Analysis of the Harmfulness of Water-Inrush from Coal Seam Floor Based on Seepage Instability Theory

A theory of seepage instability was used to estimate the harmfulness of water-inrush from a coal seam floor in a particular coal mine of the Mining Group,Xuzhou. Based on the stratum column chart in this coal mine,the distribu-tion of stress in mining floors when the long-wall mining was respectively pushed along to 100 m and to 150 m was simulated by using the numerical software (RFPA2D). The permeability parameters of the coal seam floor are described given the relationship between permeability parameters. Strain and the water-inrush-indices were calculated. The wa-ter-inrush-index was 67.2% when the working face was pushed to 100 m,showing that water-inrush is possible and it was 1630% when the working face was pushed to 150 m,showing that water-inrush is quite probable. The results show that as long-wall mining is pushed along,the failure zone is enlarged,the strain increased,and fissures developed cor-respondingly,resulting in the formation of water-inrush channels. Accompanied by the failure of the strata,the perme-ability increased exponentially. In contrast,the non-Darcy flow β factor and the acceleration coefficient decreased ex-ponentially,while the increase in the water-inrush-index was nearly exponential and the harmfulness of water-inrush in the coal mine increased accordingly.

Determining areas in an inclined coal seam floor prone to water-inrush by micro-seismic monitoring

The failure depth of the coal seam floor is one important consideration that must be kept in mind when mining is carried out above a confined aquifer.Determining the floor failure depth is the essential precondition for predicting the water-resisting ability of the floor.We have used a high-precision microseismic monitoring technique to overcome the limited amount of data available from field measurements. The failure depth of a coal seam floor,especially an inclined coal seam floor,may be more accurately estimated by monitoring the continuous,dynamic failure of the floor.The monitoring results indicate the failure depth of the coal seam floor near the workface conveyance roadway（the lower crossheading） is deeper and that the failure range is wider here compared to the coal seam floor near the return airway（the upper crossheading）.The results of micro-seismic monitoring show that the dangerous area for water-inrush from the coal seam floor may be identified.This provides an important field measurement that helps ensure safe and highly efficient mining of the inclined coal seam above the confined aquifer at the Taoyuan Coal Mine.

Comprehensive evaluation of water-inrush risk from coal floors

Lower groups of coal seams are presently being mined from water-inrush from coal floors in order to have safe production in the Yanzhou coal mining area. We need to evaluate the risk in the lower groups of coal seams in mines. Based on a systematic collection of hydrogeological data and some data from mined working faces in these lower groups, we evaluated the factors affecting water-inrush from coal floors of the area by a method of dimensionless analysis. We obtained the order of the factors affecting water-inrush from coal floors and recalculated data on depths of destroyed floors by multiple linear regression analysis and obtained new empirical formulas. We also analyzed the water-inrush coefficient of mined working faces of the lower groups of coal seams and improved the evaluation standard of the water-inrush coefficient method. Finally, we made a comprehensive evaluation of water-inrush risks from coal floors by using the water-inrush coefficient method and a fuzzy clustering method. The evaluation results provide a solid foundation for preventing and controlling the damage caused by water of an Ordovician limestone aquifer in the lower group of coal seams in the mines of Yanzhou. It provides also important guidelines for lower groups of coal seams in other coal mines.

Study on the non-linear forecast method for water inrush from coal seam floor based on wavelet neural network

Directing at the non-linear dynamic characteristics of water inrush from coal seam floor and by the analysis of the shortages of current forecast methods for water inrush from coal seam floor, a new forecast method was raised based on wavelet neural network （WNN） that was a model combining wavelet function with artificial neural network. Firstly basic principle of WNN was described, then a forecast model for water inrush from coal seam floor based on WNN was established and analyzed, finally an example of forecasting the quantity of water inrush from coal floor was illustrated to verify the feasibility and superiority of this method. Conclusions show that the forecast result based on WNN is more precise and that using WNN model to forecast the quantity of water inrush from coal seam floor is feasible and practical.

Numerical simulation of the floor water-inrush in working face influenced by fault structure

Used numerical simulation method to study the floor water-inrush mechanism in working face which was influenced by fault structure, and set up many kinds of models and performs numerical calculation by fully using large finite element soft-ANSYS and element birth-death method. The results show that the more high the underground water pressure, the more big the floor displacement and possibility of water-inrush; the floor which has fault structure is more prone to water-inrush than the floor which not has fault structure, the floor which has multi-groups cracks is more prone to water-inrush than the floor which has single-group cracks. The numerical simulation result forecasts the water-inrush in working face preferably.

RESEARCH ON DEEP COAL SEAM MINING FLOOR STARTA WATER BURSTING INFLUENCED FACTORS BASED ON ANALYTIC HIERACHY PROCESS

Deep coal seam mining floor strata water bursting is a complicate nonlinear system, whose factors are coupling and influencing themselves. It built the analytic structure model for deep coal seam mining floor strata water bursting, the judgment matrix was found by the expert scoring method, the contribution weights of the influenced factors were given out by the equation analytic process. The thirteen controlling factors and five main controlling factors were put award by analyzing weights, so the result was basically conform to the field practice. The expert scoring method and analytic process can convert the objective fact to the subjective cognition, so it is a method that can turn the qualitative into the quantitative. This can be relative objectively and precisely to study the question of many factors and grey box.

Mechanism of water-inrush from fault induced by mining near the working face

Adopted the fractal tree-like failure model, and established the renormalization group transform function of fractured fault, and investigated the mechanism of water-inrush from fault, and found out the critical probability of water-inrush from fault caused by fault fracture. The results indicate： when the failure rate P is less than the critical failure rate Pc=0.206 3, the failure of the system is just partial. When P is more than the critical failure rate Pc=0.206 3, the random distributed crannies concentrate to certain domain of attraction （such as the maximum shear stress face in the fault） gradually. The process will continue until the crannies run-through, forming conductivity channel, and cause water-inrush from fault.

Investigation into the deformation of a large span roadway in soft seams and its support technology

We investigated the deformation failure mechanism of surrounding rock from the aspect of engineering support for a roadway in seams with soft roofs and soft floors and observed the large displacement of the roadway in these soft seams.The result shows that the deformation area is quite large,and settlement of the roof is evident and displacement of the side walls is also obvious.We considered rock bolt-cable coupling for roadway support in seams with soft roofs and floors,in which the cable should be fixed at key positions.As well,we designed an optimal scheme to support a roadway in soft seams of the Shizuishan Second Mine in Ningxia,China.Field monitoring results show that bolt-cable coupling support has achieved the aims of roadway stability control and minimizes deformation.

Roadway failure and support in a coal seam underlying a previously mined coal seam

The influence of an upper,mined coal seam on the stability of rock surrounding a roadway in a lower coal seam is examined.The technical problems of roadway control are discussed based on the geological conditions existing in the Liyazhuang Mine No.2 coal seam.The stress distribution and floor failure in the lower works after mining the upper coal is studied through numerical simulations.The failure mechanism of the roof and walls of a roadway located in the lower coal seam is described.The predicted deformation and failure of the roadway for different distances between the two coal seams are used to design two ways of supporting the lower structure.One is a combined support consisting of anchors with a joist steel tent and a combined anchor truss.A field test of the design was performed to good effect.The results have significance for the design of supports for roadways located in similar conditions.

煤层采动底板突水物理模拟试验研究进展与展望

【目的】底板突水受特定地质构造、水-岩-应力及采掘扰动等因素叠加作用影响,具有复杂性、隐蔽性、突发性等特点。【方法】物理模拟试验能较好地还原底板岩层与承压水赋存环境、直观展现采动底板裂隙扩展及突水路径演化全过程、实时获取灾变各阶段多源数据信息,因而在底板突水研究方面具有独特优势。【结果和结论】对底板突水经典理论、标准规范、模拟试验及工程实践等方面的研究成果进行了回顾,重点梳理了试验加载装置及水压模拟方式、相似材料研制及其特性指标、监测技术及其观测系统设计3个方面的研究进展,其中在模拟水-岩-应力耦合环境下的三维模型底板突水全过程信息捕捉方面有较大突破。面对数智化研究大背景,分析当前底板突水物理模拟试验领域存在的不足,并据此指出未来应重点关注大型三维底板突水综合试验平台研制、基于标准化的多特性相似材料配比数据库建立、多相多场多维耦合监测预警系统构建、人工智能等数智化技术融合应用研究等发展方向。提出的思考有助于从装置、材料、技术等方面提升未来物理模拟试验水平,从而更好支撑煤矿底板水害数智化防治基础研究工作高质量发展。

特厚煤层底板断层破坏与顶板垮断联动效应的CFDEM模拟研究

特厚煤层采场空间大、覆岩扰动范围广,顶板垮断产生的强扰动加卸荷载易导致底板断层破坏加剧。通过数值模拟研究特厚煤层底板断层突水与顶板垮断联动效应机理规律是开展水害防治的基础,关键在于掌握加卸载下岩体渐进破坏与裂隙流耦合特征。构建加卸载下拉、剪损伤演化方程,结合有效偏/球应力为基本变量的屈服准则与塑性势函数,得到完整岩块的塑性损伤本构;建立拉/剪、混合型加卸载过程中塑性位移与强度劣化关系,以平方拉剪应力与B-K准则为初始、完全断裂准则,形成非贯通裂隙断裂本构;提出岩块分离、压缩、剪切判据,结合实验数据建立离散块体间挤压、剪切摩擦本构与剪胀方程。基于质量/动量守恒、状态方程,并结合流体体积与浸没边界方法,形成裂隙岩体气−水二相流模拟理论。由此形成CFDEM数值计算程序,并将加卸载下塑性损伤、断裂、挤压/摩擦、流体属性分别赋予实体单元(岩块)、黏聚力单元(非贯通裂隙)、接触对(贯通裂隙)、欧拉单元(水和气)。根据宁武煤田北部矿区工程地质条件,建立特厚煤层底板断层突水与顶板垮断联动效应数值计算模型。结果表明:①CFDEM耦合程序及相应的理论模型可数值实现特厚煤层覆岩及底板断层从(准)连续体到离散体转化,以及地下水在裂隙中运移;②模拟条件下特厚煤层含断层底板的采动裂隙包络线呈w形,最深处超过55 m位于断层及其上盘,最浅处23 m位于断层下盘,而无构造底板处的破坏深度为24~36 m,已导通奥灰含水层;③特厚煤层底板普遍出现二次破坏现象。表现为无构造底板在超前工作面处破坏深度为24.0~29.3 m,但在采空区内普遍增加至31.5~36.0 m;断层及其上盘在超前工作面处裂隙总开度为0.34~0.86 m,但在采空区内迅速增加至3.6 m,形成突水优势通道。④底板断层突水与顶板垮断联动效应的根源在于覆岩高位关键岩层垮断失稳、砌体梁下沉与二次断裂,并导致底板二次破坏,突水风险加剧。

新集矿区深部1煤层底板奥灰岩溶突水危险性评价

奥灰岩溶裂隙含水层是影响华北型煤矿深部开采的重要水害,在水-岩相互作用下奥灰含水层易导致煤层底板突水。为进一步认识奥灰岩溶突水问题,文章以新集矿区深部1煤层开采为例,利用矿区近些年最新积累的奥灰钻孔资料,选取断层强度指数、断层交叉点与尖灭点、含水层水压、富水性、隔水层等效厚度、脆塑比7个因素作为奥灰岩溶突水的主控因素,并结合层次分析法(analytic hierarchy process,AHP)确定各主控因素影响权重。运用地理信息系统(geographic information system,GIS)空间分析功能建立各主控因素专题图,通过对专题栅格图归一化处理,将各主控因素按照权重进行空间复合叠加,最终获得1煤层底板奥灰岩溶突水危险性评价分区结果。将评价结果与突水系数法计算结果对比分析可知,基于GIS的煤层底板突水危险性评价方法更符合矿区实际地质情况,可以为矿区深部煤层开采与水害防治工作提供参考依据。

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.

基于孔间直流电透视的煤层底板采动破坏电阻率时移变化规律与机理

煤层采动过程中,底板应力状态的改变会产生变形与破坏,而不同煤层采动过程中底板破坏具有一定的规律。目前基于直流电阻率法的煤层底板水害监测主要集中于底板变形与破坏的电阻率响应特征上。为了研究工作面回采过程中煤层底板的电性时移变化特征,采用孔间直流电透视观测系统和时移电阻率反射系数法,通过数值模拟和现场试验揭示了煤层底板采动破坏电阻率时移规律。首先,针对典型地电模型,对比单独反演和时移电阻率变化率的结果,验证了孔间直流电透视时移方法的可靠性。然后,针对煤层底板采动破坏,分析了采动过程中底板承压水导升与底板破坏带的电性响应规律与特征,并讨论了时移电阻率反射系数确定煤层底板破坏深度的可行性,为野外施工提供理论依据。最后,通过现场监测试验,获得工作面回采过程中煤层底板的电性变化特征,并采用时移电阻率反射系数R确定了工作面底板岩层的破坏深度为15 m。结果表明:利用孔间直流电透视法获得的煤层底板采动破坏电阻率时移特征可在一定程度上消除了监测数据中的地层因素和随机噪声影响,且时移电阻率反射系数可用来确定煤层底板破坏深度。该方法将探测目标从单一的研究地质异常转换到对煤层采动过程中工作面底板破坏的全生命周期动态监测,进而实现了工作面底板结构破坏的精细刻画。

基于微震监测技术的煤矿底板突水预警研究

煤矿底板突水是矿山生产中的主要灾害之一,其破坏性极大,因此,研究有效的突水预警技术具有重要意义。以董家河煤矿22517工作面为例,构建了微震监测系统,并对底板进行突水预警。监测数据显示,该煤矿的底板微震事件总共有191个,其中能量超过1000 J的微震事件仅为18个,占全部微震事件的9.63%,同时,该系统检测到的底板破坏深度约为11.01 m,与底板钻孔声波仪测试计算的数据仅相差0.22 m。这些数据可以说明研究所提出的微震监测技术能够有效预测煤矿底板的突水事故,起到了良好的预警作用,为煤矿开采作业的水害风险防范提供了可靠的技术支持。

煤层底板含水层区域注浆改造浆液扩散范围现场示踪试验

近年来,为解放底板高承压灰岩水上煤炭资源,华北煤田普遍采用地面定向钻技术,对太原组薄层灰岩进行区域性注浆加固改造(习称“底板区域治理”),以全面封堵灰岩岩溶裂隙并阻断垂向导水通道。该技术中,与浆液扩散范围(半径)密切相关的“水平分支孔”孔间距设计问题,一直备受学界和业界的广泛关注。皖北矿区底板区域注浆工程量大,特别是深部资源开采,将有数十亿元的注浆工程,有必要查清浆液扩散范围真实数据。为此,以皖北矿区恒源煤矿为研究基地,依托Ⅱ63采区底板区域治理工程,设计并实施浆液扩散范围示踪试验,在中间的水平分支孔(Z8-7)投放荧光剂(示踪剂),在两侧的水平分支孔(Z8-6、Z8-8)以及交叉分支检测孔(Z8JC)取岩屑样鉴别荧光水泥,以获得浆液扩散范围,进而在浆液扩散影响因素分析基础上,构建恒源煤矿底板区域注浆治理浆液扩散范围计算公式。结果表明:①综合岩屑现场及室内鉴别结果分析,获得恒源煤矿Ⅱ63采区底板区域注浆浆液扩散范围为38.3~44.0 m,且水泥分布密集区在水平分支孔浆液扩散范围30 m以内,该区域内注浆效果最佳。②通过现场岩屑快速鉴别与室内岩屑精准鉴别,取得的浆液扩散范围基本一致,证明了荧光示踪浆液扩散范围的有效性。③通过对比分析,认为在计算参数、边界约束等符合实际注浆工况条件下,浆液扩散范围理论计算和数值模拟结果,与现场示踪试验实测结果较为接近。④利用示踪试验过程中的压水试验及注浆参数、钻遇构造及水文地质响应等数据,考虑重力、构造、地下水径流等因素影响,借助SPSS非线性拟合软件,得到恒源煤矿Ⅱ63采区底板区域注浆浆液扩散范围计算公式。⑤基于恒源煤矿受注层实际地质、水文地质条件,利用拟合的浆液扩散范围计算公式得出Ⅱ63采区Z8场地浆液扩散范围为37.8~42.9 m,与浆液扩散范围示踪试验实测结果相近,计算公式可在类似条件下推广应用。本次煤矿底板区域注浆浆液扩散范围现场示踪工程试验,不仅取得了浆液扩散范围的真实数据,而且阐明了浆液扩散与多种地质、水文地质因素之间的内在联系,揭示了超深、超长定向钻注浆浆液扩散机理,构建了浆液扩散范围计算公式,为类似条件下底板区域治理工程水平分支孔孔间距的合理设计提供了参考依据。

近距离煤层底板应力分布规律及巷道布置研究

为探究上煤层遗留煤柱对底板的应力影响及下煤层回采巷道的合理布置,以唐山沟煤矿为研究对象,运用理论分析和数值模拟等方法并综合多种影响因素构建了上煤层遗留煤柱与铰接岩块的协同承载结构模型和底板应力传递计算模型,对上煤层遗留煤柱下底板应力及影响因素展开研究。结果表明:上煤层遗留煤柱对底板的应力影响以垂直应力为主,影响程度随底板深度的增加而降低;遗留煤柱下底板应力增高区呈椭球形,对底板应力增高区的影响因素展开分析,得到了不同因素对应力增高区范围影响的量化关系,其中煤柱峰值应力对底板应力增高区分布起决定性作用;根据底板应力分布特征并结合理论计算及数值模拟结果,确定唐山沟煤矿8煤遗留煤柱与11^(-1)煤回采巷道合理错距值应为20~25 m。该研究揭示了上煤层遗留煤柱下底板应力传递机理,明确了底板应力增高区的分布及影响因素,并得到了巷道-煤柱合理错距值的确定方法,可为下煤层回采巷道的合理布置提供理论依据。

底板突水危险性评价研究进展

回顾了煤层底板突水危险性评价的发展历程,提出其危险性评价的体系:指标(指标体系的建立)—方法(评价方法的选取)—工具(处理工具的革新),并对3个环节进行总结。指出指标体系的发展不再是因素集的扩充,而是因素与因素之间非线性关系的处理以及对以开采条件及地质条件为两大基本要素集的化繁为简;将现有方法依据处理数据的逻辑分为3类:以数据的基础信息为基准,将原始数据对评价对象所产生的大小、高低、优劣性影响进行考量、排序及综合形成评价结果的第一类方法;对数据列进行人工评判、加工分析、拓展和延伸,挖掘数据的潜在信息,并形成最终评价结果的第2类方法;整理具有相同指标的数据集,通过数据信息处理技术发现数据间的共有信息,从而获得最终评价结果的第3类方法。指出未来评价方法的发展方向一方面是对突水系数法的传承,修正其在厚、巨厚、极薄隔水层的不良表现,另一方面是对机器学习新型方法的创新,对其本身及组合模型进行开发与应用。提出了处理工具所需实现的三大目标:矿井立体化模型的建立、评价结果的动态化演示、“定位、定量、定概率”三定指标的实现。分别探讨了三者面临的问题并阐述具体解决手段。在上述基础上,总体阐明了煤层底板突水危险性评价体系各环节的研究展望。

中组煤上覆煤层开采冲击荷载扰动下底板破坏深度研究

为研究近距离煤层中上煤层开采冲击荷载扰动下底板破坏发育情况,采用理论计算、数值模拟、现场观测等方法观察近距离煤层开采扰动下底板破坏范围,以半无限平面体理论结合摩尔-库伦破坏准则及屈服条件为基础,分析了顶板垮落冲击动荷载及静载作用下工作面底板下任意一点应力状态,计算得出底板破坏深度17.32m;对近距离煤层开采进行数值模拟,走向方向推进25m后,原位塑性区发育基本稳定,底板塑性区在逐步回采过程中发育呈现以煤壁下方塑性区“先垂直后水平扩散”特点,底板最大破坏深度16.12m;采用钻孔呈像法对工作面采动前后底板破坏进行观测,工作面下方底板破坏深度范围在16.85m附近,分析得出中组煤层61煤层开采扰动对下煤层62煤层、63煤层顶板稳定性造成破坏,验证了冲击荷载理论模型的可靠性,开采62煤层、63煤层需加强顶板支护。研究结果为近距离煤层开采扰动下底板破坏对下煤层影响范围提供参考。

静动载作用下巷道底板突水过程及关键致灾因素模拟

针对静动载联合作用下巷道底板突水问题,结合工程实例采用数值模拟软件FLAC^(3D)构建模型,从应力场、位移场及破坏区共同耦合作用角度出发,分析了动静载叠加作用下的底板突水通道形成过程及作用机制,探讨了关键致灾因素对巷道底板突水的作用程度。研究结果表明:静载与动载应力场叠加,导致底板应力集中程度和范围在深度方向扩大;巷道底板受动载作用后破坏深度和范围加大,有效隔水层厚度减少,底板突水的风险性增加;巷道底板突水通道的形成主要与动载幅值、持时及承压水水压有关,其中动载幅值对突水作用程度较大,当动载幅值超过临界值时,巷道底板破坏深度显著增加;持时的增大使得动载作用的时间特征减弱,更加接近于静载作用,巷道底板发生拉伸破坏的可能性降低;承压水水压的增大,使得作用在巷道底板下岩层的有效应力减小,岩体强度降低,底板破坏深度增加。采用单因素分析法对比发现,各致灾因素对底板突水的影响程度依次为:动载幅值>动载持时>承压水水压。