Experimental Research On Mechanical Characteristics And Constitutive Models Of Marble Under High Confining Pressure

With the economic construction in China,the construction of large-scale hydropower projects,the development of underground space and the exploitation of coal resources,the rock engineering problems under the action of deep high stress are increasing.At the same time,the problem of excavation and unloading of deep underground engineering has been I am troubled by the civil engineering builders in China.In this paper,a combination of experimental research and theoretical analysis is used to establish an improved Duncan-Chang addition and unloading constitutive model.The main research contents of this paper are as follows:（1）Under the test conditions provided by the RMT-150C rock mechanics test system,the uniaxial compression test,the conventional triaxial test and the triaxial unloading test of marble were carried out to analyze the mechanical properties of marble.For the strength characteristics,the peak strength of the unloading test under different confining pressures is lower than the peak strength under the corresponding triaxial compression test,and the cohesion force c of the shear strength parameters is also reduced,so the unloading will cause the strength of the marble.Deterioration of characteristics;analysis of deformation parameters,found that the elastic modulus of marble increases with the increase of confining pressure,and its variation law satisfies the functional relationship of E=-31593.73e^-σ3/40.44+41161;The failure modes of the lower marble are obviously different:the failure under the uniaxial compression test is brittle tensile,the failure under the high stress triaxial compression test is ductile failure;the failure of the triaxial unloading confining pressure test is shear failure.（2）Under the confining pressure of 40 MPa,the unloading confining pressure test of different initial unloading levels was carried out.The initial unloading level n was0.7,0.8 and 0.9,respectively,and the strength characteristics of the marble samples were analyzed.The test results show that when n is 0.7,0.8,0.9,the average value of the deviatoric stress intensity of marble is 114.32MPa,127.69MPa,140.16MPa,that is,the greater the initial unloading level,the higher the strength of marble;and the strength of marble.Compared with the initial unloading point stress value,the increase of 16.32MPa,14.69 MPa,13.16 MPa,respectively,that is,the lower the initial unloading level n,the greater the value of the deviator stress increase.（3）Under the confining pressure of 50 MPa,the unloading confining pressure test of different axial loading rates is performed,and the axial loading rates are 0.005 mm/s,0.01 mm/s,0.02 mm/s,and 0.05 mm/s,respectively.The strength characteristics of marble samples were analyzed.The test results show that the average deviatoric stress of marble is 144.42 MPa,151.48 MPa,151.94 MPa and 164.05 MPa when the axial loading rates are 0.005 mm/s,0.01 mm/s,0.02 mm/s,and 0.05 mm/s,that is,the smaller the axial loading rate,the lower the strength of the marble.（4）Analyze the characteristics of the addition and unloading stress and strain curves of marble under high stress,and derive the improved Duncan-Chang plus and unloading constitutive model based on the Duncan-Chang model.Finally,the improved Duncan-Chang is used.The constitutive model is compared with the experimental results.The improved Duncan-Chang constitutive model can accurately describe the mechanical properties of marble under high stress,and the form is simple,and there is no need to artificially set the yield point.The parameters can be determined through experiments.