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.

Key technologies and equipment for a fully mechanized top-coal caving operation with a large mining height at ultra-thick coal seams

Thick and ultra-thick coal seams are main coal seams for high production rate and high efficiency in Chinese coal mines, which accounts for 44 % of the total minable coal reserve. A fully mechanized top-coal caving mining method is a main underground coal extraction method for ultra-thick coal seams. The coal extraction technologies for coal seams less than 14 m thick were extensively used in China. However, for coal seams with thickness greater than 14 m, there have been no reported cases in the world for underground mechanical extraction with safe performance, high efficiency and high coal recovery ratio. To deal with this case, China Coal Technology ＆ Engineering Group, Datong Coal Mine Group, and other 15 organizations in China launched a fundamental and big project to develop coal mining technologies and equipment for coal seams with thicknesses greater than 14 m. After the completion of the project, a coal extraction method was developed for top-coal caving with a large mining height, as well as a ground control theory for ultra-thick coal seams. In addition, the mining technology for top-coal caving with a large mining height, the ground support technology for roadway in coal seams with a large cross-section, and the prevention and control technology for gas and fire hazards were developed and applied. Furthermore, a hydraulic support with a mining height of 5.2 m, a shearer with high reliability, and auxiliary equipment were developed and manufactured. Practical implication on the technologies and equipment developed was successfully completed at the No. 8105 coal face in the Tashan coal mine, Datong, China. The major achievements of the project are summarized as follows： 1. A top-coal caving method for ultra-thick coal seams is proposed with a cutting height of 5 m and a top-coal caving height of 15 m. A structural mechanical model of overlying strata called cantilever beam-articulated rock beam is established. Based on the model, the load resistance of the hydraulic support with a large mining height for top-coal caving method is determined. With the analysis, the movement characteristics of the top coal and above strata are evaluated during top-coal caving operation at the coal face with a large mining height. Furthermore, there is successful development of comprehensive technologies for preventing and controlling spalling of the coal wall, and the top-coal caving technology with high efficiency and high recovery at the top-coal caving face with a large mining height. This means that the technologies developed have overcome the difficulties in strata control, top-coal caving with high efficiency and high coal recovery, and enabled to achieve a production rate of more than 10 Mtpa at a single top-coal caving face with a large mining height in ultra-thick coal seams; 2. A hydraulic support with 5.2 m supporting height and anti-rockburst capacity, a shearer with high reliability, a scraper conveyor with a large power at the back of face, and a large load and long distance headgate belt conveyor have been successfully developed for a top-coal caving face with large mining height. The study has developed the key technologies for improving the reliability of equipment at the coal face and has overcome the challenges in equipping the top-coal caving face with a large mining height in ultra-thick coal seams; 3. The deformation characteristics of a large cross-section roadway in ultra-thick coal seams are discovered. Based on the findings above, a series of bolt materials with a high yielding strength of 500-830 MPa and a high extension ratio, and cable bolt material with a 1 × 19 structure, large tonnage and high extension ratio are developed. In addition, in order to achieve a safe roadway and a fast face advance, installation equipment for high pre-tension bolt is developed to solve the problems with the support of roadway in coal seams for top-coal caving operation with a large mining height; 4. The characteristics of gas distribution and uneven emission at top-coal caving face with large mining height in ultra-thick coal seams are evaluated. With the application of the technologies of gas drainage in the roof, the difficulties in gas control for high intensive top-coal caving mining operations, known as ＂low gas content, high gas emission＂, are solved. In addition, large flow-rate underground mobile equipment for making nitrogen are developed to solve the problems with fire prevention and safe mining at a top-coal caving face with large mining height and production rate of more than 10 Mtpa. A case study to apply the developed technologies has been conducted at the No. 8105 face, the Tashan coal mine in Datong, China. The case study demonstrates that the three units of equipment, i.e., the support, shearer and scraper conveyor, are rationally equipped. Average equipment usage at the coal face is 92.1%. The coal recovery ratio at the coal face is up to 88.9 %. In 2011, the coal production at the No. 8105 face reached 10.849 Mtpa, exceeding the target of 10 Mtpa for a topcoal caving operation with large mining height performed by Chinese-made mining equipment. The technologies and equipment developed provide a way for extracting ultra-thick coal seams. Currently, the technologies and equipment are used in 13 mining areas in China including Datong, Pingshuo, Shendong and Xinjiang. With the exploitation of coal resources in Western China, there is great potential for the application of the technologies and equipment developed.

Experimental investigation into stress-relief characteristics with upward large height and upward mining under hard thick roof

According to geological conditions of No. 3 and No. 4 coal seams （namely A3 and B4） of the Pan＇er coal mine and the parameters of panels 11223, 11224, and 11124 with fully-mechanical coal mining, we built 2D similar material simulation and FLAC3D numerical simulation models to investigate the development of mining-induced stress and the extraction effect of pressure-relief gas with large height and upward mining. Based on a comprehensive analysis of experimental data and observations, we obtained the deformation and breakage characteristics of strata overlying the coal seam, the development patterns of the mining-induced stress and fracture, and the size of the stress-relief area. The stress-relief effect was investigated and analyzed in consideration with mining height and three thick hard strata. Because of the group of three hard thick strata located in the main roof and the residual stress of mined panel 11124, the deformation, breakage, mining-induced stress and fracture development, and the stress-relief coefficient were discontinuous and asymmetrical. The breakage angle of the overlying strata, and the compressive and expansive zones of coal deformation were mainly controlled by the number, thickness, and strength of the hard stratum. Compared with the value of breakage angle derived by the traditional empirical method, the experimental value was lower than the traditional results by 3°-4°below the hard thick strata group, and by 13°-19° above the hard thick strata group. The amount of gas extracted from floor drainage roadway of B4 over 17 months was variable and the amount of gas per month differed considerably, being much smaller when panel 11223 influenced the area of the three hard thick strata. Generally, the stress-relief zone of No. 4 coal seam was small under the influence of the hard thick strata located in the main roof, which played an important role in delaying the breakage time and increasing the breakage space. In this study we gained understanding of the stress-relief mechanism influenced by the hard thick roof. The research results and engineering practice show that the main roof of the multiple hard thick strata is a critical factor in the design of panel layout and roadways for integrated coal exploitation and gas extraction, provides a theoretical basis for safe and high-efficient mining of coal resources.

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.

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.

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 W9-15 101 fully mechanized caving face with was carried out in a geological model of large mining height in the Liuhuanggou Colliery, in Xinjiang Uigur Autonomous Region. The roof overlying strata movement law in the stope of a fully mechanized caving face with large mining height was studied and show that the roof overlying strata in the stope of a fully mechanized caving face with large mining height can be formed into a stable arch structure; the fracture rock beam is formed resembling a ＂bond beam＂, but it has essentially the structure of ＂multi-span beams＂ under the big structure of the stable arch. The roof overlying strata movement law in the stope of a 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 of the structure of ＂multi-span beams＂. But because of the differences between the mining heights, the peak pressure in the stope of a fully mechanized caving face with large mining height is smaller while the affected area of abutment pressure is wider in the front of the working face; this is the obvious difference in abutment pressure between the stope of a fully mechanized caving face with large mining height and that of the common.

Technological optimization of fully mechanized caving mining face with large mining heights

Fully mechanized cave mining with large mining height is a new mining method, due to its large mining thickness and lower roadway excavation, the technology has been widely used in China＇s thick seam mining. In order to improve the top-coal recovery ratio of fully mechanized cave mining with large mining height, a study was conducted on optimizing the caving process, based on the mechanized caving face 1302N in Longgu Coal Mine. This was achieved by improving the PFC numerical calculation methods, and establishing a more accurate model system. On this basis, the recovery ratio of the top coal in different drawing intervals and technologies was investigated in order to achieve a reasonable caving process. The top-coal tracking system was used for practical surveying of the recovery ratio of top coal.

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.

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。

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。

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。

基于MATLAB大采高液压支架稳定性仿真研究

针对液压支架存在失稳等重大安全隐患,以某型大采高液压支架为研究对象,对支架前倾、后仰、侧翻、滑移4种失稳进行分析,运用MATLAB仿真的方法对不同采高、底座宽度、极限倾角、煤层倾角、加载载荷下的支架重心高度等进行仿真分析和研究。研究结果表明:随着支架极限倾角的增加,支架重心高度呈现逐渐减小的趋势;随着支架底座宽度增加,支架重心高度呈现逐渐增加的趋势;随着采高高度的增加,最大、最小煤层倾角呈现逐渐减小的趋势;随着支架底座宽度增加,最大、最小煤层倾角呈现逐渐增加的趋势;随着加载载荷增加,煤层倾角呈现逐渐减小的趋势。该研究为液压支架稳定性、安全可靠性提高等方面提供理论基础。

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。

深地煤炭资源安全高效智能化开采关键技术与实践

深地煤炭资源地质赋存复杂,智能化开采是深地资源安全、高效、绿色发展的必由之路。智能化开采成套技术与装备能否适应千米深井复杂地质环境、控制围岩稳定并驱动装备跟随煤层自动推进是影响煤炭安全高效开采、减少作业人员、降低劳动强度的关键。山东能源集团聚焦千米深井智能化开采围岩控制理论,提出了以强度耦合、刚度耦合和稳定性耦合为核心的支架-围岩智能耦合关系,并形成与之相适应的智能耦合控制逻辑;为突破超大采高智能综采开采工艺及超高煤壁围岩控制技术瓶颈,提出了超大采高液压支架工作阻力“双因素控制法”,发明了三滚筒采煤机及其配套开采方法,研制了与超大采高智能综采相匹配的液压支架及配套系统;针对超大采高综放开采智能化放煤理论与围岩控制难题,提出超大采高综放支架-围岩耦合协调采放空间控制方法,创新了超大采高综放“马鞍形”开采工艺,研制了7 m超大采高智能综放开采液压支架及配套系统;研发了无反复支撑、快速循环自移的单元式超前支架,解决了回采巷道超前支护距离长、支护技术与装备适应性差的问题;开发了基于惯导和精准地质模型的智能采煤控制系统,解决了深部矿井工作面设备智能控制及困扰连续生产的难题;搭建了千米深井智能化开采综合管控平台,实现了千米深井重大灾害多源异构数据融合与管控。上述核心技术在山东能源集团赵楼煤矿7302工作面、东滩煤矿3308工作面等多个工作面进行了智能化开采示范建设,取得了良好的应用效果,所获成果整体推动了我国深地煤炭资源安全高效智能化开采水平,可以为类似矿井智能化工作面建设提供理论与技术借鉴。

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。

深部特厚煤层综放沿空掘巷煤柱优化及巷道支护

为研究深部大采高综放工作面窄煤柱沿空掘巷巷道矿压控制问题,以国能宁煤集团枣泉煤矿2^(-2)特厚煤层130203大采高综放工作面回风巷道为背景,基于实用矿山压力理论,建立了巷道围岩内、外应力场动态结构力学模型,运用理论计算和数值计算针对不同尺寸煤柱煤体应力对比分析,将原留设15 m护巷煤柱缩小至5 m进行了煤柱优化。结果表明:在稳定的内应力场掘巷有利于巷道的稳定性,避免了顶板事故及冲击地压相关灾害的发生,现场5 m小煤柱护巷工程应用中,130203回风巷道小煤柱侧变形量为1050 mm,实体煤帮变形量为400 mm,两帮呈现不对称性变形,底板局部底鼓量为1400 mm;深部特厚煤层综放开采沿空掘巷采用5 m小煤柱护巷方案设计正确,极大改善了巷道围岩的应力环境,整体设计满足生产要求,现场应用良好。130203工作面小煤柱沿空掘巷技术成功应用,为矿井开采提供了可靠的科学依据。

大采高工作面柔模沿空留墙掘巷技术

柔模混凝土沿空留巷技术已应用多年,在中厚煤层和薄煤层开采下均取得了较好的支护效果,但在厚煤层大采高工作面,因巷道高、巷旁支护压力大、混凝土早期强度低易受压损坏难以有效支撑顶板。大采高工作面矿压显现剧烈,巷旁维护难度大,故此提出一种新型的预浇墙柔模混凝土沿空留墙掘巷新技术,即在上工作面回采前,刷煤扩帮后提前预浇柔模混凝土墙体,提高煤帮整体支撑力的同时,解决柔模混凝土墙短期无法有效承载顶板来压的难题;待回采一定距离后,再沿墙滞后掘进下工作面回采巷道,且掘进方向与上工作面回采方向一致,缓解接续紧张,最终实现无煤柱开采。以王庄煤业3503工作面回采留设预浇墙为工程背景,建立了沿空留墙掘巷围岩结构力学模型,理论计算得出墙体力学支护参数,并通过现场应用验证了该技术的可实施性。结果表明:理论计算分析确定了墙体高宽比为5 m×1.5 m,混凝土强度C30即可满足留墙支护要求;沿墙掘进巷道总体变形量小,顶底板和两帮最大移近量仅为260 mm和125 mm,墙体最大受压18 MPa,小于墙体自身承载力;下工作面临近巷道掘进115 m后即趋于稳定。该技术应用全阶段效果良好,满足巷道使用要求,有效解决了大采高工作面沿空留巷重大技术难题,也可为相似工况无煤柱开采提供技术借鉴。

西部大采高工作面保护煤柱宽度优化研究

保护煤柱尺寸一直是三下开采研究的热点问题,特别是在西部大采高软弱覆岩特厚煤层开采条件下,其对地表建筑物安全的影响有待进一步研究。以榆树湾井田20119工作面为例,综合利用数值模拟和概率积分法确定了合理保护煤柱宽度,并进行现场验证。结果表明:随着煤柱宽度的减小,地表沿X方向的水平移动呈现倒“S”型趋势,沿Y方向的移动呈现倒“U”型趋势,地表的最大下沉量随煤柱宽度的减小而不断减少;结合概率积分法对保护煤柱宽度进行预计,确定优化后的煤柱宽度为180 m;对现场村庄进行实时监测,地表下沉和倾斜值均满足现场施工要求,验证了保护煤柱宽度的合理性。