Mechanism Study On Rock Cutting Process Induced By Disc Cutters Using A Smoothing Particle Hydrodynamics Method

With the implementation of the “One Belt,One Road” and “Transportation Power”strategies,China has become the largest tunnel construction country with the highest growing speed all over the world.To construct the high-speed railways,urban rail transit and regional water transfer projects in the future,a large number of traffic and hydraulic tunnels will be built,therefore,the demand for full-face tunnel boring machines(TBMs)keeps growing.Rock breaking by disc cutters is the critical process for TBM tunnelling including two fundamental physical processes of dense core evolution and crack propagation,performs as an important basis for the cutterhead system design and penetration parameter selection.disc cutter,along with the selection of tunneling parameters.In view of the fact that it is difficult to reproduce the mechanism of the dense core evolution and force transmission in the rock breaking simulation using the element deletion strategy based on the traditional finite element method,which causes the phenomenon of "rock excessive under the cutter,and rock inadequate breaking beside the cutter",the method of coupling smooth particle hydrodynamics(SPH)and traditional finite element method(FEM)is used to construct a numerical model of the rock breaking process by TBM disc cutters.A full-scale TBM cutterhead penetration performance testing platform is used to carry out the rock breaking test of disc cutter to explore the influence of cutters spacing and penetration on the rock breaking performances.First,a numerical model of the rock breaking process by TBM disc cutters based on the FEM-SPH coupling method using the explicit dynamics module of software ABAQUS,and the modified Mohr-Coulomb elastoplastic constitutive model is assigned the rock sample,furthremore,the strain-based mesh-particle transformation mechanism implemented.Afterwards,the physical processes of uniaxial compression and Brazilian splitting performed in laboratory as well as the numerical simulations,so as to construct an accurate and reliable rock material model.According to the motion characteristics of disc cutters with rotation and revolution,the numerical model of rock breaking by two CCS-profile disc cutters with a diameter of 432 mm built.Second,based on the 2.6m full-scale TBM cutterhead penetration performance testing platform in the State Key Laboratory of Shield and Tunneling Technology penetration tests are carried out to verify the established numerical model.A cylinder specimen with the height of400 mm was poured using C40 concretet.Furthermore,nine tests are conducted with the cutterhead penetration varying 2.5 to 8.8 mm/rev and the cutterhead rotational speed varying from 1.9 to 5.9 rev/min.The real-time load acquisition module is used to measure the normal force of disc cutters and sieving tests are conducted to examine the rock mucks between neigboring cutting grooves.The normal forces,tangential forces and rock mucks quantity of the numerical simulations and experiment test are compared,verifying the reliability of the numerical method and model.Finally,based on the verified numerical model 12 sets of rock breaking simulations are conducted with the cutter spacing varying from 60 to 120 mm and the cutter penetration varying from 2 to 10 mm/rev.The dense core evolution and crack propagation mechanisms are analyzed,and the normal force,tangential force,rock muck amount,specific energy and macro crack distribution are studied.The optimal cutter spacing is confirmed as 82 mm and the optimal penetration is confirmed as 8 mm/rev.This research uses a new FEM-SPH coupling method to construct an accurate and reliable numerical model to investigate the rock breaking process induced by TBM disc cutters,which breaks through a common defect of traditional numerical simulations,and obtains beneficial conclusions on the selection of cutter spacing and penetration parameters.It provides a new method for the study of rock breaking mechanism of disc cutters,and has certain theoretical significance and application value for guiding the design of the TBM cutterhead and disc cutter as well as the penetration parameters.