Research On Creep Intrinsic Model And Numerical Simulation Of Red Sandstone Under Different Loading Methods

As a fundamental property of rocks,the rheological properties of rocks play an important role in the long-term stability of rock engineering.It is important to conduct research on the rheological properties of rocks under different stress paths for engineering guidance.In this paper,uniaxial graded loading and graded unloading creep tests are conducted on typical red sandstone to investigate the rheological properties of red sandstone under different loading methods,and the corresponding creep models are established respectively,and the secondary development of graded unloading creep models is completed by using FLAC^3D numerical software.The main research contents of this paper are as follows:（1）Basic mechanical property tests,including uniaxial compression test and Brazilian splitting test,were carried out on standard red sandstone specimens to obtain the parameters of uniaxial compressive strength,elastic modulus and tensile strength of this red sandstone.Based on the basic mechanical tests,the numerical model was established by using PFC^2D software,and the parameter calibration of the numerical specimen was completed,and the long-term strength of this red sandstone characterized by the dilation stress was determined by numerical tests.（2）The uniaxial graded loading creep test and graded loading and unloading creep test of red sandstone were carried out,and the creep characteristics,creep rate characteristics and viscoelastic characteristics of red sandstone were analyzed according to the results.The study shows that the instantaneous deformation and stress level show strong linear characteristics;when the stress level is low,the axial creep rate shows a variation law similar to the inverse proportional function,and when the stress level is high,the axial creep rate image shows an inverted"U"variation law;the creep deformation of red sandstone has the characteristics of coexistence of viscous,elastic and plastic.（3）The identification of the corresponding creep model is completed based on the analysis of the test results,and then the creep equation and the three-dimensional expansion of the creep model in the one-dimensional stress state are derived.The Levenberg-Marquardt optimization algorithm in the least squares method is used to fit the test data,determine the creep model parameters and verify the accuracy of the creep model.It is shown that the fitted curves are in good agreement with the experimental curves,which fully indicates that the corresponding creep model can better reflect the creep properties of red sandstone under different loading methods.（4）Finite difference discretization of the creep equation of grading and unloading was completed,and the secondary development of the creep model of grading and unloading was completed by using FLAC^3D software.The numerical analysis of the red sandstone was carried out by taking the average values of the parameters of the fitting results of the graded plus unloading creep test,and the correctness of the graded plus unloading creep model was verified by comparative analysis.Figure[45]Table[9]Reference[84]...