基于微震监测的超前支承压力分布特征研究

为了定量研究煤矿采场超前支承压力的分布规律,采用固定工作面的方法,研究了采煤工作面前方微震事件的分布特征,在此基础上通过微震波波形分析和反演,进行了工作面前方视应力的分布特征研究.结果表明,采用固定工作面能更好的反映超前支承压力与微震监测参数的关系,同实测超前支承压力曲线一样,视应力曲线同样具有明显的单峰值结构,通过分析工作面前方视应力分布曲线可以获得描述超前支承压力分布特征的所有参数.     

变长工作面采场顶板破断机理的力学模型分析

为了深入研究变长工作面采场顶板的破断特征和垮落形态,以工作面长度由大变小的"刀把式"采场为研究背景,运用弹性薄板理论构建了5种不同支承边界条件下的顶板力学模型,通过理论计算得出了大小采面基本顶断裂前后的挠度、弯矩和应力变化,并理论分析了顶板破断的力学机理.研究表明:大面采场顶板首先在板边四周形成"O"形破断,而后在中部形成平面的"X"形破断,两者贯通后构成顶板的"O-X"型破断;小面采场顶板先在顶板中部形成空间"X"形破断,而后与四周形成的"O"形破断交合贯通构成顶板的"X-O"型破断.运用数值模拟方法探究了变长工作面采场顶板塑性区的分布范围和应力场的演化规律,模拟结果对大小采面的顶板破断形态进行了有力验证.     

不等长工作面覆岩破坏规律的数值模拟分析

针对不等长工作面煤层开采日渐增多的现状,采用数值模拟与理论分析相结合的方法,对采场覆岩的破坏特征及支承压力的分布状态进行系统研究,并相应模拟出工作面前方应力场与位移场的演化规律。结果表明：工作面自开切眼开始向前推移,推进到工作面“见方”期或斜长的整数倍位置时,顶板活动剧烈,覆岩空间结构发生新旧更替,形成了“0”型破断区;不等长工作面推进过程中岩层运移极不规则,推进距离在衔接面前后20～30m的范围内,应力波动较大,数值变化明显;回采期间支承压力对覆岩活动产生了重要影响,其大小约为水平应力的1．5～2倍;就采动过程中竖向位移的变化而言,巷帮移近量远大于顶底板变形量,故工程实践中应特别注意对巷帮及顶板的加固和维护。     

推采陷落柱工作面支承压力状态演变规律研究

针对工作面推采陷落柱时面临的矿压威胁,充分考虑陷落柱的形成过程及其围岩地质特征,构建了陷落柱"四带"地质力学模型,并运用理论分析、数值模拟和相似模拟相结合的方法就推采陷落柱工作面支承压力演变规律进行了系统性研究.结果表明:陷落柱诱发的围岩应力在水平方向上可划分为柱体低应力带、柱边应力降低带、外围应力升高带和原岩应力稳定带;当工作面靠近及推过陷落柱时,均会产生采场超前支承压力与陷落柱应力四带耦合现象,其支承压力演变过程可分为耦合发生、耦合增强、柱体吸收、二次耦合和耦合渐散5个阶段;而推采陷落柱工作面的矿压规律与支承压力状态演变及岩体性质结合紧密.靠近陷落柱时,叠合高应力集聚的破碎顶板使支架承受更大载荷.推进陷落柱时,虽然柱体内的低应力起点使柱体区域应力呈一般水平,但陷落柱作为一个整体易沿弱面发生溃泄,尤其对于弱胶结松散陷落柱,矿压显现更加明显.     

热采井不同注汽速率的储层压力场数值模拟

在注蒸汽热采井中,注汽速率是影响油藏压力场分布的重要因素.基于油藏温度场与渗流场耦合理论,通过数值模拟的手段研究了热采井不同注汽速率对油藏压力场的影响.研究表明:注汽速率越大对储层压力的影响范围越大,而当注汽速率达到一定值后,储层压力场的影响范围增幅较小.该研究结果为油田现场选择合理的注汽速率提供了理论依据.     

单体支柱工作面顶板压力计算的探讨

根据现场实测，采用统计回归与理论分析方法，对鸡西矿务局单体支柱工作面顶板压力计算方法进行了分析和研究，利用采高与直接顶厚度的比值确定老顶岩层作用在直接顶的压力，最后推导出较实用的顶板压力计算方法，并在鸡西进行了应用。     

采场风流参数计算数学模型和数值计算方法

本文利用渗流理论和管路漏流流动规律及采空区与相邻风流通道交界面上的力学关系、流量关系,建立了一整套采场风流参数计算数学模型,并介绍了解算采空区风流参数的有限元方法。利用现场实测流量结果作为边界条件进行了计算、计算所得采空区边界上的压力值与实测值吻合很好。     

基于残余瓦斯含量的顺层钻孔抽采有效半径阶梯式测定法

为确定瓦斯抽采合理钻孔间距,有效减少或消除抽采空白带,基于瓦斯抽采相关标准与行业规范,以突出煤层采煤工作面瓦斯含量临界值、采煤工作面回采前煤体可解吸瓦斯含量、采煤工作面瓦斯抽采率和预抽率作为抽采达标的4项基本指标,根据4项基本指标计算得出残余瓦斯含量最小值,将其作为考察指标,对顺层钻孔瓦斯抽采有效半径测定方法进行探索,提出阶梯式测定法.使用该测定法对山西霍尔辛赫煤业有限责任公司3号煤层瓦斯抽采有效半径进行现场测试,同时基于含瓦斯煤的流固耦合动态模型对测试结果进行数值模拟验证.结果表明:阶梯式测定法现场测试结果与数值模拟结果基本吻合,在该矿合理预抽期内,抽采有效半径为1.52 m,合理钻孔间距为2.50 m.研究结果对于完善瓦斯抽采有效半径测定方法、确保瓦斯抽采达标具有参考作用.     

三软煤层切顶成巷二次复用围岩应力及变形演化规律

为研究"三软"煤层条件下切顶卸压自成巷道二次复用期间围岩稳定性,以中兴煤矿1200试验工作面为工程背景,对自成巷道在"采—留—用"期间的扰动因素进行分析,通过数值模拟和现场实测,对自成巷道在二次复用期间的围岩应力演化规律和变形特征进行研究.结果表明:"三软"煤层条件下自成巷道在二次回采期间的超前支承应力影响范围约为40 m,应力峰值距工作面约10 m;巷道顶底板均处于较低的应力水平,采场侧向应力最大值远离实体煤帮,而矸石帮侧采空区始终处于较低的应力水平,该技术有效地切断了顶板的部分应力传递路径,提高了自成巷道在二次复用期间的稳定性;围岩变形随着工作面走向可大致分为缓慢变形区,加速变形区和剧烈变形区.     

放顶煤开采顶煤移动与破坏规律的数值分析

结合现场实际采用数值模拟的方法，研究了放顶煤开采的支承压力形成规律，分析了采高和支架阻力对顶煤应力和位移分布的影响，为顶煤破碎机理的分析和顶煤移动，运动规律的研究提供了依据。     

A case study of the stability of a non-typical bleeder entry system at a U.S. longwall mine

Longwall abutment loads are influenced by several factors, including depth of cover, pillar sizes, panel dimensions, geological setting, mining height, proximity to gob, intersection type, and size of the gob.How does proximity to the gob affect pillar loading and entry condition? Does the gob influence depend on whether the abutment load is a forward, side, or rear loading? Do non-typical bleeder entry systems follow the traditional front and side abutment loading and extent concepts? If not, will an improved understanding of the combined abutment extent warrant a change in pillar design or standing support in bleeder entries? This paper details observations made in the non-typical bleeder entries of a moderate depth longwall panel—specifically, data collected from borehole pressure cells and roof extensometers,observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction. The primary focus was on the extent and magnitude of the abutment loading experienced due to the extraction of the longwall panels. Due to the layout of the longwall panels and bleeder entries, the borehole pressure cells(BPCs) and roof extensometers did not show much change due to the advancing of the first longwall. However, they did show a noticeable increase due to the second longwall advancement, with a maximum of about 4 MPa of pressure increase and 5 mm of roof deformation. The observations of the conditions showed little to no change from before the first longwall panel extraction began to when the second longwall panel had been advanced more than 915 m. Localized pillar spalling was observed on the corners of the pillars closest to the longwall gob as well as an increase in water in the entries. In addition to the observations and instrumentation, numerical modeling was performed to validate modeling procedures against the monitoring results and evaluate the bleeder design.ITASCA Consulting Group's FLAC3 D numerical modeling software was used to evaluate the bleeder entries. The results of the models indicated only a minor increase in load during the extraction of the longwall panels. These models showed a much greater increase in stress due to the development of the gateroad and bleeder entries--about 80% development and 20% longwall extraction. The FLAC3 D model showed very good correlation between modeled and expected gateroad loading during panel extraction. The front and side abutment extent modeled was very similar to observations from this and previous panels.     

Abutment pressure distribution for longwall face mining through abandoned roadways

Abutment pressure distribution is different when a longwall panel is passing through the abandoned gate roads in a damaged coal seam. According to the geological condition of panel E13103 in Cuijiazhai Coal Mine in China, theoretical analysis and finite element numerical simulation were used to determine the front pressure distribution characteristics when the longwall face is 70, 50, 30, 20, 10, and 5 m from the abandoned roadways. The research results show that the influence range of abutment pressure is 40 to 45 m outby the face, and the peak value of front abutment pressure is related to the distance between the face and abandoned roadways. When the distance between the longwall face and abandoned roadways is reduced from 50 to 10 m, the front abutment pressure peak value kept increasing. When the distance is 10 m, it has reached the maximum. The peak value is located in 5 to 6 m outby the faceline. When the distance between the longwall face and abandoned roadways is reduced from 10 to 5 m, the front abutment pressure sharply decreases, the intact coal yields and is even in plastic state. The peak value transfers to the other side of the abandoned roadways. The research results provide a theoretical basis for determining the advance support distance of two roadways in the panel and the reinforcement for face stability when the longwall face is passing through the abandoned roadways.     

Numerical investigation on the assessment and mitigation of coal bump in an island longwall panel

This study presents a numerical investigation to assess the risk of coal bumps and produces a stress–relief technology using boreholes to mitigate risk during the extraction of an island longwall panel.Based on the geological condition in an island longwall panel in the Tangshan Coal Mine,Tangshan,China,a numerical FLAC3D(Fast Lagrangian Analysis of Continua in 3 Dimensions) model was established to determine and to map the zones in the panel with a high risk for coal bumps.The results of the numerical modeling show that the roof deformation starts to occur at more than 30 m ahead of the longwall face and the deformation starts to accelerate after a distance of 10 m in front of the longwall face.Large and rapid roof deformation is considered to be an important precursor of coal bump occurrence during the extraction of an island longwall panel.Based on the numerical results,a stress–relief technology using boreholes,which was employed to release abutment pressure,was investigated through numerical methods.The modeled results suggest that the peak stress concentration could be released by drilling boreholes in the zones prone to coal bumps.The effectiveness of the stress release increased with the borehole length and decreased with the borehole spacing.     

煤矿深井采场矿压显现及其控制特点

根据采场围岩控制原则、垮落带岩层的判别式、裂隙带老顶在触矸处的下沉量计算式和移动支承压力与采深的关系,分析了采深对采场矿压显现不同参数的影响,并通过实测加以验证根据岩性随采深的变化,讨论了深井采场可能出现的冒顶事故,并提出了相应的控制,认为采深对矿压显现的影响在采场支护方面不明显,而煤壁片帮将随采深增加而加剧。深部围岩逐渐变碎强度有所降低。深部采场应加强对垮睦顶事故的防治,把顶板护好。     

Longwall mining under gateroads and gobs of abandoned small mine

Due to the use of outdated mining technology or room and pillar mining process in small coal mines, the coal recovery ratio is only 10–25%. In many regions of China, the damage area caused by the small coal mines amounted to nearly one hundred square kilometers. Therefore, special mining techniques must be taken to reclaim the wasted resource in disturbed coal areas. This paper focuses on the different mining methods by analyzing the longwall panel layout and abandoned gateroad(AG) distribution in the abandoned area of Cuijiazhai coal mine in northwestern China. On the basis of three-dimensional geological model, FLAC3 D numerical simulation was employed. The abutment pressure distribution was simulated when the panel face passed through the disturbed areas. The proper angle of the inclined face was analyzed when the panel face passed through the abandoned gateroads. The results show that the head end of the face should be 13–20 m ahead of the tail end. The pillars on both sides of abandoned gateroads had not been damaged at the same time, and no large-area stress concentration occured above the main roof.Therefore, the coal reserves of disturbed areas can be successfully recovered by using underground longwall mining.     

Investigation of overburden behaviour for grout injection to control mine subsidence

This paper describes a field and numerical investigation of the overburden strata response to underground longwall mining, focusing on overburden strata movements and stress concentrations. Subsidence related high stress concentrations are believed to have caused damage to river beds in the Illawarra region, Australia. In the field study, extensometers, stressmeters and piezometers were installed in the overburden strata of a longwall panel at West Cliff Colliery. During longwall mining, a total of 1000 mm tensile deformation was recorded in the overburden strata and as a result bed separation and gaps were formed. Bed separation was observed to start in the roof of the mining seam and gradually propagate toward the surface as the longwall face advanced. A substantial increase in the near-surface horizontal stresses was recorded before the longwall face reached the monitored locations. The stresses continued to increase as mining advanced and they reached a peak at about 200 m behind the longwall face. A numerical modelling study identified that the angle of breakage (i.e., the angle of the boundary of caved zone) behind the longwall face and over the goaf was 22–25° from vertical direction. This is consistent with the monitoring results showing the high gradient of stresses and strains on the surface 150–320 m behind the mining face.     

Bleeder entry evaluation using condition mapping and numerical modeling

One of the most common critical areas of longwall mining in terms of ground stability are the gateroad and bleeder entries. These critical entries provide much-needed safe access for miners and allow for adequate ventilation required for dilution of hazardous airborne contaminants and must remain open during mining of a multi-panel district. This paper is focused on the stability of the longwall entries subjected to a single abutment load such as bleeders, first tailgate, and last headgate. First tailgate and last headgate are also referred to as blind headgate and tailgate. A study of a longwall district through conditions mapping, support evaluations, and numerical modeling was conducted and evaluated by researchers from the National Institute for Occupational Safety and Health(NIOSH). The condition mapping and support evaluations were performed on entries that spanned the previous five years of mining and relied on a diverse selection of supports to maintain the functionality of the entry. Numerical modeling was also conducted to evaluate various support types with further investigation and comparison to the condition mapping.The study demonstrated the importance of the abutment load decay versus distance from the gob edge,the potential for a reduction in material handling related injuries, as well as optimal usage of secondary and standing support.     

Effects of longwall-induced stress and deformation on the stability and mechanical integrity of shale gas wells drilled through a longwall abutment pillar

This paper presents the results of a comprehensive study conducted by CONSOL Energy, Marcellus Shale Coalition, and Pennsylvania Coal Association to evaluate the effects of longwall-induced subsurface deformations on the mechanical integrity of shale gas wells drilled over a longwall abutment pillar.The primary objective is to demonstrate that a properly constructed gas well in a standard longwall abutment pillar can maintain mechanical integrity during and after mining operations. A study site was selected over a southwestern Pennsylvania coal mine, which extracts 457-m-wide longwall faces under about 183 m of cover. Four test wells and four monitoring wells were drilled and installed over a 38-m by84-m centers abutment pillar. In addition to the test wells and monitoring wells, surface subsidence measurements and underground coal pillar pressure measurements were conducted as the 457-m-wide longwall panels on the south and north sides of the abutment pillar were mined by. To evaluate the resulting coal protection casing profile and lateral displacement, three separate 60-arm caliper surveys were conducted. This research represents a very important step and initiative to utilize the knowledge and science obtained from mining research to improve miner and public safety as well as the safety and health of the oil and gas industries.     

Deep cover bleeder entry performance and support loading: A case study

Several questions have emerged in relation to deep cover bleeder entry performance and support loading:how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understanding of the rear abutment extent warrant a change in standing support in bleeder entries? To help answer these questions and to determine the current utilization of standing support in bleeder entries, four bleeder entries at varying distances from the startup room were instrumented,observed, and numerically modeled.This paper details observations made by NIOSH researchers in the bleeder entries of a deep cover longwall panel—specifically data collected from instrumented pumpable cribs, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction.The primary focus was on the extent and magnitude of the abutment loading experienced by the standing support.As expected, the instrumentation of the standing supports showed very little loading relative to the capacity of the standing supports—less than 23 Mg load and 2.54 cm convergence.The Flac3D program was used to evaluate these four bleeder entries using previously defined modeling and input parameter estimation procedures.The results indicated only a minor increase in load during the extraction of the longwall panel.The model showed a much greater increase in stress due to the development of the gateroad and bleeder entries, with about 80% of the increase associated with development and 20% with longwall extraction.The Flac3D model showed very good correlation between expected gateroad loading during panel extraction and that expected based on previous studies.The results of this study showed that the rear abutment stress experienced by this bleeder entry design was minimal.The farther away from the startup room, the lower the applied load and smaller the convergence in the entry if all else is held constant.Finally, the numerical modeling method used in this study was capable of replicating the expected and measured results near seam.