Study On The Creep Mechanical Properties Of Artificial Frozen Sandy Mudstone In The Cretaceous Strata Of Western China

Coal resources are important energy sources for China's industrial development.In order to effectively solve the shortage of coal resources in eastern and central China,a new upsurge of mine construction has appeared in Western China.The western area of mining area must pass through Cretaceous high moisture,Cretaceous soft rock has the properties of low strength,weak cementation,the artificial freezing method through the water rich strata,the mechanical properties of frozen soft rock directly affects the stability of frozen wall,in order to ensure the safe production of the mine.The rock to instantaneous and creep test at different temperature as the main line,combined with the rheology theory and theory of creep damage,creep damage mechanics model reflect the law of the Cretaceous frozen soft rock,has important theoretical value and practical significance for the safety and stability of correct prediction and effective control of construction problems.In this paper,Xinzhuang coal mine freezing shaft as the background,from the Cretaceous stratigraphic sandy mudstone as the research object,to obtain the basic physical parameters of rock and thermal physical parameters,to explore the effect of temperature on thermal properties of rocks,results show that with the temperature decrease,gradually reduce the specific heat capacity of frozen soft rock,thermal diffusion coefficient increased gradually.The triaxial compression tests of Cretaceous frozen soft rock under different low temperature conditions have obtained instantaneous mechanical parameters of soft rock,and analyzed the effects of different low temperature conditions on compressive strength and elastic modulus of rock.The results show that the lower the temperature,the lower the rock strength.With a significant increase,the elastic modulus is also increasing,and the relationship between rock peak strength,elastic modulus and freezing temperature is given.Through the results of triaxial creep compression tests under different confining pressures and different freezing temperatures,it can be concluded that the frozen soft rock in the Cretaceous strata has obvious three-stage creep properties,and its creep characteristics are significant.The deformation of rock is composed of instantaneous deformation and creep deformation.The load level continuously increases the initial creep rate and gradually weakens with time.The larger the confining pressure,the longer the creep attenuation stage and the rock ductility increases;the lower the freezing temperature is,the softer it is.The creep of rock decreases the brittleness and the creep rate of the creep stage has little effect,but the steady-state creep rate has the tendency of increasing with the stress level;the rock sample is judged by the non-stability creep method.The long-term intensity is determined and the estimated results are conservative for engineering use,which is 50%of the instantaneous failure strength.In order to effectively describe the creep acceleration stage,an elasto-plastic damage body was constructed to optimize the Nishihara model,and the creep life was introduced using the Lematrie strain equivalence hypothesis.The expression of Kachanov damage rate was improved,and the Cretaceous freeze softness was established.The three-stage damage constitutive model of the whole process of rock creep is given,and the determination method of five parameters is given.Finally,the creep damage model of the rock is verified by test data.The results are consistent with the creep damage model established in this paper.The reliability has a certain guiding significance for the stability of the frozen shaft wall.