Vibration analysis of rock breaking by TBM rolling cutter assisted with various depth kerfs

Abstract

Kerfing on the tunnel working face is one of effective ways to promote the performance of tunnel boring machines (TBMs) in hard rock masses, since the rock mass integrity is reduced. When TBM cutter cuts along the midline of two kerfs, the lateral cracks generated from the cutter tip could propagate to the bottom of adjacent kerfs, thus improving the cutting efficiency. However, the cutter vibration under such circumstance was rarely investigated. To analyze the impacts of kerf depth and cutter penetration on the cutter vibration, a series of full-scale linear cutting tests were conducted on two granite samples with high strength. Kerfs of different depths were processed by the saw before each cutting on one sample, while conventional cuttings without kerfs were performed on the other one to make a comparison. A vibration monitoring system was installed in the cutter holder, three axial accelerations and forces of the cutter were recorded during the tests. Rock mucks were collected and sieved to obtain the muck mass and coarseness index. It was found the intense cutter vibration induced by the intact rock cutting could be alleviated by kerfs. The most severe vibration was found in the cutter normal direction thus needed to be focused on. A greater cutter penetration depth made the vibration more intense. The kerf depth had quadratic correlations with various vibration parameters, indicating there was a critical depth beyond the which the vibration could be greatly alleviated, while the higher rock breaking efficiency could be also guaranteed. The critical depth obtained was about 6–9 mm within the range of experimental design. Variational mode decomposition (VMD) was introduced to extract two main subbands and their central frequencies in the frequency domain. The central frequency of the lower frequency band had a bell-shaped correlation with the kerf depth, the critical depth was still found at 6 mm. The findings are conducive to the design of the kerf-assisted TBM tunnelling and the prolongation of cutter life.