Study On The Variable Stiffness Behavior Of The Supported System Of Tunnel Boring Machines

The tunnel boring machines (TBM) play a very important role in the devel-opment of national heavy equipment mechanical systems, which is widelyused to excavate the hard rocks. Their supporting systems contact with thetunnel surfaces directly during the process of excavation. With the help ofboth the supporting systems and the cutter heads, the tunnel is constructedcompletely. The end of the thrusting system contacts with the naked roughtunnel surfaces during the process of excavation. The interfacial contact stiff-ness is bound to be changed immediately with the brittle characteristic ofrocks, the huge impacts and vibrations on the thrusting systems, the roughnessof tunnel surfaces, the fatigue of rocks caused by deformation, damages anduncertain forces in the contact areas. As a result, the dynamic characteristicscan’t be predicted and the excavating direction and gesture will change andthen may cause some unpredictable accidents. It is sure that these may lead tohuge economic losses.Therefore, it is quite necessary to have a research about the discipline ofthe interfacial contact stiffness between the supporting systems and the tunnel rough surfaces. The contact mathematical models are built to study the rela-tionships between surface roughness, crisp characteristics of rocks, the varia-ble external loads and contact stiffness. All of these theoretical works aresupposed to be a guidance of practical works. The whole thesis can be gener-ally summarized as follows,(1) The mathematical models and characteristic analysis of differentrough surfaces.The normal and tangential contact stiffness mathematical formulas aregiven based on fractal theories which are derived on the characteristics ofTBM supporting systems’ contact with tunnel rough surfaces. Further re-searches about the relationships between the contact stiffness and fractal di-mensions, height scaling parameters, hardness of rocks, elastic modulus, sur-face roughness and the failure and damages of rocks and the variable externalforces are obtained. Results show that the increasing of normal forces willgive rise to the increasing of normal contact stiffness. However, the disciplineof tangential stiffness is closely related to the loading routine of tangentialforces. When normal forces are constant and tangential forces increase, thetangential stiffness will decline with the increasing of tangential forces. Theincreasing of both normal and tangential forces give rise to the increasing oftangential stiffness. In another situation, the supporting system is loaded a force firstly and then a constant force is loaded whose direction is changingwith time in a certain angle. The results show that the tangential stiffness goesup with the increasing of tangential stiffness when the forces are less than acertain value. The tangential stiffness is about to go down with the increasingof tangential forces when the forces are more the certain value.(2) The simulation of contact stiffness with different parameters of roughsurfaces.The3D contact models about the contact between supporting system andrough surfaces are built based on fractal formulas which can be used to obtainthe characteristic points on the rough tunnel surfaces. With the help of finiteelement analysis software ABAQUS, results of the relationships between thecontact stiffness and forces are in coincidence. Based on the result, the meth-ods of FEA are employed to study the relationship between contact stiffnessand complex rocks in the contact area and double supporting systems. Resultsshow that rocks with different physical characters will have an effect towardseach other during the deformation. The contact stiffness of double supportingsystems is less than two times of single supporting system.(3) The characteristic of interfacial contact stiffness under variable pa-rametersThe fuzzy arithmetic methods are employed to analyze the contact stiff- ness because the components of rocks in the contact areas vary quite a lot.This section mainly deals with the uncertain relationships between the contactstiffness and uncertain elastic modulus, height scaling parameter in the con-tact areas. Results show that the fuzzy arithmetic model can be employed topredict the variable ranges and probability of contact stiffness.