| As one of the world's most advanced large-scale general finite element software,ABAQUS has been widely used in various industries,but its existing function cannot fully meet the various industries some requirements of the advanced users,such as the program existing models of geotechnical material is limited or has some defects,especially for rock mass material,there is no suitable constitutive model to describe the non-linear failure characteristics.Therefore,in this paper,based on its secondary development platform,using Fortran language and backward euler implicit integration algorithm,an user material subroutine(UMAT)has been development and applied to the case analysis,the main research work is as follows:(1)The Hoek-Brown strength criterion was introduced;its various equation forms were listed as well.The presentation of the Hoek-Brown criterion is an irregular curvy hexagonal pyramid in the principal stress space,which leads to the occurrence of numerical singularity on the edges of the pyramid.In this paper,the circle arc is used to instead of the original yield surface nearby the sharp angle,namely "circle".The circular arc that yield function expression is deduced.Meanwhile,to reflect the characteristic of the poor tensile strength of rock mass,a tension cut-off surface was employed to form the whole modified composite yield surface.(2)The fully implicit backward Euler integral regression algorithm was applied for stress update.Considering associated flow rule,first order derivative of yield function and second order derivative of potential function were derived to form the consistent stiffness matrix to ensure the high accuracy and fast convergence of numerical computations.To facilitate the application of this modified Hoek-Brown criterion,a 3-D user-defined material subroutine(UMAT)was developed in the finite element program-ABAQUS.Using indoor conventional triaxial compression test and uniaxial tensile test,and modelling the circular tunnel and piles-rock mass interaction and tunnel excavation to demonstrate the validity of the program,as well as the applicability in ture three-dimension problem.This paper dissussed the principle and application method of the approximation to nonlinear Hoek-Brown criterion by using the linear Mohr-Coulomb criterion,and compared the different mechanical behavior under two kinds of criterions.Meanwhile,the influence of the dilatancy angle was expounded briefly.In additions,this paper discussed the spatial effects of tunnel excavation,and studied the tunnel longitudinal deformation curve(LDP curve)and the mechanical behavior of surrounding rock under different excavation rates and different initial stress conditions.Besides,the Convergence-Confinement method and its application condition were introduced.(3)The qualitative and quantitative methods were introduced in order to acquire the Hoek Brown material parameter values.Nonparametric statistical method was putted forward to research Hoek-Brown parameters sensitivity.Latin sampling procedure was compiled in Matlab.With a tunnel model,the sensitivity of the parameters on the deformation of surrounding rock was studied.Then the size and the order of parameters' sensitivity were obtained.(4)Fristly,the equivalent Mohr-Coulomb strength reduction technique as well as its advantages and disadvantages were illustrated.Then,the strength reduction technique based on Hoek-Brown strength criterion was proposed and deduced.When used Hoek-Brown strength reduction technique to a rock mass,compared with the equivalent Mohr-Coulomb model,the position of the slip surface obtained by the Hoek-Brown is shallower and the.shape of it is steeper,which agree well with the characteristics of slip surface of rock slope.Finally,the author tried to use Hoek-Brown strength reduction technique in the stability analysis of underground cavern.The overall safety factor can be obtained.Meanwhile,the damage location and potential failuresurface can be precisely predicted. |
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