| Recently, shield machine was widely used in many areas, such as construction of water conservancy and hydropower culverts, urban underground engineering and construction of artificial canal, underground tunnel, mine, mountain railway and highway tunnel. As one of the main cutters of shield machine in the cutterhead, disc cutter's cutting performance directly affects the excavation efficiency of shield machine. The paper comes from the topic "cutting mechanism of rock and theory of cutterhead design", which is the sub-project of the National Key Basic Research and Development Program of China (973 Program). The paper has attached great importance to rock-fragmentation characteristics and vertical cutting vibration, in order to improve structure design, tool life, adaptability of the cutter, optimize tool configuration in cutterhead and achieve the aims of 1 and lower energy consumption in tunnel excavation.The paper complete contents as below:1) Based on kinematics analysis of rock-fragmentation process of disc cutter, reasonably simplifying the problem, respectively building 2-D discrete element models of single cutter breaking rock with inclined joints, double cutters breaking rock without joints and with horizontal joints under the condition of single specific formation, the crack propagation of microcrack under different confined pressures, parameters of joints, cutter spacing and cutting orders was observed. Based on the propagation direction of crack and the formation rule of fragment,12 typical types of breaking modes while breaking rock by TBM cutters were concluded. Finally, the rock-fragmentation characteristics was analyzed in the respects of efficiency of breaking rock, the propagation ability of crack and rock broken lumpiness.2) Considering the effects of initial stress distribution of the cutters on crack propagation, Hertz elastic contact theory was introduced into the simulation. A discrete finite element model indenting into sandstone by TBM double-edged spherical tooth hob was established. Comparing the simulation and literature results, the influence law of cutting edge shape on rock-fragmentation characteristics during breaking process was acquired.3) In the vibration system consisting of a single disc cutter and rock, the cutter is inevitably quivering during the breaking process because of the characteristics of step-crushing and the snake-like phenomenon. The general differential equations of vertical vibration of disc cutter suitable for breaking hard rock, soft rock and soil were respectively established by adopting displacement constraint and force constraint as the lower boundary condition. Taking the disc cutter designed for experiments mentioned in this paper rolling granite as the example, the dynamic simulation analysis was done.4) Based on the existing linear cutting test-bed, an observation experiment is designed, in which double-edged spherical tooth hob indents into sandstone. The phenomena of rock crushing and bursting were captured by the high speed camera successfully and the formation process of compacting rock core was discontinuously recorded by the general digital camera skillfully. The related theory derived from the simulation result was verified.5) The experiment of the designed cutter rolling concrete was carried out on the test-bed. The macroscopical phenomenon of concrete-crushing was observed, the changing law of rock broken lumpiness and the characteristics of three-axis force were obtained. |
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