Study On The Control Theory And Technology By Injecting Liquid And Freezing Of The Coal And Gas Outburst During Uncovering Coal Seam In Cross-Cut

The coal and gas outburst is a kind of dynamical phenomenon, which the fragmentized coal in excavate process and the gas sprayed the work space out of the coal seam suddenly under the pressure.It is a main gas disaster faced with in coal mining in our country.The coal and gas outburst is the most dangerous and intensest when uncovering coal seam in cross-cut. With the mining depth increase, the existing proof-outburst measures in our country is relatively difficult to reduce coal seam gas content, release gas in advance and lower its pressure to prevent the coal and gas outburst effectively. In the paper, according to the advantages and disadvantages of the existing outburst-proof technology, based on the mechanism of the coal and gas outburst when uncovered coal seam in cross-cut, the techniques process of injecting liquid into coal seam and the application of the artificial freezing technology, a new outburst-proof method by injecting liquid and freezing is put forward when uncovered coal seam in cross-cut.Based on the theory analyses, experiment research and numerical simulation, the feasibility of its theory and technology basis is researched deeply. The mostly contents and conclusions is as follows:(1)The main power energy resulting in the coal and gas outburst is elastic strain energy and gas expansion energy when uncovered in cross-cut. The gas expansion energy is the main power of gas outburst among them. According to the energy equation of coal and gas outburst, the gas outburst mainly depends on the balance of the power energy and consume energy in the course of dynamic formation. When the gas outburst power energy quantitative change or mutate to a critical value, and this critical value beyond the needed consume energy while the gas-flow pass through the fracture angle joint channel, the gas outburst can occurrence instantly or later;(2) The new method will be proved effective on preventing the gas outburst according to the coal seam gas adsorption quantity "V" increase, the gas pressure "P" reduce and the disperse muzzle velocity "ΔP" lower, the coal mechanical properties improvement, the risk coefficient of gas outburst in discharge pressure zone decline and the elasticity energy difference reduce between the protected rock and coal seam after the coal seam to be uncoverd of work face in cross-cut is injected liquid into and frozen;(3)With the reformed WY-98A adsorption constant determinator, the CH4 adsorption constants "a,b" of coal seam have been obtained at a low temperature (T≤0℃) for the first time. Through data fitting, when the temperature T is below 0 celsius degree, the sorption isotherm of CH4 in the coal still belongs to "I" adsorption type. It can be used to characterize the CH4 adsorption model of coal at a low temperature for with the Langmuir equation. With the different temperatures and the same pressure of the same coal sample, the adsorption capacity and temperature was linear negative correlation approximatively between them. With the decrease of adsorption temperature, coal methane adsorption capacity increased;(4) By the uniaxial compressive strength experiment with the moulded samples, after injected liqiud into and frozen, their deformation is divided into four stages:compaction stage, flexible segment stage, plastic yield stage and destruction stage.With the freezing temperature falling, the uniaxial compressive strength of the test ones increases obviously; changing of Poisson's ratio is not obviously, but the whole trend is augment. The uniaxial compressive strength and elastic modulus value of the mould will be maximum at-20℃;(5) Through the cement trough model coal freezing experimentation, it shew that the freezing section, whose radius is R, is revolved around the freezing tube centre.the formed freezing coal column is patulous with the freezingtime. With the cold offered incessantly from the freezing tube, the radius "R" is rising incessantly, the temperature in tube is declining, the coal, gas, and water in the trough is frozen into the firm freezing structure finally, so the uniaxial compression strengths and elastic modulus of coal models and the other mechanical property will be increased. In the same freezing time, the more near to the freezing tube, the more cold will be gain by coal and the temperature is lower;(6)With the Rock Failure Process Analysis software-RFDA2D from Northeast University, establishing gas and solid coupling mathematics model of the outburst process when uncovering coal seam at cross-cut, setting the physics mechanical property parameters of coal seam corresponding to its freezing temperature and water content, simulating the process of uncovering the 6# freezing coal seam at 2# cross-cut of-400 level in Long Jia Shan mine under the different freezing temperature. The simulation showed that the gas outburst will not happen when the coal tempreture is frozen under-15℃；(7) With the ANSYS finite element, according to the construct parameters in the work face of uncovering coal seam at 2# cross-cut of-400 level in Long Jia Shan mine, establishing the numerical simulation calculate model of the temperature field in freezing section, analyzing its expand nephogram in different period, deciding the effective range, average temperature, closure time of ice zone and expand velocity. The simulation showed that the more near to the freezing center, the more fast the temperature of the 6# coal seam will decline.After 35-40 days, the 6# coal in freezing zone is strong enough to prevent coal and gas outburst;(8)After the coal seam injected into and frozen of the working face in uncovering at cross-cut, the gas power supply of the coal and gas outburst will reduce, the resistance to the gas outburst will rise, accordingly, it will help to effectively prevent the coal and gas outburst when uncovering coal seam at cross-cut.So, combining the advantages of injecting liquid and freezing in this research with the future exploitation depth of coal mines in our country, the method can be applied widely to the working face with low permeability and deep mining. It is important to reduce the gas disaster accidents of coal mines in our country.