Response characteristics of gas pressure under simultaneous static and dynamic load:Implication for coal and gas outburst mechanism

Coal and gas outbursts are dynamic disasters in which a large mass of gas and coal suddenly emerges in a mining space within a split second.The interaction between the gas pressure and stress environment is one of the key factors that induce coal and gas outbursts.In this study,first,the coupling relationship between the gas pressure in the coal body ahead of the working face and the dynamic load was investigated using experimental observations,numerical simulations,and mine-site investigations.It was observed that the impact rate of the dynamic load on the gas-bearing coal can significantly change the gas pressure.The faster the impact rate,the speedier the increase in gas pressure.Moreover,the gas pressure rise was faster closer to the impact interface.Subsequently,based on engineering background,we proposed three models of stress and gas pressure distribution in the coal body ahead of the working face:static load,stress disturbance,and dynamic load conditions.Finally,the gas pressure distribution and outburst mechanism were investigated.The high concentration of gas pressure appearing at the coal body ahead of the working face was caused by the dynamic load.The gas pressure first increased gradually to a peak value and then decreased with increasing distance from the working face.The increase in gas pressure plays a major role in outburst initiation by resulting in the ability to more easily reach the critical points needed for outburst initiation.Moreover,the stronger the dynamic load,the greater the outburst initiation risk.The results of this study provide practical guidance for the early warning and prevention of coal and gas outbursts.

Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway:The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents.An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system.We investigated the release characteristics of main energy sources in coal seam,and obtained the dynamic characteristics of outburst two-phase flow in a roadway.Additionally,we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure.The results indicate that the outburst process exhibits pulse characteristics,and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon.The outburst energy is released in stages,and the elastic potential energy is released in the vertical direction before the horizontal direction.In a straight roadway,the impact force oscillates along the roadway.With an increase in the solid–gas ratio,the two-phase flow impact force gradually increases,and the disaster range extends from the middle of the roadway to the coal seam.In the area near the coal seam,the disaster caused by the two-phase flow impact is characterized by intermittent recovery.In a bifurcated roadway,the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow,and the impact force tends to weaken with increasing solid-gas ratio.The impact force is asymmetrically distributed;it is higher on the left of the bifurcated roadway.With an increase in the solid-gas ratio,the static pressure rapidly decreases,and the bifurcated structure accelerates the attenuation of static pressure.Moreover,secondary acceleration is observed when the shock wave moves along the T-shaped roadway,indicating that the bifurcated structure increases the shock wave velocity.

Mechanism of gas pressure action during the initial failure of coal containing gas and its application for an outburst inoculation

Faced with the continuous occurrence of coal and gas outburst(hereinafter referred to as“outburst”)disasters,as a main controlling factor in the evolution process of an outburst,for gas pressure,it is still unclear about the phased characteristics of the coupling process with in situ stress,which induce coal damage and instability.Therefore,in the work based on the mining stress paths induced by typical outburst accidents,the gradual and sudden change of three-dimensional stress is taken as the background for the mechanical reconstruction of the disaster process.Then the true triaxial physical experiments are conducted on the damage and instability of coal containing gas under multiple stress paths.Finally,the response characterization between coal damage and gas pressure has been clarified,revealing the mechanism of action of gas pressure during the initial failure of coals.And the main controlling mechanism during the outburst process is elucidated in the coupling process of in situ stress with gas pressure.The results show that during the process of stress loading and unloading,the original gas pressure enters the processes of strengthening and weakening the action ability successively.And the strengthening effect continues to the period of large-scale destruction of coals.The mechanical process of gas pressure during the initial failure of coals can be divided into three stages:the enhancement of strengthening action ability,the decrease of strengthening action ability,and the weakening action ability.The entire process is implemented by changing the dominant action of in situ stress into the dominant action of gas pressure.The failure strength of coals is not only affected by its original mechanical strength,but also by the stress loading and unloading paths,showing a particularly significant effect.Three stages can be divided during outburst inoculation process.That is,firstly,the coals suffer from initial damage through the dominant action of in situ stress with synergy of gas pressure;secondly,the coals with spallation of structural division are generated through the dominant action of gas pressure with synergy of in situ stress,accompanied by further fragmentation;and finally,the fractured coals suffer from fragmentation and pulverization with the gas pressure action.Accordingly,the final broken coals are ejected out with the gas action,initiating an outburst.The research results can provide a new perspective for deepening the understanding of coal and gas outburst mechanism,laying a theoretical foundation for the innovation of outburst prevention and control technologies.

Application of dynamic set-pair analysis in coal and gas outburst prediction

Analyzed the factors which affected the coal and gas outburst,then established the corresponding indicator system.Built a dynamic set-pair analysis prediction model which combined of Markov model and set-pair analysis model,and then it applied to coal and gas outburst prediction.Finally,compared the prediction results with the actual results As provided a reference to the coalmine in safety decision-making.The research results indicate that there are four districts in high dangerous level,two districts in middle level and one district in low level,which consistent with the actual situation;the dynamic set-pair analysis model has a good effect in predicting coal and gas outburst.Especially in the continuous time intervals,according to the data of mined exploration and the connec- tion degree analysis,we can deduce the dangerous levels of unexplored districts from the historical data.In different districts,the relevant indicators can be adjusted accordingly,so as to enhance the accuracy of the prediction.

Coal and gas outburst dynamic system

Coal and gas outburst is an extremely complex dynamic disaster in coal mine production process which will damage casualties and equipment facilities, and disorder the ventilation system by suddenly ejecting a great amount of coal and gas into roadway or working face. This paper analyzed the interaction among the three essential elements of coal and gas outburst dynamic system. A stress-seepage-damage coupling model was established which can be used to simulate the evolution of the dynamical system, and then the size scale of coal and gas outburst dynamical system was investigated. Results show that the dynam- ical system is consisted of three essential elements, coal-gas medium （material basis）, geology dynamic environment （internal motivation） and mining disturbance （external motivation）. On the case of CI 3 coal seam in Panyi Mine, the dynamical system exists in the range of 8-12 m in front of advancing face. The size scale will be larger where there are large geologic structures. This research plays an important guid- ing role for developing measures of coal and gas outburst prediction and prevention.

煤与瓦斯突出潜在危险区(带)预测

煤矿的生产和实践证明 ,发生在矿井中的动力现象具有分区和成带的特点。文章探讨了把煤、岩和瓦斯作为一个体系 ,采用力学方法的划分问题。根据对煤岩复合样及含瓦斯煤样在复杂应力状态下力学性质的分析 ,基于对Drucker-prager理论的修正和完善 ,建立了它们的断裂判据 ,并给出了计算稳定性系数和潜在弹性应变能密度的公式 ,提出了按这两个指标划分煤与瓦斯突出潜在危险区 (带 )

吴寨矿西翼采区煤与瓦斯突出危险性分析

吴寨矿己17煤层与具有突出危险性的矿井十矿、十二矿相邻,采掘延伸达到或超过垂深50m时必须确定煤层的突出危险性。根据地质资料和实测数据,结合邻近矿井瓦斯动力现象,应用单项指标对吴寨矿己17煤层进行了瓦斯突出危险性研究。结果表明,在标高-450m以浅,吴寨矿西翼采区己17煤层无煤与瓦斯突出危险性。

马家沟矿0521动力现象分析及其预测

通过对马家沟矿0521动力现象分析,分别用初始释放瓦斯膨胀能指标法、综合指标法和残余瓦斯含量法判别分析了马家沟10水平0521掘进工作面,在理想石门揭煤条件下发生突出的危险性。结果表明,10水平在石门揭煤条件下具有发生突出危险。

长虹公司二_1煤层煤与瓦斯突出危险性区域预测

在分析长虹公司二1煤层瓦斯动力现象特征和瓦斯基础参数测定的基础上,确定了煤与瓦斯突出区域预测指标的临界值,结合瓦斯地质分析结果,对长虹公司二1煤层煤与瓦斯突出危险性进行了区域预测。

一起综掘机割岩诱导瓦斯动力现象分析及防治对策

依据煤与瓦斯突出的基本原理,通过地应力、外载扰动及瓦斯内能等激发煤与瓦斯突出的3个因素,对一起综掘机割岩震动诱导的瓦斯动力现象进行分析,结果表明,执行了区域防突措施后残存瓦斯压力已不具备发动突出动能的煤体,在地应力和外力作用下仍然能够发生煤与瓦斯突出。对深部开采煤与瓦斯突出机理和突出指标临界值问题进行了探讨,指出应注重预防综掘机割岩震动诱导作用,并给出了同类条件下防治煤与瓦斯突出事故的对策。

高瓦斯综放工作面动力现象分析及治理

大水头矿东103工作面掘进过断层期间,发生冒顶事故,并伴随大量的煤与瓦斯涌出。通过对事故现象分析,是掘进过断层期间发生的一般动力现象,而不是突出引起的动力现象,并针对性的提出预防和治理措施,确保掘进面的安全快速掘进。

采煤工作面消突综合评价技术体系

在消突评价机理及现状研究的基础上,依据相关法律法规,提出了一套采煤工作面消突综合评价技术体系,补充了目前消突评价技术在低指标突出方面验证的缺陷,简化了评价程序,消除了评价指标重复考察。通过现场应用实践,验证了该技术的可行性及准确性。