Mechanical Behavior and Rock Breaking Mechanism of Shield Hob Based on Particle Flow Code (PFC) Method

During the construction of tunnel using shield method, the rock breaking performance of hob is one of the key factors that determines the successful construction of subway tunnel. In this study, a mechanics model of shield hob based on the Colorado School of Mines (CSM) model and a discrete element model of shield hob based on particle flow code (PFC) are established on the basis of the shield construction of ultrahigh hard rock section from Agricultural and Forestry University Station to Hongtang Station of Fuzhou Metro Line No. 5. These models are used to reveal the rock breaking law under different hob types (single-edged hob, double-edged hob and edge hob) and numbers (single hob, double hobs, three hobs and full hobs). Laboratory test results show that the discrete element model based on PFC has high accuracy. Numerical simulation results show that the vertical force and rolling force of the single-edged hob and double-edged hob increase with the increase in the distance between the installation position of the hob and the centre of the cutter, whereas that of the edge hob are less affected. With the increase in the number of hobs, the hard rock gradually forms a through joint from a single crack, and the vertical force and torque of a single hob decrease. Comparative results of the theoretical and numerical simulation show that the maximum errors of vertical force and torque are 10.9% and 47.3%, respectively, and they are 11.3% and 37.5% of the rated value of No. 552 shield machine of China Railway. These values meet the engineering requirements and can provide reference for shield selection and shield tunnel construction in the future.