Meitan xuebao (Mar 2024)
Influence of the position and depth of pre-cutting kerfs on the rock breaking by SBM cutter
Abstract
The combination of water-jet and disc-cutter rock breaking is a key technology to improve the rock breaking efficiency of the full-face shaft boring machine and achieve the mechanized development of deep resources. It is a crux problem of selecting reasonable parameters for pre-cutting kerfs. In this paper, firstly, it examined the working characteristics of rock breaking with a disc-cutter driven by a conical cutter-head. Then, based on the cohesive element method, a discrete-continuous coupled numerical model for rock breaking with a disc-cutter under pre-cutting kerfs conditions was established. Comparing the intact rock mass, the influence of different pre-cut kerfs distances and depths on the stress and rock fragmentation characteristics of the rock breaking was analyzed. The three stage characteristics of dense core formation, blocky rock slag formation, and Hertz crack propagation during rock cutting with a disc-cutter were elaborated. The asymmetric fragmentation characteristics of the rock mass and the formation mechanism of rock slag in different regions were presented. Finally, a comprehensive analysis was conducted from four aspects: the force acting on the disc cutter, the rock breaking area, the specific energy consumption for rock breaking, and the degree of rock slag crushing, and the optimal range of distance and depth values for pre-cutting kerfs was determined. The research results indicate that the pre-cutting kerfs can significantly reduce the penetration force and lateral force during the rock breaking process of the SBM cutters. Compared with intact rock masses, the peak penetration force decreased by 44.0%−10.3%. The peak lateral force decreased by 35.2%−6.5%. When the spacing and depth of pre-cut kerfs are small, it will limit the range of rock breaking by the disc-cutter, and at the same time make the fragmentation of the rock mass smaller, resulting in an increase in specific energy consumption for rock breaking. As the pre-cut depth increases, the rock breaking volume first increases and then tends to be stabilized, while the specific energy consumption first decreases and then remains unchanged. Finally, it was determined that the cutting distance was 70−90 mm, and the best rock breaking effect was achieved when the cutting distance was 60−80 mm. The rock breaking volume was doubled compared to the case without cutting, and the specific energy consumption for rock breaking decreased by 69.2%. This provides a reference for the parameter design and determination of the cutter head.
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