Research On Effects Of Moisture On The Gas Desorption And Mechanical Properties Of Coal

It is difficult to avoid the effects of moisture in the process of mining, in order to ensure the safe and efficient in exploitation of coal and gas outburst seam, it is important to study the effect of moisture on the gas and stress distribution in coal seam. This paper takes the geological conditions of 8101 gushing face in Wolonghu coal mine as the background, integrated uses research methods such as theoretical analysis, laboratory experiments, numerical simulation, field-proven and so on, to study the effect of moisture on the adsorptive gas and mechanical properties as well as the stress evolution in coal seam, and make considerations and practical recommendations of gas control in gushing coal face, providing a reference for similar geological conditions in coal mining.The paper uses the homemade high-pressure adsorption- injection- mixing-desorption test device from the national engineering research center of coal mine gas control, The device solves the problem of water injection after adsorption equilibrium. Through the experimental data, we discussed the displacement and replacement effect and inhibited desorption effect on the adsorptive gas in coal, and verified by the actual gas emission and gas content. The displacement effect show: at the same adsorptive equilibrium pressure, the greater the moisture content, the larger the the replacement amount of adsorptive gas in coal, when the moisture content reach at 9% ~ 11%, the replacement amount of adsorptive gas in coal can reach at 25%~35%, when more than 11%, the displacement and replacement effect of moisture on the adsorptive gas i s not obvious. The inhibited desorption effect show: at the same adsorptive equilibrium pressure, the greater the moisture content, The smaller the amount of gas desorption and there is a limit, when the moisture content reach at 9% ~ 11%, the inhibited efficiency of 120 min gas desorption is between 45% ~ 55%.Field data show: Increasing the moisture content of coal, firstly, Adsorbed gas in coal will be affected by displacement effect, part of the adsorbed gas be replaced as free gas which could be released ahead of mining. When the coal seam relief or be taken off, gas desorption would be inhibitory, Making gas desorption and desorption rate of wet coal is less than dry coal, gas emission of working face will reduce.Through mechanics experiments under different moisture content, we have been gotten the effect law of moisture on the mechanical parameters of shaped coal. With the increases of water content, the compressive strength decreases, the peak strain increases, the elastic modulus decreases, friction angle and cohesion also decreases gradually; the variation of compressive strength, peak strain, elastic modulus, cohesion and the moisture content accord with index, while a linear relationship between friction Angle and moisture content; The greater the confining pressure, the greater the effects of moisture content on the compressive strength, peak strain and elastic modulus. In order to study the effect of moisture on the stress evolution during coal mining, adopting the FLAC3 D numerical simulation method, and analysising the different results of mining under different moiture content in coal seam with 4 MPa confining pressure, the results show, due to the effects of moisture, the mechanical properties of the coal seam are change, compared to the normal area near the open-off cut, the concentrated stress in front of woking face with moiture appeares different degree of reducement and the relief zone appeares different degree of increasement.