| At this stage in the mining of coal mine,more than half of them belong to the highly gassy mine or even the outburst mine.In the coal mine safety accidents,gas accident's intensity is the biggest and the casualties are most serious.For either the families,the coal mining enterprises or the country,the consequences of gas accidents are insufferable.So that the primary task of coal mining is to prevent and control gas accidents due to it is not only related to the safe production of coal mine,but also affects the sustainable development of our country.High efficiency and large scale to extra gas and exploit CBM are the basic means to prevent gas accidents and utilize gas.And the difficulty of gas drainage depends on the occurrence and seepage characteristics of gas in coal seam.Based on the previous studies,the seepage property of 3# coal seam samples in Guandi coal mine with different moisture content and gas pressure and the characteristics of acoustic emission during the experiment were studied by using electro hydraulic servo three shaft seepage experiment device andacoustic emission detector.It has certain guiding significance for the prevention and control of gas accidents in coal mining and the use of hydraulic fracturing to improve gas drainage effect.The main results are organized as the following:(1)The gas pressure and the permeability of coal sample has obvious nonlinear relationship,which has a high fitting degree with the quadratic polynomial.In certain conditions of moisture content,with the increase of gas pressure,the the coal sample permeability has changed,and with the increase of gas pressure,permeability of coal sample firstly decreased and then increased.The whole experiment process form the obvious tendency of "V",has obvious Klinkenberg effect.When the axial pressure is 4MPa and the confining pressure is 3MPa,the critical gas pressure is 1.0MPa.(2)When the gas pressure is constant,the permeability and seepage velocity decreases with the increase of the moisture content of the coal sample,and the decreasing speed becomes slow,they have high fitting degree with the quadratic polynomial.When the gas pressure is 0.5MPa,the permeability decreases by up to 92.9% with the moisture content of coal sample vary from 0.19% to 2.12%.(3)With different gas pressure or different moisture content,the axial stress-strain relation is similar when the coal samples are subjected to axial stress.When moisture content is constant,with the increase of the gas pressure,the axial stress enters the peak in advance,after the peak value,the axial stress declines at a slower rate.The smaller the gas pressure,the stronger the brittleness of coal sample,while the greater the gas pressure,the stronger theplasticity of coal sample.When the gas pressure is constant,comparing with coal samples of low moisture content,the high moisture content coal samples axial stress drops slowly after reaching peak value,and the failure types tend to the plastic damage.(4)Under the condition of different gas pressure or moisture content,the AE event rate earlier than axial stress reaches the maximum.Gas has a softening effect on coal,in the process of increasing the gas pressure,the failure types of coal are changed from sudden failure to stable failure.The higher moisture content,the rate of AE event is smaller,the axial strain span is smaller,and the duration of AE event rate is shorter than samples with lower moisture content. |
PDF Full Text Request