| Coal and gas outburst is a complicated dynamic disaster during underground mining,which usually occurs in coals accompanying by sudden ejection of large amount of coals and gases,resulting in significant damage to equipment and may even cause fatalities.With the extension of coal mining to the deep,the risk of coal and gas outburst continues to increase.Therefore,the mechanism and evolution process of coal and gas outburst is significant to accurately predict and thus prevent outbursts.In this paper,the methods of theoretical analysis,experimental testing,numerical simulation,and engineering application are used.The mercury intrusion meter and HCA device are adopted to measure the pore structure and gas adsorption/desorption parameters of outburst prone coal.The dynamic failure characteristics of outburst prone coal are studied by using separated Hopkinson pressure bar system.The mechanical strength relationship between experimental scale coal samples and engineering scale coal mass was established.The fluid flow law within fractured coals is obtained via the measurement of coal permeability during failure process.The above experimental results will be used as the basic parameters of numerical simulation.The geo-dynamic system is proposed for causing-mechanism of coal and gas outburst,which consists of three essential parts-gas-bearing coal and rock mass,geo-dynamic environment and mining disturbance.The interaction among the three essential parts is elaborated in detail.The evolution of the geo-dynamic system,including initiation,formation,development and termination,is analyzed.The formation criterion C1,mechanical instability criterion C2 and energy instability criterion C3 of outburst geo-dynamic system are developed.The coupling process of multi-physical fields during coal and gas outburst is analyzed,and the governing equations of stress,hydraulic and damage fields are derived to develop stress-damage-seepage coupling model within outburst prone coal seam.This coupling model is solved using Comsol Multiphysics by conduting the simulation of compression-seepage within coal sample.The evolution of outburst geo-dynamic system is studied,as well as the laws of gas migration,stress and energy transfer,transformation and dissipation in the system.The 3D spatial models of outburst geo-dynamic system and outburst geological mass are recovered,which provides the target area for prevention and control measures of outbursts.The simulation results of volume of coal and rock mass are in good agreement with that in situ.Based on the outburst geo-dynamic system,the elimination mechanism of "stress relief+pressure reduction" for coal and gas outburst is put forward.Aiming at the actual field,the outburst elimination scheme of the gas extraction technology of cross-layer drilling from floor roadway combined with hydraulic punching and borehole drilling is put forward.The effectiveness of the outburst elimination is simulated and verified by field application.The mechanism of geo-dynamic system provides a theoretical basis for the prediction and prevention of coal and gas outburst. |
PDF Full Text Request