Investigation of indentation by the indenter/cutter of a mechanical excavation machine is important to explain the mechanics of rock cutting, and to improve tunnelling performance in mining and civil engineering applications. In this paper, an attempt is made to investigate indenter/rock interaction under various indenter profiles to understand the stress distribution and crack propagation in rock, as a function of indenter profile. The indenter/cutter profile is a primary parameter for rock cutting research. Numerical modelling is carried out using FRANC2D to determine the resulting stress distribution and discrete crack propagation, and to allow a comparison of the stress intensity factors (KI ) in front of the crack tips. In addition, rock chipping induced by two neighbouring constant cross-section (CCS) disc cutters is modelled for different cutter spacings. The numerical models of cutter spacing are validated by comparison with field data supplied from an ongoing tunnelling project.


Mechanical excavation machines are widely used in civil tunnelling and subway construction, and in driving mine openings, such as drifts, ventilation shafts, and raises. In general, two types of cutting tools are used in mechanical excavation machines:

  • drag bits, and

  • indenters.

Machines that use the indentation cutting principle include Tunnel Boring Machines (TBMs), mobile miners, shaft borers and drills. Machines that use drag bit cutting include longwall shearers, road headers and continuous miners. Over 90% of TBMs are used for civil engineering purposes e.g. road tunnels, rail tunnels, hydroelectric scheme applications, sewers, rapid transit systems, military tunnels, etc. Significant research on rock indentation dates from the 1970's (e.g. Wagner & Schuman, 1971; Nishimatsu, 1972; Cook et al., 1984; Pang et al., 1989; Lindqvist et al., 1994; Kou, 1998; Liu, 2003; Chen & Labuz, 2006). Rock removal on cutting is determined by the discontinuous process of the spalling of chips.

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