Evaluation of roof cutting by directionally single cracking technique in automatic roadway formation for thick coal seam mining

Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery,reduce roadway excavation and improve mining safety.In this method,roof cutting is the key process for stress relief,which significantly affects the stability of the formed roadway.This paper presents a directionally single cracking(DSC)technique for roof cutting with considerations of rock properties.The mechanism of the DSC technique was investi-gated by explicit finite element analyses.The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment.On this basis,the optimized DSC technique was tested in the field.The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock,thus,achieve directionally single cracking on the roadway roof.The DsC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway.Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting.

Overburden fracture evolution laws and water-controlling technologies in mining very thick coal seam under water-rich roof

Considering the danger of water inrush in mining very thick coal seam under water-rich roof in Majialiang Coal Mine,the universal discrete element(UDEC)software was used to simulate the overburden fracture evolution laws when mining 4#coal seam.Besides,this study researched on the influence of face advancing length,speed and mining height on the height of the water flowing fractured zones(HWFFZ),and analyzed the correlation of face advancing length and change rules of aquifer water levels and goaf water inflow.Based on those mentioned above,this research proposed the following water-controlling technologies:draining the roof water before mining,draining goaf water,reasonable advancing speed and mining thickness.These water-controlling technologies were successfully used in the feld,thus ensured safely mining the very thick coal seam under water-rich roof.

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.

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.

Fracture mechanics model of fully mechanized top coal caving of shallow coal seams and its application

Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using the fracture mechanics theory. The relationships between the fracture length of the roof and the working resistance of the supports were discovered, and the correlations between the load on the overlying strata and the ratio of the crack's length to the thickness of the roof were obtained. Using a working face of Jindi Coal Mine, Xing county Shanxi province as an example, the relationships between the fracture length of the roof and the working resistance of the supports were analysed in detail. The results give a design basis in hydraulic top coal caving supports, which could provide useful references in the practical application. On-site experiment proves that the periodic weighting step interval of the caving face is 15–16 m, which is basically consistent with the theoretical analysis results, and indicates that the mechanized caving hydraulic support is capable of meeting the support requirements in the mining of a super-thick but shallowly buried coal seam.

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.

The relation between modes of lithologic association and interlayer-gliding structures in coal mine

As a case study of the Panji No.1 Coal Mine in Anhui Province, based on thesite measured and statistical data, summarized the lithologic associations, characteristicsand distribution laws of interlayer-gliding structures and tectonic coal in the No.11-2 coalseams.The results show that 9 modes of lithologic association can form interlayer-glidingstructures.It is more easy for rock slip to occur when the lithologic associations are mainroof + coal seam + immediate floor type, compound roof+immediate roof + coal seam +immediate floor type and immediate roof + coal seam + immediate floor type.Lithologicassociations of roof and floor are the precondition to the formation of interlayer-glidingstructures.

A case study of multi-seam coal mine entry stability analysis with strength reduction method

In this paper,the advantage of using numerical models with the strength reduction method(SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated.A coal mine under variable topography from the Central Appalachian region is used as a case study.At this mine,unexpected roof conditions were encountered during development below previously mined panels.Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-and-pillar panels.Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries.The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations.The SRM-calculated stability factors were compared with observations made during the site visits,and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case.It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines.

Controlling Effects of Surrounding Rock to Coal Seam Gas Occurrence

Surrounding rock of coal seam was one of the important factors to gas occurrence. The coal seam gas occurrence was studied by the index of roof strata thickness or sand content rate;we found that there were certain shortcomings. In order to reasonably evaluate the influence of coal seam surrounding rock on gas occurrence in Panji mining area, we quantitatively evaluated the effect of coal seam surrounding rock on gas occurrence by influence coefficient of roof strata thickness, and built six mathematical models of the variational gas content in the mining area which is divided into six gas geological units. The results shows that the coal seam gas content is mainly influenced by 20 mroof strata in each gas geological unit, the gas content presents the tendency of increase, and with the influence coefficient of strata thickness increases, they exist a significant linear relationship.

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。

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。

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。

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。

下峪口煤矿23306下工作面回采巷道合理错距研究

近距离煤层采空区下回采巷道合理错距的确定对巷道安全高效掘进意义重大。以下峪口煤矿为工程背景,采用理论分析及现场试验的方法,对23306下进顺采空区下回采巷道合理错距进行研究。得出下峪口煤矿23306下进风顺槽合理留设错距为22 m,根据23306下进顺错距留设情况提出支护方案并根据巷道顶底板及两帮位移变化情况进行监测验证,监测发现巷道各测点顶底板及两帮的移近量均小于450 mm,大多时间内两帮的移近量小于350 mm,煤柱帮的深基点和浅基点的位移变化量基本一致,且随着巷道的掘进,未出现较大变形,说明采用22 m错距可实现围岩变形稳定,研究可为类似条件巷道安全高效生产提供经验和参考。

近浅埋多层厚硬顶板大采高综放工作面矿压显现规律研究

针对榆神矿区近浅埋多层厚硬顶板条件下,“大周期”来压支架立柱下缩量大、煤柱应力集中系数高、稳定性差等强矿压问题,采用了数值计算、微震和煤体应力监测等技术手段,对覆岩破断运动及工作面来压规律进行了分析研究,结果表明:覆岩破断运动上,多层厚硬顶板较大的“垂向离层空间”和“自下而上”的顺次交替垮落孕育了顶板“高+低层位组合破断”的时空基础;“高低层位顶板组合破断”是“大周期”来压增强的关键诱因;同时,煤柱应力的时空演化受控于多层厚硬顶板的破断垮落。矿压显现上,工作面“大周期”立柱下缩量平均可达945 mm,持续距离12.10 m,并可由2~5次连续强来压组成;巷道煤柱应力集中系数达到1.80~2.30,影响范围为工作面前方126 m至后方471.3 m,具有明显的“高强度、大范围、长上升期”特点。针对该条件下的强矿压防治,分别提出了“弱化低位顶板、优化破断结构”和“弱化高位顶板、改变破断次序”的技术思路,并取得的了较好的应用效果。

深孔聚能预裂爆破切顶卸压机理与应用

为解决悬顶导致的煤柱及邻近巷道高应力和大变形问题,结合工作面顶板地质条件,提出深孔聚能预裂爆破切顶卸压专项方案,采用数值模拟及现场试验对卸压效果开展综合研究。研究结果表明,煤层顶板在切顶后垂直应力减幅为21.62%,预裂切顶措施可显著降低煤柱及邻近巷道围岩应力水平。试验发现,炮孔内轴向贯穿裂缝明显,可实现采空区顶板及时垮落。顶底板在切顶后累计位移量减幅达59.27%,巷道两帮及顶底板移近变形得到有效控制,煤柱垂直应力增量显著降低。实践证明,采用深孔聚能预裂爆破切顶卸压效果显著,可大幅提高作业效率,为类似矿压防治工程提供借鉴。

大采深高承压水条件下煤层底板突水问题及解决对策

在当前煤矿普遍面临大采深、底板高承压水、高地应力等采掘条件下,正确评价煤层底板承压水突水危险是做好防治水工作的基础。以河南省受底板灰岩承压水突水威胁的大水矿井为例,就底板破坏深度计算、突水系数计算及临界值、脆弱性指数法、不同水文地质单元的“双层水位”效应等问题进行了剖析。分析表明:在大采深和高地应力开采条件下,底板破坏深度较现有用经验公式计算得到的值偏大,一些矿井突水系数虽小于全国临界值,但回采过程中却发生了突水,脆弱性指数法有待于规范化。此外,井田范围内水文地质条件存在着时空变化,甚至会出现“双层水位”等现象。鉴于此,提出了建立大采深和高地应力开采条件下的底板破坏深度计算模型、确定矿区或矿井范围的临界突水系数值、规范脆弱性指数评价方法、查明水文地质条件的时空变化和不同单元的水动力参数、制定同各单元水文地质条件相适应的防治水措施等各项对策。

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。

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。