To improve the penetration rate of tunnel boring machine (TBM) in hard rock and reduce the cutter force

high pressure water jet assisted TBM rock breaking has been initially applied in industry. To investigate the rock breakage mechanism of disc cutter assisted by precutting kerfs

a 3D particle flow simulation was performed based on the indentation test of hard rock with hydraulic cutting kerfs. The variation of indentation force and indentation stiffness with kerf depth was studied. The evolution of crack propagation and contact force chain parallel and perpendicular to the cutter axis are revealed. The variation of tensile and shear cracks with kerf depth and kerf spacing and the corresponding failure mode and failure mechanism are discussed. The results show that the indentation stiffness and indentation force of the first indentation decrease linearly with the increase of kerf depth

and that of the second indentation are less than that of the first indentation. Moreover

the change of kerf spacing between 50 and 80 mm has no significant effect on the peak force. With the increase of kerf depth

the inclined boundary angle of the concentrated force chain under the cutter becomes larger. As a result

the failure tends to be inclined downward. When the kerf spacing increases

the failure mode changes from the inclined failure towards another kerf to inclined failure towards the middle rock ridge. The research results can provide some reference for the layout between TBM disc cutters and water jet nozzles and the selection of kerf depth.