of worn 17“ disc cutters have been studied graphically, and a method for calculating the surface of contact between the disc cutter and rock as a function of the cutter tip width has been developed. Moreover, a new equation has been proposed to predict normal and rolling cutting forces whose results are in good agreement with the reported laboratory values. As a final step, the hard rock TBM parameters of the Kani Sib water conveyance tunnel have been studied after replacement of worn disc cutters. The results show that replacing the worn disc cutters leads to an increase in penetration rate and a decrease in thrust force, resulting in an increase in specific penetration. On average, specific penetration increases by ≈35 %.