Basic Experimental Study On The Negative Pressure Effect Of Damage And Failure Of Coal Under Uniaxial Loading

In order to study the strength variation characteristics of coal in different pressure(including negative pressure)environment,a combination of laboratory test and theoretical analysis was used to construct a negative pressure environment coal body mechanics experimental system,which was applied by means of acoustic emission monitoring technology.The advanced theoretical knowledge of damage mechanics and fractals is used to analyze the influence of air pressure and loading rate on the mechanical properties of coal.The morphological characteristics of loaded fracture under negative pressure are studied,and the negative pressure effect of coal uniaxial load damage is revealed.(1)The experimental system of coal body mechanics in negative pressure environment is constructed,which can carry out uniaxial compression test under different air pressure(including negative pressure)environment,and can realize real-time monitoring of parameters such as stress,displacement and acoustic emission.(2)The uniaxial compression experiments of coal bodies under four negative pressure environments(0.030MPa、0.055MPa、0.070MPa、0.087MPa)were carried out.For comparison,atmospheric pressure(0.1MPa)and three different gas pressure conditions(0.2MPa、0.5MPa、1.0MPa).The experimental results show that with the increase of negative pressure,the strength of coal body increases,and the strength of coal in negative pressure environment is obviously higher than that under normal pressure and gas-containing environment.(3)Mechanical experiments were carried out on the influence of different air pressure and loading rate on coal strength.Five loading rates were set,including 0.001mm/s,0.005mm/s,0.01mm/s,0.05mm/s and 0.1mm/s.For comparative study,four environments were set,namely,negative pressure(0.087MPa),atmospheric pressure(0.1MPa),and gas(0.5MPa and 1.0MPa).The experimental results show that the degree of coal fragmentation increases with the increase of loading rate,and the coal strength decreases logarithmically under the four air pressure environments.(4)The acoustic emission response characteristics of coal body under uniaxial loading failure process are analyzed,and the damage normalization law of coal body during load failure is obtained by using AE energy “normalization” method.The results show that with the increase of air pressure,the damage variable of coal body increases gradually;with the increase of loading rate,the damage variable increases first and then decreases.(5)Using the calculation method of box dimension in fractal theory,the fracture morphology characteristics of coal body after uniaxial load failure are analyzed.The results show that with the increase of gas pressure,the fractal dimension of fracture increases logarithmically.With the increase of loading rate,the fractal dimension of fracture increases first and then decreases.This result is consistent with the trend of damage variable.Through the experiment of uniaxial compression of coal under different air pressure and loading rate,theoretical research was carried out by using the knowledge of damage mechanics and fractals,and the negative pressure effect of coal uniaxial load damage was revealed.Figure [187] table [9] reference [57]...