Experimental Study On Mechanical Seepage And AE Characteristics Of Coal Treated At Low Temperature

The coal seams in China are generally high in gas content and low in permeability,and there are many mines with potential gas outburst and high gas mines.Gas control has become one of the main tasks of coal mine safety control in China.At the same time,gas as a companion product of coal mining has a high use value.On the basis of effective control of gas and prevention and control of outburst,whether gas can be efficiently extracted has become the focus of coal mine safety production research.In the aspect of prevention and control of coal and gas outburst,some experts have put forward the technology of low temperature freezing.At the same time,the effect of low temperature cracking of liquid nitrogen can increase the permeability of coal seam and improve the efficiency of gas extraction,both of which have the same technical means.In order to apply these technical means to coal mines,it is necessary to study the mechanical and acoustic emission characteristics of raw coal after low temperature.At the same time,combined with the actual situation,it is of great significance to study the seepage and acoustic emission characteristics of raw coal after low temperature treatment under the thermal mechanical coupling.In this paper,theoretical analysis and experimental research are used to systematically study the evolution of the internal structure of raw coal in the process of low-temperature treatment and the mechanical seepage and acoustic emission characteristics of coal samples after low-temperature treatment.The research contents and main results are as follows:(1)Acoustic emission test of low-temperature cold treatment:In the process of low-temperature treatment,the coal sample produces obvious acoustic emission signal,which intuitively shows the destructive effect of low-temperature on the internal structure of the coal sample;the lower the cold treatment temperature is,the more serious the damage is;the acoustic emission signal of the coal sample under the same cold treatment temperature is different in each period,and the acoustic emission signal can be roughly divided into three stages Stage: intensiveoutbreak stage,intermittent active stage and calm stage.(2)Uniaxial compression test of coal sample:(1)the peak strength and damage strength of raw coal sample increase first and then decrease with the decrease of low-temperature treatment temperature;the strain of coal sample increases obviously after low-temperature treatment,but the increase amplitude decreases with the decrease of temperature;the ratio of damage strength / peak strength increases with the decrease of temperature.(3)Triaxial test of coal and rock under low temperature treatment by thermo mechanical coupling:(1)the peak strength of coal sample decreases gradually with the decrease of cold treatment temperature,the resistance to deformation decreases with the decrease of temperature,and the brittleness increases with the decrease of overall compressive strength.(2)With the decrease of cooling temperature,the AE peak count and AE energy increase.(3)The gas permeability of coal sample treated by cold shock at low temperature is obviously increased compared with that at normal temperature;the maximum permeability change rate of coal sample is MK = 0.0368 from normal temperature to low temperature;the permeability change rate increases with the decrease of temperature when it enters low temperature;through data fitting,it can be seen that the gas permeability of coal with gas has an exponential relationship with temperature,and the permeability increases with the decrease of cold shock temperature The permeability change rate decreases first and then increases.