Fault-Induced Coal Burst Mechanism under Mining-Induced Static and Dynamic Stresses

Fault is a common geological structure that has been revealed in the process of underground coal excavation and mining.The nature of its discontinuous structure controls the deformation,damage,and mechanics of the coal or rock mass.The interaction between this discontinuous structure and mining activities is a key factor that dominates fault reactivation and the coal burst it can induce.This paper first summarizes investigations into the relationships between coal mining layouts and fault occurrences,along with relevant conceptual models for fault reactivation.Subsequently,it proposes mechanisms of fault reactivation and its induced coal burst based on the superposition of static and dynamic stresses,which include two kinds of fault reactivations from:mining-induced quasi-static stress(FRMSS)-dominated and seismic-based dynamic stress(FRSDS)-dominated.These two kinds of fault reactivations are then validated by the results of experimental investigations,numerical modeling,and in situ microseismic monitoring.On this basis,monitoring methods and prevention strategies for fault-induced coal burst are discussed and recommended.The results show that fault-induced coal burst is triggered by the superposition of high static stress in the fault pillar and dynamic stress from fault reactivation.High static stress comes from the interaction of the fault and the roof structure,and dynamic stress can be ascribed to FRMSS and FRSDS.The results in this paper could be of great significance in guiding the monitoring and prevention of fault-induced coal bursts.

Numerical simulation of spatial distributions of mining-induced stress and fracture fields for three coal mining layouts

In this study, the spatial distributions of stress and fracture fields for three typical underground coal mining layouts, Le, non-pillar mining （NM）, top-coal caving mining （TCM） and protective coal-seam mining （PCM）, are modeled using discrete element software UDEC, The numerical results show that different mining layouts can lead to different mining-induced stress fields, resulting in diverse fracture fields, For the PCM, the mining influenced area in front of the mining faces is the largest, and the stress concentration factor in front of the mining faces is the lowest, The spatial shapes of the mining-induced fracture fields under NM, TCM and PCM differ, and they are characterized by trapezoidal, triangular and tower shapes, respectively, The fractal dimensions of mining-induced fractures of the three mining layouts decrease in the order of PCM, TCM and NM, It is also shown that the PCM can result in a better gas control effect in coal mines with high outburst potential, The numerical results are expected to provide a basis for understanding of mining-induced gas seepage fields and provide a reference for high- efficiency coal mining,

Coupling mechanism between mining-induced deformation and permeability of coal

The coupling mechanism between mining-induced mechanical behavior and gas permeability of coal is effectively obtained in laboratory.This study means significant understanding of the prevention of coal-gas outburst.The testing samples of coal were drilled from the 14120 mining face at the depth of690 m.Based on the redistribution of stress during the excavation,the coupling test between mechanical state and seepage has been designed using the triaxial servo-controlled seepage equipment for thermofluid-solid coupling of coal containing methane.It is the result that there are two main factors influencing the mining-induced mechanical behavior of coal,such as the change ofσ_1-σ_3 andΔσ_1-Δσ_3.The failure mode mainly depends on the value ofσ_1-σ_3,and the peak strength value mainly depends on the value ofΔσ_1-Δσ_3.The difference of mechanical response between geostress and mining-induced stress has been obtained,which can be a theoretical support for safe mining such as reasonable gas drainage,prevention of coal-gas outburst and gas over-limit.

Multistage hydraulic fracturing of a horizontal well for hard roof related coal burst control:Insights from numerical modelling to field application

Multistage hydraulic fracturing of horizontal wells(MFHW)is a promising technology for controlling coal burst caused by thick and hard roofs in China.However,challenges remain regarding the MFHW control mechanism of coal burst and assessment of the associated fracturing effects.In this study,these challenges were investigated through numerical modelling and field applications,based on the actual operating parameters of MFHW for hard roofs in a Chinese coal mine.A damage parameter(D)is proposed to assess the degree of hydraulic fracturing in the roof.The mechanisms and effects of MFHW for controlling coal burst are analyzed using microseismic(MS)data and front-abutment stress distribution.Results show that the degree of fracturing can be categorized into lightly-fractured(D≤0.3),moderately fractured(0.3<D≤0.6),well-fractured(0.6<D≤0.9),and over-fractured(0.9<D≤0.95).A response stage in the fracturing process,characterized by a slowdown in crack development,indicates the transition to a wellfractured condition.After MFHW,the zone range and peak value of the front-abutment stress decrease.Additionally,MS events shift from near the coal seam to the fractured roof layers,with the number of MS events increases while the average MS energy decreases.The MFHW control mechanisms of coal bursts involve mitigating mining-induced stress and reducing seismic activity during longwall retreat,ensuring stresses remain below the ultimate stress level.These findings provide a reference for evaluating MFHW fracturing effects and controlling coal burst disasters in engineering.

Study on the Safety and Prevention Technology of Coal Mining under the River in Xingyuan Coal Mine

Coal mining-induced surface subsidence poses significant ecological and infrastructural challenges, necessitating a comprehensive study to ensure safe mining practices, particularly in underwater conditions. This project aims to address the extensive impact of coal mining on the environment, infrastructure, and overall safety, focusing on the Shigong River area above the working face. The study employs qualitative and quantitative analyses, along with on-site engineering measurements, to gather data on crucial parameters such as coal seam characteristics, roof rock lithology, thickness, water resistance, and structural damage degree. The research encompasses a multidisciplinary approach, involving mining, geology, hydrogeology, geophysical exploration, rock mechanics, mine surveying, and computational mathematics. The importance of effective safety measures and prevention techniques is emphasized, laying the foundation for research focused on the Xingyun coal mine. The brief concludes by highlighting the potential economic and social benefits of this project and its contribution to valuable experience for future subsea coal mining.

Deformation characteristics and reinforcement technology for entry subjected to mining-induced stresses

The entry at Zhangcun coal mine in Lu＇an coal mining area in Shanxi Province suffered from severe mining-induced stresses with the heading face driven oppositely to an adjacent working face. In this paper, the characteristics of deformation and failure of the entry were investigated in terms of the tempo-spatial relations between heading and working faces through field study and numerical modeling. The three-dimensional （3D） finite difference models were built to investigate stresses, displacements and damages in the surrounding rocks of the entry and the working face. The field study includes selection of reinforcing methods and materials, design parameters, and determination of cable prestress. The monitoring data of entry deformation and stress along the cables during every stage were presented. The state of the reinforced entry was evaluated based on the monitoring data. The results demonstrate that before the heading face of the entry crosses the adjacent working face, the influence of advanced abutment pressure caused by adjacent working face upon the entry is not significant. After they cross each other, however, the lateral abutment pressure will have an evident impact on the entry. The displacement rate of the entry will be greatly increased and reaches a certain value within a certain distance between the heading face and the working face. Then, it will increase again with the presence of secondary mining-induced pressure on the entry when the present working face advances. The fully-grouted cable with short length, high strength and high prestress is an effective way to reinforce the entry suffering from severe mining-induced stresses, which greatly reduces the displacement and failure possibility of the entry. Finally, the principles and recommendations for reinforcing design of entries suffering from severe mining-induced stresses were proposed according to field study, numerical modeling and experiences from other coal mines. Problems encountered in field study and suggestions for reinforcement were also discussed.

Theoretical description of drawing body shape in an inclined seam with longwall top coal caving mining

Understanding the characteristics of drawing body shape is essential for optimization of drawing parameters in longwall top coal caving mining.In this study,both physical experiments and theoretical analysis are employed to investigate these characteristics and derive a theoretical equation for the drawing body shape along the working face in an inclined seam.By analyzing the initial positions of drawn marked particles,the characteristics of the drawing body shape for different seam dip angles are obtained.It is shown that the drawing body of the top coal exhibits a shape-difference and volume-symmetry characteristic,on taking a vertical line through the center of support opening as the axis of symmetry,the shapes of the drawing body on the two sides of this axis are clearly different,but their volumes are equal.By establishing theoretical models of the drawing body in the initial drawing stage and the normal drawing stage,a theoretical equation for the drawing body in an inclined seam is proposed,which can accurately describe the characteristics of the drawing body shape.The shape characteristics and volume symmetry of the drawing body are further analyzed by comparing the results of theoretical calculations and numerical simulations.It is shown that one side of the drawing body is divided into two parts by an inflection point,with the lower part being a variation development area.This variation development area increases gradually with increasing seam dip angle,resulting in an asymmetry of the drawing body shape.However,the volume symmetry coefficient fluctuates around 1 for all values of the seam dip angle variation,and the volumes of the drawing body on the two sides are more or less equal as the variation development volume is more or less equal to the cut volume.Both theoretical calculations and numerical simulations confirm that the drawing body of the top coal exhibits the shape-difference and volume-symmetry characteristic.

Research on attenuation characteristic of sound wave in coal or rock body

In order to using power sound wave increase permeability of coal, rules of attenuation of sound wave in coal should be studied. In this paper, characteristic and mechanism of attenuation of sound wave in coal was researched according to acoustic theory and attenuation coefficients was estimated by acoustic parameter of coal. The research results show that the main attenuation mechanism of sound wave in coal is absorption attenuation and scattering attenuation. The absorption attenuation includes viscous absorption, thermal conduction absorption and relaxation absorption. Attenuation coefficient of sound wave in gaseous coal is 38.5 Np/m. Researches on attenuation characteristic of sound wave will provide the theoretical basis for power sound wave improving permeability of coal and accelerating desorption of coal bed gas.

Failure behavior of a rock-coal-rock combined body with a weak coal interlayer

Using an MTS 815 testing machine,the deformation and failure behavior of a rock-coal-rock combined body containing a weak coal interlayer has been investigated and described in this paper.Uniaxial loading leads to the appearance of mixed cracks in the coal body which induce instability and lead to bursts in coal.If the mixed crack propagates at a sufficiently high speed to carry enough energy to damage the roof rock,then coal and rock bursts may occur-this is the main mechanism whereby coal bumps or coal and rock bursts occur after excavation unloading.With increasing confining pressure,the failure strength of a rock-coal-rock combined body gradually increases,and the failure mechanism of the coal interlayer also changes,from mixed crack damage under low confining pressures,to parallel crack damage under medium confining pressures,and finally to single shear crack damage or integral mixed section damage under high confining pressures.In general,it is shown that a weak coal interlayer changes the form of overall coal damage in a rock-coal-rock combined body and reduces the overall stability of a coal body.Therefore,the whole failure behavior of a rock-coal-rock combined body in large cutting height working faces is controlled by these mechanisms.

Joint Bearing Mechanism of Coal Pillar and Backfilling Body in Roadway Backfilling Mining Technology

In the traditional mining technology,the coal resources trapped beneath surface buildings,railways,and water bodies cannot be mined massively,thereby causing the lower coal recovery and dynamic disasters.In order to solve the aforementioned problems,the roadway backfilling mining technology is developed and the joint bearing mechanism of coal pillar and backfilling body is presented in this paper.The mechanical model of bearing system of coal pillar and backfilling body is established,by analyzing the basic characteristics of overlying strata deformation in roadway backfilling mining technology.According to the Ritz method in energy variation principle,the elastic solution expression of coal pillar deformation is deduced in roadway backfilling mining technology.Based on elastic-viscoelastic correspondence principle,combining with the burgers rheological constitutive model and Laplace transform theory,the viscoelastic solution expression of coal pillar deformation is obtained in roadway backfilling mining technology.By analyzing the compressive mechanical property of backfilling body,the time formula required for coal pillar and backfilling body to play the joint bearing function in roadway backfilling mining technology is obtained.The example analysis indicates that the time is 140 days.The results can be treated as an important basis for theoretical research and process design in roadway backfilling mining technology.

Theory and test research on permeability of coal and rock body influenced by mining

Stress distribution rules and deformation and failure properties of coal and rockbodies influenced by mining were analyzed.Experimental research on permeability of coaland rock samples under different loading conditions was finished in the laboratory.In-situmeasurement of coal permeability influenced by actual mining was done as well.Theoryanalysis show that permeability varied with damage development of coal and rock understress,and the influence of fissure on permeability was greatest.Laboratory results showthat under different loading conditions permeability was different and it varied with stress,which indicated that permeability was directly related to the loading process.In-situ testsshowed that permeability is related to abutment stress to some degree.The above resultsmay be referenced to gas prevention and drainage.

Nonlinear multi body dynamic modeling and vibration analysis of a double drum coal shearer

The double drum coal shearer is widely applied for the underground coal exploration in the mining industry.The vibration and noise control are significant factors for the stability design of the double drum coal shearer.In this paper,the vibration properties of a double drum coal shearer are firstly investigated.The horizontal,transverse and torsional vibrations of the motor body and the angle displacements of the rockers are taken into account.The walking units and the hydraulic units are modeled by the stiffness-damping systems.The nonlinear equation of motion of the double drum coal shearer is established by applying the Lagrange’s equation.The nonlinear vibration response of the system is calculated by using the Runge Kutta numerical method.The effects of the shearing loads,the equivalent damping and stiffness of the walking units,the inclination angels of the rockers and the equivalent damping and stiffness of the hydraulic units on the vibration properties of the system are discussed.

Mechanical behaviors of coal measures and ground control technologies for China's deep coal mines-A review

This paper reviews the major achievements in terms of mechanical behaviors of coal measures,mining stress distribution characteristics and ground control in China’s deep underground coal mining.The three main aspects of this review are coal measure mechanics,mining disturbance mechanics,and rock support mechanics.Previous studies related to these three topics are reviewed,including the geo-mechanical properties of coal measures,distribution and evolution characteristics of mining-induced stresses,evolution characteristics of mining-induced structures,and principles and technologies of ground control in both deep roadways and longwall faces.A discussion is made to explain the structural and mechanical properties of coal measures in China’s deep coal mining practices,the types and dis-tribution characteristics of in situ stresses in underground coal mines,and the distribution of mining-induced stress that forms under different geological and engineering conditions.The theory of pre-tensioned rock bolting has been proved to be suitable for ground control of deep underground coal roadways.The use of combined ground control technology(e.g.ground support,rock mass modification,and destressing)has been demonstrated to be an effective measure for rock control of deep roadways.The developed hydraulic shields for 1000 m deep ultra-long working face can effectively improve the stability of surrounding rocks and mining efficiency in the longwall face.The ground control challenges in deep underground coal mines in China are discussed,and further research is recommended in terms of theory and technology for ground control in deep roadways and longwall faces.

DETECTION OF IGNEOUS BODIES IN HUAIBEI COAL MINESBY HIGH RESOLUTION MAGNETIC SURVEY

The present paper investigates the application of high resolution magnetic survey to detecting igneous bodies. The slight difference in magnetism between igneous bodies and their surrounding rocks is measured first and then the magnetic survey data are processed to determine whether there exist igneous bodies by analog among several measuring lines, and finally the modified Marquart inversion was used to determine the occurrence and distribution of the igneous bodies.

建筑物下特厚煤层镁渣基全固废连采连充开采技术与实践

我国建筑物下压煤量巨大,同时煤矸石、粉煤灰等煤基工业固体废弃物排放量日益增加,严重制约地方经济社会发展。以榆林麻黄梁煤矿为试验矿井,针对其特厚煤层、建筑物下压煤、充填成本高等问题,提出了特厚煤层全固废连采连充开采技术。采用四阶段工序并将特厚煤层分为上、下2部分二次回采压覆煤炭,最大程度控制地面沉降。为降低充填原材料成本,采用化学优化剂对镁渣进行源头改性,抑制镁渣冷却粉化,稳定水化活性,协同粉煤灰、脱硫石膏等煤基固废,研发了改性镁−煤渣基胶凝材料。采用改性镁−煤渣基胶凝材料胶结煤矸石、粉煤灰制备了全固废充填材料。针对麻黄梁煤矿四阶段强、弱充填强度要求,设计不同配比的改性镁渣基充填材料试验,优选配比并应用于井下充填。论述了膏体充填系统与充填接顶方法。麻黄梁煤矿全固废胶结充填工艺试验显示,井下28 d龄期充填体钻芯平均单轴抗压强度超设计强度27%,钻芯浸出毒性满足相关国家标准要求,成功回收了建筑物下压覆煤炭资源,社会经济效益显著。麻黄梁煤矿特厚煤层全固废胶结充填开采实践为国内类似矿井提供了有益借鉴,同时为我国大型煤炭基地的“煤−电−化−冶”固废大规模资源化利用提供了新的思路。

济阳坳陷潜山风险勘探方向浅析

济阳坳陷油气资源丰富,但随着勘探程度的不断深入,古近系常规油气藏的勘探难度不断加大,亟需拓展新领域,保障资源有效接替。济阳坳陷地层发育齐全,前古近系潜山分布广、厚度大,勘探潜力显著,但受限于深层潜山形成时间早、经历地质演化历程复杂、深部地震资料品质差等因素,勘探效果相对较差。近年来,随着实验技术持续攻关、基础地质研究不断深化、地震资料处理手段更加丰富,潜山钻探获得了不少好苗头,形成了多期构造共控成山、多套源岩联合供烃、多元共控优势成储、多种模式有序控藏的潜山油气成藏认识。通过对已发现油气藏的深入解剖,同时借鉴邻区的勘探经验,明确了济阳坳陷深层潜山勘探的风险方向和勘探目标,为济阳坳陷油气勘探潜力的进一步挖掘指明了方向。具体来讲,各层系的风险勘探方向为:太古界潜山内幕的断缝体、断溶体圈闭等;下古生界隐蔽性断块圈闭以及内幕颗粒滩、沿层溶蚀作用形成的岩性圈闭;上古生界埋深大于2000m的深层煤系气藏;中生界裂缝-砂体双控的岩性圈闭。

顶煤运移轨迹监测实验平台研制与教学实践

为丰富“采矿学”课程实践教学内容,促进本科生对综合机械化放顶煤开采技术的了解,该文研制了顶煤运移轨迹监测实验平台。实验平台包括模型框架、综放支架、辅助铰轮、磁场发射装置、轨迹识别装置和数据采集系统,平台基于电磁波技术精准定位顶煤位置和精准识别顶煤运移轨迹,可用于研究煤层地质赋存条件、开采技术条件等对顶煤运移规律的影响。实验设计了“模型搭建、标志点安装、模拟放煤、数据采集、轨迹反演”等环节,培养了学生团队合作和创新思考能力。

基于正交设计的大比例模型采场煤体相似材料配比试验研究

针对传统模型材料难以满足大比例模型采场材料需求,结合大比例模型相似模拟试验特点及相似理论,以陶粒、河沙、粉煤、水泥和石膏为原料,设计正交试验,测试试件的物理力学等参数。结果表明:大比例模型采场材料基本特征为低容重、高强度。煤体材料密度随陶粒/骨料比值的增大而减小,抗压强度和抗拉强度随陶粒/骨料、水膏比的增大而减小,随水胶比的增大而增大,弹性模量、黏聚力和内摩擦角随陶粒/骨料和骨胶比的增大而减小。通过多元线性回归分析反算大比例模型采场煤体相似材料配比模型,并通过试验得到不同尺寸试件各试验指标误差在20%内波动,证实了该配比模型的可靠性。

煤矿采动影响体微生物采残煤与CO_(2)-粉煤灰协同充填关键技术

煤矿采空区是我国实现“双碳”目标的重要突破口,煤炭开采形成的、能够富集煤层气、为后期微生物活动和矿化充填提供底物和空间的地质体定义为采动影响体。以采动影响体为研究对象,提出了采动影响体微生物采残煤与CO_(2)-粉煤灰协同矿化充填关键技术,并从必要性和可行性2个方面阐述了该技术在采动影响体资源二次开发、CO_(2)安全封存以及燃煤电厂粉煤灰固废高效处置等的广阔前景。其总体思路是将采动影响体作为一个厌氧发酵“工厂”,高产高效产甲烷菌群作为“劳动者”对“工厂”已有的原材料——残煤、薄煤层和分散有机质以及注入的CO_(2)进行加工,其“产品”是甲烷,进而实现微生物采残煤和CO_(2)资源化。同时,CO_(2)与碱性的粉煤灰结合,在实现了CO_(2)矿化封存的同时,也实现了采动影响体的充填。该技术涉及的关键科学问题包括采动影响体类型划分与有机质特征、采动影响体原位条件下厌氧发酵产甲烷机制、微生物-CO_(2)-粉煤灰协同矿化/固化机制以及微生物采残煤与充填关键技术示范工程建设。实验室物理模拟采动影响体原位条件实验表明其中残煤和富含有机质的泥页岩能够在微生物作用下生成生物甲烷,且添加少量的粉煤灰能够进一步强化甲烷的产出。物理模拟地下水补给的动态实验表明营养物质的补给对厌氧发酵系统的影响尤为重要,补给循环周期为14 d的厌氧发酵系统恰与产甲烷菌群繁殖的周期一致,能够保证厌氧发酵系统的持续高效运行。高钙粉煤灰-CO_(2)-矿井水协同胶结的试件经过28 d的养护后抗压强度为12.31 MPa,其矿化封存潜力约为21.99 m3 CO_(2)/t(粉煤灰),说明粉煤灰在实现采空区固化的同时能够实现CO_(2)减排。此外,基于微生物采残煤与粉煤灰充填目的对工程试验靶区进行优选,地下水滞留区是CO_(2)矿化和粉煤灰充填的最佳场所,因采掘活动自然形成的自然圈闭和人工充填形成的圈闭是较有利的工程试验靶区之一。针对这些靶区提出了微生物采残煤与CO_(2)-粉煤灰协同充填关键技术,旨在为中国碳减排和采空区生态环境治理提供一条新的技术路径。

预裂炮孔近区煤体爆破损伤特性研究

为探究工作面预裂炮孔近区煤体动力损伤及应力传递过程,选用HJC、RHT损伤模型,对单孔装药及双孔爆破工况开展爆破模拟。研究结果表明:单孔爆破下RHT模型的损伤随时间呈近似线性增长,HJC模型的爆破损伤随时间呈二次函数增长;单孔爆破中峰值压力与爆心距呈二次函数;双孔爆破下HJC、RHT模型的爆炸近区压力峰值相差2.27%,但远区峰值压力差值≥8.0 MPa;双孔爆破下RHT模型应力波传播:两孔贯穿-后向外扩展;HJC模型应力波传播:由爆破孔向四周扩展,后作用孔间区域;单孔/双孔爆破中HJC模型能量吸收时间分别为RHT模型的6~10倍,RHT模型可表征煤岩爆破演化。研究成果可为工作面安全高效施工提供参考。