Study On Outburst-free Effect In Stress-relief Seam Based On Gas Content Method

The key to coal and gas outburst prevention is determining the outburst-free range accurately.However,there exists none-uniformity of criterion theory in determination of outburst-free range in first-mined seam at home and abroad.Besides,the protective range detected in field is usually greater than the stipulated one,which suppresses safe and efficient production of coal mines.Thus,in order to exactly determine the outburst-free range in stress-relief seam,this paper researches on the outburst-free discrimination method in stress-relief seam based on gas content method by means of theoretic analysis,experimental study,numerical simulation and field test,with gas content being outburst index.Moreover,the relationship between protective range of stress-relief seam and burst-free range is investigated as well.Then,the research results have been applied into field test in 513C15 working face in Xiejiaji NO.1mine of Huainan mining group.The main tasks accomplished by this essay are as followed.From perspective of energy conversion,its energy conversionis analyzed during outburst with combination of 13 times of coal and gas outburst examples.The source of outburst is elastic potential energy and gas expansion potential mainly.Beside,the elastic energy released during outburst takes a small proportion in whole outburst energy,with the gas expansion energy being the majority.In addition,the main gas expansion energy is provided by desorbed gas.Hence,gas content can better reflect the dangerous gas factor,greatly affecting the occurrence and intensity of outburst.To study the influence of main factors on outburst intensity during coal and gas outburst,this paper self-developed a set of testing device for simulating coal and gas outburst.In order to detect the testing data effectively,the high-speed gas flow gauge,low-speed gas flow gauge,solid stress sensor,temperature sensor and gas pressure sensor are installed.Therefore,21 times coal and gas outburst simulating tests are conducted in all.Throughout simulating tests,the influences of gas content,ground stress,gas pressure,moisture rate,grain size and outburst caliber on outburst intensity are analyzed.Besides,the variation of gas content and temperature during outburst is studied,and the function relation between gas content and outburst intensity is fitted.Then,the main factors that influence the intensity of coal and gas outburst,such as gas content,gas pressure,ground stress,moisture rate,are analyzed by gray correlation degree method.Consequently,the correlation degree descending sequence is gas content,gas pressure,ground stress,moisture rate,which indicates that the most influential factor is gas content.According to basic theory of coal rock swelling deformation and gas flow,combining with engineering project in 513C15 working face in Xiejiaji NO.1 mine of Huainan mining group,the parameters of volumetric strain,porosity and permeability are defined and solid-fluid coupling model of gas containing coal rock are established by COMSOL Multiphysics numerical simulating software.Thus,the protective range in stress-relief seam is determined by swelling amount of C13 seam and its outburst-free range is determined by gas content.Additionally,the relationship between outburst-free range and protective range in stress-relief seam is analyzed.It is found that the outburst-free range is greater than protective range.To determine gas content in stress-relief seam accurately and rapidly,the sampling device and technique by double-tube positive pressure reflux is developed.The drilling rod is double-tube organized,which can sample and drill at the same time.Besides,it can sample at any borehole position accurately.For its positive pressure drilling design,it can sample at a deeper position compared to the traditional method,with its sampling distance up to 85m.moreover,the desorption speed of coal specimens sampled by this method is quicker than the one sampled by the traditional method.For 513C15 working face in Xiejiaji NO.1 mine of Huainan mining group,its outburst-free effect in stress-relief seam is discriminated by gas content method.,further to decide its burst-free range.Moreover,the original and residual gas contents in stress-relief seam are measured right before and after the exploitation of first-mined seam by adopting gas content detection techniquein coal seams.Therefore,whether it is a outburst-free region is determined according to the gas content threshold of coal and gas outburst.Consequently,the ascending sequence of stress-relief angel and outburst-free angel along slope direction of C13 stress-relief seam is theoretic stress-relief angel,simulated stress-relief angel,simulated outburst-free angel and actual outburst-free angel.Besides,the ascending sequence of stress-relief angel and outburst-free angel along striking direction of C13 stress-relief seam is theoretic stress-relief angel,simulated stress-relief angel,simulated outburst-free angel and actual outburst-free angel.By the discrimination research on outburst-free effect in stress-relief seam by gas content method,it is advantageous in scientificity,ration,accuracy and convenience by determining outburst-free range based on gas content threshold.In addition,The research results can further reflect the protective function of stress-relief seam in exploitation of first-mined seam.Besides,the conclusion is correspondent with the gas dynamic phenomenon at scene and identification results of related units,which proves it feasibility in outburst-free range determination by gas content method,Furthermore,it provides basis for parameter design of gas drainage boreholes in stress-relief seam,ensuring its effectiveness,security and economy,which is of great significance for safe and efficient production in coal mines.