Deformation mechanism of surrounding rocks and key control technology for a roadway driven along goaf in fully mechanized top-coal caving face

The variation of the stress in the bolted surrounding rocks structure of the roadway driven along goaf in a fully mechanized top coal caving face with moderate stable conditions are studied by using numerical calculation. The essential deformation characteristics of the surrounding rocks in this kind of roadway are obtained and the key technology of bolting support used under these conditions is put forward.

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 pro- posed; these include pouring water, stopping leakage in upper and lower comers of the working face, choking off the goaf and cov- eting the coal. CO concentrations were controlled within two years to less than 15×10^-6 at the upper comer by applying these tech- nologies at the 1410 working face of the Huafeng coal mine. Our method has significant theoretical value and is of practical impor- tance in controlling spontaneous coal combustion occurring at a fully mechanized caving face with large obliquity in deep mines.

Study of mechanical principle of floor heave of roadway driving along next goaf in fully mechanized sub-level caving face

Abstract On the basis of analyzing floor strata mechanical circumstance of the roadway, the mechanical model was established. The relative displacement of roadway floor, narrow pillar floor coal mass and floor strata was calculated, the results showed that the high abutment pressure on coal mass beside the roadway was the main reason to lead to relative displacement of floor strata. And the roadway floor heave come mainly from three aspects. Firstly, the roadway floor strata is easily fractured by the stretch stress. Secondly, because the high abutment pressure is greater than the uniaxial compressive strength of floor strata, when the roadway floor strata are fractured, the coal mass floor strata at the same depth will be fractured, and broken rock will fluid into the open roadway. Thirdly, comparing with the coal mass floor, the roadway floor is relative ascending.

Stability Control of Gob-Side Entry Retaining in Fully Mechanized Caving Face Based on a Compatible Deformation Model

The stability control of gob-side entry retaining in fully mechanized caving face is a typical challenge in many coal mines in China.The rotation and subsidence of the lateral cantilever play a critical role in a coal mine,possibly leading to instability in a coal seam wall or a gob-side wall due to its excessive rotation subsidence.Hence,the presplitting blasting measures in the roof was implemented to cut down the lower main roof and convert it to caved immediate roof strata,which can significantly reduce the rotation space for the lateral cantilever and effectively control its rotation.Firstly,the compatible deformation model was established to investigate the quantitative relationship between the deformation of the coal seam wall and the gob-side wall and the subsidence of the lateral cantilever.Then,the instability judgments for the coal seam wall and gob-side wall were revealed,and the determination method for the optimal roof cutting height were obtained.Furthermore,The Universal Distinct Element Code numerical simulation was adopted to investigate the effect of roof-cutting height on the stability of the retained entry.The numerical simulation results indicated that the deformation of the roadway could be effectively controlled when the roofcutting height reached to 18 m,which verified the theoretical deduction well.Finally,a field application was performed at the No.3307 haulage gateway in the Tangan coal mine,Ltd.,Shanxi Province,China.The field monitoring results showed that the blasting roof cutting method could effectively control the large deformation of surrounding rocks,which provided helpful references for coal mine safety production under similar conditions.

Statistic constitutive equation of top-coal damage for fully mechanized coal face with sublevel caving

Under the action of abutment pressure in front of fully mechanized coal face with sublevel caving(CFSC),top-coal over CFSC deformed.In the process of whole de- formation of top-coal,it changed from continuum elastic mass to non-continuum plastic mass contained fissures,become a loose body.According to its bearing characteristics and mechanical properties,top-coal mass can be divided into four deformation zones along the winning direction of CFSC,i.e.initial stress zone,elastic zone,plastic zone and loose zone.Top-coal in plastic zone located in the post-peak zone of the stress-strain curve for top-coal.With equivalent strain principle of damage mechanics and mathemati- cal theory of statistic,combining the movement law of top-coal,set up a constitutive equa- tion with damage statistics for top-coal in different position in CFSC.The equation illus- trated the mathematical relationship among top-coal bearing capacity,horizontal confining pressure along the winning direction of CFSC and mechanical properties of top-coal mate- rial.The conclusions not only provide a basis for numerical computer simulations on damage deformation and failure mechanism for top-coal,but also further promote the ap- plication of damage mechanics in CFSC.

Distribution laws of abutment pressure around fully mechanized top-coal caving face by in-situ measurement

In order to obtain the distribution rules of abutment pressure around the 1151 （3） fully mechanized top-coal caving （FMTC） face of Xieqiao Colliery, the KSE-II-1 type bore-hole stress gauges were installed in the tailentry and headentry to measure the mining-induced stress. The distribution rules of the front and side abutment pressure were demonstrated. The results show that distribution rules of stress are obviously different in the vicinity of the face and entries. The peak value of abutment pressure in the protective coal pillar and face are located commonly in front of the working face along the strike, and they are located at the stress-decreased zone near the face. There is no stress peak value in the lateral coal mass beside the headentry in front of the face on the strike, and the peak value of abutment pressure appears at the rear area of the face. There are stress peak values both in the protective coal pillar and in the lateral coal mass beside the headentry to the dip.

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.

Reliability analysis of the velocity matching of coal cutting and caving in fully mechanized top-coal caving face

The matching relationship between coal cutting and caving in fully mechanized top-coal caving face is analyzed in detail from the angle of reliability. The coupling equation of reliability is established correspondingly, and the mathematical equation of the coefficient of velocity matching of coal cutting and caving is obtained, which meets a certain reliability demand for making the working procedure of coal caving not influence coal cutting of coal-cutter. The results show that the relationship between the coefficient of the velocity matching and the reliability of coal cutting and caving system is linear on the whole when R <0.9. It is pointed out that different numerical value should be selected for different coal face according to different demand for reliability.

Numerical simulation on the delivery law of gob gas of fully mechanized caving face

According to the cover rock caving features,the gob of fully mechanized caving face was divided into 3 zones: natural collected zone,pressure effecting zone and press stable zone.Based on these and the gob gas flow control equation,and considered the in- fluence to the mining fissured zone of gas drainage,also made use of CFD software,we found an not uniform 3D numerical model of gob gas seepage and got the gas emission law in gob of fully mechanized caving face (with or without discharge measures),and this can guide the engineering practice in some aspects.

Back-and-forth mining for hard and thick coal seams—research about the mining technology for fully mechanized caving working face of Datong Mine

The article introduced the key technology, mining process, and back-and-forth mining method for the caving working face of hard-thick coal seams in Datong mine, and researched this innovations process, optimized the systemic design and working face out-play, tried to perfect the caving mining technology of hard-thick coal seams further.

Investigation on the stress field characteristic of top coal at FMTC faces under the influence of caving thickness

In the background of the technology condition and the geological condition of the 1151（3） fully mechanized top-coal caving face （FMTC face）, and by means of taking nonlinear 3D numerical simulation, the stress redistribution rules of top coal with different thick coal seam were obtained by investigation on the numerical simulation of the redistributions of the stress with different coal seam＇s thickness. The research showes that there exists a certain difference on the stress distributions of the top coal at face, the maximum principal stress is located near to the tailentry＇s corner. The vertical stress＇s peak of the top coal decreases and the distance ahead of face position increases as the once mining thickness of the coal seam increases. At the same coal seam, the vertical stresses＇ peak of top coal gradually decreases from the top to the bottom, the peak＇s position is basically the same and its changes are gradually obvious with the thickness of coal seam increas- ing. The vertical stress of top coal places in a low stress state at a certain range ahead of face and over the face, which reveals the essence that the support loads are generally low under the condition of FMTC. The study supplies the theoretical foundation for the support design and selection, the theory of top coal＇s fragmentation, the movement rules of top coal and improving the recovery of top coal.

STUDY ON PRODUCTION SYSTEM OPERATION REGULARITY OF FULLY MECHANIZED SUBLEVEL CAVING MINING AND SEQUENTIAL OPERATION

According to a lot of practical data in Liujialiang Mine and reliability theory and result of computer simulation, operation regularity of fully mechanized sublevel caving mining production system in the condition of gently inclined complicated geological structure and production shortcomings are found out and reliability of system and output of the working face are predicted finally.

综放工作面围岩控制与智能化放煤技术现状及展望

分析了厚及特厚煤层智能化综放工作面围岩控制技术与智能化放顶煤技术发展现状及存在的问题,从巷道围岩高效支护、工作面超前支护、坚硬特厚顶煤冒放性、液压支架位姿监测及智能化放顶煤5个方面提出了工程实际需求。针对综放工作面实现安全、高效、智能化开采存在的技术难题与工程需求,对综放工作面围岩控制技术、智能化放煤技术进行了研究:构建了坚硬特厚煤层顶煤悬臂梁力学模型,研发了提高顶煤冒放性及放出率关键技术,实现了坚硬特厚煤层超大采高综放开采;研发了单元式超前液压支架顶梁可旋转自复位装置,实现了液压支架顶梁根据巷道顶板倾斜角度自动旋转支护,有效提高了单元式超前液压支架对巷道顶底板的适应性;提出了采用巷道支护液压支架替代传统锚网支护结构的思路,具有支护效率高、成本低、节省工作面超前支护等优点;开发了基于立柱与尾梁千斤顶行程的综放液压支架支护姿态监测装置与算法,提高了液压支架支护姿态解算效率与精度;提出了基于透明地质模型、煤量监测装置与煤矸识别装置融合的智能放煤控制方法,可有效解决多夹矸层特厚顶煤智能化放煤技术难题。提出智能地质保障技术、机器视觉精准测量与智能感知技术、综放工作面设备智能精准自适应控制技术、综放工作面数字孪生技术等是智能化综放开采技术与装备的发展趋势。

近距离煤层采空区下综放工作面巷道合理位置研究

近距离煤层综放工作面开采空间大,采动强度高,下位煤层回采巷道受上煤层采动影响存在应力集中、巷道支护困难等问题,因此近距离煤层综放工作面巷道合理位置的选取对后期支护控制起到关键性作用。以西露天煤矿2煤层和1煤层1分层为研究对象,综合考虑了上煤层开采时的底板应力降低区域和下煤层开采时的极限平衡区域,确定了下煤层巷道的合理位置应在距离实体煤柱内错22.79 m以上的区域。基于上述理论计算结果,分析了上煤层开采后底板应力分布规律及不同内错距下巷道围岩变形破坏特征及规律,结果表明:①距离采空区底板越近,应力最大值与最小值相差越明显;②随着内错距不断增大,围岩应力和应力集中系数呈现急剧降低-缓慢增大-稳定的趋势,在内错距20~25 m内应力及应力集中系数相对较小;③巷道围岩塑性区范围呈现先减小后增大的趋势,当巷道处于内错20,25 m时巷道围岩破坏相对较小;④巷道变形量随着内错距增大而逐渐减小,当内错距增加至25 m时,巷道围岩移进量基本保持不变;⑤确定巷道合理内错距为20~25 m。工程应用结果表明:巷道采用内错距24 m布置时,巷道围岩松动破坏深度及变形量均在可控范围内,进一步证明了该内错距的合理性。

综放面强动压区巷道变形破坏特征及锚索强化支护机理研究

针对山西宁武榆树坡煤业有限公司5107综放工作面开采强度大、超前支护劳动强度高、动压区巷道变形严重等问题,监测分析综放工作面超前段巷道围岩变形破坏特征,建立了巷道顶板锚索支护力学结构模型,基于冒落拱理论与悬吊理论精准量化动压区回采巷道所需强化支护强度,建立数值模拟模型分析综放工作面超前支承压力分布规律,优化综放面强动压区回采巷道锚索强化支护参数并进行工业性试验。结果表明,综放工作面动压区回采巷道超前支护强度整体不足,巷道顶板起伏剧烈,侧帮严重鼓出,严重制约安全生产;结合冒落拱理论与悬吊理论分析了巷道厚煤层开采顶煤破坏冒落特征,精准量化了动压区回采巷道超前段所需强化支护强度为33.74 kN/m^(2);通过数值模拟确定了“3根全长锚固补强锚索”,最外侧锚索向外倾斜15°的补强支护方式可有效控制动压区回采巷道围岩变形;进行了现场工业性试验,试验表明5107工作面回风巷顶底板、左右帮变形分别为81、189、134、145 mm,锚索补强支护条件下回风巷超前段围岩平整规则、整体稳定性良好。

两次采动影响下小煤柱巷道切顶卸压围岩控制技术

为解决多次采动影响下留小煤柱巷道矿压显现剧烈、围岩变形量大的问题,提出了“切顶卸压+顶、帮锚索补强”联合控制技术。以贾家沟煤矿10115运输巷为工程背景,分析了切顶卸压位置、高度与巷道围岩垂直应力分布的关系,给出切顶卸压关键参数,并研究了留小煤柱巷道在切顶卸压后受两次采动影响下的矿压显现规律。结果表明:切顶卸压后,煤柱上的应力峰值随切顶深度的增加呈指数降低;10115运输巷在邻近工作面一次采动过程中巷道围岩变形依次呈现出无变形、缓慢变形、快速变形和围岩稳定的变化规律,本工作面二次采动过程中巷道围岩变形依次呈现出明显变形和剧烈变形的规律;巷道围岩在受二次采动影响时变形更加剧烈,巷道变形量为一次采动时的3.0~7.5倍。

注氮条件下大采高综放工作面采空区自燃“三带”的分布规律

为解决大采高综放工作面因采高大、回采率低、开采扰动强等造成采空区遗煤自燃危险性增大的问题,以宁夏某煤矿大采高综放工作面为研究对象,应用渗透率演变方程和气体流动模型,分析注氮前后氧浓度时空演化规律及采空区自燃“三带”分布特征。结果表明:采空区氧浓度在注氮条件下呈现出中部大,两侧小的倒“U”型分布;在氧浓度划分下,氧化带范围呈现出先增大后减小的半月形,最大宽度由未注氮时的100 m缩小到50 m;在风速划分下,氧化带较未注氮时整体向工作面方向前移了15 m左右,有效降低了自燃危险区范围。

胡家河煤矿综放工作面矿压显现规律预测及主控因素研究

现有工作面矿压显现规律预测方法中,基于数值模拟与统计回归的方法无法实现对工作面矿压显现规律的实时精准预测,深度学习方法存在超参数较多且难以设置、模型训练速度慢等问题。针对上述问题,以胡家河煤矿402102回采工作面采动过程中监测到的煤体内部应力变化时序数据为基础,将基于粒子群优化的门控循环单元(PSO-GRU)应用到回采工作面矿压显现规律预测中。采用PSO算法对GRU进行优化,构建PSO-GRU模型,实现对超参数的自动寻优,从而提高GRU的训练速度和预测精度。以预测结果为依据,采用层次分析法建立402102回采工作面矿压主控因素评价指标体系,将顶板条件、回采工艺、煤层赋存、地质构造确定为影响工作面矿压的一级指标,进一步细分出具有代表性的14个二级指标。测试结果表明:(1)与未经优化的GRU模型相比,PSO-GRU模型的均方误差(MSE)降低了83.9%,均方根误差(RMSE)降低了59.8%,平均绝对误差(MAE)降低了59.0%,决定系数R2提升了28.9%。(2)PSO-GRU模型对矿压数据预测的拟合度达0.980以上,具有良好的非线性拟合能力和泛化能力。(3)地质条件中的煤层赋存因素对回采工作面矿压的影响最大,权重为0.47;可人为干预的影响因素中工作面推进速度对矿压的影响最大,权重为0.13。

近距离煤层厚硬顶板综放开采强矿压显现规律研究

针对厚硬顶板大采高综放工作面回采过程中强矿压的现象,以神东矿区某矿井近距离煤层厚硬顶板综放工作面为背景,通过现场实测和室内试验等方式,研究工作面矿压显现规律及覆岩破断特征。研究表明:(1)42105综放工作面老顶初次来压步距大,来压强度高,远超工作面支架额定工作阻力,工作面呈现出中部来压集中、强度高且较为频繁的特征;(2)近距离厚硬顶板下回采工作面时,重复采动下工作面覆岩破坏高度更大,尤其是上位关键层破断后带动下位关键层同时破断,并带动其控制的上覆岩层及上方采空区同步下沉,岩层载荷逐层向下传导至工作面,上下位关键层破断的协同作用,从而造成了工作面来压强烈。