Numerical Study On Rock Fragmentation Mechanism And The Influence Factors Of Breaking Efficiency By TBM Cutters

At present,the construction method of full-section rock boring machine(TBM)has been widely used in the construction of traffic tunnel,urban subway tunnel and water conservancy and electric power tunnel.The efficient rock breaking by TBM cutter is a key problem to achieve TBM efficient tunneling.The influence of different rock breaking factors on rock fragmentation mechanism and rock breaking efficiency by the cutter is the premise of optimizing the design of TBM cutter head,improving rock breaking efficiency and reducing tool wear.In this paper,the mineral structure model is introduced into numerical simulation by DICE2 D discrete element program.A rock breaking model with double cutter and gage cutter was established to systematically analyze the stress evolution,AE event distribution,cutter force,formation,and specific energy of rock chips formation in the process of rock fragmentation at mineral scale.With exerting the different confining stress conditions,the numerical models for cut successively by two normal cutter and two gage cutters are built.The influences of the confining stress,cutter spacing,installation angle,transition radius and angle on the cutter force,rock crack propagation mode,broken rock quantity and rock fragmentation energy can be analyzed specifically by the numerical simulation analysis.The main conclusions obtained from the study are as follows:(1)Rock damage zone can be divided into three damage zones: crushing zone,crack concentration zone and raw rock zone.The rock crack propagation mode is different for the two installation modes of the cutter.(2)With the increase of cutter spacing,the specific energy of rock fragmentation decreases first and then increases,while the rock fragment area increases first and then decreases;With the increase of confining stress,the specific energy of rock fragmentation firstly increases and then decreases,while the rock fragment area firstly decreases and then increases,and the optimal cutter spacing gradually decreases.In terms of the size distribution of rock chips and specific energy,the influence of cutter spacing is greater than that of confining stress.The influence of confining stress on rock damage depth and cutter force is greater than that of cutter spacing.(3)When the gage cutter invades,with the increase of installation angle,the lateral crack propagation tends to be away from the center of the cutter head,and the lateral force coefficient generally increases with the increase of installation angle.The amount of rock fragmentation and the proportion of failure dissipated energy decrease,and the specific energy of rock fragmentation increases firstly and then decreases.The larger the transition radius is,the less influence the installation angle has on the cutter force,crack propagation mode,rock damage area and energy dissipation.(4)For rock fragmentation with gage cutter double cutter in sequence without confining stress,rock fragmentation amount increases firstly and then decreases with the decrease of installation angle difference,and rock fragmentation specific energy decreases firstly and then increases.With the increase of confining stress,the rock fragmentation efficiency decreases firstly and then increases.