Study On Creep Characteristics Of Anthracite Under Different Porosity And Pore Water Pressure

Some researches have shown that the creep deformation will occur when the coal pillar remaining in the mine is affected by the overburden rock for a long time,which will lead to the instability of the coal pillar.Up to now,abundant research results have been obtained on the creep properties of water-bearing coal and rock.The creep constitutive model of water-bearing coal and rock can accurately describe the influence of water content of coal and rock on its creep properties,this lays a theoretical foundation for the study of creep characteristics of coal and rock mass under different porosity and pore water pressure.However,in the past,the research results mainly focused on the creep properties of coal under the influence of temperature,axial pressure and surrounding rock,while the research on the influence of pore water pressure and porosity on the creep properties of coal is less,this paper takes No.3 coal(anthracite)in Guanlingshan Coal Mine,Qinshui Coalfield,Shanxi Province as the research object and classifies its porosity based on CT scanning technology,u NIAXIAL creep tests with different porosity,triaxial creep tests with the same pore water pressure under different porosity and triaxial creep tests with the same porosity under different pore water pressure are carried out,a creep model of coal with different porosity under the action of pore water pressure is established and the relevant parameters in the equation are fitted,and the constitutive model is embedded in FLAC-3D numerical simulation software,the creep law of anthracite under different porosity and pore water pressure is simulated,and based on the creep law of anthracite under different porosity and pore water pressure,the creep model of anthracite is established,taking the Guanlingshan coal industry in Qinshui Coalfield of Shanxi Province as the engineering background and based on the actual geomechanical conditions of No.3 coal seam,a numerical calculation model is established to study the stability of the coal pillar left behind in No.3 coal seam and the space-time evolution of the coal pillar.The results showed that:(1)the samples of anthracite with different POROSITY experienced four stages:transient deformation,decay creep,stable creep and accelerated creep.With the increase of porosity,the strength of creep failure gradually decreased and the initial strain gradually increased;(2)with the increase of loading level,the instantaneous strain of specimen decreases gradually,and the time to enter the stable creep stage decreases;(3)the strength of samples with the same porosity is obviously different under the action of pore water pressure,and the weakening effect of Pore water pressure on coal and rock samples is obvious.The results show that the instantaneous strain decreases with the increase of pore water pressure when the axial stress is applied;(4)when the pore water pressure is the same,the instantaneous strain of the specimen increases with the increase of the porosity,which indicates that the pore water pressure has softening effect on the specimen,the instantaneous strain of the specimen increases to a certain extent;(5)with the increase of porosity and pore water pressure,the time of coal sample entering the accelerated creep stage is shorter;(6)the creep law of the 10 m width coal pillar accords with the typical creep law,that is,the slow creep stage,the stable creep stage and the accelerated creep stage,the displacement of the coal pillar will continue to increase with time,until the coal pillar is destroyed;The coal pillar whose width is 15 m,20m and 25 m only occurs the slow creep stage and the stable creep stage,the subsequent displacement will not increase,and the coal pillar will keep the stable state.