## 5 Discussion
Although the range of the contact force increased in a fluctuating manner with increasing penetration depth, the overall growth rate was low. The contact force range of the disc cutter with a blade width of 22 mm increased approximately linearly with increasing penetration, with a relatively stable growth trend, and the standard deviation of the contact force was closer to that of the disc cutter with a blade width of 19 mm. The contact force range of the disc cutters with blade widths of 25 mm and 28 mm generally showed a near-linear growth trend, and the standard deviation of their growth trend was relatively stable. However, the overall values of range and standard deviation were obviously greater than those of the disc cutters withblade widths of 19 mm and 22 mm. In terms of the influence range of the disc cutter during rock breaking, it can be clearly seen that the influence range increased with increasing blade width, but the shape remained basically unchanged. At present, most of the research on shield disc cutters is focused on the influence of the shield tunnelling parameters on the rock-breaking behaviour of the disc cutter. In this paper, the influence of the geometric configuration of a single disc cutter on rock-breaking behaviour was analysed in detail, in order to be able to provide certain guidelines for the selection of disc cutters during shield tunnel construction. Although founded on a study of a single disc cutter, this is only a small part of the total rock-breaking behaviour of the shield machine, and therefore the rock-breaking behaviour of the group of disc cutters present in the cutter-head should be further explored. In follow-up research, in order to validate the rock-breaking behaviour of a single disc cutter, a more detailed and systematic study of the rock-breaking behaviour of groups of disc cutters will be carried out. In the current rock-breaking simulation of a shield disc cutter, the HJC model was used as the constitutive model for the rock. However, previous studies have seldom determined the parameters of the HJC model of the targeted rock, rather mainly opting to use existing HJC models. In addition, most of the parameters are taken from the concrete HJC model. In this paper, the parameters of the HJC constitutive model were determined for the diorite in the Jinan area, so the simulation results are more accurate and closer to the actual situation in engineering practice. The HJC model is used for the simulation of rock and concrete under large deformation and high strain rates. In the early stage, it was mainly used in high-speed interactions such as bullet-concrete penetration. For the rock-breaking behaviour of the disc cutter, the speed of the disc cutter is relatively slow (the running speed of the disc cutter is generally \(\leq\)2 m/s), so the HJC model has certain limitations when simulating rock-breaking behaviour in the cutter-rock interaction, and is different from the actual situation. Therefore, in follow-up research, a new constitutive model should be developed according to the characteristics of the rock-breaking behaviour of the disc cutter to ensure a better match between the simulation and the actual construction. In the actual shield construction, the disc cutter can easily maintain a penetration of about 10 mm in soft and medium-hardness rock formations (strength less than 30 MPa). In hard rock formations (strength greater than 50-100 MPa), penetration is generally 5-10 mm. However, it is difficult for the disc cutter to penetrate the rock, and the penetration is difficult to maintain. In extremely hard rock formations (strength greater than 120 MPa) and soft-hard mixed formations, it is difficult to penetrate the rock and the damage to the disc cutter will be more serious. At the same time, in order to reduce the amount of cutter damage, the penetration degree is generally maintained below 5 mm, and in most cases even less than 3 mm.