Mechanical Analysis Of Rock Breaking By Disc Cutter During Shield Tunneling In Mixed Face Ground Conditions

In order to meet the shield machine's needs of the subway, railway, abstraction works and other large engineering constructions, China is carrying out related works about R&D, design and manufacture of domestic shield with independent intellectual property rights. It is always one important subject needed to solve for shield industry to master the interaction mechanism of the shield cutterhead and the surrounding rock. The interaction involves the calculation of rock breaking by shield disc cutter, which is the main parameter to determine the shield thrust, and also the basis for calculating other shield parameters. Based on the above backgrounds, by the basic theory of dimensional analysis, this paper carries out the mechanical analysis of rock breaking by disc cutter and the cutterhead forces in the mixed face ground conditions.The main contents and achievements of this dissertation are as follows:(1) The motion equation of the operating point on the disc cutter blade has been established in the fixed coordinate system. By the dimensional theory, the problem of the normal rock breaking force by the disc cutter has been studied, and the functional form with most factors for calculating the normal rock breaking force by disc cutter is attained, then the empirical statistical regression formula for calculating the normal rock breaking force by the 17" disc cutter is determined based on the existing data of the linear cutting test by disc cutter. Meanwhile, the methods and procedures of inversely calculating the normal rock breaking force by the total thrust during shield tunneling are proposed through analyzing the shield loads.(2) By the dimensional theory, the problem of vertical surrounding rock pressure on the shield shell has been studied, and the functional form for calculating the vertical surrounding rock pressure is attained, then the formulas of calculating the vertical surrounding rock pressure for the category IV and V surrounding rock are determined based on the field measured data.(3) For the features of the typical soft and hard composite formation, the area ratio model of tunnel circular cross-section is established. By using dimensional theory, the parametric analysis about shield cutterhead forces is carried out in the soft and hard composite formation, then the dimensionless functional forms for calculating overturning moment and unbalanced force of cutterhead are established.(4) On the basis of calculation study of the rock breaking force by disc cutter, the related formulas for calculating shield cutterhead forces in the typical soft and hard composite formation are established, and the corresponding calculation program is also compiled by C language. With the calculation program, the cutterhead force simulations are carried out under the conditions of shield tunnelling in the typical combinations of soft and hard strata, and some laws and experience are attained.(5) With the explicit nonlinear dynamic analysis program of LS-DYNA, the process of the rock breaking by disc cutter has been simulated, then the movements and forces of disc cutter and rock fragmentation are analyzed during the rock breaking by disc cutter, the distribution function of contact pressure between the disc cutter and rock is also attained. And the process of initial penetration of rock by shield cutterhead has also been simulated, the variation of the effective thrust and the characteristics of rock mass failure during the initial invasion are gotten.