Effect mechanism of nitrogen injection into fire-sealed-zone on residual-coal re-ignition under stress in goaf

Coal is the one of foundations of energy and economic structure in China,while the unsealing of coal mine fres would cause a great risk of coal re-ignition.In order to explore the infuence of pressure-bearing state on the re-ignition characteristics for residual coal,the uniaxial compression equipped with a temperature-programmed device was built.The scanning electron microscope,synchronous thermal analyzer and Fourier transform infrared absorption spectrometer was applied to investigate the microscopic structure and thermal efect of the coal samples.Moreover,the microscopic efect of uniaxial stress on coal re-ignition is revealed,and the re-ignition mechanism is also obtained.As the uniaxial stress increasing,the number,depth and length of the fractures of the pre-treated coal increases.The application of uniaxial stress causes the thermal conductivity to change periodically,enhances the inhibition of injecting nitrogen on heat transfer and prolonges the duration of oxidation exothermic.The content of oxygen-containing functional groups has a high correlation with apparent activation energy,and coal samples at 6 MPa is more probability to re-ignite while the fre zone is unsealed.Uniaxial stress could control the re-ignition mechanism by changing the structure of fractures and pores.The side chains and functional groups of coal structure are easier to be broken by thermal-stress coupling.The higher the·OH content,the more difcult coal samples would be re-ignited.The research results would lay a solid theoretical foundation for the safe unsealing of closed fre-areas underground,tighten the common bond between the actual industry and the experimental theory in closed fre-areas underground,and provide the theoretical guidance for coal re-ignition preventing.

A Numerical Investigation of the Stress Relief Zones Around a Longwall Face in the Lower Seam for Gas Drainage Considerations

Extraction of a protective coal seam (PVCS)-below or above a coal seam to be mined with the potential of coal andgas outburst risk-plays an important role not only in decreasing the stress field in the surrounding rock mass but alsoin increasing the gas desorption capacity and gas flow permeability in the protected coal seam (PTCS). The PVCSis mined to guarantee the safe mining of the PTCS. This study has numerically evaluated the stress redistributioneffects using FLAC3D model for a longwall face in Shanxi Province. The effects of mining depth, mining height andinter-burden rock mass properties were evaluated using the stress relief angle and stress relief coefficient. Verticalstress distribution, stress relief angle and stress relief coefficient in the PTCS were analyzed as the face advancedin the PVCS. The results showed that the stress relief achieved in different locations of the PTCS varied as the faceadvanced. Sensitivity analyses on the pertinent variables indicate that the stress relief in the PTCS is affected mostby the mining depth followed by the inter-burden lithology and the mining height. Furthermore, the elastic moduliof different layers within the inter-burden rock mass are more important than their uniaxial compressive strength(UCS) and Poisson’s ratio. These observations can guide gas drainage borehole design to minimize the accidentsof coal and gas outbursts.

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.

Lateral Stress Concentration in Localized Interlayer Rock Stratum and the Impact on Deep Multi-Seam Coal Mining

To explore the impact of lateral stress concentration in interlayer rock stratum on the exploitation of protected coal seam, a field experiment was carried out in a multi-seam mining structure. Lateral stress redistribution and interlayer rock failure behavior were surveyed. Then an assistant numerical investigation was implemented to evolve the effect of liberated seam mining and its influence on stress reconstruction in surrounding rock mass. The cause of lateral stress concentration and its impact were discussed finally. Key findings turn out that a certain lateral stress increases in interlayer rock stratum and concentrates on its lower region. Lateral stress concentration and interlayer rock failure are interactional. The former is an inducing factor of the latter;the latter promotes the increase of concentration degree. Extent of lateral stress concentration increases to the maximum as seam distance is about 50 m. But the efficacy of liberated seam mining decreases as the seam spacing gets larger. Protected seam mining is then classified based upon the impact of lateral stress concentration, which helps to prevent the rock burst hazard and then to achieve a reliable mining in deep mines.

基于多区组合煤体的煤与瓦斯突出动力学机制

煤与瓦斯突出(以下简称“突出”)严重影响煤炭安全开采,其背后涉及的众多科学问题仍未解决。为降低煤体力学性质各向异性对突出研究的困扰,构建多区组合煤体模型;基于上覆岩层应力分布特征及应力波传播机制确定“弱区”煤体位置,将研究对象由“突出中心体”具体为“弱区”。由于外部动载扰动是导致突出的激发条件,采用冲击试验研究应力波在层状组合煤岩体中的传播规律,构建组合煤岩体应力-应变本构模型。进而明确卸载波作用下,煤体轴向多层层裂是煤体质点内撞击形成加载冲击波在自由面反射形成拉应力波导致的;煤体径向平面,由于泊松效应形成卸载波追赶塑性加载波的情形,生成多个径向裂隙及环向裂隙,得到煤体层裂片厚度动态演化规律。从而明确在外部动载扰动下,煤体“弱区”最先破坏,轴向产生多层层裂、径向平面产生多个径向及环向裂隙的三维损伤路径。基于此,提出一种基于多区组合煤体的突出动力学机制,将突出划分为准备、启动、发展、终止四个阶段。突出准备阶段,煤体上覆岩层应力转移、集中,高瓦斯压力梯度形成,为后续煤体失稳破坏创造条件;突出启动阶段,煤体受外部动载扰动,轴向“弱区”煤体最先发生破坏、形成多层层裂,径向平面形成多个径向及环向裂隙;突出发展阶段,吸附态瓦斯解吸与游离态瓦斯积聚形成高压瓦斯抛出煤体,导致突出继续向深部煤体发展,形成二次损伤;突出终止阶段,积聚形成的瓦斯压力低于煤体抗拉强度,形成稳定的纺锤形突出腔体,突出终止。该机制初步解释了突出过程中“响煤炮”“口小腔大”突出孔洞等动力现象成因,为矿井防突工作提供了新思路。

围岩加强支护留窄煤柱护巷的可行性研究

为了减少煤矿井下资源浪费现象的发生,研究了留设不同宽度保护煤柱时,围岩塑性区及垂直应力在施工“支护-卸压-砌墙”协同控制技术前后的数值模拟对比分析。数值模拟结果表明:未采取围岩加强支护措施时,随着停采线与回风大巷之间距离的减小,煤柱垂直应力峰值呈先增大后减小的趋势,且回风大巷围岩破坏变形严重;施工“支护-卸压-砌墙”协同控制技术后,随着保护煤柱的回采,煤柱与回风大巷围岩的塑性形变区域面积占比都显著减小,且回风大巷的垂直应力峰值平均减小了25.32%,应力集中系数平均减小了27.03%;在保证煤柱及大巷围岩稳定的前提下,可适当的缩减保护煤柱的宽度,以减少煤炭资源的浪费,并可为煤矿带来较大的经济效益。

高偏应力煤巷围岩拉剪破裂特征及分区控制方法研究

为获得高偏应力巷道围岩拉剪破裂特征并提出优化支护方案,以山西某矿孤岛工作面为背景,采用理论分析、数值模拟、相似模拟相结合的研究手段,分析了高偏应力条件下巷道围岩拉剪破裂分布特征及演化规律,揭示了托顶煤巷道围岩拉剪破裂机制,提出了高偏应力条件下巷道围岩沿掘进方向的全长分区控制方法。研究结果表明:(1)当侧压系数λ为0.60时,巷道围岩两帮呈“楔形”破坏,顶底出现明显卸荷并在巷道围岩四角点处产生应力集中;侧压系数λ逐渐减小至0.24的过程中,巷道围岩以两帮破坏为基础,在剪切应力作用下“蝶叶”逐渐发育,并最终形成蝶形破裂。(2)开挖破坏区围岩的浅部存在拉剪混合破裂区域,以张拉破裂为主;围岩深部为剪切破裂。围岩破裂演化过程可划分为3个阶段,分别为环自由面的自身破坏阶段、“蝶叶”孕育扩展阶段和“蝶叶”扩展稳定阶段。(3)定义了基于巷道全长分区的应力阈值,提出了掘进巷道全长分区支护方法,可为后续采煤工作面巷道的差异化支护提供理论参考。

瑶渠煤矿大巷间煤柱尺寸确定及支护优化

为研究大巷过剥蚀区时大巷间煤柱合理尺寸及围岩稳定性,以瑶渠煤矿西采区Ⅱ回风大巷为研究对象,采用理论分析、数值模拟等研究方法,建立了煤柱尺寸计算模型,揭示了煤柱在8 m、10 m、12 m、14 m条件下巷道围岩应力、位移及塑性区的分布规律,确定了过剥蚀区大巷间煤柱的合理尺寸,并优化了西采区Ⅱ回风大巷的支护参数。研究结果表明,瑶渠煤矿西采区Ⅱ回风大巷与辅运大巷之间煤柱尺寸由14 m减小至8 m时,巷道围岩内的垂直应力由1.381 MPa增加至1.465 MPa、最大位移量增加了12.52%,塑性区逐渐贯通煤柱。当煤柱尺寸为10 m时,煤柱塑性区处于贯通的临界区域,煤柱内部具有一定的弹性核区域,且煤柱尺寸大于理论计算的9.23 m,能够满足巷道围岩的稳定性。综合考虑,确定煤柱最小合理尺寸为10 m。对10 m煤柱尺寸下西采区Ⅱ回风大巷进行支护优化,采用帮部3根锚杆支护后巷道围岩应力、位移和塑性区均显著改善,保证了巷道围岩的稳定性。

基于采空区刚度演化的采场围岩稳定性分析

为研究采空区刚度对采场围岩稳定性的影响,采用PHASE 2D有限元软件建立3种采空区刚度数值模型,其中模型Ⅰ的采空区刚度最大,模型Ⅱ最小,模型Ⅲ居中,研究了工作面前方煤体塑性区的发展规律、直接顶下沉量、覆岩垂直位移和工作面支承压力变化规律。研究结果表明,当工作面推进150 m时,3种采空区刚度下的工作面前方煤体塑性区宽度分别为2.08 mm、3.56 mm和3.13 mm,采空区刚度越大,工作面煤体塑性区宽度越小;模型Ⅰ、Ⅱ和Ⅲ的直接顶最大下沉量分别为38.8 mm、106.6 mm和96.8 mm,覆岩垂直位移最大值为44.9 mm、148.3 mm和137.4 mm;随着工作面推进,工作面前方支承压力增高系数先增大后稳定,模型Ⅰ、Ⅱ和Ⅲ支承压力增高系数峰值依次为2.1、3.7和3.4。分析认为,增大采空区刚度有利于降低工作面支承压力,提高采场围岩稳定性。

余吾矿煤/岩层组合类型划分及压裂措施

为了划分煤/岩层水力压裂组合类型,以潞安矿区余吾矿3#煤层为研究对象,通过测井解释及力学测试得出顶板岩性及力学特征;采用取心井与测井相结合识别出煤层段的煤体结构;根据水力压裂计算地应力方法结合密度测井得出了地应力状态;由此划分出水力压裂煤/岩层组合类型,并提出了不同组合类型下的水力压裂措施建议。结果表明:研究区水力压裂煤/岩层组合类型可以划分为硬岩硬煤、软岩硬煤、硬岩软煤、软岩软煤组合的过渡型和拉张型等7种类型;硬岩硬煤组合类型时,采用大排量、多液量、低/中砂比、逐级加砂方式能营造出较长裂缝并能有效支撑;软岩硬煤组合时,应避射部分煤层,防止水力压裂裂缝进入煤层与软岩交界面,影响压裂效果;硬岩软煤拉张组合时,建议采用顶板水力压裂;进行硬岩软煤过渡型水力压裂时,根据水平应力与垂直应力的差值优化压裂参数;软岩软煤组合时,不建议采用水力压裂方式进行改造。

条带充填开采巷道围岩变形及顶板导水裂隙带实测研究

以常村煤矿条带充填巷道群集中开采为宏观技术背景,依托常村煤矿CTS2-01工作面充填开采工程实践,对现场充填体强度、顶底板移近量和导水裂隙带发育高度进行实测。结果表明,充填膏体试件强度随养护时间增加而增加,井下充填体试件不同期龄的平均抗压强度比地面充填站的更高,且标准差和方差也更大;巷道变形最大为67 mm,平均变形量不超过0.5 mm/d,说明条带充填开采后工作面主巷道变形量很小,不影响正常生产;综合顶板窥视及注水试验结果判断认为,条带充填开采后,工作面顶板最大导水裂隙带发育高度小于4.0 m。研究成果可为条带式充填开采技术的推广应用提供一定的技术参考与经验借鉴。

煤柱应力区的巷道破坏特征及控制技术研究

在连续煤层开采过程中,上部采空区残余煤柱常导致下伏长壁开采工作面产生强应力,应力积累会造成回采巷道严重破坏变形。为此,以隆泰煤矿巷道的应力破坏变形过程为例进行了研究,分析了采矿巷道围岩的破坏变形过程,运用FLAC3D模拟了应力分布特征以及巷道周围垂直应力和破坏带的演化过程。结果表明,支护煤柱以下工作阻力普遍较高,平均值为9726.6kN,采空区以下普遍较低,平均值为7 655.5 k N;受影响,回采巷道在距工作面30 m以外变形破坏程度相对中等,在距9+10号工作面30 m以内变形破坏程度相对严重;基于残留煤柱集中应力分布特征,采用水力压裂控制其力学特性,改善了回采巷道应力环境。

大采高孤岛工作面沿空护巷煤柱合理宽度研究

针对转龙湾煤矿二采区孤岛工作面沿空掘进巷道煤柱留设难题,采用数值模拟,对2号工作面运输巷在不同煤柱宽度下煤柱应力分布和围岩变形程度进行了研究,最终确定了合理的煤柱宽度为19 m,并对合理的煤柱宽度进行围岩稳定性验证。结果表明,在煤柱宽度为19 m的范围内,可以有效控制围岩变形,实现巷道围岩的稳定性。该研究成果对沿空掘巷煤柱合理宽度的确定及巷道围岩控制技术的应用具有重要的理论意义和参考价值。

复杂破碎矿体采矿方法研究及提产优化实践

复杂破碎矿体难以实现安全高效回采,其采矿方法的选择仍是当今采矿技术的难题。本文以某铁矿复杂破碎采场为背景,进行采场结构参数数值模拟及提产布局协同技术研究。首先进行岩体结构面调查分析和岩石试件点荷载强度测试,进行岩体稳定性分级;其次在岩体质量分级的基础上,基于Mathew稳定图表法,在综合考虑采准工程和采场顶板与侧帮稳定性的基础上,获得采场允许暴露的结构参数:当宽度为10~18 m时,采场最大允许暴露长度为30~60 m;当采场高度小于30 m时,采场最大允许暴露长度为30~50 m;当高度大于30 m时,采场最大允许暴露长度为45~60 m。在此基础上,提出25种不同开采方案,采用FLAC3D对采场结构参数进行数值模拟优化,通过采场顶板和侧帮位移、应力、塑性区对比分析等,结合开采实际,提出在南部地质条件相对较好区域推行预控顶大直径深孔采矿法,较为破碎的北部区域采用预控顶中深孔落矿分段凿岩采矿法,并不断进行提产布局及排产优化,顺利实现设计产能。

龙泉煤矿4301工作面导水裂隙带动态发育高度研究

针对龙泉煤矿4301大采高综放工作面顶板砂岩裂隙水易突水涌入工作面的开采难题,采用理论分析和数值模拟两种研究方法,探究了4301工作面开采过程中导水裂隙带发育高度的动态演化规律。数值模拟研究表明,4301工作面推进距离小于96 m时,导水裂隙带的发育高度随工作面推进而不断增加,发育最大高度约为75 m;工作面推进距离大于96 m后,导水裂隙带发育高度变化较小,基本稳定于75 m。该研究结果与理论分析所得导水裂隙带发育范围在57~75 m基本吻合,表明数值模拟结果具有一定合理性;工作面覆岩上方K4、K5含水砂岩层处于导水裂隙带发育范围内,保水开采中应重点考虑K4、K5含水砂岩层不被破坏。研究成果揭示了龙泉煤矿4#煤层开采导水裂隙带动态发育特征及其终态发育高度,对于4#煤层开采中覆岩含水层受扰动范围的确定具有重要意义。该研究成果可为类似条件下煤炭资源的安全与绿色开采提供一定参考。

Effects of coal seam dip angle on the outburst in coal roadway excavation

The prevention and forecast of coal and gas outburst has always been one of the key issues in coal mining safety.By simulating the process of tunneling in coal seam with different dip angle through FLAC3D software,the dangerous zone in which outburst may occur and the probability of outburst near the working face were predicted through the distribution of stress,displacement and plastic zone.Then we discussed the size of unstable area in the surrounding rock through the distribution of stress and the variation curve of the displacement on the roadway wall.The results show that,with an increase of the coal seam dip angle,the risk of outburst in the working face rises gradually.And the dangerous areas in which may outburst occur moves to the upper part of coal seam.The size of unstable area in the surrounding rock increases with the increase of coal seam dip angle.

Numerical investigation on the assessment and mitigation of coal bump in an island longwall panel

This study presents a numerical investigation to assess the risk of coal bumps and produces a stress–relief technology using boreholes to mitigate risk during the extraction of an island longwall panel.Based on the geological condition in an island longwall panel in the Tangshan Coal Mine,Tangshan,China,a numerical FLAC3D(Fast Lagrangian Analysis of Continua in 3 Dimensions) model was established to determine and to map the zones in the panel with a high risk for coal bumps.The results of the numerical modeling show that the roof deformation starts to occur at more than 30 m ahead of the longwall face and the deformation starts to accelerate after a distance of 10 m in front of the longwall face.Large and rapid roof deformation is considered to be an important precursor of coal bump occurrence during the extraction of an island longwall panel.Based on the numerical results,a stress–relief technology using boreholes,which was employed to release abutment pressure,was investigated through numerical methods.The modeled results suggest that the peak stress concentration could be released by drilling boreholes in the zones prone to coal bumps.The effectiveness of the stress release increased with the borehole length and decreased with the borehole spacing.

高面板砂砾石坝堆石料力学变形特性及坝体分区研究

随着高混凝土面板砂砾石坝坝高的突破,坝体内部高应力区和坝坡、坝顶低应力区的应力差别增大,而不同应力条件下砂砾石料和块石料的力学特性存在较大差异,将影响着坝体分区及变形安全。开展砂砾石料和块石料三轴力学试验,研究不同应力条件对其力学变形特性的影响;在此基础上根据坝体应力分布特征,研究高混凝土面板砂砾石坝坝体分区。研究表明,在低围压条件下,块石料的模量系数大于砂砾石料;随着围压增加到一定程度,块石料颗粒破碎导致模量系数大幅降低,远小于砂砾石料的模量系数;为充分利用两种堆石料的力学变形特性,加强高面板砂砾石坝坝体变形控制,坝体内高、低应力区应分别采用砂砾石料和块石料填筑,提出一种基于坝体应力分布特征的坝体分区准则和优化调整方法;最终推荐一种块石料半包砂砾石料的坝体分区型式,提高了高混凝土面板砂砾石坝的综合安全性。

孤岛煤柱巷道围岩大变形破坏机理研究

针对刘庄矿120502孤岛煤柱巷道回采期间出现的大变形破坏情况,通过现场监测、理论分析、数值模拟等方法研究巷道围岩塑性区发育特征,从塑性区的形成和演变过程阐释孤岛煤柱巷道大变形破坏机理。结果表明:巷道围岩塑性区发育形态受双向主应力比影响,当主应力比较大时,塑性区形态呈蝶形分布且成蝶前后对主应力比敏感程度不同;塑性区形态成蝶后蝶叶旋转角度与主应力方向相关;相对于普通工作面,孤岛工作面回采期间受采空区侧向及工作面超前应力集中的叠加影响,主应力比增大,在巷道周围形成高偏应力环境,且最大主应力向采空区一侧偏转,使蝶叶旋转至巷道顶底和两帮位置,造成巷道围岩大变形破坏。

采空区侧煤体的应力与瓦斯分布规律研究

掌握采空区侧煤体的应力与瓦斯分布,对预测矿井沿空掘巷煤与瓦斯突出危险性以及防治突出事故具有重要指导意义。以孟津煤矿为例,通过现场实测采空区侧煤体的应力和瓦斯相对涌出量等参数,结合数值模拟得出采空区侧煤体的应力、渗透率和瓦斯分布规律及其之间的关联性。结果表明:邻近采空区煤体的应力与瓦斯相对涌出量显著降低,且采空区形成时间越久,瓦斯有效排放范围越大,煤与瓦斯突出危险性越低;采空区侧煤体的应力和瓦斯分布存在明显正相关性,煤体的卸压和塑性破坏造成煤体渗透率显著增大;采空区侧煤体的极限平衡区宽度越大,渗透率出现增大的煤体范围越大,进而引起瓦斯有效排放范围越大。12050采空区侧煤体卸压区、极限平衡区和瓦斯有效排放范围分别为19.3,23.4,28.7 m,该范围内突出预测指标均低于临界值,为12070工作面沿空掘巷防治煤与瓦斯突出提供了理论指导。