Experimental Study On Physical And Mechanical Properties Of Marble After High Temperature

In many engineering fields such as civil engineering,geological engineering and mining engineering,such as underground coal gasification,deep storage of nuclear waste,and repair&reinforcement of underground engineering fire,the strength and deformation characteristics of rocks after high temperature are inevitably involved.The physical and mechanical parameters are indispensable basic basis for rock underground engineering excavation,support design,and stability analysis of surrounding rocks.Under the conditions: confining pressure of 0MPa?15MPa,temperature of 25??800? and high temperature time of 1h?3h,ultrasonic test and conventional triaxial compression test were carried out on marble samples with different high temperature time and different temperature treatment,the change law of physical and mechanical characteristic parameters of marble,the destruction characteristics and destruction forms of marble after high temperature are studied,and the correlation analysis of physical and mechanical characteristic parameters is carried out.The main conclusions are as follows:(1)The main minerals of marble are dolomite and calcite,and the contents are 90% and 9%.The physical property threshold temperature range is about 200??300?.When the temperature exceeds 300?,the calcite is decomposed quickly,a large number of cracks appear on the surface of the dolomite particles,and the surface of marble gradually turns white.(2)After high temperature,the change rate of marble such as mass,volume,density,wave velocity,etc.increases with the increase of temperature and high temperature time in different forms and different rates.The wave velocity ratio(velocity ratio of P-wave to S-wave)decreases exponentially with increasing temperature.The dynamic elastic modulus,dynamic shear modulus and dynamic bulk modulus decrease linearly with increasing temperature,and decrease exponentially with increasing high temperature time.The dynamic poisson's ratio decreases exponentially with increasing temperature and high-temperature time.The dynamic elastic parameters of marble are positively correlated with density and wave velocity.(3)The threshold temperature range of the mechanical properties of marble is about 300?? 400?.After high temperature,the peak strength,elastic modulus,deformation modulus,poisson's ratio,shear modulus and bulk modulus of marble increase linearly or exponentially with the increase of temperature and high temperature time in different forms,different rates and different paths.The elastic modulus,deformation modulus,poisson's ratio,shear modulus,bulk modulus and peak strength of marble are all positively correlated.The coupling effect of temperature and force on rocks is nonlinear.With the increase of temperature,the elastic deformation stage of marble gradually becomes shorter,the plastic deformation of the rock increases,and the rock softens obviously.The ratio of crack closing stress,initiation stress and damage stress to peak stress increases with the increase of confining pressure.With the increase of temperature and high temperature time,the ratio of crack closing stress of marble increases obviously,and the ratio of initiation stress and damage stress gradually decreases.When the confining pressure is 0 MPa,the failure form of the marble is mainly tensile failure along the axial direction.When the confining pressure is 5 MPa?15MPa,the failure form of the specimen is mainly the shear failure of the inclined plane,and the higher the temperature,the longer the high temperature time,the greater the fracture angle of the main fracture surface.(4)After high temperature,the peak strength is positively correlated with wave velocity and density.The dynamic elastic parameters and static elastic parameters are all positively correlated.The relationship between peak strength and wave velocity&density can be expressed by a quadratic polynomial function.The relationship between dynamic and static elastic parameters can be expressed by a linear function.The above relationship can provide a powerful reference for the prediction and selection of relevant physical and mechanical parameters of marble after high temperature.