Research On Mechanical Characteristics Of Gas-beaing Coal Under The Condition Of Unloading Confining Pressure

The unloading confining pressure mechanical characteristics of gas-bearing coal and effect of unloading confining pressure under mining on gas outburst Is the key issue of safety production in coal mine. By means of mechanical testing machine MTS815 and triaxal sever-controlled seepage equipment of coal contain gas, the experimental study of unloading confining pressure of coal specimen under the condition of non-contain gas or contain gas is perfromed. According to the results of experimental study, the systematically study of the unloading confining pressure mechanical characteristics of gas-bearing coal and effect of unloading confining pressure under mining on coal and gas outburst. The main research results obtained in this paper are as follows.?By means of mechanical testing machine MTS815 and triaxal sever-controlled seepage equipment of coal contain gas, the expermental research were carried out. The test study of unloading confining pressure of coal specimen under the condition of non-contain gas was perfromed, the curve of confining pressure control of axial stress and strain were obtained. The test study of conventional triaxial compression of gas-bearing coal specimen was perfromed, complete stress-strain curve were of gas-bearing coal specimen in the process of conventional triaxial compression obtained. The test study of unloading confining pressure of gas-bearing coal specimen was perfromed, complete stress-strain curve of gas-bearing coal specimen in the process of unloading confining pressure were obtained. Meanwhile, the gas seepage chracterristics test of gas-bearing coal specimen in complete stress-strain process under the condition of conventional ftriaxial compression and unloading confining pressure was perfromed.?Base on the complete stress-strain process of coal specimen under the condition of unloading confining pressure, according to the testing data, the deformation and failure characteristics of coal specimen in the process of unloading confining pressure were derived. Base on the complete stress-strain process of gas-bearing coal specimen under the condition of conventional triaxial compression, according to the testing data, the deformation and strength characteristics of gas-bearing coal specimen in the process of conventional triaxial compression were summarized. Base on the complete stress-strain process of gas-bearing coal specimen under the condition of unloading confining pressure, according to the testing data, the deformation characteristics, failure characteristics and the confning pressure control effect of deformation and strength characteristics were educed. On the basis of test research of gas-bearing coal specimen gas seepage chracterristics, according to the testing data, the effect of complete stress-strain process of conventional triaxial compression and unloading confining pressure on gas seepage chracterristics and the confining pressure control effect of gas seepage chracterristics of gas-bearing coal in process of unloading confining pressure were summarized.?By means of energy priciple, The material continuity property?was defined, the release rate of damage strain energy?was introduced. The energy damage evolution model of gas-bearing coal specimen in the process of unloading confining pressure. Base on the testing data, the rules of Poisson's ration evolution with axial and radial strain of gas-bearing coal in process of unloading confining pressure were analyzed in detail, the determination of cohesion (c|~) and internal friction angle (?|~) and the law of confining pressure control effect of Poisson's ration of gas-bearing coal in process of unloading confining pressure were summarized. By using of phenomennal method, the constitutive model of gas-bearing coal in process of unloading confining pressure was established. On the basis of this constitutive model, the effect of unloading confining pressure rate on deformation characteristics of gas-bearing coal in process of unloading confining pressure were analyzed in detail. The constitutive mode which include effect of unloading confining pressure rate was established. Moreover the constitutive mode was verified in terms of testing results.?Throgh the analys of failure characteristics of gas-bearing coal under the condition of unloading confining pressure, the concerpt of“ratio of unloading destroying confining pressure difference”was defined whitch can describe the difficult degree of failure of gas-bearing coal under the condition of unloading confining pressure. According to the summarization of strength criterions at home and abroad and test study results, the strength criterion of gas-bearing coal under the condition of unloading confining pressure was established.?Throgh the analys of fluid-solid coupling characteristics of gas-bearing coal in process of unloading confining pressure, the permeability evolution equation of gas-bearing coal specimen in the process of unloading confining pressure which include volume strain and effective stress was proposed. The fluid-solid coupling model of gas-bearing coal in process of unloading confining pressure was established which incude stress field equation, seepage field equation, porosity evolution equation and permeability evolution equation. Then, give the definite condition of this fluid-solid coupling model.?Combind with“mechanical mechanism of coal and gas outburst”, By using of energy damage evolution model of gas-bearing coal specimen in the process of unloading confining pressure which include effect of unloading confining pressure rate and reflect time effect, the influence of unloading confining pressure under mining on coal and gas outburst was summarized. Combind with the achievements have completed, the simulation test of coal and gas outburst was perfromed, the summarization was verified in terms of this simulation test of coal and gas outburst testing results.