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.

New development of longwall mining equipment based on automation and intelligent technology for thin seam coal

The paper introduced complete sets of automatic equipment and technology used in thin seam coal face, and proposed the comprehensive mechanization and automation of safe and high efficiency mining models based on the thin seam drum shearer. The key technology of short length and high power thin seam drum shearer, and new type roof support with big extension ratio and plate canopy were introduced. The new research achievement on automatic control system of complete sets of equipment for the thin seam coal, which composed of electronic-hydraulic system, compact thin seam roof supports, high effective shearer with intelligent control system, and characterized by automatical follow-up and remote control technology, was described in this paper..

The adjusting mining technology of combining fully mechanized with individual prop,rotating,hilt,irregular form,and double unit face on thin coal seam of Tianchen Mine

Analyzed the situations and characteristics of thin coal seam mining and its mining technologies,and introduced the mining innovation technology used by Tianchen Coal Mine of Zhaozhuang Coal Company of China.This innovation technology combined the fully mechanized mining with individual props,and the working face of mining is over length,irregular form and double units.The rotational adjusting mining technology on thin coal seam is also practiced in this new mining technology.The detail technologies,such as outlays of working face and ways,mining methods,equipments of cutting,transporting and sporting,have been introduced.So that,using the synthetic and creative mining tech- nologies,Tianchen Coal Mine solves the mining problems of thin coal seam successfully.

An improved influence function method for predicting subsidence caused by longwall mining operations in inclined coal seams

Prediction of surface subsidence caused by longwall mining operation in inclined coal seams is often very challenging. The existing empirical prediction methods are inflexible for varying geological and mining conditions. An improved influence function method has been developed to take the advantage of its fundamentally sound nature and flexibility. In developing this method, the original Knothe function has been transformed to produce a continuous and asymmetrical subsidence influence function. The empirical equations for final subsidence parameters derived from col- lected longwall subsidence data have been incorporated into the mathematical models to improve the prediction accuracy. A number of demonstration cases for longwall mining operations in coal seams with varying inclination angles, depths and panel widths have been used to verify the applicability of the new subsidence prediction model.

An influence function method based subsidence prediction program for longwall mining operations in inclined coal seams

The distribution of the final surface subsidence basin induced by longwall operations in inclined coal seam could be significantly different from that in flat coal seam and demands special prediction methods. Though many empirical prediction methods have been developed, these methods are inflexible for varying geological and mining conditions. An influence function method has been developed to take the advantage of its fundamentally sound nature and flexibility. In developing this method, significant modifications have been made to the original Knothe function to produce an asymmetrical influence function. The empirical equations for final subsidence parameters derived from US subsidence data and Chinese empirical values have been incorpo- rated into the mathematical models to improve the prediction accuracy. A corresponding computer program is developed. A number of subsidence cases for longwall mining operations in coal seams with varying inclination angles have been used to demonstrate the applicability of the developed subsidence prediction model.

Theoretical description of drawing body shape in an inclined seam with longwall top coal caving mining

Understanding the characteristics of drawing body shape is essential for optimization of drawing parameters in longwall top coal caving mining.In this study,both physical experiments and theoretical analysis are employed to investigate these characteristics and derive a theoretical equation for the drawing body shape along the working face in an inclined seam.By analyzing the initial positions of drawn marked particles,the characteristics of the drawing body shape for different seam dip angles are obtained.It is shown that the drawing body of the top coal exhibits a shape-difference and volume-symmetry characteristic,on taking a vertical line through the center of support opening as the axis of symmetry,the shapes of the drawing body on the two sides of this axis are clearly different,but their volumes are equal.By establishing theoretical models of the drawing body in the initial drawing stage and the normal drawing stage,a theoretical equation for the drawing body in an inclined seam is proposed,which can accurately describe the characteristics of the drawing body shape.The shape characteristics and volume symmetry of the drawing body are further analyzed by comparing the results of theoretical calculations and numerical simulations.It is shown that one side of the drawing body is divided into two parts by an inflection point,with the lower part being a variation development area.This variation development area increases gradually with increasing seam dip angle,resulting in an asymmetry of the drawing body shape.However,the volume symmetry coefficient fluctuates around 1 for all values of the seam dip angle variation,and the volumes of the drawing body on the two sides are more or less equal as the variation development volume is more or less equal to the cut volume.Both theoretical calculations and numerical simulations confirm that the drawing body of the top coal exhibits the shape-difference and volume-symmetry characteristic.

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.

Punch Multi-slice Longwall Mining System for Thick Coal Seam under Weak Geological Conditions

Most of coal is produced from open-cut mines in Southeast Asian countries. However, the conditions of their surface mines are worsening each year： the stripping ratio is increasing, approaching economic ratio and the regulation of environmental protection. To meet the demand for coal, underground mines have to be developed in the near future. Under these circumstances, the development of new coal mines from open-cut highwalls are being planned in Southeast Asian Countries. Moreover, some of the Southeast Asian mines have thick coal seams. However, if the conventional mining systems and designs introduced in US, Australia and European Countries are applied, several geotechnical issues can be expected due to the mines＇ weak geological conditions. From these backgrounds, this paper proposed a punch multi-slice mining system with stowing for thick coal seam under weak geological conditions and discussed its applicability and suitable design by means of numerical analysis.

Prediction of face advance rate and determination of the operation efficiency in retreat longwall mining panel using rock engineering system

A new approach for prediction of face advance rete (FAR) prior to mining operation and determination of the operation efficiency after mining operation in retreat longwall mining panel is presented based upon the concepts of rock engineering system (RES). For this purpose, six longwall panels considered in Parvadeh-I coal mine. Seven major effective parameters on FAR was selected including coal mine roof rating, gas propagation, safety factor of longwall face, ratio of joint spacing to cutting depth at longwall face, longwall face inclination, panel width, floor rock mass rating. To performance evaluation of the presented model, the relationship between the average vulnerability indexes of advance operation with FAR was determined in considered panels with coefficient of determination (R2) equal to 0.884 that indicate relatively acceptable correlation and compatibility. Investigations of the research indicated that it is possible to determine the actual operation efficiency under fair conditions by a RES-based model. The inevitable reduction of FAR for each longwall panel was determined by presented model that the difference amount between the maximum possible practical face advance rate (FARmpp) and recorded actual face advance rate (FARa) indicate the operation efficiency. Applied approach in this paper can be used to prediction of FAR in retreat longwall mining panel for same conditions that can have many benefits, including better and more accurate planning for the sales market and mine operation. Also, presented method in this paper can be applied as a useful tool to determination of actual operation efficiency for other sections and extraction methods in coal mines.

A Numerical Investigation of the Stress Relief Zones Around a Longwall Face in the Lower Seam for Gas Drainage Considerations

Extraction of a protective coal seam (PVCS)-below or above a coal seam to be mined with the potential of coal andgas outburst risk-plays an important role not only in decreasing the stress field in the surrounding rock mass but alsoin increasing the gas desorption capacity and gas flow permeability in the protected coal seam (PTCS). The PVCSis mined to guarantee the safe mining of the PTCS. This study has numerically evaluated the stress redistributioneffects using FLAC3D model for a longwall face in Shanxi Province. The effects of mining depth, mining height andinter-burden rock mass properties were evaluated using the stress relief angle and stress relief coefficient. Verticalstress distribution, stress relief angle and stress relief coefficient in the PTCS were analyzed as the face advancedin the PVCS. The results showed that the stress relief achieved in different locations of the PTCS varied as the faceadvanced. Sensitivity analyses on the pertinent variables indicate that the stress relief in the PTCS is affected mostby the mining depth followed by the inter-burden lithology and the mining height. Furthermore, the elastic moduliof different layers within the inter-burden rock mass are more important than their uniaxial compressive strength(UCS) and Poisson’s ratio. These observations can guide gas drainage borehole design to minimize the accidentsof coal and gas outbursts.

Prevention of gob ignitions and explosions in longwall mining using dynamic seals

Most, if not all longwall gob areas accumulate explosive methane-air mixtures that pose a deadly hazard to miners. Numerous mine explosions have originated from explosive gas zones(EGZs) in the longwall gob. Since 2010, researchers at the Colorado School of Mines(CSM) have studied EGZ formation in longwall gobs under two long-term research projects funded by the National Institute for Occupational Safety and Health. Researchers used computational fluid dynamics along with in-mine measurements. For the first time, they demonstrated that EGZs form along the fringe areas between the methane-rich atmospheres and the fresh air ventilated areas along the working face and present an explosion and fire hazard to mine workers. In this study, researchers found that, for progressively sealed gobs, a targeted injection of nitrogen from the headgate and tailgate, along with a back return ventilation arrangement, will create a dynamic seal of nitrogen that effectively separates the methane zone from the face air and eliminates the EGZs to prevent explosions. Using this form of nitrogen injection to create dynamic seals should be a consideration for all longwall operators.

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。

基于残差优化的综采工作面煤壁点云补全方法

煤矿综采工作面巷道的数字化三维重建过程中需要完整且密集的煤壁点云数据。受遮挡、视角限制等因素影响,采集的综采工作面煤壁点云数据往往不完整且稀疏,影响下游任务,需进行煤壁点云修复和补全。目前缺少针对井下点云补全任务的数据集和网络模型,现有模型用于煤壁点云补全时存在点云密度分布不均匀、点云特征信息丢失等情况。针对上述问题,设计了一种基于残差优化的煤壁点云补全网络模型,采用监督学习方式学习点云特征信息,通过最小化密度采样和残差网络迭代优化输出完整点云。采集煤矿井下真实综采工作面煤壁点云数据,预处理后筛选可用数据,通过模拟随机空洞制作煤壁点云缺失数据集,并用缺失数据集训练基于残差优化的煤壁点云补全网络模型。实验结果表明:与经典的FoldingNet,TopNet,AtlasNet,PCN,3D-Capsule点云补全网络模型相比,基于残差优化的煤壁点云补全网络模型针对构造的缺失煤壁点云和稀疏煤壁点云补全的倒角距离、地移距离及F1分数均能达到最优水平,整体补全效果最佳;针对实际缺失的煤壁点云,该模型能够实现有效补全。

特厚煤层工作面煤厚变化电磁波透视响应特征

目的为掌握煤厚变化对特厚煤层工作面电磁波透视探测的影响,以准确圈定地质异常区,保障工作面安全高效生产。方法根据煤层工作面地质条件,利用三维仿真软件,对煤厚变化进行了电磁波透视数值模拟,并结合工作面探查实例进行了分析。结果0~20m煤厚范围,随煤厚减小,电磁波透视场强值呈抛物线下降趋势,可分为缓慢降低(煤厚≥9m)、明显降低(9m>煤厚≥5m)和快速降低(煤厚<5m)3个范围。煤厚10m以上的工作面适合于依据相对煤层变薄程度和变薄区煤厚来分析透视电磁波响应:变薄程度>1/3正常煤厚且煤厚<8m的薄煤区有明显响应,变薄区煤厚越小,透视电磁波场强降低越显著。煤厚10m以下的工作面,可以仅依据相对煤层变薄程度分析透视电磁波响应:变薄程度>1/4正常煤厚的薄煤区有明显响应,变薄程度越大,透视电磁波场强降低越显著。陕西金源招贤矿业有限公司特厚煤层1304工作面探测实例表明:正常煤厚变化及薄煤区的电磁波响应特征与数值模拟结果一致;工作面物探圈定的落差1m以上断层及薄煤区范围,与实际揭露范围相吻合。结论利用煤厚变化电磁波响应特征能够可靠地探查特厚煤层工作面地质异常区范围。

冲击地压煤层矿井间临近工作面相互采动影响分析

为了对冲击地压煤层矿井间临近工作面相互采动影响进行分析,以义桥煤矿3309工作面和唐阳煤矿432工作面为研究背景,采用数值模拟的研究方法,从巷道侧垂直应力和覆岩垂直位移两个方面研究了两工作面相互采动的影响。当两工作面开采时,3309工作面运输顺槽侧的应力增大了26.0%~28.0%,顶板位移增大了7.3%~10.1%,432工作面运输顺槽侧的应力增大了31.8%~48.8%,顶板位移增大了12.8%~19.2%。通过上述分析可以得出冲击地压煤层矿井间临近工作面相互采动时,对工作面应力集中分布及顶板运移规律均具有明显的影响。并在采取相应卸压措施的基础上,提出3条关于影响较大区域防冲补强措施的建议,以降低两工作面相互采动影响,确保工作面安全生产。

远距离斜交工作面上行开采上组煤垂直应力演化规律

为探究平煤八矿远距离煤层群斜交工作面上行开采过程中上组煤层垂直应力演化规律,采用数值模拟计算的方法展开研究。研究结果表明,己_(15)-21030工作面回采过程中与上覆戊_(9.10)-21070工作面依次形成相离、相交和重叠的空间关系,因此会使上组煤层应力增高或降低。相离区域为应力升高区,受下组煤采动影响应力整体呈升高趋势,应力集中系数最大为1.18;相交区域为卸压过渡区,戊_(9.10)-21070工作面应力由增压变为卸压,最大卸压值较原始应力降低了25%,倾向卸压影响范围为55 m;重叠区域为卸压区,受己_(15)-21030工作面采动影响卸压效果及卸压范围均进一步增大,最大卸压值较原始应力降低了40%,倾向卸压影响范围增大至180 m。将戊组煤层戊_(9.10)-21070工作面根据应力分布云图依次划分为增压区、应力过渡区、卸压区和稳定卸压区。通过现场瓦斯含量测试验证了卸压区残余瓦斯含量比原始区域残余瓦斯含量降低32.9%,远距离煤层群上行开采形成卸压区有利于瓦斯治理工作的开展。

蒙陕深埋煤层首采工作面顶板富水性和涌水量差异研究

针对蒙陕接壤区存在水文地质条件不清、水害问题多发、水资源漏失严重等问题,通过分析区内呼吉尔特矿区4个矿井首采工作面顶板地质水文地质特征、回采过程中涌水量变化及差异性,查清了矿区煤炭开采初期扰动下的水文地质条件,结果表明:四个矿井首采工作面涌水量,均随着工作面回采呈逐渐增加趋势,其中葫芦素和巴彦高勒矿井首采工作面最大涌水量分别为645.0 m^(3)/h和494.0 m^(3)/h,且七里镇砂岩含水层不同区域存在富水性差异,导致涌水量的增加呈台阶式,波动性较大,与该区域七里镇砂岩含水层厚度较薄、富水性较弱的特征一致;门克庆和母杜柴登矿井首采工作面最大涌水量分别为1372.0 m^(3)/h和938.0 m^(3)/h,且七里镇砂岩含水层整体富水性较强、富水性较均一,涌水量的增加呈平稳增加态势,波动性较小,与该区域顶板七里镇砂岩含水层厚度较大、富水性较强的特征一致。

近距离煤层采掘关系对下位巷道围岩变形规律影响研究

近距离煤层上煤层工作面与下位煤层巷道采掘关系发生变化时,巷道围岩变形失稳机理会更加复杂,而目前针对上煤层工作面与下位煤层巷道推进方向不同时巷道受载动态演化规律及失稳特征的研究较少。以陕北能东煤矿近距离煤层为研究对象,采用理论分析、数值模拟与现场实测相结合的方法,对上煤层工作面回采后下位煤层巷道的稳定性进行了研究。理论分析得出,上煤层工作面开采后所产生的底板裂隙深度为22.5 m,未发育至下位煤层巷道。按采掘空间位置关系将回采工作面与巷道分为相向、相交、背向3个状态,数值模拟当巷道与工作面的空间位置关系发生变化时下位煤层巷道围岩的变形情况,结果表明:①上煤层工作面与下位煤层巷道的采掘关系为相交与背向推进时,巷道围岩应力呈先增后减再增的趋势,在推进距离为90 m时,最大应力为6.5 MPa,应力集中系数为1.49,在推进距离为100~110 m时,巷道围岩应力降低幅度最大,降低了53.2%,在推进距离为150 m时应力最小,为0.95 MPa,之后不断增大,直到恢复至原岩应力。②巷道围岩位移量在推进距离为100~150 m时增长幅度较大,在150 m时顶板位移量达到最大,为0.036 m,随着巷道越接近边界煤柱,其巷道位移量越小。现场实测结果表明:上煤层工作面过下位煤层巷道时,巷道位移量显著增长,顶板最大位移量为3.41 cm,与数值模拟结果一致;相交推进过程中若地质条件简单可以适当加快推进速度,减小上煤层工作面开采对下位煤层巷道的影响。

基于三维曲面积分的矿压实测数据分析模型及应用

针对影响综采面正常推进的异常矿压显现进行预测与防控是减少工作面顶板事故隐患的有效措施,合理有效的矿压实测数据分析方法是关键技术之一。基于三维曲面积分理论,引入Kriging插值算法,提出一种“寻找大显现、关注异常点”的矿压数据分析模型。以顶板压力与底板比压组建三维曲顶柱体,以液压支架与累计进尺组建二维坐标面,从而建立基于三维曲面积分的矿压实测数据分析模型,并以压力曲面向割平面投影算法实现对矿压实测数据的解析与预测分析。开展神东矿区补连塔煤矿12514工作面的矿压监测数据分析,获得了矿压显现明显区域、矿压三维曲面投影模型以及实时矿压云图,提取显著来压区域8次,指向62号支架~98号支架区域6次,其中,显著来压区域持续平均距离11.9m,表明基于三维曲面积分分析模型可选取顶板运动比较剧烈的区域,相对于传统统计分析方法具有更强的针对性,验证了所提出分析模型的合理可靠性。

浅埋煤层大采高工作面地表裂隙漏风研究

为了掌握浅埋煤层大采高工作面采空区上方地表裂隙漏风规律,通过地表裂隙考察、SF 6示踪气体现场测试、数据拟合分析等方法进行地表漏风特征分析,并制定专项漏风防控措施进行治理。结果表明:大采高工作面采空区上方距离工作面20 m以上的粘土层地表区域,容易发育形成长期稳定的张开型和塌陷型裂隙;不同区域地表裂隙漏风风速呈现回风侧塌陷型裂隙>中部张开型裂隙>进风侧塌陷型裂隙,且分别距离工作面584、539、487 m后漏风风速基本为零;通过对地表裂隙回填压实和井下回风侧采空区注浆堵漏,在降低上隅角CO浓度的同时增加了O_(2)浓度,有效抑制了采空区的遗煤自燃,减少了采空区惰性气体的涌出。