Study on the influence of cutterhead cone angle on rock breaking by double disc cutters in shaft boring machines

The development and utilization of deep earth resources have become a strategic scientific and technological issue that humanity must address. Shafts serve as the vital passage to the deep earth, and full-face shaft boring machines (SBMs) are crucial for mechanized shaft construction. In this study, the inefficiency of rock-breaking with disc cutters was investigated by analyzing the SBM's unique conical cutterhead. Specifically, a mechanical model accounting for the cutterhead cone angle parameter β was developed with a flat-edged cutter as an example. The contact area pressure distribution was precisely analyzed to derive the analytical solution for the pressure distribution on rock surfaces under different β angles. This model was employed to trace the evolution of the asymmetrical Von Mises stress distribution within the rock. Through numerical simulations and penetration tests, the symmetrical breaking mechanisms and characteristics of rocks under conical cutterheads were revealed regarding stress, strain, and fracture fields. The results specify that a marked asymmetry in rock failure occurred under double disc cutter penetration. Additionally, the rock breakage region on the left of the cutter axis was larger than that on the right, especially around the lower disc. As the angle β increased, asymmetry became more pronounced, and the total rock breakage area decreased rapidly. An increase in β from 0° to 60° brought about a decrease in the rock breakage area and the specific energy consumption by 53 % and 18 %, respectively. However, the reduction in energy consumption was significantly less than that of the breakage area. Thus, cutterhead design should minimize β to within an angle of 60° while maintaining effective rock chip removal. These research results lay a theoretical foundation for the design of the cutterhead structure of shaft boring machines.