Stability analysis of longwall top-coal caving face in extra-thick coal seams based on an innovative numerical hydraulic support model

The relationship between support and surrounding rock is of great significance to the control of surrounding rock in mining process.In view of the fact that most of the existing numerical simulation methods construct virtual elements and stress servo control to approximately replace the hydraulic support problem,this paper establishes a new numerical model of hydraulic support with the same working characteristics as the actual hydraulic support by integrating numerical simulation software Rhino,Griddle and FLAC3D,which can realize the simulation of different working conditions.Based on this model,the influence mechanism of the supporting strength of hydraulic support on surrounding rock stress regulation and coal stability in front of the top coal caving face in extra thick coal seam were researched.Firstly,under different support intensity,the abutment pressure of the bearing coal and the coal in front of it presents the “three-stage”evolution characteristics.The influence range of support intensity is 15%–30%.Secondly,1.5 MPa is the upper limit of impact that the support strength can have on the front coal failure area.Thirdly,within a displacement range of 2.76 m from the coal wall,a support strength of1.5 MPa provides optimal control of the horizontal displacement of the coal.

Subsidence control method by inversely-inclined slicing and upward mining for ultra-thick steep seams

Ultra-thick steep coal seam mining will inevitably lead to the increase of greater and violent ground subsidence and deformation.A subsidence control method by inversely-inclined slicing and upward mining is proposed in this paper.By this method,the sequence of collapse of overlying strata and the direction of propagation of strata movement are changed,the extent of roof-side deformation thereby is lessened,and boundary angle of roof-side subsidence is reduced by 5°-10°.The mechanism of this mining method for control of strata movement has been evidenced by numerical simulation and experiments with similarity materials.A subsidence prediction model based on the variation of mining influence propagation angle can be used to evaluate the surface movement and deformation of the mining method.The application of the method in No.3 Mine in Yaojie mining area has yielded the expected result.

Comprehensive analysis of safe mining to heavy and steep coal seam under complex geophysics environment

In virtue of effect of N-S intensive ground stress and mining disturbance to +579E2EB_(1+2) mining site at Weihuliang Mine,the dip angle and section height is 65° and 52 m,respectively,the collapses happed frequently during mining.Firstly,mining condi- tions,spatial structure and parameters were investigated.Then physical simulation and dynamic numerical tracing and elaborate simulation relating roof and top-coal were ap- plied based on 2D-Block Program and quantitative regularity of stress at variable depths had been estimated.Furthermore,it was manifested that effective measures,i.e.,fast mining,control symmetrical top-coal-caving at dip and strike directions,optimizing ventila- tion system,active-stereo preventing gas were performed successfully in mining practice. Ultimately,the derived dynamic hazard were prevented so as to safety mining.

Research on drawing coal effects in the dipping and steep——dipping coal seams

Controllable drawing roof coal mining method is applied either to rently inclined seam or to big dipping seam. This paper sums up four corresponding methods according to conditions of our country, and analyses the coal-recovering effects and proves applicated conditions and measures for improving by "drawing coal theory of the ellipsoid". Its conclusion basically consists with practice. This work is of guiding meaning for designing drawing coal technology.

Comparative study of mining methods for reserves beneath end slope in flat surface mines with ultra-thick coal seams

The paper aims to identify a reasonable method for mining ultra-thick coal seams in an end-slope in surface mine, With a case study of Heidaigou surface coal mine(HSCM), the paper conducted a comparative research on three mining methods, namely Underground Mining Method(UMM), Highwall Mining System(HMS) and Local Steep Slope Mining Method(LSSMM). A model was firstly established to simulate the impact that UMM and HMS exert on monitoring points and surface deformation. The way that stripping and excavation amount varies with different slope angle, and the corresponding end slope stability were analyzed in the mode of LSSMM. Then a TOPSIS model was established by taking into account six indicators such as recovery ratio, technical complexity and adaptability, the impact on surface mining production, production safety and economic benefits. Finally, LSSMM was determined as the best mining method for mining ultra-thick coal seams in end slope in HSCM.

Feasibility analysis of gob-side entry retaining on a working face in a steep coal seam

Based on the decline in exploitation of coal resources, steep coal seam mining and mining face tensions continue to explore the feasibility analysis of steeply inclined faces in the gob. One of the key factors in utilizing the technology of gob-side entry retaining in steep coal seams is to safely and effectively prevent caving rock blocks from rushing into the gob-side entry by sliding downwards along levels. Using theoretical analysis and field methods, we numerically simulated the mining process on a fully-mechanized face in a steep coal seam. The stress and deformation process of roof strata has been analyzed, and the difficulty of utilizing the technology is considered and combined with practice in a steep working face in Lvshuidong mine. The feasibility of utilizing the technology of gob-side entry retaining in a steep coal seam has been recognised. We propose that roadways along the left lane offshoot body use a speciallymade reinforced steel dense net to build a dense rock face at the lower head. The results show that the lane offshoot branch creates effective roof control, safe conditions for roadway construction workers, and practical application of steeply inclined gob.

Numerical simulation analysis of covering rock strata as mining steep-inclined coal seam under fault movement

The fault is one important factor for the stability of overburden strata caused by steeply inclined coal seam. The stress and displacement change of overburden strata caused by steeply-inclined coal seam mining activity under faulting was simulated by FLAC2D finite differential program on the basis of Zhaogezhuang mining example belonging to Kailuan Mining Group. From the results, the stress and displacement clouding image after mining became complex because of the fault, that is, a kind of weak structural plane. The stress concentration region concentrated around the goaf, and also around the fault plane. As the mining depth increases, the stress and displacement within the fault zone change significantly. This movement and deformation characteristic of overburden strata can provide theoretical basis for the similar mining condition.

Hydraulic support stability control of fully mechanized top coal caving face with steep coal seams based on instable critical angle

Analyzed the support instable mode of sliding,tripping,and so on,and believed the key point of the support stability control of fully mechanized coal caving face with steep coal seams was to maintain that the seam true angle was less than the hydraulic support instability critical angle.Through the layout of oblique face,the improvement of support setting load,the control of mining height and nonskid platform,the group support system of end face,the advance optimization of conveyor and support,and the other control tech- nical measures,the true angle of the seam is reduced and the instable critical angle of the support is increased,the hydraulic support stability of fully mechanized coal caving face with steep coal seams is effectively controlled.

Study on fasART neuro-fuzzy networks for distinguishing the difficulty degree of top coal caving in steep seam

Distinguishing the difficulty degree of top coal caving was a precondition of the popularization and application of the roadway sub-level caving in steep seam. Because of complexity and uncertainty of the coal seam, the expression of influence factors was diffi-culty with exact data. According to the fuzzy and uncertainty of influence factors, triangular fuzzy membership functions were adopted to carry out the factors ambiguity, of which the factors not only have the consistency of semantic meaning, but also dissolve sufficiently expert knowledge. Based on the properties and structures of fasART fuzzy neural net-works of fuzzy logic system and practical needs, a simplified fasART model was put for-ward, stability and reliability of the network were improved, the deficiency of learning sam-ples and uncertainty of the factors were better treated. The method is of effective and practical value was identified by experiments.

急倾斜巨厚煤层复杂空间结构区微震时空演化规律及诱冲机理

煤矿冲击地压灾害的发生与空间结构密切相关,尤其在复杂空间结构区灾害发生更频繁。掌握煤层开采复杂空间结构区煤岩灾变规律并揭示其发生机制对于冲击地压防控具有重要意义。以乌东煤矿为研究背景,采用数值模拟、微震监测、理论分析等方法,研究了岩柱应力异常尺寸效应,分析了复杂空间结构区微震时空演化规律,揭示了复杂空间结构下冲击地压发生机理,评估了煤层开采不同区域的冲击危险性。研究结果表明:①急倾斜岩柱厚度更窄、出露高度更大其撬动效应更强,岩厚变异应力异常形成5个分区。②岩柱厚度更窄区域微震频次更多,能量更高,时空活动度更强,离散性更高。高应力区、应力梯度区、应力平稳区依次呈现“低频次-高能量”、“高频次-高能量”、“低频次-低能量”的微震响应特征。③特殊空间结构区域微震事件簇集且能级增大,时空活动度及离散性陡增,尤其在结构边缘该特征更明显,能量积聚及释放速率增大,冲击地压发生的概率及强度更高。位于岩柱更窄区域的特殊空间结构内微震活动更剧烈。④岩柱厚度越窄(煤柱高度越大)则岩柱向深的弯矩及能量增长速率越快,冲击危险性更高。依据结构面强度效应推断出断裂带发生滑移错动,是能量积聚与释放的优势区域。揭示冲击地压发生机理为高静载及低临界载荷共同作用,基于应力集中特征评估煤层开采不同区域的冲击危险性。

极近距离煤层开采无煤柱自成巷控制方法研究

极近距离煤层传统长壁开采,受上层遗留煤柱和采空区垮落等因素的影响,下煤层开采过程中应力环境复杂、矿压显现剧烈,易诱发巷道围岩大变形。为解决上述问题,提出了极近距离条件下巷道定向切顶–约束高强支护无煤柱自成巷控制方法。通过顶板定向预裂切顶,主动改变顶板悬臂结构,切断采空区向巷道顶板的应力传递。充分利用矿山压力和岩体碎胀特性,取消煤柱留设,结合高强支护加强巷道顶板整体性,共同实现切顶自成巷。建立了极近距离煤层开采覆岩结构模型,计算了下煤层切顶自成巷巷旁支护阻力。以典型极近距离煤层为工程背景,开展了不同开采方法的数值试验对比研究,结果表明,提出的自成巷控制方法使巷道围岩应力降低59.8%,巷道顶板变形减少70.8%,并明确了极近距离煤层开采无煤柱自成巷控制机理。在此基础上,开展了典型极近距离煤层工程设计及现场应用研究,结果表明该方法有效降低了矿压显现程度,保证了自成巷的安全稳定控制。

急倾斜煤层巷道冒落带注浆加固技术的研究与应用

急倾斜煤层巷道掘进过程中,经常受到高地应力和断层构造带的影响,易造成煤层顶板冒落,影响巷道的掘进和煤矿的安全生产。针对上述问题,以石洞沟煤矿31114运输巷为工程背景,采用KWJG-4无机双组分化学材料对冒落带破碎煤岩体进行注浆加固,将破碎围岩黏结为具有一定强度的密实体,从而有效加固冒顶区的破碎围岩,提高顶板的整体强度及完整性,改善工作面顶板的受力状况,实现掘进巷道安全、快速、高效过冒落带。对于煤矿生产过程中遇到类似巷道冒落破碎带问题,该方法具有一定的借鉴和指导意义。

急倾斜中厚煤层单一巷道放顶煤采煤方法研究与应用

为解决某矿急倾斜中厚煤层倾角及厚度变化大的开采问题,提出了“急倾斜中厚煤层单一巷道放顶煤采煤方法”。该采煤方法是沿急倾斜煤层倾斜方向划分为若干区段,每个区段沿急倾斜煤层走向仅布置1条巷道。此巷道服务于1个采煤区段,担负工作面通风、运输和行人等任务。对单一巷道放顶煤采煤方法的巷道布置、综放工艺和沿空留巷方法进行了探讨。实践表明,该采煤方法使采煤工作面形成全负压通风,避免了巷道与采空区窜风,杜绝了采空区瓦斯积聚和遗煤自燃,实现了采煤机械化,提高了急倾斜中厚煤层的开采效率和煤炭回收率。单一巷道放顶煤采煤法为类似急倾斜煤层安全、高效开采提供了技术支撑。

基于钻孔瓦斯涌出规律的突出危险性预测模型

为提高急倾斜煤层上山掘进过程中煤与瓦斯突出危险性预测的准确性,首先,基于Mohr-Coulomb准则建立钻孔瓦斯流动模型;其次,通过数值模拟定量分析钻孔瓦斯初始涌出量和瓦斯压力之间的关系;最后,使用ZTL20/1000-Z型矿用隔爆预测装置对贵州洪兴煤矿111707上山掘进面进行现场试验。结果表明:钻孔初始瓦斯涌出量与瓦斯压力呈正相关关系,其相关系数为0.977 3,钻孔初始瓦斯涌出量可以作为预测煤与瓦斯突出的一项参考指标;随着钻孔深度的增加,钻孔初始瓦斯流量会经历“稳定—增加—降低—稳定”4个阶段,钻孔瓦斯流量峰面积可以反映煤与瓦斯突出危险性。

浅埋极薄煤层无煤柱开采覆岩运移与地表损伤特征研究

为了探究浅埋极薄煤层切顶卸压无煤柱开采与常规留煤柱开采覆岩运移与地表损伤区别,以子长矿区浅埋极薄煤层为背景,基于关键层理论,得到了硬岩破断距及覆岩的垮落高度临界值的计算公式,结合3DEC数值模拟及现场试验,对比分析了无煤柱开采与留煤柱开采条件下浅埋极薄煤层覆岩运移破断及地表损伤特征,确定了极薄煤层覆岩两带高度。结果表明:当工作面回采达到60 m时,两带发育高度基本稳定,当大于60 m时,工作面后方覆岩裂隙由开裂逐渐闭合,裂隙区随工作面回采向前方移动,两带高度稳定在24.6~27.7 m;相较于常规留煤柱开采,切顶留巷无煤柱开采方式下覆岩呈连续移动变形,可有效修复煤层开采工作面两侧非连续移动变形导致的覆岩裂隙及地表损伤裂缝,消除了常规留煤柱开采方式下相邻工作面间区段煤柱两侧覆岩裂隙,现场观测较好地验证了该结果。

弱化浅层岩体防治急倾斜特厚煤层冲击地压研究

急倾斜特厚煤层受其特殊的地质、应力和开采技术条件影响,冲击地压防治方法与一般煤层存在较大差异。将理论推导、数值模拟、现场监测等方法相结合,研究了急倾斜特厚煤层的岩层弯曲和煤层能量积聚特征,提出了弱化浅层岩体防治急倾斜特厚煤层冲击地压的方法,得到了防冲关键参数,并进行了工程应用。研究结果表明,急倾斜特厚煤层岩层弯曲时内部岩体破裂释放能量是动载的主要来源,采空区两侧围岩转移、传递至煤层的水平集中应力是静载和能量积聚的主要来源;防治急倾斜特厚煤层冲击地压应弱化工作面浅层岩体的应力传递能力,来降低传递至工作面的动载扰动强度以及转移、传递至煤层的水平集中应力。基于此提出了通过浅孔爆破措施弱化急倾斜特厚煤层浅层岩体的防冲方法。现场工程应用表明,矿井补强浅孔爆破后,工作面微震事件总能量降低了42.38%、总数量增大了471.74%,说明工作面的能量释放由大能量剧烈释放逐渐转为小能量平缓释放,且未再发生过冲击显现,冲击地压危险得到有效控制。研究成果可为类似条件矿井防治冲击地压提供参考。

极近距离煤层三面临空下分层煤柱留设方法研究

针对极近距离煤层三面临空下分层煤柱留设问题,以众维煤矿下分层12052工作面作为研究对象,采用理论分析、现场试验、数值模拟相结合的手段;重点分析了极近距离分叉分层开采难点、煤柱留设原则及影响因素,校核了不同高宽比煤柱强度,研究了不同宽度煤柱应力、塑性区演化规律。结果表明:校核之后煤柱极限强度分别为9.91、11.44、12.95、14.52、16.21 MPa;随着煤柱宽度的增加,应力峰值逐渐降低;煤柱宽度大于12 m时,应力曲线呈现“马鞍形”,当煤柱留设16m时,弹性核区宽度不小于煤柱宽度的2倍,围岩变形小,巷道完整性较好。研究成果为相似地质条件下的煤柱宽度留设提供理论参考。