Study of roof stability of the end of working face in upward longwall top coal

Low recovery of longwall top coal caving (LTCC) remains one of the most difficult engineering problems in this mining method and impedes its application. The top coal left in the gob at face end accounts for a large portion of the total coal loss, and the instability of the leftover triangle coal at face end has long been a threat to the safety of miners and the mining equipment. In this paper, based on the engineering background of Ruilong mine, we explore the stability of the roof at the end of the face by using theoretical analysis, numerical simulation, and field measurement. Results reveal that in the inclined longwall top coal caving face, the immediate roof forms an “arch” structure, and the basic roof forms a “masonry beam” structure after the roof collapses; working resistance of the support calculated by the method of ultimate bearing capacity was adequate to meet the requirement of roof load; roof load of coal pillar was related to the length of key block and fracture position; and increasing the size of coal pillar could ensure the stability of both coal pillar and roof.     

综采工作面回撤巷强矿压显现机理及控制技术

为保障厚煤层综采工作面回撤巷的安全使用,以鄂尔多斯纳林河二号井31102工作面回撤巷强矿压显现为背景,通过现场监测与理论分析相结合的方法,对厚煤层综采工作面开采过程中回撤巷强矿压显现进行研究。结果表明:厚煤层综采工作面回撤巷强矿压显现,主要为工作面采动引起的超前支承压力、相邻采空悬顶引起的双向支承应力,以及回撤巷开掘引起的静载三者耦合作用的结果。根据强矿压发生机理,提出回撤巷道及相邻巷道钻孔卸压和补强支护相结合的控制方案,使其处于“强支、强卸”状态。在相邻31103工作面回撤巷实施强矿压控制技术,通过现场观测和数据分析,表明强矿压控制技术效果良好,可有效保障回撤巷的安全使用。      

Numerical simulation on tendency mining fracture evolution characteristics of overlying strata and coal seams above working face with large inclination angle and mining depth

In order to master the tendency mining-fracture-evolution characteristics of overlying strata and coal seams above working face with large inclination angle and mining depth in mining process, the 1221 working face in Zhao mine is selected as the engineering background and a mathematical model is established. The displacement variation, stress and strain of overlying strata and coal seams are simulated by using ANSYS software. In the mining process, the movement characteristics, displacement variation laws and fracture evolution characteristics of overlying strata and coal seams above working face with large inclination angle and mining depth along inclination direction are discussed. Simulation results show that with the advance of working face, the fracture development of overlying strata and coal seams is larger and larger; the area of gob is gradually expanding and the transverse stress of overlying strata and coal seams is also expanding. Stress contour of overlying strata and coal seams at both ends of gob becomes denser and denser; the activity of the overlying strata and coal seams near the up-roadway side of the gob is violent. The pressure relief zone is formed in the upper part of the strata and the roof above the gob. Large inclination angle of coal seam results in larger supporting pressure in the underside of the gob and smaller supporting pressure in the upper side of the gob. Along the inclination direction of the working face, the pressure relief zone is mainly concentrated in the outlet roadway of the working face; the fracture development and strata separation are obvious, which offer good passage for gas flow and migration.     

Hydraulic fracturing stress transfer methods to control the strong strata behaviours in gob-side gateroads of longwall mines

With hard roof conditions and the influence of side and front abutment pressures, pressure bump and large deformations periodically occur in the advanced support area of longwall face gob-side gateroads. To control the strong strata behaviours in gob-side gateroads, “directional hydraulic fracturing, to cut off the roof hanging over the adjacent gob area, and pre-fracturing of the roof, located behind the working face being extracted,” are performed. The directional initiation of hydraulic fracturing is controlled by pre-slotting, and this action guides the propagation of hydraulic fractures in three-dimensional space. The oriented fractures meet engineering requirements by cooperating with both the in situ ground stresses and the mining-induced stresses, as well as the technology of hydraulic fracturing. In field applications, hydraulic fracturing has proven to be a viable option for weakening hard roofs, destressing the side and front abutment pressures at the mining face and also transferring in situ and mining-induced stresses. Successful field tests in the Tongxin coal mine, Datong district, as well as other coal mines, show that hydraulic fracturing in both a hanging roof over an adjacent gob area and in the gob area behind the advancing working face controls the behaviour of strong strata material on the gob-side of gateroads in longwall mining and also guarantees safe extraction at the working face.     

急倾斜煤层工作面下端头区巷旁充填技术研究

采用理论分析与实践、实测相结合的方法,对急倾斜煤层工作面下端头区沿空留巷技术理论及系统工艺问题进行探讨,弄清了充填体受力的影响因素,提出了急倾斜煤层巷旁充填工艺系统。研究表明,急倾斜煤层巷旁充填体承载受采空区矸石有效充填长度、煤层赋存倾角、充填体筑设宽度以及煤岩赋存厚度的影响,受顶底板锚索安设的影响较小;单轴压缩条件下矸石碎块的承载变形规律呈阶段特征,且每一阶段内的应力-应变近似呈线性关系;充填体的承载与变形随着距离工作面位置的不同具有阶段特征,距离工作面煤壁越远,充填体承载变形率越小;以七台河新强煤矿生产实际为背景,现场实践证明,急倾斜煤层矸石混凝土充填工艺系统实施方便、操作简单,沿空留巷整体效果较为明显。     

坚硬顶板超前区域治理技术在神东布尔台煤矿的应用

坚硬顶板是岩层控制的一大难题,高位坚硬岩层的破断失稳经常会诱发强矿压灾害,严重威胁矿井的安全生产,坚硬顶板的治理是煤矿安全生产的重大难题之一。针对神东矿区布尔台煤矿煤层顶板厚度大、硬度高、垮落难等问题,分析定向长钻孔分段水力压裂的压裂机理和技术优势,基于关键层理论确定了钻孔布置层位,采用拟三维裂缝模型对压裂注入时间和注入流速对裂缝扩展的影响进行分析计算,确定布尔台煤矿42108工作面顶板压裂钻孔布置方式,沿工作面倾向方向平行布孔3个,裂缝半长41 m,压裂控制区域覆盖了整个工作面。实践表明:42108工作面在实施了坚硬顶板分段水力压裂弱化后,工作面正常支架循环末阻力同比下降3.33%;周期来压期间,支架循环末阻力同比下降6.81%;动载系数平均降低了10.88%;强矿压显现减弱,保证工作面安全回采。      

上覆硬厚岩层破断运动及断顶控制

硬厚覆岩的破断与结构将发生显著的变化。针对汝箕沟煤矿二2煤层上覆厚层石英砂岩条件,采用现场实测、数值模拟、理论分析及现场试验等方法,研究了硬厚覆岩裂隙发育特征、破断运动、矿压显现特征及断顶控制技术,为硬厚覆岩工作面灾害防治提供了依据。研究表明,硬厚石英砂岩的微观结构致密完整,呈现大面积悬空、大步距破断运动,引起强烈的支架动载,甚至导致工作面风流逆转、沟通上部采空区隐形火区;硬厚岩层破断运移后产生明显的离层空间,并在开切眼上部和工作面上部及采空区中部形成覆岩主裂隙带,且发育高度大于经验计算数值,甚至与上方采空区沟通诱发灾害;实施开切眼深孔断顶爆破及降低工作面采高,有效缩短了硬厚岩层的初次破断步距,降低了支架动载及主裂隙带高度。     

Pressure-Relief Mining of the Working Face Under the Coal Pillar in the Close Distance Coal Seams

Intensive strata behaviors are generated when the No. 8707 working face of the 8# coal seam in a coal mine is advanced by way of the pillars left over of the upper part of 7# close distance coal seam. The theoretical analysis, numerical simulation and filed measurement were utilized to obtain the rule of the stress change when the 8707 working face of the 8# coal seam passes the pillars left over of the 7# coal seam. Meanwhile, a pressure-relief mining (PRM) technology was put forward. According to the research results, when the 8707 working face in the 8# coal seam was advanced to the position that was 20 m in front of the pillar left over, the abutment pressure reached the maximum for 26 MPa and the stress concentration factor was 3.25, which was likely to give rise to the rock burst. With the advance of the working face, the abutment pressure was reduced slowly. As the 8707 working face advanced 15 m away the pillar left over, the transfixed shear failure region of 45° was found in the bedrocks of the upper and lower coal seams, which was readily to give rise to the shear rupture, leading to the rock burst. Based on the aforementioned research, this research carried out the PRM by applying the hydraulic fracturing technology on the coal roof and pillar, which can ensure the safety and efficient mining of working faces.     

基于顶板水预疏放的首采工作面涌水规律

为了建立符合蒙陕接壤区煤炭开采防治水技术体系,以纳林河二号矿井首采工作面为例,开展了覆岩破坏规律、水文地质条件、涌水量预计、顶板水预疏放等研究,结果表明:应用钻探取心、钻孔冲洗液漏失量观测和钻孔彩色电视探测手段,实测得到首采工作面导水裂缝带高度为103.23 m,裂高（导水裂缝带高度）采厚比为18.8,导水裂缝带可沟通3段含水层,其中直罗组底部含水层钻孔涌水量92.0~136.0 m3/h、水压4.0~5.6 MPa,呈"水量大、水压高、分布不均"的特点,是威胁工作面回采安全的最主要含水层。回采过程中顶板水主要由静态储存量和动态补给量构成,采用"动静储量结合法"计算得到静态储存量和动态补给量分别为2.596×106 m3和417.6 m3/h。对顶板水开展分段预疏放条件下,整个工作面回采过程中采空区涌水量与推采步距呈正相关关系,随着顶板周期性滞后垮落,导水裂缝带也周期性发育至高点（直罗组底部含水层）,采空区涌水量又呈台阶式增长。最终总预疏放水量4.235×106 m3,采空区总涌水量5.313×106 m3,首采工作面总排水量为622.8 m3/h,与预计排水量596.9 m3/h相差4.2%。涌水量准确预测和顶板水提前预疏放,是实现首采工作面防治水安全的关键,可以为鄂尔多斯盆地北部深埋区提供防治水技术支撑。      

不等长工作面台阶区域覆岩运动诱冲机制及防治

针对阳城煤矿不等长工作面台阶区域发生冲击地压灾害问题,基于工作面特殊布置方式及覆岩赋存特征,采用理论分析、数值模拟和现场实测等方法,分析了台阶区域覆岩结构运动特征和围岩应力演化规律,研究了台阶区域冲击地压诱发机制。研究结果表明：1304工作面台阶区域覆岩经历了“OX-S-C”型较为复杂的结构演变,覆岩空间结构由OX向S型转换时,顶板岩层大面积破断下沉,在台阶区域形成多个悬臂梁结构,越往高位,悬臂梁长度越大;受覆岩运动和采动应力场叠加影响,煤岩体形成高应力集中区,在顶板岩层动载冲击作用下,煤岩体弹性应变能突然释放,诱发冲击地压。采用COMSOL软件对不同卸压钻孔参数下煤体应变能分布特征进行模拟研究,优化了台阶区域卸压钻孔参数。根据模拟结果,随着钻孔孔径、孔深增大及间距减小钻孔卸压效果越明显,考虑工程实际,确定孔径为150 mm、孔深为30 m、间距为1 m为合理有效的卸压钻孔参数,并应用于1302工作面台阶区域的冲击地压防治,取得了较好的防冲效果。     

高位瓦斯抽放钻孔在降低综采工作面瓦斯浓度中的应用

林南仓属于低瓦斯矿井,但存在高瓦斯区域。煤层和采空区是瓦斯的主要来源,尤以采空涌出量大,给煤矿生产和安全带来了极大隐患。通过在1129综采工作面风道施工高位瓦斯孔,把钻孔打到采空区一侧煤层顶板以上冒落裂隙带内,用钻孔进行瓦斯抽放,使采空内的瓦斯通过裂隙带沿钻孔抽出,有效降低综采工作面瓦斯浓度,保证综采工作面正常回采和安全生产。     

Measurement of the Strong Pressure Appearance Laws with Hard Roof and Full Mechanized Mining Extra Thick Coal Seam

To master the laws of strong strata behavior of Tashan coal mine under Carboniferous coal mining process, the laws of strong strata behavior in 8107 working face was measured and analyzed. It was shown that the average initial weighting step of 8107 working face was 59.4 m. The average periodic weighting step of main roof was 16.2 m. The maximum working resistance during periodic weighting was 14,711.1 kN. The maximum working resistance during non-periodic weighting was 11,339.9 kN. The average dynamic load factor K during periodic weighting was 1.31. The stress of coal column on the side of the goaf could be divided into four zones (stress stabilization zone, stress slow-increasing zone, significant—increasing stress zone, stress reduction zone) along the strike of 8107 working face. There was a peak of lateral support pressure along the trend of 8107 working face. And the peak position was biased to the side of return airway roadway. With the increase of the distance from the down-side of return airway, the pressure peak of the inner coal body along the strike of 8107 the working face increased and the peak position decreased from the coal wall. The peak stress of coal column tended to be close to the up-side of return airway. And the distance from the down-side of return airway for the peak of inner coal was larger than that for the peak of coal pillar. The peak position of abutment pressure of hard roof was in the range of 10–25 m in front of 8107 working face under full mechanized mining extra thickness coal seam conditions. The relative stress concentration coefficient of k was 1.3–6.5. The range of 10–25 m from the front of the working face to coal wall was stress reduction zone. And the influence range of abutment pressure was about 80 m. It was of great significance to the control and practice of the surrounding rock of the stope for the mining of the hard extra-thick coal seam.     

煤层顶板导水裂缝带发育高度探测研究——以黑龙江省双鸭山双阳煤矿为例

煤层顶板导水裂缝带发育高度是煤矿设计部门在留设防、隔水煤柱时必须考虑的一个重要参数,对煤矿水体下采煤、顶板防治水具有重要意义。基于双阳煤矿水文地质补充勘探项目,在8#煤层采空区上方施工两个地面钻孔,采用地面钻孔钻井液漏失量实测法、钻孔电视摄像技术及传统经验公式法相结合的方法,综合确定8#煤层顶板导水裂缝带发育高度为43.7~45.7m,为地质条件相似矿区在合理确定开采上限、留设防（隔）水煤柱等问题提供方法和数据支持。     

淮南矿区地应力条件及其对煤层顶底板稳定性的影响

通过现场地应力测量和理论分析以及数值模拟计算,研究了淮南矿区地应力分布规律,探讨了圆形硐室围岩应力分布和不同侧压下回采工作面顶板稳定性分布。研究结果表明:淮南矿区原岩应力主要表现为自重应力场,除局部构造应力集中外,不存在高构造应力;区内侧压力系数λ值一般为0.49~1.49,平均为0.92,并且与测点距地表深度有一定的趋向性,表现为在浅部λ值较大,变化范围也大,而在深部λ值渐小,变化范围也缩小;回采工作面顶底板稳定性与侧压系数λ的大小密切相关,且随侧压系数λ的增大,顶板垂直位移减小,顶板岩层易于形成结构平衡而保持稳定,但底板垂直位移量增大,且易于形成底鼓破坏。这些认识为研究区煤层顶底板岩层支护控制提供了科学依据。      

Research on Correlation Between Abutment Pressure and Gas Drainage Flow of Coal Seam

In this paper, based on the field test of No.S3012 working face of Shan Mushu Coal Mine in Sichuan Coal Group, monitoring the abutment pressure and gas drainage flow during the mining process, studying the change law of the abutment pressure and gas drainage flow of the coal seam, and using the numerical simulation method research on the evolution of abutment pressure and displacement of coal seam during the mining process. The results shown that: with the advance of coal mining face, the abutment pressure of coal seam can be divided into stress decreasing area, stress increasing area and original stress area, and the stress state of coal seam and the pore, crack structure and permeability of coal body are obviously changed. With the advance of the mining face, the abutment pressure in front and back of the coal mining face is the moving abutment pressure, and the coal mining face to be in the pressure relief area, the front abutment pressure peak value deep into the coal body 5–10 m, the influence scope reaches the front coal mining face to 90–100 m, this area is the stress increasing area. And the evolution law of the roof displacement of goaf is similar to the elliptical with the axial ratio changes, when the ratio is close to 1, the roof subsidence affected area is similar to the shape of “O”.     

深井复合顶板条件下沿空留巷充填体水平方向稳定性分析

针对深井沿空留巷充填体常向巷道空间发生移动,分析深井复合顶板条件下充填体水平位移特征,计算顶底板对充填体的摩擦力和基于弹性地基梁理论下的采空区冒落矸石对充填体的水平挤压力。基于淮南矿区顾桥矿1115（1）工作面轨道顺槽典型深井复合顶板条件下沿空留巷工程地质条件,建立充填体力学计算模型,得到深井复合顶板条件下沿空留巷充填体内移表达式。结果表明,（1）由于复合顶板裂隙发育,垮落后具有较好的流动性,在关键块旋转下沉过程中容易对充填体产生水平挤压力,且复合顶板能够较大程度吸收关键块旋转下沉施加的给定变形,底板不易插底,充填体更易发生内移;（2）理论计算充填体位移量为0.38 m,实测位移量为0.5 m,二者能够吻合,验证了研究成果的正确性。根据充填体内移特点,提出抗剪锚杆等措施增加充填体和顶底板摩擦因数和在靠近充填体的采空区侧设置隔离桩的控制技术。     

神府?东胜矿区高强度开采顶板涌水特征及防治技术

针对我国西部矿区煤炭开采顶板水害威胁问题,以神府?东胜矿区为研究对象,统计了50个工作面的涌水量数据,总结了不同煤?水组合下5种典型的工作面顶板涌水特征:动态补给主导的持续增长型;“动?静”储量共同作用的先增后稳型;微涌水持续稳定性;水文地质条件差异化局部凸显型以及静储量主导先增后减型。针对每种涌水规律,分析了其成因机制,并提出相应的水害防治思路及措施:当工作面受侧向补给较强时,根据实际水文地质条件可采用帷幕截流措施为主、疏水降压措施为辅的防治手段;当工作面受顶板含水层静储量补给为主时,可提前疏水降压,削峰平谷;当工作面受顶板含水层局部富水区域或采空区涌水补给时,可有针对性地采取疏放、注浆治理等综合措施,消除局部水患等。研究成果对于受顶板水害威胁的西部矿区水害防治工作具有借鉴意义。      

氨氮在煤矿采空区充填矸石中的运移机制

我国西部多数煤矿区矿井水往往含有较多的生产污水,导致其氨氮含量较高,利用煤矿采空区充填矸石对矿井水进行预处理已成为矿井水及矸石资源化利用的重要措施。以神华神东煤炭集团公司保德矿矸石为充填介质、以矿井水中的氨氮为研究对象,通过模拟采空区的水文地质环境,开展柱模拟实验,结合CXTFIT 2.1软件,研究氨氮在充填矸石中的运移机制,这对于评价煤矿采空区充填矸石对矿井水的预处理效果具有重要意义。结果表明:达西流速3.12 cm/h、25℃时,Cl?在充填矸石中的运移可用CDE模型较好地表征(r2=0.999),较高的纵向弥散系数(D)、溶质分子扩散系数(D_f)、机械弥散系数(D_h)和弥散度(λ)值与充填矸石较大粒径、较长运移距离有关,淋出液中总溶解性固体(TDS)和Cl?的质量浓度呈显著线性关系;双点位吸附溶质运移模型能够较好地表征氨氮的运移过程,氨氮的阻滞系数R为23.79,其在矸石上的平衡吸附点位仅占总吸附点位的46%,一级动力学吸附速率常数α为3.5×10?4 h?1;氨氮的孔隙流速及水动力弥散系数远低于Cl?的数值,这主要与高含量的黏土矿物高岭石对氨氮的吸附有关;在649 h的氨氮运移过程中,亚硝酸盐和硝酸盐氮以及pH值均无明显变化,实验中后期TDS稳定,这进一步证实氨氮在模拟的矸石柱运移过程中以对流、弥散迁移及吸附为主,生物转化作用可以忽略。研究结果可为评价我国煤矿采空区地下水库的水质预处理技术提供重要理论依据。      

松散含水层下上提工作面压架因素敏感性分析与压架预防

为了防止类似淮南顾北矿1202（3）上提工作面再次发生突水压架事故,根据上提工作面覆岩破断特征,建立了自然拱覆岩结构力学模型,推导出低冒拱和高冒拱的拱高计算式,研究了工作面顶板断裂位置对支架载荷的影响,分别计算出松散含水层在自然拱内、拱外两种条件下的覆岩载荷,确定了滑落失稳和挤压变形失稳的压架判据。研究表明,上提工作面受到松散含水层内水的影响时,易形成高冒拱结构,拱内松散层重度增加,铰接岩块之间的接触力减小,承载关键层受到松散含水层内的水压影响,造成支架上的载荷急剧增大,导致上提工作面易发生突水压架事故。然而影响工作面突水压架既有地质因素,又有开采技术因素,盲目地增加支架工作阻力未必能降低工作面压架风险,支护成本必然急剧增加。基于此,定义了无量纲的压架敏感度指标,分析了压架因素的敏感性,并针对压架敏感性较高的因素,提出了“适当控制采高,开切眼顶板强制放顶,防止直接顶悬顶,采前疏水降压,加固工作面煤壁,提高支架支撑力,合理的设备选型,保证合理的工作面推进速度”等防压架对策,为类似条件下上提工作面安全开采提供一些理论指导。     

基于断裂力学的特厚煤层综放开采顶板破断规律研究

针对特厚煤层综放开采过程中矿压显现剧烈支架工作阻力难以确定的问题,结合特厚煤层工作面顶板岩层破断形成的悬臂梁-砌体梁力学结构模型。工作面来压阶段支架工作阻力不足时,引起砌体梁结构下沉使悬臂梁结构回转变形破断,造成上覆砌体梁结构滑落失稳压架使工作面矿压显现剧烈的特点,建立了含中心斜裂纹的悬臂梁结构破断的力学模型,应用断裂力学理论,分析了悬臂梁破断失稳的影响因素,推导了支架荷载的表达式。结果表明：裂纹倾角和长度是悬臂梁破断失稳的主要影响因素;支架荷载除与悬臂梁自身因素有关外,还与砌体梁垮落步距等因素相关。结合塔山煤矿8102综采工作面地质条件,计算了支架荷载的理论值,验证了理论分析的合理性。理论研究成果对于分析特厚煤层开采时的支架荷载的大小,合理选择支架减少顶板事故具有一定的工程实际意义。