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.

Trial of small gateroad pillar in top coal caving longwall mining of large mining height

Coal seams in Tashan Mine of Datong Coal Group in China average 15 m thick and have been mined by the top coal caving longwall mining method of large mining height. Mining height was 3.8 m and the top coal caving height was 11.2 m. The gateroad pillar between panels was 38 m. During retreat mining,serious bumps occurred in the gateroads on both sides of the pillar affecting safety production. Therefore,pillarless mining was experimented. Using numerical modeling and comparative study of cases of similar mining condition,it was decided to employ a 6 m wide pillar,rather than the previous 38 m wide pillar.Support system for the gateroads was designed and implemented. During gateroad development,pillar failure conditions and entry deformation were monitored. Hydraulic fracturing method was employed to cut off the K3 sandstone along the entry rib so as to reduce the abutment pressure induced during retreat mining. Support reinforcement method combining grouting and advanced reinforcement methods was proposed to insure stable gateroad ahead of mining. Methane drainage and nitrogen injection were implemented to eliminate hazards associated with mine fire and spontaneous combustion. Since the development of gateroad has just completed,and retreat mining has not begun,the effectiveness of the proposed methods is unknown at this point. However,monitoring will continue until after mining.The results will be published in a separate paper.

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.

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.

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.

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.

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.

Formation mechanism and height calculation of the caved zone and water-conducting fracture zone in solid backfill mining

To study the heights of the caved zone and water-conducting fracture zone in backfill mining,the failure mechanism of strata during backfill mining was analyzed,and a method for determining the heights of the two zones was proposed based on key strata theory.The movement and failure regularity of the strata above the backfilling panel were revealed through numerical simulation.Considering the geologic conditions of the CT101 backfilling panel,the height of the fracture zone was determined using the proposed method along with empirical calculation,numerical simulation,and borehole detection.The results of the new calculation method were similar to in situ measurements.The traditional empirical formula,which is based on the equivalent mining height model,resulted in large errors during calculation.The findings indicate the reliability of the new method and demonstrate its significance for creating reference data for related studies.

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.

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.

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。

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。

大倾角大采高软弱顶底板工作面分区矿压规律研究

为研究内蒙古长城二矿大倾角大采高软弱顶底板复杂开采地质条件下,1305S工作面正常区、过渡区、卸压区的矿压显现规律及特征,建立了倾斜煤层采空区冒落矸石滑移充填数值模拟模型,采用数值模拟和现场实测相结合的研究方法进行研究。研究结果表明:沿倾斜方向,1305S工作面中上部所受垂直应力呈现出过渡区>正常区>卸压区的特点,工作面下部呈现出卸压区>过渡区>正常区的特点;1305S工作面推进过程中,平均周期来压步距为13.3 m,周期来压时支架工作阻力在26.75~33.05 MPa之间,沿工作面倾斜方向顶板所受垂直应力总体呈现出工作面上部>中部>下部的特点;巷道工作面一侧的边帮变形量较大。现场实测结果表明,回风巷顶板监测最大移进量为860.18 mm,运输巷顶板监测最大移进量为367.84 mm,两巷围岩移进量呈现出回风巷>运输巷的特点。

大倾角大采高工作面上出口行人防护研究与应用

采煤工作面上出口作为工作面压力显现集中区之一,不但是人员、设备、材料的集中区,还是人员、设备和材料进出工作面的交接口。上出口行人防护对人员和设备安全的至关重要。针对上出口顶板倾角大、巷道高度变化大、高帮与巷道底板高差大、空顶面积大等问题,研究一种新型行人防护支架,以达到保证行人安全的目的。

厚煤层大采高综采面顶板破断规律及机理研究

以杭来湾煤矿首个大采高30201工作面为例,通过数值模拟、理论分析和现场实测的方法,分别对工作面开采过程中顶板破断规律进行研究。基本顶以“悬臂梁”、“砌体梁”的结构形式周期发生破断,造成工作面大、小周期来压显现。建立了工作面顶板力学模型,给出来压步距的计算方法。现场实测表明最大步距67.6 m是平均步距34.4 m的1.97倍,说明约2次小周期来压才有1次大周期来压。

负压通风条件采煤机附近高度及风速对粉尘浓度影响研究

大采高综采工作面采煤机割煤产尘是工作面的重大尘源,严重影响采煤机司机及工作人员的安全。为研究负压通风条件大采高(6m)综采工作面采煤机附近高度及风速对粉尘浓度的影响,基于自主搭建的相似实验平台和FLUENT数值模拟方法,研究了不同风速下采煤机附近不同高度及相同高度的粉尘沿程分布和采煤机处风流分布及割煤粉尘的运移,并提出了综合防尘建议。相似实验结果表明,割煤机道与回风巷道近下帮粉尘浓度随高度降低而增加,且回风隅角中煤壁和采空区附近的低风速和涡流使得粉尘浓度下降幅度很大;同一截面同一高度下粉尘浓度随风速增大而减小,风速较小时粉尘浓度变化曲线较平缓。数值模拟结果表明:采煤机滚筒风流的阻碍使得采煤机机身前的风流流动方向向采煤机偏移,高速风流会对采煤机司机产生不利影响;采煤机道空间断面上,靠近采煤机区域距离工作面顶板越近,粉尘浓度越大;建议大采高综采面通风除尘风速不应低于2m/s,采煤机下风侧20~50m粉尘扩散范围开启喷雾装置。研究结论为大采高综采面粉尘治理提供一定的参考。