Numerical Modelling Of Rock Fracture Mechanism Under Disc Cutters

Domestic and foreign engineering has been paying more and more attention to Full Face Rock Tunnel Boring Machine (TBM), because of the quicker speed of construction, the higher quality of construction, the good operating personnel working conditions, the security of construction and so on. However, the lever of TBM design by China is lower than foreign country. Being a crucial factor in influencing the performance of TBM, the Cutter Head design is one of the key issues of TBM. The mutual action between disc cutters and the rock is one of the key aspects of TBM, when the TBM is breaking the rock. Practice has shown that disc cutters cost is about one-third of the total cost of TBM working, when the TBM is breaking hard rock. It is significant to study rock fracture mechanism under disc cutters for improvement the value of theoretic and TBM engineering guide. The investigation will be helpful for the design of TBM and the arrangement of the disc cutters.This research was supported by the National Natural Science Foundation of China (Grant No.40638040), the National Basic Research Program of China (973 Program, Grant No. 2007CB209400 and 2007BAF09B01) and the National Natural Science Foundation International Research Project (Grant No.50820125405). A numerical code RFPA is applied to simulate rock fracture process under disc cutters of TBM. This paper has carried out the following research:(1) By means of reading references, the development trend of rock fracture mechanism under disc cutters at home and abroad is presented, in the field of Theoretical Derivation, Physics Experiment and Numerical Simulation. Rock fracture process induced by a single cutter is simulated by RFPA. Numerical results show that the whole fracture process has four stages:powder formation, powder nucleation, side crack initiation and propagation, and chip formation. In this paper, the effect of different confining pressure and rock is studied.(2) Rock fracture process induced by double cutters and three cutters simultaneously is studied. So dose three cutters one by one. Synergistic reaction is found between neighboring cutters.(3) The paper carries out the disc cutters spacing optimization study when the multi-cutters breaking rock. When the cutter spacing increases continuously, the specific energy ratio of energy consumes to fracture area (W/A) decreases, and then has an increased. There exists an optimum disc cutters spacing. The cutter spacing optimization of different rock is studied. The effect on the W/A by different rock is studied. It is very important to study the multi-cutters and different loading mode to breaking rock, though comparing to the research of simultaneous double cutters and three cutters and three cutters one by one breaking rock.