TBM Mucking Process Simulation Based On Discrete Element Method And A New Mucking Structure Design

Full face hard rock tunnel boring machine (TBM in short) is a kind of large complex specialized equipment which is representative to show the advanced level of manufacturing business of whole nation. Cutterhead design is directly related to boring efficiency of TBM. However, China has not mastered the key technique of cutterhead design and there is still a gap to the world first-class manufacturers. In consequence, research on TBM cutterhead design technique is of great strategic significance.The design of mucking system has influence on boring efficiency, which is the cortex issue of cutterhead design. Nevertheless, few scholars have researched on the related problems and existing cutterhead design is completed according to the designers’experiences, which are lack of theoretical support. Based on the PFC3D discrete element method simulation platform, a series research on cutterhead opening area determination, design and layout of mucking slots and new pattern of support ribs have been carried out in this paper. Details are as follows,(1) According to the influence of ballast discharge process on, particle numbers before cutterhead, discharged numbers, cutterhead inner numbers and their fluctuation four index have been chosen to evaluate mucking performance of cutterhead. Weights of these four index have been determined on the basis of fuzzy preference algorithm. In this way, fuzzy synthetic evaluation index of mucking performance have been obtained to as design gist of mucking system.(2) According to the situation that opening area determination is short of theoretical support, cutterhead models with 5.55m、6.5m、8.3、9.2m and 10.4m diameter have been built, and the mucking processes have been simulated based on the discrete element method software PFC3D. The simulation results have been evaluated using the fuzzy synthetic method, so the best opening area ranges of different diameter cutterhead have been determined and so does the Mapping relation between cutterhead diameter and opening area.(3) Based on the best opening area determined before, cutterhead models of different mucking slot geometry have been built. The mucking processes have been simulated using PFC3D. Several design rules have been obtained according to the fuzzy synthetic evaluation method:1) In order to obtain optimum mucking efficiency and stability, increasing mucking slots’number should be considered first; 2) On condition that the number of mucking slots is definite, increasing slots’length is in favor of improve mucking efficiency and stability; 3) The width of mucking slots has little effect on mucking performance as long as it is capable of allowing ballast to enter into cutterhead. Finally, two modified schemes of mucking slots layout of a engineering case have been put forward, whose mucking performance have been advanced 8.52% and 13.44% due to simulation results.(4) Aiming at the deficiency of traditional mucking plate on mucking performance, a new fold-line mucking plate design method has been proposed in this thesis on the premise not reducing stiffness and strength. The theoretical calculation method of the mucking plate structure parameters is given through the movement analysis of the ballasts inside cutterhead. And it was verified by a certain type TBM, the results showed that the comprehensive mucking performance of the improved scheme has increased by 4.46%, and the maximum stress of the cutterhead has decreased by 30.96%.