Nonlinear Creep Constitutive Model Of Rock Based On Fractional Calculus And Its Secondary Development In Flac3D

As a complex geological body,the mechanical properties of rock are the basic problems that rock engineering must face,and rheology is one of its very important properties.Rock rheology refers to the time-dependent deformation and destructive properties of rocks under external loads,temperature and humidity.Many geotechnical engineering are closely related to rock rheology.The study of rock rheology mechanics is very important to solve the practical problems of rock mechanics.The traditional rock constitutive model can only simulate the concealed linear creep stage,but can not accurately reflect the non-linear stage.Based on the fractional calculus theory,a new constitutive model for the combination of non-linear elements is proposed in this paper,and it is applied to Flac3 D software for secondary development.The main conclusions are as follows:(1)Based on fractional calculus theory,a non-linear creep constitutive model reflecting the viscoelastic-plastic properties of rock is established.The constitutive equation of the model is derived.The viscoelastic creep characteristics of the model before the stress threshold and the viscoelastic-plastic creep characteristics after the stress threshold can be well reflected.It has a certain degree of innovation.(2)Macquart algorithm based on 1stOpt data processing software platform.The triaxial creep test data of greenschist in Jinping Hydropower Station are fitted to obtain the parameters.Compared with the Boggs model,the fitting accuracy of the model is higher,which shows that the model can accurately reflect the non-linear characteristics of rock creep.(3)Based on the finite difference theory,the self-defined constitutive equation of creep model is deduced by three-dimensional difference scheme.Based on the finite difference theory,the self-defined constitutive equation of creep model is deduced by three-dimensional difference scheme.some important contents and key technologies in the process of model development are briefly introduced,and compared with the cvisc model of software,an example of uniaxial compression experiment is given to verify the effectiveness of the second development.(4)The numerical analysis of grouting reinforcement of tunnels is carried out by using Flac3 D program and the nonlinear constitutive model defined above,and the influence of grouting reinforcement on tunnel engineering is studied.By changing the parameters of surrounding rock,the model of three working conditions,namely nongrouting,vault grouting and full-ring grouting,is established,and the mechanical response of tunnel surrounding rock under three working conditions is analyzed.However,the bearing arch formed after grouting reinforcement is caused by the transfer of the upper load to the arch foot,forming a stress concentration area at the arch foot,which is not conducive to the stability of the tunnel.In the design,sufficient attention should be paid to the arch foot,which also verifies that the strength of shotcrete at the arch foot needs to be guaranteed in the actual construction process,and lock foot bolts should be added when necessary.(5)By analyzing the numerical simulation results of three working conditions: nongrouting,vault grouting and full-ring grouting,the following conclusions can be drawn: grouting reinforcement of large section weak surrounding rock tunnel can effectively improve the mechanical properties of surrounding rock in grouting area,enhance the strength of surrounding rock in grouting area,reduce the displacement of surrounding rock,and enhance the self-stability of tunnel.