Dynamic failure risk of coal pillar formed by irregular shape longwall face:A case study

Irregular shape workface would result in the presence of coal pillar, which leads to high stress concentration and possibly induces coal bumps. In order to study the coal bump mechanism of pillars, static and dynamic stress overlapping(SDSO) method was proposed to explain the impacts of static stress concentration and tremors induced by mining activities. The stress and deformation in surrounding rock of mining face were analyzed based on the field case study at 1303 workface in Zhaolou Coal Mine in China.The results illustrate that the surrounding rock of a workface could be divided into four different zones,i.e., residual stress zone, stress decrease zone, stress increase zone and original stress zone. The stress increase zone is prone to failure under the SDSO impact loading conditions and will provide elastic energy for inducing coal bump. Based on the numerical modelling results, the evolution of static stress in coal pillar as the size of gob increasing was studied, and the impact of dynamic stress was investigated through analyzing the characteristics of tremor activities. The numerical results demonstrate the peak value of vertical stress in coal pillar rises from about 30 MPa with mining distance 10 m to 52.6 MPa with mining distance 120 m, and the location of peak stress transfers to the inner zone of coal pillars as the workface moves forward. For the daily tremor activities, tremors with high energy released indicate high dynamic stress disturbance on the surrounding rock, therefore, the impact of dynamic stressing is more serious during workface extension period because the tremor frequency and average energy after workface extension are higher than those before the workface extension.

Prediction of face advance rate and determination of the operation efficiency in retreat longwall mining panel using rock engineering system

A new approach for prediction of face advance rete (FAR) prior to mining operation and determination of the operation efficiency after mining operation in retreat longwall mining panel is presented based upon the concepts of rock engineering system (RES). For this purpose, six longwall panels considered in Parvadeh-I coal mine. Seven major effective parameters on FAR was selected including coal mine roof rating, gas propagation, safety factor of longwall face, ratio of joint spacing to cutting depth at longwall face, longwall face inclination, panel width, floor rock mass rating. To performance evaluation of the presented model, the relationship between the average vulnerability indexes of advance operation with FAR was determined in considered panels with coefficient of determination (R2) equal to 0.884 that indicate relatively acceptable correlation and compatibility. Investigations of the research indicated that it is possible to determine the actual operation efficiency under fair conditions by a RES-based model. The inevitable reduction of FAR for each longwall panel was determined by presented model that the difference amount between the maximum possible practical face advance rate (FARmpp) and recorded actual face advance rate (FARa) indicate the operation efficiency. Applied approach in this paper can be used to prediction of FAR in retreat longwall mining panel for same conditions that can have many benefits, including better and more accurate planning for the sales market and mine operation. Also, presented method in this paper can be applied as a useful tool to determination of actual operation efficiency for other sections and extraction methods in coal mines.

New development of sets equipment technologies for coal mine longwall face in China

Background of the development and achievement on sets equipment technologies for coal mine longwall face in China was reviewed initially. On the theoretical side, a coupling model of hydraulic support and surrounding rock, support pa- rameters optimization and threedimensional （3D） dynamic design method were presented. On the practical side, this paper out lined some of practical issues and discussed some relative methods and technologies. In thin seam coal longwall mining, how to lower equipment height is the first problem that should be solved. Roof pressure regularity, control of rooffall and collapse, and hydraulic support stability were investigated preferentially in 5-7 m coal seam longwall mining. The application of equip- ment for longwall mining with 5-7 m cutting height in China was concluded. The characteristics of full-mechanized top coal caving for extra thick seam coal were presented. The automation of top-caving hydraulic support and relevant equipment have achieved important breakthrough. At the end of this paper, further development of China＇s coal industry and longwall mining technologies and equipment were prospected in brief. This paper gives readers a comprehensive understanding of China＇s coal mine longwall face equipment technologies. It will give help to other countries on its coal mining development.

Theoretical analysis on the deformation characteristics of coal wall in a longwall top coal caving face

Against the background of analyzing coal wall stability in 14101 fully mechanized longwall top coal caving face in Majialiang coal mine,based on the torque equilibrium of the coal wall,shield support and the roof strata,an elastic mechanics model was established to calculate the stress applied on the coal wall.The displacement method was used to obtain the stress and deformation distributions of the coal wall.This study also researched the influence of support resistance,protective pressure to the coal wall,fracture position of the main roof and mining height on the coal wall deformation.The following conclusions are drawn:(1) The shorter the distance from the longwall face,the greater the vertical compressive stress and horizontal tensile stress borne by the coal wall.The coal wall is prone to failure in the form of compressive-shear and tension;(2) With increasing support resistance,the revolution angle of the main roof decreases linearly.As the support resistance and protective force supplied by the face guard increases,the maximum deformation of the coal wall decreases linearly;(3) As the face approaches the fracture position of the main roof,coal wall horizontal deformation increases significantly,and the coal wall is prone to instability;and(4) The best mining height of 14101 longwall face is 3.0 m.

Analysis and control of hydraulic support stability in fully-mechanized longwall face to the dip with great mining height

The working condition of the hydraulic support in working face can be divided into three kinds of situations in the following： roof fall and col,lapse with cavity, advancing support and supporting. Took single support with four-pole in Iongwall face to the dip as research object, control method was studied to avoid support instability in three situations mentioned above. Based on these researches, the major factors of influencing on support stability and its controlling measures were put forward. According to specific conditions of working face 1215（3）, which is fully-mechanized and Iongwall face to the dip with great mining height in Zhangji Coal Mine, Huainan Mining Group, the effective measures was taken to control supports stability..

Systematic principles of surrounding rock control in longwall mining within thick coal seams

Effective surrounding rock control is a prerequisite for realizing safe mining in underground coal mines.In the past three decades, longwall top-coal caving mining(LTCC) and single pass large height longwall mining(SPLL) found expanded usage in extracting thick coal seams in China. The two mining methods lead to large void space left behind the working face, which increases the difficulty in ground control.Longwall face failure is a common problem in both LTCC and SPLL mining. Such failure is conventionally attributed to low strength and high fracture intensity of the coal seam. However, the stiffness of main components included in the surrounding rock system also greatly influences longwall face stability.Correspondingly, surrounding rock system is developed for LTCC and SPLL faces in this paper. The conditions for simultaneous balance of roof structure and longwall face are put forward by taking the stiffness of coal seam, roof strata and hydraulic support into account. The safety factor of the longwall face is defined as the ratio between the ultimate bearing capacity and actual load imposed on the coal wall.The influences provided by coal strength, coal stiffness, roof stiffness, and hydraulic support stiffness,as well as the movement of roof structure are analyzed. Finally, the key elements dominating longwall face stability are identified for improving surrounding rock control effectiveness in LTCC and SPLL faces.

Prevention of gob ignitions and explosions in longwall mining using dynamic seals

Most, if not all longwall gob areas accumulate explosive methane-air mixtures that pose a deadly hazard to miners. Numerous mine explosions have originated from explosive gas zones(EGZs) in the longwall gob. Since 2010, researchers at the Colorado School of Mines(CSM) have studied EGZ formation in longwall gobs under two long-term research projects funded by the National Institute for Occupational Safety and Health. Researchers used computational fluid dynamics along with in-mine measurements. For the first time, they demonstrated that EGZs form along the fringe areas between the methane-rich atmospheres and the fresh air ventilated areas along the working face and present an explosion and fire hazard to mine workers. In this study, researchers found that, for progressively sealed gobs, a targeted injection of nitrogen from the headgate and tailgate, along with a back return ventilation arrangement, will create a dynamic seal of nitrogen that effectively separates the methane zone from the face air and eliminates the EGZs to prevent explosions. Using this form of nitrogen injection to create dynamic seals should be a consideration for all longwall operators.

Monitoring strata behavior due to multi-slicing top coal caving longwall mining in steeply dipping extra thick coal seam

For studying the strata behavior due to multi-slicing top coal caving longwall mining along-the-strike direction in steeply dipping extra thick coal seams,the shield support pressures of the upper and lower slices of panel 37220 in Dongxia Coal Mine were monitored using the KJ513 dynamic monitoring system.The set up rooms adopted the "horizontal line-arc segment-inclined line" form and used different types of shield supports.The results show that the strata pressure of upper slice panel 37220-1 changed slightly along the strike direction,while along the dip direction it exhibited strong to weak pressure from bottom to top.The first weighting interval of lower slice panel 37220-2 was about 60.8 m,and the average periodic weighting interval were about 22.6 m.The strata behavior of panel 37220-2 exhibited a spatiotemporal characteristic in that periodic weighting occurred first in the middle-upper part,followed by the middle and upper parts,arc segment,and finally the lower part.During the periodic weighting,the weighting interval and intensity also exhibited strong space characteristics.The average dynamic load coefficient was 1.48 and the maximum lateral load of the side shield was 20-25 MPa.

Evaluation of coal pillar loads during longwall extraction using the numerical method and its application

It is very difficult to reasonably evaluate the loads acting on coal pillars in longwall panels during the planning of a new pillar system. The application of empirical equations is a common practice in calculating coal pillar loads while designing a new pillar. This paper proposes numerical models for evaluating coal pillar loads. The key of building a successful numerical model for calculating coal pillar loads lies in the fact that the model should represent the redistribution of stress all over the longwall panels and the surrounding areas, and it is especially important to include the characteristics of the stress rebuilding process in the gob areas, which are crucial for the building process of coal pillar loads. Based on the geo-mechanical background of the Baoshan Coal Mine, this paper details the procedures of applying numerical models to the evaluation of coal pillar loads and their local practices. The study results show it is feasible and reasonable to use numerical models to evaluate coal pillar loads.

A holistic examination of the load rating design of longwall shields after more than half a century of mechanised longwall mining

It is a commonly asked question:how big should the longwall shields be? The answer is a key aspect of a longwall mining feasibility study when the consequences of inadequately rated shields are considered.This paper addresses this question based on the measured nature of the loading environment in which shields are required to operate,the various geological and geometrical controls of that environment and the various links between their load rating,a range of other relevant shield design factors and the loss event they are required to prevent a major roof collapse on the longwall face.The paper concludes that despite the tremendous advances that have been made in shield design and load rating over the past50 years,the same drivers that caused longwall miners of the past to seek improved roof control on the longwall face via the use of ever-higher rated shields,are still as relevant today.However at the current time,the limits of the largest available longwall shields have yet to be tested,therefore industry focus for the foreseeable future should possibly be in achieving the maximum level of roof control on the face via their optimum operational use rather than considering further shield rating increases and incurring the inevitable downsides in terms of capital cost and shield weight.

Impact of geo technical factors on strata behavior in longwall panels of Godavari Valley coal field-a case study

Understanding the cantilevers formed by thick, massive beds in the near-seam overburden above longwall panels and the associated loads and strata fracturing effects developed during caving(main and periodic weightings) are key elements for the successful implementation of longwalls. Such caving mechanisms rely on the geotechnical conditions within the panel. In India, the majority of longwall downtime and/or roof failures were caused by a lack of knowledge on overburden caveability, in particular when the main and periodic weightings will impact the face and longwall support selection to effectively mitigate such weightings. Godavari Valley Coal Fields is no exception as longwall faces were adversely affected due to the presence of thick, massive beds in the near-seam overburden at both Godavarikhani(GDK) 7 and 9 Incline mines. In contrast, overburden weightings were negotiated successfully in GDK10 A and Adriyala Longwall Project(ALP) mines by detailed geotechnical studies, the use of adequate longwall support capacities, and effective operational practices. Thirteen longwall panels with varying face width, at different depths have been extracted under massive sandstone beds of 18 m to28 m thickness at GDK 10 A and ALP mines. This study elucidates that the main roof weighting interval decreases with an increase in face width and attains a constant value with further increases in face width under the same geo-mining conditions. In addition, this study also concludes that with increases in face width, the periodic roof weighting interval decreases and shield loads increase. Similarly with increasing panel width to depth ratio, the main and periodic roof weighting intervals decrease but shield loads again increase. Lastly, the strata behaviour of the longwall face retreated along up-dip direction is demonstrated. The results of this paper improves the mechanistic understanding of the impact of face width,depth and main roof thickness on periodic weighting and associated roof control problems on the longwall face.

综采面条带式充填开采覆岩运移规律及稳定性控制

针对在长壁综采面膏体条带式充填开采中存在的覆岩稳定性问题,以国能榆林能源郭家湾煤矿条带式充填开采为工程背景,采用工程模拟有限元软件ABAQUS进行数值模拟,研究长壁综采面未充填时上覆岩层运移规律以及条带式充填对上覆岩层的影响及稳定性控制。结果表明,未充填时,随着工作面的不断推进,工作面前方煤壁中部和两侧煤柱处产生应力集中现象,上覆岩层不断垮落,当开采至60 m时迎来初次来压,工作面周期来压步距为30 m,应力峰值为32.02 MPa,顶板位移峰值为3.42 m;采用条带式充填开采后,充填条带对顶板变形和应力集中现象都得到明显缓解。条带间距越小,即充填率越大,条带式充填体对上覆岩层的稳定性控制越有利。当条带间距为20 m、充填率为33%时,顶板中部和两侧煤柱的位移和应力集中均得到有效控制并基本趋于稳定,与未充填时相比,两侧煤柱应力峰值由32.02 MPa降至3.79 MPa,顶板位移峰值由3.42 m降至0.09 m。

四面采空“孤岛”综放采场矿压控制的研究与实践

论文通过理论和实践研究,提出了四面采空“孤岛”采场的顶板结构和相关矿压控制技术。此类采场矿压控制的理论问题,是采场覆岩的多层空间结构运动及其与采动应力场的关系;其工程问题,是煤柱失稳造成的灾害形式及其判定方法、煤柱失稳的灾害的控制技术以及水、火和瓦斯的控制问题。论文通过河南义马煤业集团的实例,系统介绍了灾害监测技术和控制方法。开采结果表明,论文中提出的对岩层结构的认识和采取的控制技术是正确的,可以在条件相似的矿区推广应用。

长壁工作面覆岩采动裂隙网络演化特征

以淮南张集矿1122(1)工作面为原型,制作了相似材料模型。结合分形几何理论研究了覆岩采动裂隙的分布及发育特征,并分析了覆岩采动裂隙长度与数量的分维与工作面推进长度之间的关系。研究发现:采动裂隙总数随着工作面推进长度增大而增大,且在主关键层弯曲前,裂隙总数逐渐增多;主关键层弯曲后,导致采空区中部部分裂隙闭合,而新生裂隙则不断增加。

综采工作面煤矸频谱特征

采用数字信号处理技术，实时计算煤矸放落量比例．数字滤波首先消除煤矸放落环境噪声，再应用短时窗技术将信号按10—30ms的短帧为单位来处理，根据信号特征加凯塞窗处理，提高信号的分辨率，利用快速傅里叶变换分析数据的频谱特征．实验结果给出了煤矸信号的时域波形、频域波形和三维谱图，表明落煤振动频率集中在0．8—2kHz附近，而落矸振动频率集中在3—4kHz附近，具体数值需要根据综采工作面的地质环境修正．

大倾角煤层长壁开采底板非对称破坏形态与滑移特征

底板破坏滑移是大倾角煤层开采亟待解决的关键问题之一,以2130煤矿25221大倾角综采工作面为研究背景,采用理论分析、数值计算和现场监测相结合的研究方法,系统研究了底板的破坏和滑移特征。结果表明,在采动应力和支架载荷作用下底板的力学性状发生改变,由层状连续介质状态演化为具有"结构体+结构面"的块裂介质状态;底板沿工作面倾向的破坏形态呈现为下大上小的非对称反拱,其最大破坏深度位于工作面倾向下部区域,且其破坏深度和范围随着煤层倾角的增大而减小;支架载荷对底板破坏影响有限,主要涉及采场直接底岩层;在底板重力倾向分量及支架和相邻块体载荷作用下,当滑移体存在临空面、滑移体所受主动力与滑移面相交、且主动力合力与滑移面法线方向的夹角大于滑移面的摩擦角时出现底板滑移,且底板岩体结构失稳滑移的概率随着煤层倾角的增大、支架倾斜幅度和范围的增大、直接底破碎程度的增大而增大。

深井超长工作面基本顶分区破断模型与支架阻力分布特征

开采深度和工作面长度增加导致采场矿压显现程度和空间分布特征发生改变,增加了该类采场围岩失稳类型的不确定性及控制难度。针对深井超长工作面异常矿压现象发生频率高、预测难度大等问题,采用理论分析、室内实验和实测等方法分析了该类采场基本顶破断类型和支架阻力分布特征。结果表明:开采深度增加提高了岩体中裂隙发育程度,裂隙尺寸服从对数正态分布,裂隙倾角和倾向服从正态分布;基于蒙特-卡罗模拟方法实现深井超长工作面基本顶三维重构,工作面长度增加导致基本顶中部存在裂隙的概率升高,增大了基本顶在工作面中部发生局部破断的可能性;建立深井超长工作面基本顶分区破断力学模型,采用上限定理推导出完整基本顶的整体承载能力以及基本顶中存在1条和2条原生裂隙时的局部承载能力,获得基本顶在裂隙影响区发生局部分区破断和迁移现象的力学判据;基本顶分区破断现象导致破断岩块在空间上呈非均匀分布,表现为工作面中部块度小、两端块度大的特征;分区破断模型预测结果同相似模拟实验结果吻合,解释了深井超长工作面开采实践中发现的顶板压力沿工作面方向的非均匀分布现象。

煤矿采场岩层运动与控制研究进展--纪念钱鸣高院士“砌体梁”理论40年

自1982年钱鸣高院士提出的“砌体梁”理论得到国际公认以来,煤矿采场矿山压力研究实现从定性假说到定量理论的跨越式发展。40年来,我国的采场岩层运动与控制研究已形成较系统的理论与技术体系,服务于煤炭安全、高效、绿色开采。以“砌体梁”理论学术思想为主线,综述了我国煤矿采场岩层运动与控制研究进展,并提出了今后需要发展的研究方向。“砌体梁”理论采用“梁”“薄板”模型分析基本顶破断规律,揭示了顶板断裂线位于采场煤壁前方;煤壁和矸石支撑下基本顶破断岩块回转挤压,咬合形成“砌体梁”结构;发现了“砌体梁”结构的滑落(S)失稳和回转变形(R)失稳模式,建立了S-R失稳的力学条件,提出了基于“砌体梁”结构平衡的顶板压力计算方法,首次实现了支架-围岩关系的定量分析。“砌体梁”结构采场矿山压力力学模型突破了传统定性假说,为保障煤矿的安全和高产高效作出了历史性贡献。“砌体梁”理论指导煤矿采场顶板控制取得系列进展,如支架-围岩三耦合关系、顶板动载荷模型、支架阻力确定的二元准则、中厚板模型、大空间采场远-近场模型等。在“砌体梁”理论的基础上,钱鸣高院士于20世纪90年代中期提出了关键层理论,建立了下至采场、上至地表全覆岩运动过程的力学联系,实现了采场矿压、岩层移动和地表沉陷研究的统一。“砌体梁”理论与关键层理论指导了我国煤矿采场矿山压力与岩层控制研究,在采场矿压控制、覆岩裂隙分布、采动应力分布、岩层移动与开采沉陷等方面取得重要成果,为煤炭绿色开采与科学采矿奠定了基础。岩层运动与控制理论的进一步发展需集中到岩层运动统一场理论,基于采动岩层控制的灾害防治与减损技术,复杂条件岩层运动规律,岩层运动可视化技术和智能岩层控制技术等方面。

采场覆岩空间破裂与采动应力场的微震探测研究

介绍了用微地震定位监测技术揭示的采场覆岩空间破裂与采动应力场的关系。认为存在 4种由采动引起的岩体破裂类型。展示了 3种典型采动边界条件下覆岩破裂与采动应力场的关系。提出了由微震事件分布推断区段煤柱稳定性的方法。

基于海量矿压监测数据的采场支架与顶板状态智能感知技术

超前感知综采工作面顶板来压并预判冒顶事故、自主评价支护参数的适应性,是提高综采工作面安全高效及智能化水平的基础。围绕综采工作面支架与顶板状态智能感知的核心问题,基于综采工作面电液控制液压支架海量监测数据,开发了综采工作面支架与顶板状态智能感知系统(SSRI);结合大数据挖掘及工作循环分析技术,提出了用于支架压力分析的多因次工作循环特征参数;研究了安全阀开启、割煤及邻架移架、地质等多种因素影响下的单台支架承载特征及支架群组载荷转移分布规律;在深入解读支架阻力及活柱下缩时序曲线所蕴含的支架与围岩相互作用关系的基础上,构建了支架与顶板状态智能感知模型,实现了对顶板来压的预测、冒顶预警、支架适应性及支护质量评价,初步建立了基于海量矿压监测数据的采场支架与顶板状态智能感知技术体系。结果表明:①额定工作阻力不应作为评价支架承载能力的惟一或主要指标,初撑力、额定工作阻力及安全阀开启特性等参数共同决定了支架的承载特性及承载能力;②充分挖掘分析海量矿压监测数据,可以实现采场顶板灾害智能预警、支护质量评价及故障诊断等研究目标;③对海量监测数据的深入分析与利用是实现综采工作面支架围岩耦合自适应控制、支护参数自适应调整等智能化开采目标的前提与基础。