Study On Constitutive Model And Damage Evolution Characteristics Of Sandstone Under Periodic Loading And Unloading

In rock underground engineering,especially in tunnel or underground roadway,the stress field of underground rock will change,the original stress condition of rock material will be destroyed,and the new stress field will be formed.With the continuous excavation,the surrounding rock materials will be broken into the period of the formation of the new equilibrium state for a long time.In addition,the emphasis of rock underground project safety is to study the mechanical response of rock materials,in which the constitutive evolution relationship of rock damage is an essential link.Therefore,according to the Weibull mathematical dispersion formula and unified criterion system,the relationship between sandstone damage evolution under the condition of periodic loading and unloading is established.In addition,the process of rock damage constitutive factor analysis,rock microelement strength analysis and rock elastic modulus analysis are carried out.The results show that the fitting is better by fitting and comparing all kinds of test data.The functional expressions of each parameter are derived by formula,and the control variable method is introduced to compare and analyze the damage constitutive parameters,and the actual physical significance of each parameter is obtained.According to the parameter variables and the test threshold,the modified new sandstone damage evolution relationship is established.Finally,according to parameter and energy method,the evolution law and characteristics of damage variables in different directions are further clarified.In order to reduce the amount of data analysis and ensure the feasibility of the test,the typical test curve was selected and the data of the 1st,13th and 25th addition-unloading were fitted and analyzed.The results show that:(1)The constitutive relation of sandstone damage under periodic loading and unloading state is well fitted with mechanical damage and chemical-mechanical coupling damage test data,and the correction parameters are high.It shows that the constitutive relation meets the mechanical response of sandstone damage and has high feasibility and rationality.(2)The control variable method is used to analyze the different parameters,and the practical significance of the parameters is determined,that is,the F0 of the parameters can show the strength characteristics of the rock specimen under the macroscopic state,and the m of the parameters can show the strength distribution characteristics of the rock specimen under the microscopic.(3)According to the Weibull parameters and test threshold,a new damage evolution relationship of sandstone specimen is established,which will meet the actual situation in theory.(4)According to the Weibull parameter and energy method,the damage change of the specimen is discussed,and the image and fitting expression of the damage factor and stress and strain relation of each addition-unloading grade are obtained,which will be beneficial to the better development of the damage constitutive evolution relationship of the rock specimen.Figure[26]Table[4]Reference[56]...