Experimental Study On Seepage And Acoustic Emission Characteristics Of Coal And Rock Under Thermo-mechanical Coupling Action

Raw coal not only plays a dominant role in China's energy composition,but also accompanies a large number of clean resources-coal bed methane.How to develop and utilize coal bed methane safely and efficiently has become a hot spot.However,with the increase of mining depth,the ground temperature and stress show an increasing trend,which not only seriously affects the underground mining activities,but also affects the permeability of coal seam,which undoubtedly adds a difficult problem to the extraction and utilization of coal seam gas.Therefore,the raw coal and briquette produced at 18506 working face of Malan Coal Mine are taken as research objects.The mechanical seepage and acoustic emission characteristics of coal under Thermo-mechanical action are tested by using the improved WYS-800 microcomputer controlled electric hydraulic servo device of three triaxial test and digital acoustic emission monitoring system.The theoretical basis for gas extraction and prevention of coal and rock dynamic disasters is provided.The specific research is as follows:(1)Conventional triaxial tests:(1)The peak strength of raw coal increases with the increase of confining pressure and loading rate,and the greater confining pressure,the greater elastic modulus;(2)There is a blank period in the initial stage of acoustic emission.With the increase of confining pressure,the blank period of acoustic emission becomes longer and the activity of acoustic emission decreases.(3)With the increase of confining pressure,the maximum ringing count decreases and the amplitude increases.But the larger the loading rate,the larger the maximum ringing count and the smaller the amplitude.(2)Acoustic emission test of raw coal and briquette under uniaxial compression:(1)the uniaxial peak strength of briquette increases with the increase of temperature,while raw coal is on the contrary.At the same treatment temperature,the peak strength of briquette is larger than raw coal;(2)During the whole process of deformation and failure,the number and amplitude of acoustic emission events of raw coal are larger than that of briquette at the same temperature.Amplitude of briquette concentrates in the range of 40-60 dB,and there are few acoustic emission events with amplitude over 70 dB,which only occur near the inflection point of stress-time curve and peak stress,and with the increase of temperature,the acoustic emission events with amplitude over 70 dB decrease;the acoustic emission events of raw coal concentrate in the range of 40-70 dB,and the acoustic emission events with amplitude over 70 dB almost run through the whole deformation process;The amplitude of acoustic emission event of raw coal is larger than briquette during macro-instability fracture.With the increase of temperature,the maximum amplitude of raw coal and briquette decreases.(3)Triaxial test of gas-bearing raw coal under thermal-mechanical coupling:(1)With the increase of temperature,the compressive strength and residual strength of coal sample decrease;at the same axial force,the radial strain and volumetric strain of coal sample decrease with the increase of temperature,and the peak radial strain and volumetric strain decrease with the increase of temperature;(2)The permeability-strain curve shows a V-shaped change pattern.With the increase of axial strain,the permeability decreases first and then increases;Under the same axial strain,the higher the temperature,the lower the permeability;The initial permeability and minimum permeability of raw coal containing gas decrease with the increase of temperature,and the higher the temperature,the more gentle the permeability change trend.(3)With the increase of temperature,the acoustic emission signal appears earlier and more active,the maximum ring count decreases,the energy increases,and the cumulative ring count and cumulative energy corresponding to peak stress increases.