Analysis of the Risk of Water Breakout in the Bottom Plate of High-Intensity Mining of Extra-Thick Coal Seams

In order to clarify the danger of water breakout in the bottom plate of extra-thick coal seam mining, 2202 working face of a mine in the west is taken as the research object, and it is proposed to use the on-site monitoring means combining borehole peeping and microseismic monitoring, combined with the theoretical analysis to analyze the danger of water breakout in the bottom plate. The results show that: 1) the theoretically calculated maximum damage depth of the bottom plate is 27.5 m, and its layer is located above the Austrian ash aquifer, which has the danger of water breakout;2) the drill hole peeping at the bottom plate of the working face shows that the depth of the bottom plate fissure development reaches 26 m, and the integrity of the water barrier layer has been damaged, so there is the risk of water breakout;3) for the microseismic monitoring of the anomalous area, the bottom plate of the return air downstream channel occurs in the field with a one-week lag, which shows that microseismic monitoring events may reflect the water breakout of the underground. This shows that the microseismic monitoring events can reflect the changes of the underground flow field, which can provide a reference basis for the early warning of water breakout. The research results can provide reference for the prediction of sudden water hazard.

Behaviors of overlying strata in extra-thick coal seams using top-coalcaving method

Accidents such as support failure and excessive deformation of roadways due to drastic changes in strata behaviors are frequently reported when mining the extra-thick coal seams Nos.3e5 in Datong coal mine with top-coal caving method,which significantly hampers the mine's normal production.To understand the mechanism of strata failure,this paper presented a structure evolution model with respect to strata behaviors.Then the behaviors of strata overlying the extra-thick coal seams were studied with the combined method of theoretical analysis,physical simulation,and field measurement.The results show that the key strata,which are usually thick-hard strata,play an important role in overlying movement and may influence the mining-induced strata behaviors in the working face using top-coal caving method.The structural model of far-field key strata presents a 'masonry beam' type structure when'horizontal O-X' breakage type happens.The rotational motion of the block imposed radial compressive stress on the surrounding rock mass of the roadway.This can induce excessive deformation of roadway near the goaf.Besides,this paper proposed a pre-control technology for the hard roof based on fracture holes and underground roof pre-splitting.It could effectively reduce stress concentration and release the accumulated energy of the strata,when mining underground coal resources with top-coal caving method.

Prediction of upper limit position of bedding separation overlying a coal roadway within an extra-thick coal seam

Failure of the surrounding rock around a roadway induced by roof separation is one major type of underground roof-fall accidents.This failure can especially be commonly-seen in a bottom-driven roadway within an extra-thick coal seam("bottom-driven roadway"is used throughout for ease of reference),containing weak partings in their roof coal seams.To determine the upper limit position of the roof interlayer separation is the primary premise for roof control.In this study,a mechanical model for predicting the interlayer separation overlying a bottom-driven roadway within an extra-thick coal seam was established and used to deduce the vertical stress,and length,of the elastic,and plastic zones in the rock strata above the wall of the roadway as well as the formulae for calculating the deflection in different regions of rock strata under bearing stress.Also,an approach was proposed,calculating the stratum load,deflection,and limiting span of the upper limit position of the interlayer separation in a thick coal seam.Based on the key strata control theory and its influence of bedding separation,a set of methods judging the upper limit position of the roof interlayer separation were constructed.In addition,the theoretical prediction and field monitoring for the upper limit position of interlayer separation were conducted in a typical roadway.The results obtained by these two methods are consistent,indicating that the methods proposed are conducive to improving roof control in a thick coal seam.

Numerical Study on an Applicable Underground Mining Method for Soft Extra-Thick Coal Seams in Thailand

The EGAT Mae Moh Mine is the largest open pit lignite mine in Thailand and it produces lignite about 16 million tons annually. In the near future, the pit limit of the mine will be reached and underground mine will then be developed through the open pit in the depth of 400 - 600 m from the surface. However, due to the challenges for underground mining such as poor geological conditions, extra thickness (20 - 30 m) of coal seams, and weak mechanical properties of coal seams and the surrounding rock, the success possibility of underground mining and an applicable underground mining method is being investigated at the present. The paper discusses the applicability of multi-slice bord-and-pillar method for the soft extra thick coal seams in the Mae Moh mine by means of numerical analyses using the 3D finite difference code “FLAC3D”.

Strata behavior in extra-thick coal seam mining with upward slicing backfilling technology

Based on the character of upward slicing backfilling mining and the condition of Gonggeyingzi coal mine in Inner Mongolia,this paper describes the studies of the strata behavior and the stress distribution in the process of backfilling mining in extra-thick coal seams.This was achieved by setting up and analyzing the elastic foundation beam model using the ABAQUS software.The results show that:(1) With the gradual mining of different slices,the roof appears to bend continuously but does not break.The vertical stress in the roof decreases and the decreasing amplitude reduces,while the tensile stress in the roof grows with the mining slices and the maximum tensile stress will not exceed the allowable tensile stress.(2) The front vertical stress at the working face exceeds the rear vertical stress and both show a trend of decrease with decreasing amplitude of decrease.(3) The slices mined early have more influence on the surrounding rock than the later ones.Similarly,the strata behavior experiences the same trend.The field measured data show that the roof does not break during the mining process,which is consistent with the conclusion.

Disasters of gas-coal spontaneous combustion in goaf of steeply inclined extra-thick coal seams

In light of the escalating global energy imperatives,mining of challenging-to-access resources,such as steeply inclined extra-thick coal seams(SIEC),has emerged as one of the future trends within the domain of energy advancement.However,there is a risk of gas and coal spontaneous combustion coupling disasters(GCC)within the goaf of SIEC due to the complex goaf structure engendered by the unique mining methodologies of SIEC.To ensure that SIEC is mined safely and efficiently,this study conducts research on the GCC within the goaf of SIEC using field observation,theoretical analysis,and numerical modeling.The results demonstrate that the dip angle,the structural dimensions in terms of width-to-length ratio,and compressive strength of the overlying rock are the key factors contributing to the goaf instability of SIEC.The gangue was asymmetrically filled,primarily accumulating within the central and lower portions of the goaf,and the filling height increased proportionally with the advancing caving height,the expansion coefficient,and the thickness of the surrounding rock formation.The GCC occurs in the goaf of SIEC,with an air-return side range of 41 m and an air-intake side range of 14 m,at the intersection area of the“<”-shaped oxygen concentration distribution(coal spontaneous combustion)and the“>”-shaped gas concentration distribution(gas explosion).The optimal nitrogen flow rate is 1000 m3/h with an injection port situated 25 m away from the working face for the highest nitrogen diffusion efficacy and lowest risk of gas explosion,coal spontaneous combustion,and GCC.It has significant engineering applications for ensuring the safe mining of SIEC threatened by the GCC.

Demonstration Project of Safe and Efficient Mining Operations in Extra-thick Coal Seam

Mineable coal reserves in thick and extra-thick seams account for 44% of the total deposit in China. Fullymechanized top-coal caving technology is a new mining method of safe and efficient underground operations in extra-thick seams in China. The development of fullymechanized top-coal caving technology in China, which was successfully applied in Face 8105 in Tashan Coal Mine, Datong, Shanxi, China, is analyzed in this paper.Studies on movement pattern of top-coal and roof from fully-mechanized top caving face in 14–20 m extra-thick seams have been carried out. A series of key technologies were successfully developed, including strata control technology, equipment for high-efficient and high-recovery top caving operations, and safety guarantee technology for low gas occurrence and high gas emission. As a result, the fully-mechanized top-coal caving Face 8105, with large mining height in Tashan Coal Mine, has achieved a recovery rate of 88.9% and an average equipment operation rate of 92.1%. With coal production of 10.84 Mt in 2011,the demonstration project is a technology and equipment breakthrough for fully-mechanized top-coal caving face in extra-thick coal seams with large mining height.

山西平朔矿区上石炭统太原组11号煤层沉积地球化学特征及成煤微环境

山西平朔矿区上石炭统太原组11号煤层具有中硫、高灰、较高有机硫的特征,但其中各煤分层的基本性质差异较大,指示其成煤微环境显著变化。地球化学研究表明,Ca/ (Ca +Fe)、Th/U、Al/Ti、V/Zn、δEu、δCe可作为指示11号煤层沉积水介质盐度的标志,St,d、So ,d/Sp,d可分别作为指示水介质氧化还原程度和酸碱度的标志,Ad、V/I、ΣREE可作为指示水介质动力条件的标志。在此基础上,分析了该煤层成煤微环境特征及其演化历程,认为11号煤层形成于波动式海进的半咸水—咸水沉积环境。在此过程中,海水对泥炭沼泽的影响经历了3个发展阶段:第1阶段,泥炭形成于微咸—半咸水条件,水动力条件逐渐增强;第2阶段,泥炭形成于半咸水—咸水条件,水动力条件总体上相对较强,沼泽水体从逐渐加深演化为显著变浅;第3阶段,泥炭形成于半咸水环境,海水影响再次逐渐增强,在泥炭沼泽演化末期水体显著变深,动力条件明显减弱,还原性显著增强。

双系煤层采动导水裂隙演化规律的 FDEM耦合模拟研究

采动覆岩裂隙分布演化是防治顶板水害、实现煤矿地下水资源保护的基础,其数值结果准确性的关键在于采动覆岩连续-离散转化及其耦合力学响应特征。在纯拉、纯剪断裂模式下引入弹塑性损伤力学,结合Benzeggagh-Kenane断裂准则,得到准脆性岩石在拉、剪复杂应力下的混合型韧性断裂(MD)本构方程;构建离散块体接触状态判据,结合直剪实验数据与Sargin剪切摩擦关系,导出适用于多种法向应力下的粗糙结构面压缩-剪切摩擦(SF)本构方程。在此基础上,编制有限元V离散元(FDEM)数值计算程序,实现采动覆岩“连续”-“离散”介质转化过程。在数值计算中,分别将摩擦和断裂属性赋予结构面(接触对)、零厚度黏聚力单元,通过共享节点力的方式实现岩石断裂-摩擦耦合。采用断裂力学实验和直剪试验识别材料参数并验证MD-SF本构方程的合理性。在此基础上,模拟研究双系煤层采动导水裂隙随工作面推进的演化规律。结果表明:(1) MD-SF本构方程组及相应的FDEM数值计算方法,可实现岩体从连续介质到离散介质的转化过程,较好反映准脆性岩石混合型韧性断裂及粗糙结构面的剪切摩擦响应;(2)模拟条件下,岩层与煤层间距越小,导水裂隙总宽度随大,且开采过程中裂隙总宽度是覆岩运动稳定后的2.26~7.11倍,表明采动过程中更容易出现水害;(3)高岭土砂岩显著的韧性破坏特征能有效控制其内导水裂隙高度,但在双系煤层重复开采扰动下,覆岩裂高比为20.8,远超经验公式所得结果。采动覆岩导水裂隙高度成果在大同矿区得到应用和检验,为进一步开展采动覆岩运动、水体下安全采煤、保水采煤设计等提供理论支撑。

软煤储层顶板水平井穿层工况下压裂缝扩展模型

为了探索煤层顶板中水平井向目标层穿层压裂的裂缝扩展规律,以华北石炭–二叠纪煤田为例,运用断裂力学、损伤力学以及流体力学等经典理论并结合现场实测资料,开展了压裂缝延伸距离与压裂时间时空演化规律的建模与验证。首先,基于原生裂缝特性、渗透特性以及压裂射孔段附加应力等因素,提出了顶板水平井垂向造缝的起裂压力计算公式;其次,在考虑裂缝性煤岩体损伤效应的基础上,引入Dougill损伤因子,将该计算模型拓展为延伸压力计算模型;最后,基于改进的经典PKN裂缝模型和压裂液滤失理论,建立了连续穿层工况下压裂缝延伸距离与压裂施工时间的函数关系。实践验证表明,根据理论模型合理调配时间参数,可以控制穿层裂缝的延伸距离。

大同矿区特厚煤层综采放顶煤技术

针对大同侏罗纪的坚硬顶板与坚硬煤层特殊条件,通过对预采顶分层处理坚硬顶板然后再综放开采下部煤层,在顶煤中布置工艺巷对顶煤和顶板实施弱化破碎控制技术等试验,研究了侏罗纪煤层硬煤冒放和顶板控制的理论技术,实现了"两硬"特厚煤层条件下的综采放顶煤的安全开采。同时,对于大同矿区石炭纪的煤层厚度大、结构复杂、受火成岩侵入等难题,采用高精度微地震监测系统和全景式数字钻孔电视等技术,初步掌握了顶煤与围岩的运移规律,开发了专有综放技术及装备。

利用三维地震资料计算曲堤地区煤层相对厚度

曲堤地区煤层发育 ,是胜利油区最有潜力的煤成气勘探目标之一。该区钻井资料较少 ,煤层的横向厚度难以控制 ,其资源量计算有困难。根据不同岩层的地震属性及本区煤层发育特点 ,尝试了利用地震瞬时振幅、瞬时相位和瞬时频率信息计算煤层厚度。

石炭系煤层掘进巷道漏顶原因分析及治理措施探讨

本文针对同煤集团某矿石炭系煤层掘进巷道因煌斑岩倾入、揭露断层等原因,造成顶板受应力影响发生局部漏顶进行全面分析,制定了相关治理安全技术措施,对石炭系煤层掘进巷道治理局部漏顶具有现实指导意义。

朝阳石炭系煤层中的漂砾

作者在辽宁省朝阳煤矿北腰矿井石炭系煤层内获石英岩漂砾。漂砾层厚约几 cm,漂砾多呈圆形或椭圆形,倾斜产出,长约2.5—4cm,宽约2.2—3.5cm,厚约1.2—1.5cm。砾石呈深灰色,表面光滑,有一层薄膜,无棱角,具裂缝。煤的变质程度低,灰分高。推测系华北地台型聚煤盆地北缘古陆震旦系石英岩被风化剥蚀,随水流长距离搬运,并泛入泥炭沼泽而形成的。

大同煤田石炭二叠纪煤层对比及分布特征研究

大同石炭二叠纪煤田煤层对比及分布特征研究是一项重要的基础性工作。通过对煤层对比依据相关因素的分析,一方面可以提高对大同石炭二叠纪煤田煤层赋存状态和煤层层位确定的认识,另一方面有助于提高对聚煤规律与分布特征的认识,对同煤集团石炭二叠纪矿井的安全高效生产具有重要意义。

华北石炭系、二叠系煤层含气性及前景

据丰富的资料对华北石炭、二叠系煤层含气性进行了研究。提出了煤层演化变质程度、煤岩组分中镜质组含量、灰分产率、顶板岩性和上覆有效地层厚度是影响煤层含气性的主要地质因素。依据影响煤层含气性因素对华北石炭系、二叠系煤层含气性前景进行了初步分析。

石炭二叠纪山4~#煤层煌斑岩侵入及对现场生产的影响分析

通过采取坑道透视、钻孔资料及实际巷探等方法对石炭二叠纪山4#煤层煌斑岩侵入区域进行研究并预测侵入范围,有效地解决了工作面布置及提高资源回收率。并通过煌斑岩侵入区域分析,提前制定应对措施,保证工作面按照设计进行掘进及开采。

大同煤田石炭二叠系煤层顶板导水裂隙带发育规律研究

根据侏罗纪煤层地质特征及其开采方法,通过理论分析,研究侏罗纪煤层开采、采空区形成过程中的围岩破裂特征及其时空演化规律。针对双纪煤层地质及水文地质特征,分析石炭二叠纪煤层开采过程中及开采后,双纪煤层间岩层的变形破坏、垮落和移动规律,计算分析导水裂隙带高度,及其与侏罗纪采空区底板裂隙带的连通机制,研究揭示大同矿区侏罗纪采空区围岩裂隙发育与积水运移规律,及其对石炭二叠纪煤层安全开采的影响,考虑到双系煤层开采复杂的工作面布置以及多煤层开采对覆岩岩性结构的扰动,相似材料模拟法弥补了经验公式法的不足,动态模拟煤层开采过程中上覆基岩变形破坏的范围及塑性分布情况,导水裂隙带高度模拟结果更接近实测值。

顶板破碎煤层联合支护方式的改进

顶板支护作为煤矿开采过程的重中之重,直接关系到煤矿企业的综合生产效益以及煤矿职工的生命安全。为提高顶板支护的安全可靠性,针对石炭系煤层岩体强度较低、易造成顶板破碎的特性,对联合支护方式进行了改进。在锚杆+锚索联合支护的基础上,提出一种以锚杆+锚索+金属网+组合锚索作为承载结构,配合局部串钢针+局部架棚支护+喷浆处理的联合支护方式。实践表明,该支护方式结构简单、施工方便,能够有效提高石炭系中厚煤层顶板破碎时的支护强度,使煤层顶板的稳定性和安全性得到显著增强。

石炭二叠纪5^#煤层顶板支护技术的研究与应用

介绍了大同煤矿集团挖金湾煤业公司虎龙沟煤矿石炭二叠纪5#煤层顶板支护技术的改进研究与应用。