Mechanism of rock burst caused by fracture of key strata during irregular working face mining and its prevention methods

To study the occurrence mechanism of rock burst during mining the irregular working face,the study took irregular panel 7447 near fault tectonic as an engineering background.The spatial fracture characteristic of overlying strata was analyzed by Winkler elastic foundation beam theory.Furthermore,the influence law of panel width to suspended width and limit breaking span of key strata were also analyzed by thin plate theory.Through micro-seismic monitoring,theoretical analysis,numerical simulation and working resistance of support of field measurement,this study investigated the fracture characteristic of overlying strata and mechanism of rock burst in irregular working face.The results show that the fracture characteristic of overlying strata shows a spatial trapezoid structure,with the main roof being as an undersurface.The fracture form changes from vertical‘‘O-X"type to transverse‘‘O-X"type with the increase of trapezoidal height.From the narrow mining face to the wide mining face,the suspended width of key strata is greater than its limit breaking width,and a strong dynamic load is produced by the fracture of key strata.The numerical simulation and micro-seismic monitoring results show that the initial fracture position of key strata is close to tailgate 7447.Also there is a high static load caused by fault tectonic.The dynamic and static combined load induce rock burst.Accordingly,a cooperative control technology was proposed,which can weaken dynamic load by hard roof directional hydraulic fracture and enhance surrounding rock by supporting system.

A forecasting and forewarning model for methane hazard in working face of coal mine based on LS-SVM

To improve the precision and reliability in predicting methane hazard in working face of coal mine, we have proposed a forecasting and forewarning model for methane hazard based on the least square support vector (LS-SVM) multi-classifier and regression machine. For the forecasting model, the methane concentration can be considered as a nonlinear time series and the time series analysis method is adopted to predict the change in methane concentration using LS-SVM regression. For the forewarning model, which is based on the forecasting results, by the multi-classification method of LS-SVM, the methane hazard was identified to four grades: normal, attention, warning and danger. According to the forewarning results, corresponding measures are taken. The model was used to forecast and forewarn the K9 working face. The results obtained by LS-SVM regression show that the forecast- ing have a high precision and forewarning results based on a LS-SVM multi-classifier are credible. Therefore, it is an effective model building method for continuous prediction of methane concentration and hazard forewarning in working face.

Spatial-temporal variation features and law of gas concentration in the fully mechanized working face under the condition of intermittent ventilation

Based on the fluid mechanics and mass transfer theory,a mathematical model of the spatial-temporal variation of gas was derived to avoid the gas accident caused by the main fan stopping ventilation under the condition of intermittent ventilation in the tunnel.According to the actual parameters of the tunnel,a numerical calculation model was established.The spatial-temporal variation of gas concentration in the fully mechanized working face under the condition of intermittent ventilation was calculated by using the commercial package Fluent,and the correctness of the calculated results was verified by the actual monitoring data of the mine.Firstly,the gas concentration was calculated under different wind velocities at driving face in coal tunnel,and the result showed that the gas can be carried effectively by the wind when the wind velocity is about 1.8 m/s.Secondly,the distributions of wind velocity and gas concentration at driving face were studied at 1.8 m/s,and the result showed the gas concentration increased gradually with the distance close to the outlet,but the gas concentration almost kept constant at the height of driving face.Thirdly,the distribution of gas concentration was investigated with time after the ventilation was stopped and restarted,respectively.The gas concentration of test point gradually increased with the increment of downtime,when the downtime was 40 min,the gas concentration of test point 3 reached the maximum value.The gas concentration increased gradually and reached the maximum after10 min of restart,then sharply decreased and kept constant.

Theoretical and numerical analysis of coal dust separated by centrifugal force for working and heading faces

In order to meet engineering needs of Chinese underground coal mines,a new dust-collecting fan,a device of dust separated by centrifugal force in driven cyclone passageway(DCCP)was designed.In centrifugal dust removal section(CDRS)of DCCP,a general equation is derived from the principle of force equilibrium.According to CDRS structure parameters and fan running parameters,the general equation is simplified,and the simplest equation is calculated numerically by MATLAB.The calculation results illustrate that increasing quantity of air current is against dust removal,but it is beneficial to dust removal by increasing the radius of driven spiral blade and increasing the particle diameter of coal dust.The conclusions show that the dust-collecting structure parameters coupled with the fan running parameters is a novel optimization approach to dust-collection fan for working and heading faces,which is especially suitable for Chinese underground mines.

Research on time structure characteristic of gas concentration sequence in the working face

In the procedure of coal industry production, the losses of the persons and economy caused by the gas explosion accidents are most serious, therefore, prevention and control of the gas explosion accident of the coal mines is an important issue needed to be solved urgently in the safety production work of our coal mines. The characteristic of time structure variation index characteristic was analyzed about gas concentration sequence of three measure points in the NO. 1I 1024 working face. It was found that the value of time variation about three measure points was mostly 1〈δ≤1.5, and gas emission presented consistently strong-clustering state twice, and the value of time variation presented continuous variation state in the active stage of gas concentration. Complex characteristics of the value indicated gas emission was continuously variable in time or space and presented the complex nonlinear characteristics. So the characteristic about gas emission system was correctly depicted and analyzed to gas emission system according to the relation of its state variation and essential of nonlinear system. The result also provided reliable warranty for its continued nonlinear research on gas emission.

Determining the rational layout parameters of the lateral high drainage roadway serving for two adjacent working faces

To determine the rational layout parameters of the lateral high drainage roadway(LHDR) serving for two adjacent working faces, a mechanical model of the LHDR under mining influence was established, and the overburden fissure, mining-induced stress distribution rules were analyzed. First, the development characteristics of mining-induced overburden fissure and the stress distribution law of the upper section of the working face were analyzed. Second, by analyzing the distribution law of vertical stress at different layers, the lateral distance of the LHDR was determined as 25 m. Third, by analyzing the surrounding rock deformation effect, stress distribution law, and overburden fissure distribution law of the LHDR at the heights of 20, 25, and 30 m away from the roof, the rational horizon of the LHDR was determined to be 25 m. Finally, an example of a LHDR located 25 m above the roof of the No. 2 coal seam and 25 m away from the No. 2-603 working face was presented. Results show that when the No. 2-603 coalface is being mined, the surrounding rocks lag 80 m or even further and the working face tends to be stable. The relative deformations of the roof and floor of the roadway and both of its walls were 583 and 450 mm,respectively. The reduction rate of the roadway section was 21.52%–25.32%. The section of the roadway was sufficient to extract the pressure relief gas in the overburden of the No. 2-605 working face. The average gas concentration and the pure volume at the branch pipeline were 24.8% and 22.3 m^3/min,respectively, showing that the position of high-level boreholes was reasonable.

The main projects and development status of noise forecasting and controlling on working face in coal mine

Noise from the machine on coal working face seriously influenced the miners' physical and mental health, and also, due to the noise, there may be a major hidden danger in safety from accidents as all safety warning signals may be masked by the noise. This paper summarized the features of mine environmental noise on working face, such as the variety of noise sources, the continuity of high intensity and slow attenuation in narrow space, etc.The main projects about noise forecasting and controlling on working face was emphatically expounded;the development status about mines machinery noise mechanism and environmental noise acoustic characteristics of space-time of these main research topics were also introduced.

Research and Application of Airflow Recirculation System in Working Faces with Leaking Airflow

In order to develop the technology of the controlled recircuIation of airflow in the world, some formulas about the airflow recirculation system in the working face with leaking airflow are deduced,which reduces the error between calculating and real values. on the base of the application of the formulas mentioned above, the problem about lack of airflow in the working face 2712 was solved successfully in Xiandewang Coal Mine.

Study of energy-efficient heat resistance and cooling technology for high temperature working face with multiple heat sources in deep mine

In the present research,we proposed a scheme to address the issues of severe heat damage,high energy consumption,low cooling system efficiency,and wastage of cold capacity in mines.To elucidate the seasonal variations of environmental temperature through field measurements,we selected a high-temperature working face in a deep mine as our engineering background.To enhance the heat damage control cability of the working face and minimize unnecessary cooling capac-ity loss,we introduced the multi-dimensional heat hazard prevention and control method called"Heat source barrier and cooling equipment".First,we utilize shotcrete and liquid nitrogen injection to eliminate the heat source and implemented pressure equalization ventilation to disrupt the heat transfer path,thereby creating a heat barrier.Second,we establish divi-sional prediction models for airflow temperature based on the variation patterns obtained through numerical simulation.Third,we devise the location and dynamic control strategy for the cooling equipment based on the prediction models.The results of field application show that the heat resistance and cooling linkage method comply with the safety requirement throughout the entire mining cycle while effectively reducing energy consumption.The ambient temperature is maintained below 30℃,resulting in the energy saving of 10%during the high-temperature period and over 50%during the low-temperature period.These findings serve as a valuable reference for managing heat damage in high-temperature working faces.

Study on the characteristics of ground pressure behaviors in working face with great mining height at different advance speeds by similarity model experiment

Presently most of research results on strata behaviors were concluded under the normal （moderate） advance rate conditions. Comparing with normal advance rate, fast advance rate and slow advance rate may cause some new changes of strata behaviors. The characteristics of ground pressure behaviors in working face with great mining height at different forward speeds were studied by similarity model experiment in laboratory. Its conclusion provides a theoretic basis for ground pressure controlling.

Back-and-forth mining for hard and thick coal seams—research about the mining technology for fully mechanized caving working face of Datong Mine

The article introduced the key technology, mining process, and back-and-forth mining method for the caving working face of hard-thick coal seams in Datong mine, and researched this innovations process, optimized the systemic design and working face out-play, tried to perfect the caving mining technology of hard-thick coal seams further.

Migration law of respirable dust on a super-long fully mechanized double-shearer working face

In order to understand the migration law of respirable dust and gain reasonable design parameters for dust control on a super-long double-shearer fully mechanized working face, this paper describes research carried out using a numerical simulation package(Fluent) based on gas-solid coupling dispersed multiphase flow model and field measurement to research different technology modes, dust distribution law at different intervals where shearers work in opposite directions on the lower 9303 face, No. 2 Jining Mine,Yankuang Coal Mining Co. Results show that the concentration of dust 3–6 m away from the shearers working in the same directions was large, while the impact area of respirable dust near the shearer increased significantly to 5–6 m with the distance between two shearers working in opposite directions.The concentration of dust on a double-shearer face was considerably higher than that of a face with one shear under the combined effect of wind speed on the face and disturbed wind around the shearer, while the dust concentration near the shearer on the return side was considerably higher than that on the inlet side. The concentration of dust on a double-shearer face along the airflow declined slowly so that dust was hard to control. Simulation results confirmed the results of field measurement, which could provide reference for dust prevention design.

Analysis of English literary works based on face theory

Brown ＆ Levinson＇s face theory is an important theory in Pragmatics and it is an influential theory in expounding the phenomenon of politeness. Through an analysis of the functions of ＂face＂ in English literary works, this article intends to shed new lights on literary pragmatics.

Mode-I-crack compression modeling and numerical simulation for evaluation of in-situ stress around advancing coal workfaces

The relatively high stress probably leads to generation of a fractured or even instable area around a working coalface. Also, the generated weak area often evolves into an easy-infiltrating field of water/gas to greatly increase probability of accident occurrence. To reveal the distribution of high stress around working faces, we put forward the mode-I-crack compression model. In this model, the goaf following a working face is regarded as a mode-I crack in an infinite plate, and the self-gravity of overlaying strata is transformed into an uniform pressure applied normal to the upper edge of the model crack. Solving this problem is based on the Westergaard complex stress function. For comparison, the software RFPA-2D is also employed to simulate the same mining problem, and furthermore extendedly to calculate the stress interference induced by the simultaneous advances of two different working faces. The results show that, the area close to a working face or the goaf tail has the maximum stress, and the stress is distributed directly proportional to the square root of the advance and inversely proportional to the square root of the distance to the working face. The simultaneous advances of two neighboring working faces in different horizontals can lead to extremely high resultant stress in an interference area.

三角煤柱孤岛工作面冲击地压防治技术研究

为解决近邻三角形煤柱孤岛工作面冲击地压防治问题,分析了国内该条件下导致冲击地压的研究现状;以唐山矿Y392工作面为研究对象,通过理论分析得出了以大埋深、上覆不规则煤柱、本层三角形煤柱、孤岛工作面冲击地压的主控因素;采用FLAC3D建立了数值模型,分析了本层三角形煤柱孤岛工作面的应力分布规律;提出了通过顶板预裂调控冲击地压主控因素的防冲方法;最后通过现场工程实践,建立并实施了以顶板预裂为主的冲击地压防治技术,通过应力法和钻屑法验证了顶板预裂对该条件下的冲击地压防控具有良好的效果。

基于地表沉陷数据反演的采动覆岩空隙时空演化规律

为明确采动覆岩空隙演化与地表下沉规律,采用现场实测和数值模拟方法,分析相似工作面的地表沉陷与覆岩空隙实测数据,标定研究工作面离散元数值模型参数,分析采动覆岩空隙时空演化规律。结果表明:42106浅埋工作面的地表下沉过程为开始—快速—缓慢—稳定,测点地表下沉速度呈现先增加后减小的几字形。充分采动前覆岩走向空隙率随推进距离增加而增大,充分采动后覆岩走向与倾向空隙率随工作面推进距离增加而减小。

综采工作面端面破碎支护技术应用分析

平泉煤矿15109工作面过断层应力区,面临煤壁垮落严重、局部端面冒漏、支架载荷大等技术难题;从围岩应力、支护方式以及煤层结构等方面分析端面破碎原因,拟对端面破碎围岩采用“超前管棚注浆+柔性纤维网+玻璃钢锚棚+人工假顶”联合支护技术;新支护技术应用后,控制了断层应力区围岩破碎现象,减小了端面冒漏范围,后期工作面回采中煤壁最大片帮长度不足1.5 m,片帮深度不足0.6 m,最大端面距为0.37 m,取得了显著应用成效。

高河能源掘进工作面产尘机理及运移规律数值模拟研究

高河能源公司掘进工作面产尘强度大且回采深度逐年增加,在空气流场的作用下,常规治尘措施难以对粉尘进行有效拦截。为此,对掘进工作面产尘机理及运移规律开展数值模拟研究。首先,开展现场掘进过程压入式、抽出式风量测试,随后建立掘进工作面DPM模型,构建掘进面物理模型,得到巷道中粉尘浓度分布与粒径分布特性。最后开展掘进过程粉尘浓度分布测试。试验结果表明:掘进机司机位置处总尘浓度最高值、平均浓度、呼尘浓度最高值、平均浓度;转载机位置总尘、呼尘浓度的平均值;控风风筒后方总尘、呼尘浓度的平均值,经与数值模拟结果与现场实测结果对比,模拟精度大于85%,与现场情况基本一致。

钱营孜煤矿W3233工作面涌水动态演化特征及影响因素分析

在煤矿开采规模、强度以及深度不断增加的背景下,矿井所面临的水文地质条件呈现多样性,工作面涌水动态演化特征及影响因素也变得更为复杂。以钱营孜煤矿褶曲和断层构造较发育的W3233工作面为研究对象,采用影响因素分析、三维地震勘探方法,探讨了采动影响下工作面涌水动态演化特征,并对矿井水位动态影响因素进行分析。矿井水位动态影响因素主要存在自然因素与人为因素两大类,自然因素包括了地质因素和地表因素,通过构建含水层水位影响因素层次结构体系,利用层次分析法计算出各影响因素的影响权重,其中地质构造、矿井疏放水、注浆治理分别为0.3543,0.2867,0.1433。

ZY4800/11/22大倾角液压支架设计特点及优化措施

新疆拜城东兴泰煤矿1103综采工作面平均倾角为45°,最大处可达50°,针对该矿煤层赋存条件和特点,设计了ZY4800/11/22大倾角液压支架。文中阐述了大倾角液压支架的定义和ZY4800/11/22大倾角液压支架的设计特点,并根据工作面总体布置要求,对该工作面首、尾架液压支架进行了优化设计,为类似煤层开采在装备配套及开采工艺上提供了有效的途径和方法。