| The shield thrust system in machines, driven by hydraulic systems providing large forces, is a key part of the shield machine. It does not only perform the task of driving shield ahead in the process of tunneling, but also control the attitude of the machine to ensure that the machine can advance along the expected path consequently for constructing the planned tunnel line. Therefore the rational analysis and design for thrust system plays an important role in the whole machine which can work well. In this paper, the key characteristics theories for driving system in Earth Pressure Balance (EPB) shield machines emphasizing on the characteristics of force transmission, deformation and natural frequency under variable stiffness were investigated. According to the characteristics above, the layout for thrust system applying in engineering was optimized. Finally, the dimensional design for reduced-scale model with diameterΦ628mm was given.The characteristics for force transmission were researched. Based on the mechanical model for driving system, the optimization function was introduced for the uniform force on segments which will be cracked by large thrust. Through analysis of the Lagrange function, the even, the four-group and the uneven systems force spatial ellipses were constructed. After eccentricity for force spatial ellipse being regarded as force performance index, the force transmission characteristics for three kinds of systems were intensively studied to seek the kind of thrust system which is suitable for the given geological condition.On the ground of the analysis for properties on stiffness for thrust system, the characteristics for deformation were studied. Base on hyperstatic compatibility, the spatial deforming ellipse for the driving system has been discovered. Applying the model to the thrust systems, the characteristics for the deforming ellipse of even and non-uniform arrangement systems have been analyzed in detail under variable stiffness caused by the compressibility of oil in hydraulic cylinders. The deformation for several kinds of thrust systems which has the effect on the control precision was given.The mothed of adopting frequency line to study the vibrational characteristics in driving systems was proposed in paper. In the light of changing rate in thrust system with the extension of hydraulic cylinders, the model of vibration was built. Through the model, the frequency line for thrust system was discovered in the progress of solving eigenvalues for feature matrix. Applying the frequency line to the thrust system in engineering application, the natural frequencies in three directions for the even system and uneven system were analyzed. The ranges of natural frequency in thrust systems have been obtained to provide the theoretical foundation for avoiding the resonanceOn the basis of the characteristics above, the optimization layout for the thrust sytem with diameter 6.34m was given. Consdering the minimum deformation and avoiding the resonance, the basic principle for the design is good force transmission performce. Finally, in line with the similarity theories, the reduced-scale shield cutting and thrust system in which the layout for jacks was optimized were designed and put up. Keywords: EPB Shield Machines; Thrust System; Spatial Force Ellipse; Variable Stiffness; Natural Frequency...
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