Research On The Process Of The Outburst Coal Body Fracture And Two-phase Flow Migration Under The True Three-dimensional Stress

Coal and gas outburst(hereinafter referred to as outburst)caused by the rupture of gas-containing coal and rock is an extremely complex dynamic disaster in the coal mining process,which has been a serious threat to the safety of coal mines and the development of mining in our country.The depletion of shallow coal resources forces coal mining to deepen,leading to changes in the conditions for coal seams to occur.High geo-stress,high gas pressure,high temperature and low permeability have become typical characteristics of coal occurrence.The complex geological environment makes the interaction mechanism of coal and gas has become more and more complicated.The conditions for coal resources are in contradiction with the strong demand that people face.The geo-stress in deep mining is larger than that in shallow ones.High geostress has caused frequent occurrences of coal and gas outburst accidents,making some mines with no outburst hazard develop into prominent ones.The mine not only caused damage to equipment and property,but also caused injury and even death to personnel.Combining the coal and gas outburst accident cases at the accident site and the analysis of the research results of scholars at home and abroad,it can be seen that the geo-stress plays an important role in the process of coal and gas outburst.For this reason,this paper carried out physical simulation experiments of coal and gas outburst under different true three-dimensional in-situ stress conditions,focusing on the analysis of the multi-parameter evolution in the coal body during the rupture of the outburst coal body and the coal-gas two-phase flow in the roadway after the outburst.Considering that physical simulation cannot monitor the evolution of parameters such as cracks and internal stress,combined with numerical simulation to further explore the fracture process and development mechanism,the main research work carried out and the research results obtained are as follows:(1)A detailed description is given of the three-dimensional geo-stress distribution in the fractured coal body during the outburst incubation and development stage.The gas pressure and gas flow field changes in the fractured coal body during the outburst development stage are analyzed in-depth and systematically,and the relationship between gas pressure and ground stress is discussed.The development process of coal fracture under the coupling of stress,expounds the fracture characteristics of coal.(2)Aiming at the deficiencies in the numerical simulation analysis methods of coal and gas outbursts and the physical simulation test results of coal and gas outbursts,the discrete element numerical simulation analysis method was used to carry out numerical simulations on the process of coal and gas outbursts,and different places were explored.The dynamic evolution process of coal rupture during outburst development under stress conditions and its quantitative characterization method,based on the statistics of the movement speed of coal particles near the outburst opening,reveals the evolution process of outburst strength over time.(3)In-depth discussion on the movement law of coal-gas two-phase flow in the roadway.First,according to the pneumatic conveying project,the pneumatic conveying state of the coal-gas two-phase medium is divided,and the temporal and spatial distribution characteristics of the impact force of the coal-gas two-phase flow in the roadway are analyzed,and then the pulverized coal deposited in the roadway is broken after the outburst.The characteristics are analyzed to clarify the relationship between the particle size distribution law,fractal dimension,crushing work,etc.of the outburst coal after crushing and the initial ground stress level,which provides experimental data support for revealing the energy dissipation in the process of coal and gas outburst.In the end,considering the disaster caused by the coal-gas two-phase flow,based on the actual measurement data of the impact force,the criteria for determining the safety critical value in the roadway space are established,and the damage levels of the human body and structures are divided,and the impact in the roadway space is given.The catastrophic evolution process of force,in view of the insufficient single factor criterion given by the safety critical value,the comprehensive criterion of the two-phase flow disaster based on the dual factors of overpressure and impulse is further discussed.