The influence of inter-band rock on rib spalling in longwall panel with large mining height

In order to improve rib stability,failure criteria and instability mode of a thick coal seam with inter-band rock layer are analysed in this study.A three-dimensional mechanical model is established for the rib by considering the rock layer.A safety factor is defined foy the rib,and it is observed that the safety factor exhibits a positive correlation with the thickness and strength of the inter-band rock.A calculation method for determining critical parameters of the rock layer is presented to ensure the rib stability.It is revealed that incomplete propagation of the fracture at the hard rock constitutes a fundamental prerequisite for ensuring the rib stability.The influence of the position of the inter-band rock in the coal seam on failure mechanism of the rib was thoroughly investigated by developing a series of physical models for the rib at the face area.The best position for the inter-band rock in the coal seam is at a height of 1.5 m away from the roof line,which tends to provide a good stability state for the rib.For different inter-band rock positions,two ways of controlling rib by increasing supports stiffness and flexible grouting reinforcement are proposed.

Failure mechanism and control technology of longwall coalface in large-cutting-height mining method

The stability control of longwall coalface is the key technology of large-cutting-height mining method.Therefore,a systematic study of the factors that affect coalface stability and its control technology is required in the development of large-cutting-height mining method in China. After the practical field observation and years of study,it was found that the more than 95% of failures in coalface are shear failure. The shear failure analysis model of coalface has been established,that can perform systematic study among factors such as mining height,coal mass strength,roof load,support resistance,and face flipper protecting plate horizontal force. Meanwhile,sensitivity analysis of factors influencing coalface stability showed that improving support capacity,cohesion of coal mass and decreasing roof load of coalface are the key to improve coalface stability. Numerical simulation of the factors affecting coalface stability has been performed using UDEC software and the results are consistent with the theoretical analysis. The coalface reinforcement technology of large-cutting-height mining method using the grouting combined with coir rope is presented. Laboratory tests have been carried out to verify its reinforcement effect and practical application has been implemented in several coal mines with good results.It has now become the main technology to reduce longwall coalface failure of large-cutting-height mining method.

Technical parameters of drawing and coal-gangue field movements of a fully mechanized large mining height top coal caving working face

Under fully mechanized, large mining height top coal caving conditions, the shield beam slope angle of the support increases due to the enlargement of the top coal breaking and caving space. This results in a change of the caving window location and dimensions and, therefore, the granular coal-gangue movement and flows provide new characteristics during top coal caving. The main inferences we draw are as follows. Firstly, after shifting the supports, the caved top coal layer line and the coal gangue boundary line become steeper and are clearly larger than those under common mining heights. Secondly, during the top coal caving procedure, the speed of the coal-gangue flow increases and at the same drawing interval, the distance between the coal-gangue boundary line and the top beam end is reduced. Thirdly, affected by the drawing ratio, the slope angle of the shield beam and the dimensions of the caving window, it is easy to mix the gangue. A rational drawing interval will cause the coal-gangue boundary line to be slightly behind the down tail boom lower boundary. This rational drawing interval under conditions of large mining heights has been analyzed and determined.

Similar material simulation research on movement law of roof over-lying strata in stope of fully mechanized caving face with large mining height

Similar material simulation test was carried out in a geological model ofW_(9-15)101 fully mechanized caving face with large mining height in the Liuhuanggou Colliery,in Xinjiang Uigur Autonomous Region.The roof overlying strata movement law in thestope of a fully mechanized caving face with large mining height was studied and showthat the roof overlying strata in the stope of a fully mechanized caving face with large miningheight can be formed into a stable arch structure; the fracture rock beam is formed resemblinga 'bond beam', but it has essentially the structure of 'multi-span beams' underthe big structure of the stable arch.The roof overlying strata movement law in the stope ofa fully mechanized caving face with large mining height is similar to that of the common,fully mechanized caving stope, which is determined by the deformation and instability ofthe structure of 'multi-span beams'.But because of the differences between the miningheights, the peak pressure in the stope of a fully mechanized caving face with large miningheight is smaller while the affected area of abutment pressure is wider in the front of theworking face; this is the obvious difference in abutment pressure between the stope of afully mechanized caving face with large mining height and that of the common.

Mode of overlying rock roofing structure in large mining height coal face and analysis of support resistance

The mining space of large mining height coal face is large,the range of movement and caving of rock strata is large and the stability of supports at coal face is low and damage rate of supports is high,which significantly affects the safe and efficient production of coal mines.By similar simulation experiment and theoretical analysis,the mode of fractured roofing structure of large mining height coal face and the method of determination of reasonable support resistance of the support was evaluated.Analysis shows that the structural mode of "combined cantilever beam – non-hinged roofing – hinged roofing" of the large mining height coal face appears at the roofing of large mining height coal face.The supporting factor of caved gangue at the gob is introduced,the calculating equations of the fractured step distance of roofing were derived and conventional calculating method of caved height of roofing was corrected and the method of determination of the length and height of each structural area of the roofing was provided.With reference to the excavating conditions at Jinhuagong coal mine in Datong minefield,the dimensions of structural areas of the roofing of the coal face were determined and analyzed,and reasonable support resistance of the height coal face was acquired.By selecting Model ZZ13000/28/60 support and with procedures of advanced pre-cracking blasting,the safe production of large mining height coal face was assured.

Analysis and key control technologies to prevent spontaneous coal combustion occurring at a fully mechanized caving face with large obliquity in deep mines

In order to prevent spontaneous coal combustion occurring at a fully mechanized caving face with large obliquity in deep mines in China,we have analyzed the characteristics of spontaneous coal combustion and explain theoretically the factors affecting spontaneous coal combustion,such as rock bursts,high temperatures,high ventilation resistance,slow advancing speed and large obliquity mining.Key technologies to prevent spontaneous combustion occurring in sharply inclined seams in deep mines are proposed;these include pouring water,stopping leakage in upper and lower corners of the working face,choking off the goaf and covering the coal.CO concentrations were controlled within two years to less than 15×10-6 at the upper corner by applying these technologies at the 1410 working face of the Huafeng coal mine.Our method has significant theoretical value and is of practical importance in controlling spontaneous coal combustion occurring at a fully mechanized caving face with large obliquity in deep mines.

Development and prospect on fully mechanized mining in Chinese coal mines

Fully mechanized mining(FMM)technology has been applied in Chinese coal mines for more than 40 years.At present,the output of a FMM face has reached 10-million tons with Chinese-made equipment.In this study,the new developments in FMM technology and equipment in Chinese coal mines during past decades are introduced.The automatic FMM technology for thin seams,complete sets of FMM technology with ultra large shear height of 7 m for thick seams,complete sets of fully mechanized top coal caving technology with large shear height for ultra-thick seams of 20 m,complete sets of FMM technology for complex and difficult seams,including steeply inclined seams,soft coal seams with large inclination angle,and the mechanized filling mining technology and equipment are presented.Some typical case studies are also introduced.Finally,the existing problems with the FMM technology are discussed,and prospect of FMM technology and equipment applied in Chinese coal mines is put forward.

Suitable retention and recovery technology of floor coal at ends of fully mechanized face with great mining heights

在大采矿高度的脸的网关主要沿着煤缝接的房顶被驾驶。为网关高度限制， 13 m 地板煤被保留，离开在脸结束的三角形的地板煤，引起煤的损失。为了改进煤恢复率并且在煤采矿保证设备的效率，面对，我们在脸结束调查了合适的保留方法和地板煤的恢复技术。上面的地板煤能被 shearer 直接与地板 dinting 恢复。在推进了地板 dinting 以后，更低的地板煤被 shearer 与地板 dinting 恢复并且为在一道拖拽网关保护煤方面保留步。地实践证明这个方法能改进恢复与大采矿高度在充分使机械化的工作的脸评估的煤。

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 collapse with cavity,advancing support and supporting.Took single support with four-pole in longwall 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.

大倾角大采高工作面煤壁失稳机理分析

大倾角大采高工作面煤壁灾变易诱使支架-围岩系统失衡,导致围岩稳定性控制复杂化,故煤壁灾变防控对保障工作面安全生产十分关键,而科学化防控技术的前提是明晰煤壁失稳孕育机制,为此采用数值计算及理论分析法展开研究。研究结果表明:大倾角大采高工作面煤壁承压倾向分区异化,下部区域应力集中程度较中部、上部高,集中区范围由下至上减小,垂向中部应力值较低,应力极值及走向位置与回采距具有正相关性,煤壁揭露前后邻域承压环境会突变,且承压态随煤体破坏演变异化,煤体承压结构会由非连续态经压实过渡为类连续状,而后整体移动至阈值后发生破断结构离散化。煤壁前方塑性区随采动作用不同幅度扩展,其稳定性受制于回采距及速度,低速回采、回采距离增加时煤壁稳定性逐步降低,塑性破裂发育区煤体为支承压力等动载、静载主承体,煤壁失稳是支承压力与扰动区内煤体自身抗压性能动态失衡,由运移、变形等承压行为量变诱发煤体结构质变而破断失稳,承压非对称性及多向耦合造成煤壁失稳分区及范围倾向扩展。

松软煤层大采高工作面煤壁片帮机理及深浅孔交替超前预注浆加固技术研究

目的为探究松软煤层大采高工作面煤壁片帮机理,并对片帮严重的松软煤层大采高工作面煤壁进行有效控制,方法利用材料力学理论得到煤壁片帮的频发位置,引入煤壁剪切破坏准则,得出松软煤体煤壁片帮的主控因素。并以李村煤矿1305工作面为例,通过FLAC3D建立数值模型,以煤壁最大位移、煤体破坏深度、支承压力大小和支承压力峰值位置4个因素作为参考比较对象,通过引入正交试验法,研究了煤层埋深、内摩擦角、黏聚力、抗拉强度以及支护强度对煤壁片帮的影响程度。结果结果表明:煤体自身的物理力学性质(内摩擦角和黏聚力)是影响煤壁片帮的主要因素,其次煤体的赋存条件(埋深)也是一个较为关键的影响因素。结论工业性试验基于正交试验结果提出了大采高综采工作面深浅孔交替超前预注浆加固技术,有效控制了李村煤矿1305工作面煤壁片帮严重情况,为其他类似地质条件大采高综采工作面煤壁片帮控制提供了借鉴。

基于微震监测的浅埋8 m超大采高综采面矿压规律现场监测研究

以陕北矿区某矿2203浅埋超大采高综采面为工程背景,采用微震监测技术,对浅埋超大采高综采面矿压规律进行了研究。结果表明:单日微震事件数达到峰值后,综采面继续回采8.25~11 m内,能量大于103J的事件增多,微震事件能量及支架压力达到峰值,随后顶板出现垮落现象。综采面初次来压前,微震总能量为6.40×10^(3)J,矿压显现期间为1.07×10^(4)J,总能量增长67%;由于综采面矿压显现与微震最大能量峰值出现一致,通过2次最大能量峰值时综采面位置可以确定综采面周期来压步距。2203综采面初次来压步距为24.75 m,周期来压步距为27~35.25 m,由此确定,顺槽超前支护距离为36 m,实践表明,2203综采面采用ZCZY10300/31/55D型超前液压支架满足巷道超前支护的要求。微震监测是矿压显现规律分析的有效手段,采用液压支架压力变化与微震能量协同分析的方法研究超大采高综采面的矿压规律是可行的。

厚煤层大采高综放工作面覆岩断裂演化规律研究

大采高综放开采易形成强烈的矿压显现,上覆岩层的断裂演化规律对工作面安全生产至关重要。以羊场湾煤矿160206工作面为工程背景,运用相似模拟试验、数值模拟和理论分析的综合研究方法,对大采高综放工作面覆岩的断裂过程与覆岩运移规律进行系统研究。研究表明:导水裂隙带内岩层随工作面推进表现为“台阶下沉”,同层岩层下沉趋势沿走向表现为“急剧下降—稳定(最大值)—快速上升—稳定(最小值)”。工作面覆岩运动场由两区分布(加速下沉区、缓慢下沉区)演化为三区分布(加速下沉区、缓慢下沉区、稳定区)。对离层演化与地表下沉规律进行了定量描述,运用理论计算表达式深入地剖析了地表的动态下沉机理及其相关因素。结合相似模拟与数值模拟的试验结果,提出了覆岩断裂演化的形态变化特征:覆岩断裂形态由“单等腰梯形”演化为“双等腰梯形”,表土层影响区由“矩形”演化为“倒梯形”。分析了覆岩中垮落区、离层区、压实区、裂隙富集区的动态演化过程:垮落区逐渐增大至一定程度,高度小幅度降低并趋于稳定,离层区由下至上逐渐发育并随工作面向前移动,离层区逐渐闭合形成压实区,且压实区逐渐增大并最终保持稳定,裂隙富集区位于采空区前后端部并随工作面向前移动。

6~10 m厚煤层超大采高液压支架及其工作面系统自适应智能耦合控制

厚煤层储量及产量占我国原煤总储量及产量的一半,通过梳理厚煤层开采历史沿革,总结了我国厚煤层开采40年来的技术及装备研发实践,系统分析了以高端大采高液压支架及围岩智能耦合理论为代表的6~10 m大采高综采高效智能化综采技术及装备研究进展,提出了大采高支护理论及围岩智能耦合控制的突破是厚煤层一次开采高度突破的首要因素,完善的感知体系建立是液压支架自适应支护的前提,数字技术的应用为大采高工作面高效推进及装备智能协同控制提供了新的技术途径;阐明了大采高综放液压支架与围岩耦合关系,剖析了采高增加对硬煤层冒放性的有利影响,提出了基于煤矸识别、放煤机构控制的“纯煤段记忆放煤+煤岩分界模糊段人工反馈式干预放煤”的智能放煤控制策略;分析了大采高开采“采–运”协同智能耦合控制关键技术,构建了基于采煤机牵引速度与刮板输送机链速间联动调节的工作面装备间多机异构耦合自适应协同控制模型;研发了厚煤层开采中10 m超大采高液压支架,分析了厚煤层开采不断突破开采高度极限的新认识,从开采装备、控制系统等方面提出厚煤层一次开采高度的突破的研发方向。

超大采高综采工作面支护技术及装备研究现状

超大采高一次采全厚开采具有开采效率高、资源回收率高等特点。为探求超大采高综采技术进一步突破,分析其工作面围岩稳定性控制可行性,在调研超大采高综采发展历程的基础上,总结了超大采高综采工作面围矿压显现及煤壁片帮规律,分析了现有超大采高液压支架整体技术特征及其适用性能,并介绍了10 m超大采高工作面液压支架基本情况。通过分析发现:工作面矿压显现强度与采高基本呈现正相关关系,采高越大,工作面支护阻力越大,且煤壁片帮是困扰超大采高开采高效推进的主要因素之一,通过提高工作面液压支架的初撑能力能有效减小煤壁应力;液压支架随工作面采高增加,选型工作阻力增大,支架中心距加宽,大梯度过渡方式在提供可靠支护的同时,能有效提升端头区资源回收率;为适应大体量开采装备运输,超大采高工作面煤巷断面增加,超前支架工作阻力增大;工作面配套液压支架通过设计手段、整体结构、制造工艺等方面优化升级以提升可靠性及适应性;相对较低采高工作面支护,超大采高开采更注重支护过程中的安全技术需求,需要完善架前煤矸防护、架间防尘降尘、安全的后期维检等安全措施;工作面围岩稳定性控制及其配套装备是超大采高综采技术发展及推广的重点,从支护参数选择、支护结构设计到液压支架制造、后期维检的超大采高液压支架全寿命开发是支撑超大采高开采高效推进的基础。