Study On Variable-order Fractional Stress Relaxation Model Of Rock Mass Structural Surface

Rock is a kind of complex and heterogeneous geological material,which contains various complex structural planes and joint planes.In the construction of rock engineering such as tunnel and slope,the long-term mechanical properties of rock structural planes determine the stability of rock engineering.Rock stress relaxation describes the phenomenon that the rock deformation remains unchanged and the stress level decreases with time after excavation and lining.The previous rock engineering practice and theoretical research show that failure to fully consider the influence of rock stress relaxation often leads to major safety accidents,such as rock burst or collapse accidents during construction.Aiming at the above problems,the paper studies the rock stress relaxation constitutive model,adjusts the Kelvin model based on VO FD variable order fractional order calculus,and deducts the rock viscosity coefficient by combining with the damage mechanics theory,thus obtaining the variable order fractional stress relaxation model for rock.Using MATLAB to existing scholars to parameter test data fitting and using ABAQUS subroutine CREEP secondary development on the model,and embedded into the finite element analysis software in the experiment and engineering application,on the one hand,to simulate the stress relaxation test of the rock structure surface rock under different Angle gear block structure stress relaxation of the rules;On the other hand,it is embedded in the shield tunnel to analyze the force of the tunnel after excavation and lining.The main contents and conclusions of this paper are as follows:(1)The software element is processed by the variable order fractional order theory,and the variable order fractional Kelvin model is obtained in parallel with the elastic element.The viscosity coefficient is corrected by the damage theory,and the problem that the variable order fractional Kelvin model does not convergence under the initial stress condition is solved.(2)It is found that the curve of the model is in good agreement with the experimental data.Therefore,the model can reflect the stress relaxation law of rock structural plane,and can be applied in rock engineering to provide a certain reference for engineering.(3)The model of rock structural plane was established through ABAQUS,and the numerical simulation test of shear stress relaxation was carried out.The simulation results were compared with the experimental data,and it was found that the model embedded in ABAQUS numerical simulation could better simulate the shear stress relaxation test of rock.(4)Two groups of rock shear models with different sawing tooth sections were established,and the finite element analysis was carried out.It was found that the shear of tooth sections with different angles would affect the shear stress of rock and the attenuation mode of stress relaxation,but the stress relaxation curves of different shear were similar,including two stages of accelerated relaxation and stable relaxation.(5)Based on the established finite element model,the construction process of shield tunneling was simulated by ABAQUS software.The simulation results show that the tunnel has obvious stress relaxation behavior and the deformation variation decreases with time until it remains constant.