Constitutive Model For Creep Damage Of Coal And Rocks Around Bored Holes In Water-containing Gas Drainage

Gas extraction is an important means of mine gas control.However,with the extension of the extraction time,the creep of the coal around the gas extraction hole threatens the stability of the borehole and the safe mining of the coal seam.At the same time,during the drilling process of the underground working face,it usually exists a lot of water.Water can soften and sludge coal rock,resulting in obvious changes such as volume expansion and creep in the borehole.With the extension of gas drainage time and the change of water content,the creep damage process of coal rock around the borehole variable and complex.Therefore,there is an urgent need to study the creep damage law of water-gas drainage holes.The creep constitutive model can reflect the creep law of the borehole well,but the existing models rarely consider the influence of water damage on the creep characteristics of the borehole.In order to better reflect the damage laws of drilling,it is necessary to start with the creep model and establish a creep constitutive model that can reflect the changes of water damage and acoustic parameters during the entire creep process.In the dissertation,through the staged loading creep test in the laboratory,using the acoustic emission detection system and the ultrasonic monitoring system,combined with the on-site drilling acoustic effect detection,and using the theoretical knowledge of statistical damage mechanics,a constitutive model study on coal and rock creep damage around boreholes for gas drainage.The main research contents are as follow:(1)It is found that the Nishihara model does not reflect the creep law of the accelerated creep stage very well.Based on the Nishihara model,the viscoplastic elements in the accelerated creep stage can be described by series and parallel,and the Nishihara model is improved.Based on the definition of coal and rock damage,a creep constitutive model that can reflect changes in water damage and acoustic parameters is established.(2)Using the YYY200 electronic creep test machine to carry out the staged loading creeptest of porous coal rock with different water content,studied the effect of water content on the creep characteristics of porous samples,and analyzed the moisture content on porous coal rock The influence law of the body damage variable,combined with the creep constitutive equation that can reflect the change law of water damage,obtains the parameter evolution law reflecting the water damage model,and compares the creep test value of the water-bearing coal-bearing rock mass with the calculated value of the model,To verify the rationality of the water-based creep damage model,and to provide a theoretical basis for exploring the influence of water content on the creep damage damage of coal and rock around the borehole of gas drainage.(3)Through acoustic detection technology,the characteristic parameters and ultrasonic parameters of the acoustic emission data during the creep process of this staged loading are analyzed,and the influence of different water content on the acoustic characteristics of the porous coal rock body during the creep process is studied.The relationship between the damage value of the cumulative ringing count and the water content and the relationship between the damage value of the ultrasonic wave velocity and the water content are discussed,and the evolution law of acoustic damage of porous coal rock with different water content is discussed.By comparing the creep test value with the model calculation value,the rationality of the creep constitutive model that can reflect the change rule of acoustic parameters is verified.(4)By detecting the acoustic effect of creep damage on the gas drainage borehole in Yuwu coal mine,the parameters of ultrasonic waveform,amplitude,wave speed,damage variable and other changes with the time of hole formation and water-containing environment are obtained The acoustic test results were compared with the parameters of the creep constitutive model that can reflect the laws of acoustic characteristics.It was found that the field test,indoor test,and model parameters were consistent with each other,which verified the correctness of the test results and the creep constituencies that could reflect the laws of acoustic characteristics.The rationality of the construction model.The test results provide some guidance for the acoustic monitoring of gas drainage boreholes.