Experimental Research On Coal And Gas Outburst Under Heterogeneous Condition

Coal and gas outburst is the unstable release of gas and stress energy stored in coal seam.According to a large number of case statistics,the geological structure of the outburst site usually is complicated,and faults and folds are very developed.In order to further study the impact of local tectonic zones on the occurrence and development of outburst,and the conditions needed for outburst induced.Taking Xin tian Coal Mine,Da ping Coal Mine and Ma chang Coal Mine as examples,this paper makes a comprehensive analysis of the geological conditions of outburst sites,the characteristics of outburst accidents and the causes of outburst.And select the sample of wo long hu coal seam.The pore transformation of coal samples by tectonic action has been systematically studied from theoretical and experimental aspects,and its influence on gas desorption performance and the transformation of mechanical properties of coal sample.Based on this,to start the coal and gas outburst simulation test and local soft coal of coal and gas outburst simulation test.The main research conclusions of this paper are as follows.1)The outburst accidents mainly occur in the tectonic zone,and the outburst strength is relatively large.The outburst coal body has a high degree of pulverization,the geological structure of the outburst site is complicated,and the faults and folds are well developed.This means that the occurrence of most outburst accidents is closely related to the tectonic action near the outburst.Due to the tectonic action,there are a lot of tectonic coal near the outburst.And the dominant stress and energy source of tectonic deformation is from the tectonic stress.2)Low temperature liquid nitrogen adsorption test results show that,coal is a porous body containing micro pores,small pores,mesopores and macro pores.For samples of the same coal sample with different particle sizes in gas isothermal desorption experiment,The gas desorption rate of small-size coal samples at their initial time is much larger than that of large-size coal samples.in the first minute,the proportion of gas desorption to total desorption is also larger.This indicates that in the process of geological evolution of coal seam,as the degree of coal sample breakage increases,initial gas desorption performance of coal sample is getting better and better.Both raw coal and structural coal accord the law that with the increase of confining pressure,the compressive strength and elastic modulus increase accordingly.But the compressive strength and elastic modulus of tectonic coal are obviously lower than that of raw coal.3)Based on the similarity criterion,we design and manufacture the true triaxial coal and gas outburst simulation test system.On the basis of the same molding pressure of 48 MPa,five groups of coal and gas outburst simulation tests with the molding pressure of 0.2mpa,0.25 mpa,0.35 mpa,0.4mpa and 0.5mpa were carried out.The results show that there is a critical value of coal and gas outburst,and the critical value of this experiment is between 0.25 and 0.35 mpa.The protruding coal powder is distributed in a shuttle-shaped strip on the ground with obvious purging traces,which is caused by the outburst coal body springing out from the protruding mouth in the form of jet.With the increase of pressure,the outburst strength also increases,the degree of hole damage is higher,and the degree of coal seam fracture is higher,which indicates that in the field,gas pressure is an important determinant of coal and gas outburst strength.On the basis of coal and gas outburst test,do the experiment that the coal and gas outburst test under the condition of local soft coal area and the influence of soft coal area on the occurrence and development of coal and gas outburst is further discussed.The soft coal area is located in the middle of briquette,The size is set at 0.14m×0.13m×0.2m,and 0.02 m coal pillar is reserved between the soft coal area and the front wall of the experimental chamber.There are two kinds of protrusion phenomena in the protrusion test: protrusion and non-protrusion.The critical gas pressure threshold in the local soft coal area is lower,ranging from 0.25 MPa to 0.30 MPa.Compared with the test without soft coal area,outburst of #R3~#R5 test set of throw coal and outburst intensity are relatively less.As the pressure increases,the number of fractures increased obviously,the average thickness decreased,and the lobes were no longer regular and complete.As the distance from the outburst hole increases,the thickness of the fracture increases.Under different gas pressures,the average seam crack thickness in soft coal area test is close to that in non-soft coal area test.4)From the perspective of energy research based on local soft coal zone exists prominent conditions,The main difference between the coal body in the soft coal area and the surrounding normal area coal is mainly the strength of the coal body.The presence of soft coal area changes the prominent energy dissipation density distribution of the coal before exposure.The outburst energy consumption of coal body in soft coal area is much lower than that of surrounding normal coal body,it means that the coal body in the soft coal area can outburst under low stress and gas conditions.In soft coal area,coal pillar which needs to be reserved is exposed,which means that the sealing action of the coal pillar disappears.Under the condition of local soft coal area,outburst will take the lead in soft coal development,When developed to the edge of soft coal area weak residual outburst energy is enough to overcome the surrounding normal area of coal outburst energy consumption,outburst will continue to develop towards surrounding coal bodies.