Loading Coal Anisotropy Ultrasonic Response Characteristics

Geophysical exploration technology is the protection of coal mine safety and coal-bed methane development,coal is carried out under loading conditions for the use of ultrasound experiments measuring acoustic logging technology of coal structure and material composition to provide theoretical and experimental basis.This paper studies the native structure of coal ultrasonic loading conditions-strain response characteristics for the purpose,through the different ranks of Eight Mine Pingdingshan different directions cleat coal samples at room temperature ultrasonic uniaxial loading conditions-testing laboratory strain analyze its elastic strain response differences.research shows:(1)When the stress is not loaded three coal samples and shear wave velocity and attenuation coefficient there are differences between the two directions generally parallel and perpendicular to bedding bedding direction quite different,and there is vertical stratification the minimum vertical and horizontal direction velocity,attenuation coefficient is small,indicating the direction of the vertical stratification of coal in the most powerful ultrasonic attenuation.This is along the Z direction coal compaction effects related to the maximum.(2)In the loading state,Qs common than Qp,which meant that the actual coal seam absorption of longitudinal wave attenuation effect is greater than the shear wave.Coal testing in certain parameters,select shear waves are detected as an advantage.Coal sample is greater than the attenuation coefficient of anisotropy velocity anisotropy coefficient,which also shows the quality factor Q may be an anisotropic than the speed of the coal samples more sensitive parameters.(3)In two coking coal as the stress increases,the vertical and horizontal velocity and attenuation anisotropy trends in both directions parallel to the bedding are different,Y direction vertical and horizontal velocity and attenuation anisotropy coefficient greater than under normal circumstances X direction.It also indirectly shows the degree of variation fractured coal seams to have differences.(4)During loading coal with the stress rises gradually increased,but the growth rate in the low-stress period than high stress zone.When 0-2MPa low stress range,increase significantly faster,when the stress is higher than 2MPa,the growth rate beganto slow.For three kinds of coal samples,its trends and the like,a large area of low stress velocity growth rate decreased rapidly to reach the maximum value.Furthermore,there are differences in three coals like compressive strength,the same kind of metamorphic grade is also different coal sample in three directions.Maximum points different ranks of coal samples occur at different stress loading place.(5)For the three kinds of state under loading rank coals like it,after the bulk modulus changes are the first to arrive on the whole increased from a maximum point or steady decline after a period of time,this process includes coal samples pore closure,opening and development phases;for a particular rank coal samples,the loading state in three coal bulk modulus also increases the stress load increases,but three the direction of increasing the volume modulus of the speed differences.Under normal circumstances are the bulk modulus in both directions parallel to bedding is larger than the vertical direction bedding.This paper studies the native structure of coal under stress conditions of the ultrasound-strain response characteristics for the purpose by the same mining area,different cleats directions,different rank structure of native coal ultrasonic testing laboratory at room temperature swing conditions,analysis of that elastic stress response differences;...