Study on gob-side entry retaining technique with roadside packing in longwall top-coal caving technology

Pointed out some technical difficulties of gob-side entry retaining with roadside packing in longwall top-coal caving technology (LTCT), and analyzed the function mecha-nism of roadside filling body. Theory analysis shows the mechanical properties of high water material fit for the feature of deformation of gob-side entry retaining in LTCT, and gob-side entry retaining in LTCT face is one of effective ways to increase the recovery ra-tio of mining district.

Three-dimensional experimental study of loose top-coal drawing law for longwall top-coal caving mining technology

Based on the loose medium flow field theory, the loose top-coal drawing law of longwall top-coal caving（LTCC） mining technology is studied by using self-developed three-dimensional（3D） test device. The loose top-coal drawing test with shields and the controlled test without shields are performed in the condition without any boundary effect. Test results show that shields will cause reduction in drawing volume of coal in the LTCC mining. The deflection phenomenon of drawing body is also observed in the controlled test, which is verified that the deflection of drawing body is caused by shield. It is found that the deflection angle decreases with increasing caving height, with the maximum value of atailand the minimum value of 0. In addition, the formula to calculate the drawing volume is proposed subsequently.The deflection of drawing body is numerically simulated using particle flow code PFC3 Dand the proposed formula to calculate drawing volume in LTCC is also verified.

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.

Longwall Top-Coal Caving in Thinner Thick-Seam and Research on Light Hydraulic Support

The application of light hydraulic support highlights the advantages of longwall top-coal caving (LTC) in thinner thick-seams (3. 0~ 5. 0 m). Considering the problems in practice, the developing of its new series will promote the mining of LTC with light hydraulic supports. Some relevant technical problems of the caving technology and the future of this series of supports are analyzed in this paper with several new opinions.

Numerical and theoretical investigations of the effect of the gangue-coal density ratio on the drawing mechanism in longwall top-coal caving

Discrete element calculations of the top-coal drawing process for diferent gangue-coal density ratios were conducted to investigate the efect of the gangue-coal density ratio on the drawing mechanism in longwall top-coal caving.The efects were analyzed for the drawing body,the top-coal boundary,and the recovery of top coal.The results show that for increasing density ratio,the initial drawing body on the goaf side is farther away from the drawing support and its width and volume gradually increase.The upper part of the sickle-shaped drawing body extends near the initial drawing body with increasing density ratio in the normal cycling stage,and the distance from the drawing body to the initial drawing body is its maximum width.The larger the density ratio,the smaller the height of the top coal above the goaf at the end of the initial drawing process.The height of the top-coal boundary decreases with increasing density ratio,until it reaches a limit.In a normal cycle,due to hysteretic development,the top-coal boundary moves toward the goaf until the density ratio is approximately 2.0,which is consistent with the physical experiment results.Finally,increasing the advance length of the working face is benefcial for increasing the overall recovery of top coal.

THE BASIC MECHANICS PROBLEMS AND THE DEVELOPMENT OF LONGWALL TOP-COAL CAVING TECHNIQUE IN CHINA

Since the middle of 1980’s, the longwall top-coal caving technique has beveloped rapidly in China. At present, it is one of the main approaches in the thick coal seam mining. This peper describes some mechanica problems of the caving technique, such as the damage and failure of the top-coal, the strata behaviors in the caving face, and the relation of the support and the surrounding rock. In order to employ the caving technique in a widespred scope, the problems such as the caving technique in the hard coal seam, the moving and running of the loose top-coal,and the upper floating of the gas etc. should be systematically systematically studied.

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.

Surface Movement Regularity of Super-Wide Mining Face With Top-Coal Caving

No.4326 super-wide panel of Wangzhuang Coal Mine ( in which the fully-mechanized top-coal caving longwall mining method was used) was monitored for dynamic characteristic of surface movement. The dynamic surface movement in and after mining was predicted by using the Mining Subsidence Prediction System. The results indicate that after mining, the surface above the super-wide panel reaches a state of full subsidence, making the No.309 national highway above the panel be located on the flat bottom of the subsidence basin so that the influence of mining activity in both sides of 4326 panel on the national highway is the smallest.

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.

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.

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.

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.

Current Situation and Prospect of Top-Coal Caving Technology in China

A great development has been achieved on thick seam longwall top-coal caving technology in China for the recent years, which has raised face output and efficiency and reduced production cost greatly. In this paper, achievements in its production, safety and theoretical research and future tasks are discussed.

Mating model on production capacity for the system of cutting coal and drawing top-coal in FMMSC

Being a safe and highly-efficient mining method, fully mechanized mining with sublevel caving （FMMSC） was extensively employed in Chinese coal mines with thick seam. In order to make drawing top-coal furthest to parallel work with shearer cutting coal, decrease failure ratio of rear scraper conveyor and increase safe production capacity of equipments, based on production technology, set up the mating model of safe production capacity of equipments for the system of drawing top-coal and shearer cutting coal in coal face with sublevel caving. It is mean capability of drawing top-coal adapted to the capability of shearer cutting coal in a working circle in the coal face that was deduced. The type selection of equipment of rear scraper conveyor can be tackled with this mating model. The model was applied in FMMSC in Yangcun Coal Mine, Yima Coal Group of China. With the mating light-equipments, the coal output in coal face attained 1.05 Mt in 2004. It gained better technical-economic benefit.

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．

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。

煤矿综采放顶煤工作面高浓度粉尘的综合防治

煤矿综采放顶煤工作面开采强度大、产尘尘源多、粉尘浓度高，因而对尘毒的治理难度大。为此，提出了治理的总体思路、防治方案并在几十个煤矿综采放顶煤工作面推广，取得了很好的效果。

综放开采煤层支承压力分布规律现场实测分析

依据谢桥矿1151(3)综放面开采地质及技术条件,采用钻孔应力计对工作面回采过程中煤柱和工作面煤层及巷帮侧向实体煤的应力进行观测。研究分析表明,在非对称开采条件,回采期间工作面及巷道周围煤层应力分布规律明显不同,煤柱和工作面煤层沿走向在工作面前方存在支承压力峰值,但巷帮侧向实体煤沿走向在工作面前方并不存在应力峰值,其峰值在采空区后方,而煤柱和巷帮侧向实体煤沿倾向均存在应力峰值,邻近工作面煤柱及工作面煤层应力均处于降低区。

综放工作面巷道沿空侧松散煤体漏风强度测算方法研究

测算巷道松散煤体的漏风强度分布状况及动态变化规律， 对松散煤体的自然发火预测技术的研究具有重要意义． 由于巷道松散煤体的实际漏风速度极小（０－００１ ～０－５ ｃｍ／ｓ） ， 因而目前测风、测压技术在实际应用中存在诸多问题． 为此， 提出了通过实测巷道沿空侧松散煤体钻孔氧气浓度推算漏风强度的方法， 并分析了巷道松散煤体在自燃过程中热风压对漏风强度的动态影响． 该方法在东滩煤矿４３０８ 综放工作面沿空巷道自燃性预测中得到成功应用．

采场上覆岩层结构理论及其新进展

回顾了采场上覆岩层结构理论的发展过程,介绍了平面结构模型各个发展阶段的主要学术观点及其新进展,重点阐述了采场上覆岩层结构的稳定性及综放采场顶板结构理论的研究现状,提出了大范围顶板控制问题如采动覆岩空间结构与应力场的动态关系、顶板的异常压力控制等问题,这些问题是今后采场矿压研究的重点,并介绍了这些方面的最新研究成果。