Research On The Mechanical Properties And Energy Evolution Of Marble Under Triaxial Unloading Conditions

With the mining of shallow mineral resources exhausted,domestic and foreign mines have successively entered deep mining.Under the conditions of deep mining,excavation of roadways,tunnels and other projects is a typical process of rock unloading,and it is easy to induce rock bursts and other dynamic disasters.Seriousl y threaten the safety of construction personnel and equipment.In this paper,the triaxial loading and unloading tests of marble were carried out to study the mechanical properties of marble under different confining pressures and different unloading rate conditions(stress paths),energy evolution mechanisms,nonlinear energy evolution models,and unloading failure strength criteria.The unloading constitutive model was established and the following research results were mainl y achieved:(1)The triaxial loading and unloading tests of marble were carried out.In the conventional triaxial tests,the deformat ion modulus decreased first and then slowly decreased;Poisson's ratio decreased first and then increased slowly as the deviator stress increased;In the macroscopic view,shear failure is dominant,and in the mesocosm fracture is dominant;the acoustic emiss ion is relatively concentrated in the initial stage of loa ding and the destruction stage.In the triaxial unloading test,the deformation modulus first increases with decreasing confining pressure,then largely jumps and decreases rapidly,while the Poisson's ratio increases sharply with the unloading of confining pressure;macroscopically,the longitudinal cracking occurs.Composite fractures such asshear failure are dominant,and mesostructure fractures mainly along cement;acoustic emission characteristics are basically consistent with conventional triaxial tests.(2)The evolution characteristics and evolution model of the damage energy of the triaxial loading and unloading of marble are studied.Under normal loading conditions,the energy at the stress pea k point is greater than that of uniaxial compression;the initial elastic energy ratio increases with the increase of axial strain.In the three-axis unloading test,under the same confineng pressure and different unloading rates,the el astic energy,dissi pated energyand dissipated energy ratio of the rock sample increase with the increase of the axial strain;the same unloading rate,different confining pressure The proportion of elastic energy stored in rock increases with the increase of confineng pressure;with the increase of confining pressure and unloading rate,the energy dissipated by rock sample at the unloading point increases.In the triaxial loading and unloading tests,when the stress reaches 81.63% and 80.55% of the peak stress respectively,t he system enters into the bifurcation bifurcat-ion zone.When the peak stress reaches 84.75% and 83.93%,the system enters a chaotic state.(3)The strength criterion of the triaxial unloading failure of marble is analyzed,and the unloading constitutive model is established: the Mogi-Coulomb strength criterion has good fitting effect on the unloading axial pressure and simultaneous unloading confining pressure test results;marble is obtained according to the criterion.The angle of rupture surface is app roximately 66.54°.The theoretical value is in good agreement with the experimental results.Based on the experimental results,the rock unloading constitutive model is deduced.In this paper,uniaxial compression,triaxial loading and unloading tests were carried out to study the mechanical properties of marble under different stress paths.The rock failure mechanism was studied from the perspective of energy,and the strength criterion was established by simply relying on the st ress strain relationship or its size.The failure criteria study the defects of the rock failure mechanism and provide a new idea for the in depth study of rock unloading failure mechanism.The study of rock unloading mechanical properties and evolution mechanism not onl y reveals the mechanical mechanism of unloading induced rock burst,but also has a good reference and application value for deep underground engineering.