| Coal and gas outburst is a very complicated and serious phenomenon of mine dynamic disaster.Although domestic and foreign scholars have conducted extensive research on coal and gas outburst mechanism and many achievements have been obtained,the evolution process and mechanism of coal and gas outburst are still not completely grasped and remain urgent problems to be solved.In this paper,the examples of coal and gas outburst were analyzed,a variety of outburst features and forms were summarized,the changes trend of outburst characteristics were obtained.The simulation experiments for intensity of outburst were carried out,the empirical intensity of outburst formulas of gas pressure,ground stress and initial diffusion velocity indexes are provided,and the similar macro characteristics evolvement law of outburst were obtained.The mechanical and energy conditions for outburst were determined based on the theoretical research of a variety of outburst features and outburst forms.The evolution process of cracks in the coal and the shape of outburst hole were gained by numerical simulation,and the mechanism was discussed in the process of outburst development.A new method of preventing and controlling coal and gas outburst by static blasting technology was put forward,and the feasibility and effect of this method were verified by the industrial application test.The following main research achievements have been obtained in this paper:(1)Based on investigation of 136 times of coal and gas outbursts in Hongyang No.2 coal mine,studies on the dynamic phenomena,outburst types,outburst times,outburst hole characteristics,outburst intensity,gas emission,outburst location,operation mode,ground stress environment and coal mass strength were conducted.Three types of coal sudden pour,five types of coal sudden extrusion and typical outburst were classified and the spatial distribution regularity of outburst locales were obtained.The results showed that the macroscopic characteristic of outbursts in Hongyang No.2 coal mine shifted from coal sudden pour type to typical outburst type with the increase of the burial depth,the dominant factor of outburst occurrence was the gas,but the regional distribution of outburst locales was formed due to the ground stress control.(2)According to the similarity theory,the three-dimensional similar model test system for coal and gas outburst was developed to scale based on the actual characteristics of mining and coal seam of Hongyang No.2 coal mine.The parameters such as apparent relative density,porosity and compressive strength of the sample of coal were gained during coal sample forming.The briquetting pressure which ensured the accuracy and reliability of the coal and gas outburst simulation test were determined.Studies on the characteristics of coal and gas outburst occurrence and the change rule of outburst intensity under different gas pressures,ground stresses and initial velocities of diffusion of coal gas and other conditions were conducted by similar simulation experiment,the coupling relationship between the outburst intensity,the outburst distances,the relative outburst intensity and the gas pressures,the initial velocities of diffusion of 12 coal beds in Hongyang No.2 Coal Mine was obtained.The outburst rule,controlled influential factors and the action mechanism were verified and explained in this paper.(3)The research of characteristics and evolution process of outbursts occurred in hongyang No.2 coal mine indicates the mechanical criterion of coal and gas outburst is not unique,based on research of failure of coal and rock caused by the microscopic crack propagation,the five kinds of instability and outburst mechanical models are established respectively according to outburst characteristics,outburst types and coal failure types occurred in Hongyang No.2 Mine.The corresponding mechanical criteria for coal instability are obtained and the correctness were verified by examples.(4)The key structure model were supplemented based on the law of gas pressure distribution of coal wall,and the critical conditions of mechanical and energy condition for occurrence of outburst were determined.The phenomenon that the macroscopic characteristic of outbursts shifts from coal sudden pour type to typical outburst type and outbursts are more likely to occur with the increase of the burial depth in hongyang No 2 coal mine is explained and the mechanism of characteristic evolution is clarified through the theoretical analysis of key structure model established in this paper and by the theory of the stress-relaxed zone width.(5)The evolution process of outbursts under different gas pressures,different ground stress conditions,different coal mass strengths,different homogenizing conditions were simulated by the RFPA2D-flow software,a seepage-damage coupling analysis system for rock failure process.The process of the outburst developments such as the fissure initiation and expansion of the coal mass,the split coal mass and thrown coal mass,the outburst hole beginning to form,expansion and shrink,were reproduced and the rule of stress changes of coal mass were discussed.The research showed that,in the process of outburst development,the effect of ground stress made the outburst hole develop towards the wedge shape,while the effect of gas pressure made the outburst hole develop towards spherical shape,and finally the outburst hole shape was the result of the joint effect.The evolution process were further revealed in its entirety and the mechanism of the outburst were discussed roundly in this paper.(6)82%of the coal and gas outbursts in Hongyang No.2 coal mine were caused by disturbances.To this end,a new idea of slowly fracturing coal or rock and increasing gas permeability of coal to prevent and control outburst was proposed,three representative types of soundless cracking agent were developed for improving crushing effect and a new expansion pressure measuring device was designed.The industrial applications test for removing outburst in coal workface and in cross-cut before uncovering coal were carried out by using static blasting technology,and the feasibility and the practicability of the technology were validated,then a new method of using static blasting technology to prevent and control coal and gas outburst was provided. |
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