Study on Excavation and Wear Characteristics of Disc Cutter for Extended Tunnel Boring Machine

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The aim of the research is to experimentally improve that the effectiveness of the edge excavation of the extended T.B.M cutter bit is much more higher than that of the conventional plane excavation. The excavation experiment was carried out using disc cutter bit cutting the edge part of the mortar, Oya stone, andesite and granite rock specimens of two degrees of freedom having diameter of 32 cm and thickness of 15 cm with the cutting depth per round of 0.2〜1.0 cm, and cutting space of 0.5〜5.0 cm. Three types of model disc cutter bit made of S45C metal with the tip angle α of π/6, π/4 and π/3 rad were used at the excavation tests. The diameter and thickness of the model disc cutter bit were 15.0 cm and 1.5 cm respectively. The power of rotation and power of thrust were calculated based on the measured values of normal, tangential and lateral force acting to the cutter bit. Then, the specific cutting energy was calculated as the ratio of the excavation power, i.e. the sum of power of rotation and power of thrust, to the amount of excavation per second. The result shows that specific cutting energy increases, with excavation depth per round while it decreases hyperbolically with the increment of cutting space. However, it was also observed that the tip angle exerts insignificant affect on the specific cutting energy. Moreover, it was found that the optimum excavation, i.e. minimum specific cutting energy, could be achieved at the ratio of cutting space and cutting depth per round of 5.0. Finally, it was observed that the excavation efficiency of the edge excavation can be 10〜50 times higher while its amount of wear can be much smaller compared with the plane excavation method.