Study On The Damage Constitutive Theory And Rheological Properties Of Sandstone Under Triaxial Loading

With the vigorous development of infrastructure construction in my country,the engineering challenges faced by rock engineering have become more and more severe.From the beginning of construction to the long-term operation process,the rock mass continues to bear various forms of loads,which brings potential safety hazards to the project..Therefore,it is of great practical significance to study the mechanical characteristics and deformation characteristics of rocks under different loads to avoid engineering accidents.As an important means to study the law of rock deformation and failure,theory and experiment can not only simulate the actual stress state of rock well,but also summarize the physical and mechanical properties of rock under different stress states.In this paper,taking red sandstone as the test object,indoor uniaxial/triaxial compression test,creep test and cyclic loading and unloading test were carried out,and the stress-strain curve,deformation and failure characteristics,damage evolution law,Constitutive relation and parameter physical meaning.The main research work and conclusions of this paper are as follows:(1)Based on the results of uni/triaxial compression tests,it is known that the macromodulus of sandstone changes with the deformation.Based on this,a sandstone damage constitutive model is established.This model has the advantages of few parameters and clear physical meanings of parameters.The damage constitutive model can quantify the initial damage of the rock,and the in-situ modulus of the rock can be calculated reversely through the initial damage,which provides a new idea for the determination of the in-situ modulus of the rock.(2)Because the sandstone has obvious grain cementation structure and contains a large number of grains,it meets the statistical characteristics.In this paper,the sandstone constitutive relation established by Maxwell statistical distribution model can not only reflect the various stages of the stress-strain curve well,but also the model parameters have clear physical meanings.(3)Through the unfolded creep test and cyclic loading and unloading test,the law of deformation evolution with time is obtained,which verifies the applicability of the unified sandstone creep model.(4)Based on the unified creep model of sandstone under static and dynamic loads,the parameters of the creep model are studied.The research results show that under the action of constant load,the initial fluidization parameter increases with the increase of the load,indicating that the fluidization deformation capacity of the system is enhanced,and the overall stability of the system becomes worse;when the load is constant,with the increase of the confining pressure,the initial fluidization parameter decreases,the fluidization deformation ability of the system weakens,and the overall stability of the system becomes better.Under the action of cyclic loading,the initial fluidization parameter increases with the increase of stress amplitude and loading frequency,indicating that the initial strain rate of the system also increases,that is,the stronger the initial deformation capacity is.(5)Under the action of cyclic loading and unloading,derived parameters can be obtained based on the unified creep model: aging parameters and recovery parameters.The aging parameters and recovery parameters reflect the strength of the system’s aging and recovery capabilities,respectively,and the ratio of the aging parameters to the recovery parameters reflects the final state of the sample.When the stress amplitude is constant and the loading frequency increases,the aging parameter shows a trend of first increasing and then decreasing than the recovery parameter,indicating that the fatigue degree of the rock system first increases and then decreases with the increase of the frequency;the stress amplitude remains unchanged with the loading frequency.When increasing,the aging parameter first increases and then tends to be stable,indicating that the fatigue degree of the rock system increases first and then tends to be flat with the increase of the amplitude.