Research And Application Of Rheological Instability Of Small Coal Pillars

Rock burst is one of dynamic disasters in coal mine,At present.the prevention and control of rock burst in China is still facing a severe situation,and the rock burst accident has not been effectively curbed.In recent years,most scholars have begun to pay attention to the time effect of rock burst,but the relevant research theory is not complete.The time effect of rock burst is actually the incubation process of rock burst.The pillar rock burst caused by instability of coal pillars accounts for a certain proportion of rock burst accidents.Rational coal pillars is a very effective regional prevention measure for rock burst.When working face mining is deployed in rock burst mine,roadways without coal pillars or small coal pillars should be preferentially selected.Because small coal pillars are more prone to rheological deformation,there is still the possibility of coal pillar rock burst.Therefore,the study of rheological instability of small coal pillars has important theoretical significance and practical value for preventing rock burst.In this paper,the rheological instability of small coal pillars is studied by combining theoretical research with engineering practice.Based on the in-depth analysis of the rheological models of eight typical composite elements,the stress,strain,strain rate and energy changes of the six-element composite rheological model under different stress conditions were studied.The results show that,whether creep under constant stress or uniform rheological,the deformation of elastic element is the main one in the early stage,and the deformation of inelastic element is the main one in the later stage.The increase of inelastic stress,inelastic strain and inelastic energy increment is obvious.The difference between constant stress creep and uniform rheological is that the rate of change of energy increment is different.When constant stress creep occurs,the rate of change of energy increment decreases gradually,but when uniform rheological occurs,the rate of change of energy increment increases gradually.The six-element rheological model was used to analyze the development process of rock burst in small coal pillars.During the development process before the occurrence of small coal pillar rock burst,the strain energy of elastic elements constitutes the accumulation of total energy,and the dissipated energy of viscous elements is consumed in the process of coal body damage.In the early stage of the development process of rock burst,energy accumulation is dominant,and in the later stage,energy dissipation is dominant.The mechanism of rheological instability of small coal pillars is revealed and the criterion is established.Under the condition of low stress,the stress in the small coal pillar is less than the compressive strength,and the rheological rate is small.It takes a long time to rheologicaldeformation,and the strength decreases gradually,so that the coal pillar-roof deformation system can reach the unstable equilibrium state,and the rock burst will occur due to external disturbance.Under the condition of high stress,the stress in the small coal pillar is greater than the compressive strength,and the rheological rate is larger.Only a short time of rheological deformation is needed.The coal pillar-roof deformation system is always in an unstable equilibrium state,and the rock burst occurs when the external disturbance occurs.The analytical solution of lag time of rock burst in small coal pillars is obtained.The lag time of small coal pillar is related to the elastic modulus,rheological rate and initial stress of roof.Under high and low stress conditions,the lag time of rock burst decreases with the increase of elastic modulus and rheological rate of roof,but there is a limit value beyond which there is no lag time for coal pillar rock burst and rock burst occurs directly.When the elastic modulus of roof is the same,the lag time of rock burst decreases with the increase of stress.Under the same rheological rate,the lag time of rock burst decreases with the increase of stress.The harder the roof is,the shorter the lag time of rock burst is.The paper has 46 figures,2 tables and 86 references...