The Influence Law Of Loading Rate On Mechanical Properties Of Sandstone And Its Application

Under the action of external load,the rock often shows not only the elastic and plastic properties,but also the viscosity properties related to the loading rate.In practical engineering,the mechanical properties of rock under different loading rates are often very different,for example,the excavation speed and tunneling speed of underground cavern and tunnel,the stress change caused by flood discharge and water storage of reservoir dam,the stress change caused by oil and gas exploitation and other engineering problems,the loading rate is related to the law of stress redistribution of surrounding rock and stratum.Therefore,in the construction and operation stage of the project,it is of great significance to study the mechanical properties of rock under the action of loading rate for the safety and stability of the project.Based on the engineering problem of the influence of natural gas injection and production rate on the surrounding rock of aquifer underground gas storage,this thesis studies the influence of strain rate on the mechanical properties of sandstone,and carries out the stability analysis of the surrounding rock of aquifer underground gas storage.The main contents of this paper are as follows:(1)By carrying out the conventional triaxial compression test with different radial deformation loading rate and the conventional triaxial unloading test with different unloading rate,the peak strength,Poisson’s ratio,modulus of elasticity,cohesion,angle of internal friction and loading rate of sandstone specimens all show a nonlinear growth trend.The"strengthening" effect of confining pressure on the peak strength of sandstone specimens is weakened,and the axial strain corresponding to the peak strength of sandstone specimens is reduced.(2)Analyze the elastic viscoplastic properties of the loading rate effect of sandstone,separate the elastic,plastic and viscoplastic strains,with the increase of loading rate,the deflection angle ψ of viscoplastic flow direction increases gradually,the viscoplastic body strain increases faster than that of viscoplastic body strain,and the sandstone specimen is more likely to have viscoplastic body strain;the slope of axial stress viscoplastic axial strain curve increases.With the increase of unloading rate,the slope of curve of axial stress and viscous axial strain increases;with the decrease of confining pressure and axial stress,the deflection angle ψ of viscoplastic flow direction increases.(3)The Drucker Prager model considering loading rate is selected to study the constitutive model of sandstone rate effect.The non related flow law is adopted.The deflection angle ψ of viscoplastic flow direction is used to replace the internal friction angle.The method of solving model parameters is determined.The analytical method is used to verify the comparison between model and test results,which can better reflect the effect of loading rate on the mechanical properties of sandstone.(4)Use the finite element analysis software ABAQUS to simulate the rate effect of conventional triaxial compression test to verify the model.The stability analysis of the surrounding rock of the underground aquifer gas storage is carried out,and five representative working conditions are set up to study the influence scope and stability characteristics of the gas injection of gas wells on the surrounding rock of the gas storage under different injection rates and injection times,analysis the effects of injection pressure,injection time and operation life on the deformation,stress,pore pressure and flow of gas storage.At the end of gas injection stage,with the increase of gas injection pressure and the extension of gas injection time,the pore pressure,vertical displacement,gas injection and production capacity of the reservoir increase,and the horizontal stress of the reservoir decreases.With the increase of gas injection pressure,the range of reservoir plastic zone and creep zone increases obviously;with the extension of gas injection time,the range of reservoir plastic zone increases obviously,and the range of creep zone changes little.