Numerical and experimental research on the rock-breaking process of tunnel boring machine normal disc cutters

A common drawback presented by several numerical rock-breaking studies was that the rocks beneath disc cutters were cut off excessively while the rocks between disc cutters remained, which usually resulted in a smaller cutter spacing than the proper value. To overcome this limitation, the constitutive equations of different rock parts were defined separately using VUMAT, an ABAQUS-based material subroutine. The constitutive model of rock was an application of the Drucker-Prager yield criterion coupled with the Lemaitre damage model. Full-scale rock-breaking tests on a rotary cutting machine were conducted, and 25 groups of orthogonal numerical simulations were carried out. By comparing the normal force, rolling force, and specific energy of numerical results with those of experimental results, the optimal values of the defined parameters D (c1), k, and B were determined to be 9a similar to"10(-4), 0.1 and 0.8, respectively. With the presented numerical method and the determined parameters, the influences of cutter spacing on normal force, rolling force, and specific energy were studied. Both the normal and rolling forces of the first cutting generally remained constant, whereas the forces of the second cutting generally increased linearly with the cutter spacing. The optimal cutter spacing for the studied rock type (Hard sand rock collected from West Qinling tunnel) was approximately 72 mm, which was in accordance with the cutter spacing of the tunnel boring machine applied in this tunnel project.