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• Penetration behavior of disc cutter assisted by high pressure water jet was studied. • Deeper kerf could reduce cutter force and promote rock breakage significantly. • Most surface cracks initiate in cutter end and propagate to kerf boundary obliquely. • Higher kerf depth and smaller kerf spacing urge internal cracks bend to kerf bottom. • Minimum shear load increases linearly with optimal failure depth and kerf spacing. To achieve greater efficiency of TBM driving and lower cutter maintenance costs in hard rock formations, the TBM integrated high pressure water jet system was developed. By examining the working modes of water jets and disc cutters, this paper investigates the mechanical response and failure mechanisms for the simple case in which a water jet is first used to cut, followed by disc cutter rock breaking. As disc cutters use penetration-type rock breaking, laboratory quasi-static penetration tests and numerical simulations were carried out for kerf specimen precutting with a high pressure water jet. The influence of kerf parameters on the mechanical behavior of rock breaking was studied, and the mechanisms of surface and internal cracks and fractures were revealed and discussed. The results show that peak penetration force decreases with the increase of kerf depth, and slightly increases with the increase of kerf spacing. The specific energy decreases significantly with the increase of kerf depth and gradually becomes stable once the kerf depth becomes greater than 18.14 mm. The internal cracks formed in shallower kerf specimens mainly include shallow tensile cracks and deep vertical split cracks. However, the internal cracks of deeper kerf specimens incline and bend, extending towards the bottom of the kerf. The theoretically obtained minimum shear load, optimal failure depth, and fragment area all increase with kerf spacing, but the angle of the shear plane remains approximately 45°. These findings may provide some reference for the design and construction of TBMs integrated with high-pressure water jets. [ABSTRACT FROM AUTHOR]