Study On Rheological Model Of Soft Rock Considering Damage And Its Engineering Application

There are few rheological constitutive models provided by commercial software such as FLAC3D and ABAQUS which can calculate the rheology of soft rock,and these are almost linear.In fact,the elastic modulus,strength and viscosity coefficient of rock are affected by the factors of geological structure,groundwater seepage,weak intercalation and artificial disturbance,their values are gradually deteriorated with time.Therefore,the damage factor is introduced to characterize the deterioration of rock mechanical properties in the traditional linear rheological constitutive model.The nonlinear damage rheological model can more accurately predict the nonlinear deformation characteristics of soft rock in actual rock engineering.The main research contents of this paper are as follows:(1)Connect the Kelvin body and Nishihara model in series,establish an improved Nishihara rheological constitutive model.According to the creep deformation characteristics of red bed soft rock in central Yunnan,the traditional Nishihara rheological constitutive model can not well describe the deformation characteristics of soft rock in decelerated creep and constant creep stage,so the Kelvin body and Nishihara model are connected in series.The improved Nishihara rheological constitutive model can better describe the creep deformation characteristics of the first and second stages of the red bed soft rock in central Yunnan.(2)Introduce a time dependent damage factor into the improved Nishihara rheological model.Since the improved Nishihara rheological model can not describe the accelerated creep characteristics of soft rock,the degradation of mechanical properties of rock materials is considered by introducing time-dependent damage factors into the deformation modulus and viscosity coefficient of rock materials.The characteristics of accelerated creep deformation and failure of soft rock can be well described.(3)Derive the finite element schemes of the rheological constitutive equation and its basic variables in detail after considering the damage of rock.In the working environment of Microsoft Visual Studio,using Fortran language to develop a finite element program of damage viscoelastic-plastic rheology for soft rock tunnel.And using the incremental iterative method of variable stiffness and the accelerated convergence algorithm of constant matrix to improve the convergence,accuracy and calculating speed of the program.(4)According to the uniaxial compression creep test of red bed soft rock in central Yunnan,using the damage creep model and the numerical inversion method,the creep mechanical parameters under different axial compression stress conditions of laboratory uniaxial compression creep test of red bed soft rock in central Yunnan are obtained.It is found that the deformation and failure characteristics of soft rock are more in line with the actual situation after considering the damage of rock.In addition to,the rheological parameters of soft rock are affected by the stress level,and the stress level is greater,the rheological parameters is larger,the two show exponential or logarithmic relationship.(5)Taking the diversion tunnel in Central Yunnan as the research object,the rheological stability of tunnels with three kinds of buried depth are analyzed separately in the forms of no support,pre-reinforced support and primary support excavation.The rule of rock deformation,the distribution rules of stress and plastic zone are given.The study shows that the reasonable pre-reinforcement and primary support of the tunnel can obviously restrain the deformation of the surrounding rock,the depth and distribution of the failure zone,and the magnitude and distribution of the stress has obvious effect.The calculated results can provide theoretical basis and practical guidance for the actual tunnel excavation and support effect,as well as the secondary lining time and the reserved deformation of the tunnel.