Instability characteristics of the cracked roof rock beam under shallow mining conditions

To establish the movement relationship for the roof breaking under shallow mining conditions, the mechanical model of the roof rock beam was built, then the structure instability process of the roof rock beam was analyzed. The changing criterion of the vertical displacement was established and the relationship between the deflection and the rotary motion of roof block was determined. Regarding a mining face in Shangwan Mine, the responsing laws of the deflection and horizontal thrust of the roof rock beam were obtained through FLAC3D numerical analysis. The results show that the structure instability of the cracked roof rock beam depends on the interaction between the vertical load and the horizontal thrust.For the roof rock beam, when the vertical load keeps constant, the horizontal thrust fluctuating rises with increasing deflection. The horizontal thrust increases constantly with the deeper buried depth and the smaller span.

Experimental and numerical simulation on the sliding process of roof rock blocks triggered by dynamic disturbance

With the excavation of underground opening,the roof rock block may fall under external dynamic disturbance.In this paper,the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks.A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance.The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique.The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system.Therefore,the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves.Meanwhile,it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient,or decreases in a parabolic function with the increasing trapezoid internal angle.Finally,a case study on the roof block sliding of the roadway at a gold mine was conducted,and it is concluded that the sliding of the key block resulted from the coupled effects of"shear driving"and"low friction"driven by stress wave propagation,regardless of a single or multi-layer rock block system.These results may provide technical guideline for preventing rock-falling accidents caused by blasting distur-bances in underground mining.

Rock characterization while drilling and application of roof bolter drilling data for evaluation of ground conditions

Despite recent advances in mine health and safety, roof collapse and instabilities are still the leading causes of injury and fatality in underground mining operations. Improving safety and optimum design of ground support requires good and reliable ground characterization. While many geophysical methods have been developed for ground characterizations, their accuracy is insufficient for customized ground support design of underground workings. The actual measurements on the samples of the roof and wall strata from the exploration boring are reliable but the related holes are far apart, thus unsuitable for design purposes. The best source of information could be the geological back mapping of the roof and walls, but this is disruptive to mining operations, and provided information is only from rock surface.Interpretation of the data obtained from roof bolt drilling can offer a good and reliable source of information that can be used for ground characterization and ground support design and evaluations. This paper offers a brief review of the mine roof characterization methods, followed by introduction and discussion of the roof characterization methods by instrumented roof bolters. A brief overview of the results of the preliminary study and initial testing on an instrumented drill and summary of the suggested improvements are also discussed.

Comprehensive assessment on dynamic roof instability under fractured rock mass conditions in the excavation disturbed zone

The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine, China. The rock mass was particularly weak and fractured. There occurred 6 large-scale dynamical roof falls in the excavation disturbed zone （EDZ） with the collapsing volume of 216 m^3. First, the field detailed geological environment, regional seismic dynamics, and dynamic instability of roadways were generally investigated. Second, the field multiple-index monitoring measurements for detecting the deep delamination of the roof, convergence deformation, bolt-cable load, acoustic emission （AE） characteristic parameters, total AE events, AE energy-releasing rate, rock mass fracture, and damage were arranged. Finally, according to the time-space-strength relations, a quantitative assessment of the influence of rock-mass damage on the dynamic roof instability was accomplished.

Physical Modeling of Influence of Rock Mass Structure on Roof Stability

Based on the developing degree of structure planes in coal roof, whole, blocky and heavily fractured structure models are built up. Through simulation test of similar materials, the distribution of deformation, failure and underground pressure induced by coal mining in coal roof with different rock mass structures are analyzed. The test results indicate that the distances of first and periodic weighting of main roof and the height of caving and fracture zone decrease with the increment of fractures in roof rock mass. From whole to blocky and heavily fractured structures, abutment pressure ahead of working face reduces and the peak value of abutment pressure migrates to inside of roof rock mass.

Evaluation of load transfer mechanism under axial loads in a novel coupler of dual height rock bolts

The effective reinforcement of two or more overlying layers of mine openings in a single installation is usually done by coupling of two standard rock bolts mainly during the extraction of medium-thick coal seams.However,field observations show that the couplers of multiple bolts often degrade or break mostly at their connections.These types of failures can be avoided by strengthening the couplers of such multi-bolts assemblies.To achieve this,a novel threaded coupler system with an expansion shell was suggested in this paper.The newly designed coupler consists of a threaded tapered-plug-cumconnector with an expansion shell for connecting and tightening two standard rock bolts.An analytical model for evaluating the load distribution along the coupler subject to axial load was derived.Numerical analysis was performed to analyse the load transfer,deformation,and strains across the coupler including the factor of safety for the bolt-coupler-resin and bolt-coupler-expansion shell.The results validated the analytical model of the proposed coupler design,which provides better anchorage near the interface of the host rock mass.Thus,the developed coupler design would reduce the failures of the proposed coupler and stabilize laminated roof strata above the medium-thick coal seams in underground mines.

近距离煤层群采空区下切眼掘进及支护技术研究

为确保近距离煤层群开采下部工作面切眼安全掘进,以5303采煤工作面切眼为研究对象,结合现场情况针对性提出切眼掘进及支护安全技术,并进行工程应用。在5303采煤工作面切眼掘进期间,通过层间距(切眼与上覆采空区间)持续探测、切眼顶板注浆及分次掘进方式确保大断面切眼掘进安全;通过锚网索、单体+工字钢架棚方式维护大跨度切眼围岩稳定。工程应用后,5303采煤工作面切眼得以安全高效掘进,切眼围岩变形量较小,表明现场采用的掘进及支护技术可满足近距离采空区下大跨度切眼施工需要。

三角煤柱孤岛工作面冲击地压防治技术研究

为解决近邻三角形煤柱孤岛工作面冲击地压防治问题,分析了国内该条件下导致冲击地压的研究现状;以唐山矿Y392工作面为研究对象,通过理论分析得出了以大埋深、上覆不规则煤柱、本层三角形煤柱、孤岛工作面冲击地压的主控因素;采用FLAC3D建立了数值模型,分析了本层三角形煤柱孤岛工作面的应力分布规律;提出了通过顶板预裂调控冲击地压主控因素的防冲方法;最后通过现场工程实践,建立并实施了以顶板预裂为主的冲击地压防治技术,通过应力法和钻屑法验证了顶板预裂对该条件下的冲击地压防控具有良好的效果。

Failure of hanging roofs in sublevel caving by shock collision and stress superposition

Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased confining pressure and reduced free surface were its main characteristics.In order to break down a hanging roof,a new method based on shock wave collision and stress superposition was developed.In this method,two blastholes containing multi-primer at different positions are simultaneously initiated at first.By doing this,a new free surface and a swell room can be created.After these holes are fired,a long delay time is given to the next blasthole so that the fragments from the first twohole blasting have enough time to fall down.This new method was applied to three hanging roofs in one production area,and all of them were successfully broken down.Field inspection indicated that almost no damage was caused in the nearby drifts/tunnels due to the new method.In addition,the far field vibrations were found to be smaller than the maximum vibrations induced by some other blasts.

深井工作面顶板巷道卸压参数确定及控制技术研究

为解决深井工作面巷道顶板受深部采动应力而诱发的围岩大变形现象,采用理论分析及现场试验等方法,建立了应力拱力学模型并推导得出顶板巷道卸压高度计算公式,确定了某矿17191(1)瓦斯综合抽采巷合理切顶位置位于47.3 m高度的中细砂岩,为保证切顶效果,须设置49.9 m以保证将此岩层切落。确定了现场切顶卸压关键参数并进行工业性试验,采用了切顶爆破后,巷道最大高度由初始3.5 m降至3.24 m,断面收缩率为7.4%,有效控制了瓦斯抽采巷围岩稳定,巷道断面满足巷道正常抽采要求,保证了工作面安全稳定生产。

Deformation and failure of stratified weak roof strata of longwall roadway

A comprehensive underground monitoring was conducted in a coal mine. The purpose of this research was to clarify the deformation and failure behavior of stratified weak roof strata of longwall roadway in adverse ground conditions. The field investigation incorporating a range of geotechnical instrumentation was conducted over a period of time ever since the formation of opening the site was buried into the goaf of a retreating longwall panel. The roof layer deformation and failure characteristics associated with the three stages of heading development, after development and before extraction, as well as after longwall extraction were identified on the basis of field investigation and analytical study, the results clearly demonstrated that how the roof deformation and failure progress were strongly related to these three stages of the mining activities mentioned.

深部沿空巷道锚固围岩破坏失稳能量驱动机理

深部沿空巷道受侧向顶板断裂所产生的动载影响,锚固围岩易产生大变形,甚至破坏失稳。以山东省孙村煤矿31120工作面上平巷为工程背景,首先采用YTJ20型岩层探测记录仪获得了锚固顶板裂隙发育规律及以脆性张裂破坏为主的破坏方式。然后,通过相似材料模拟试验方法获得了深部沿空巷道侧向顶板前期、过渡期和后期3个运动阶段典型特征,并分析了不同阶段锚固围岩破裂演化及能量释放规律;其中过渡期运动阶段锚固围岩内部应力、变形量急剧增大,裂隙发育明显,能量释放显著,对沿空巷道锚固围岩稳定性影响最大。最后,构建了侧向顶板断裂运动下沿空巷道结构力学模型,给出了锚固围岩输入能量与可抵抗能量定量计算方法,揭示了侧向顶板断裂诱发锚固围岩破坏失稳能量驱动机理,并定义了失稳能量判据,即当作用在沿空巷道锚固围岩上的能量大于锚固围岩可抵抗能量时,将发生破坏失稳。进一步地,提出了锚固围岩失稳风险等级划分方法和相应地控制技术,计算结果表明,31120工作面沿空巷道锚固围岩失稳风险等级为中风险。采取加强支护措施后,沿空巷道顶底板及两帮移近量分别减小35.47%和35.71%,锚索受力减小23.43%,变形速度明显降低,锚固围岩能量积聚程度减小。

底板动压巷道压裂弱结构体应力转移控制技术

为了满足煤矿安全生产的需要,许多巷道都会布置在煤层底板中,如部分运输大巷、排水巷道、瓦斯抽采巷道等。采动应力容易造成底板巷道围岩应力升高,加剧底板巷道围岩变形,造成支护永久失效、顶板下沉、巷道底鼓、两帮收敛等破坏。针对此,提出了在应力传递路径上实施水力压裂,在指定的区域制造出一定空间形态的水压裂缝网,形成压裂弱结构体,实现区域范围内的应力转移,从而降低巷道区域范围内的应力,控制巷道的围岩稳定性的控制技术,并通过理论分析及现场工程验证等方式,揭示了底板动压巷道压裂弱结构体应力转移的力学机制,建立了相应的力学模型,对压裂弱结构体的合理位置、范围等影响因素进行了求解。得出:(1)压裂弱结构体使局部应力场发生明显变化,出现应力升高区和应力降低区,应力降低区主要分布在弱结构体与采动应力连线的方向上,主要集中在一个拱形的范围内;由于膨胀效应,在与应力来源垂直的方向上产生应力集中,出现应力升高区。(2)最大主应力变化幅度与压裂弱结构体的长轴长L、短轴长H、到巷道的距离P、与巷道连线的水平夹角β、压裂层的强度C及内摩擦角α、压裂的损伤变量D等有关。其中到巷道的距离P对卸压效果影响最大,损伤变量D对卸压效果影响最小。(3)采用提出的计算方法设计了淮北矿业集团袁店一矿的103运输集中巷的卸压方案,工程应用结果表明,底板动压巷道变形速率明显减缓,验证了底板强动压巷道压裂弱结构体应力转移模型的合理性。

矿震与冲击地压防治研究进展

矿震与冲击地压是采矿领域亟待解决的热点、难点和瓶颈问题,为了有效控制矿震与冲击地压,综述矿震定义与分类、矿压假说及矿震与冲击地压防治技术,回顾切顶卸压理论及其在中厚金矿采空区处理与卸压开采、中厚及以下煤矿沿空留巷中的应用,并比较其与110工法的差异。据此,给出矿震定义,指出矿震与冲击地压发生的条件类似,针对厚矿体开采提出深埋坚硬顶板控制爆破切槽放顶技术。研究表明:控制爆破切槽放顶技术仍然是未来矿震与冲击地压防治中释放并转移高地压的主要方法,它还可将深埋厚矿体的“砌体梁”简化成弹簧岩梁承载体系。

巷帮煤体整体滑脱型冲击地压锚杆防冲支护原理及工程实践

冲击地压是目前严重影响煤炭安全有效开采的灾害之一,研究锚杆防冲支护原理和技术对防治巷道冲击地压灾害具有重要意义和价值。通过对巷帮煤体整体冲入型冲击地压发生的地质条件以及破坏特征进行总结分析,认为坚硬顶板与坚硬煤层是此类型冲击地压的重要地质特征,而巷帮煤体整体滑脱是其主要冲击破坏特征。在此基础上,以巷帮滑脱煤体为研究对象,建立了顶板-巷道-底板复合结构体力学模型,建立了巷帮煤体发生水平滑移的极限平衡方程,并对各个参数进行分析。结果表明:由于顶板反弹使巷帮煤体竖直方向压力降低,巷帮煤体被构造应力推入巷道发生冲击地压。基于该发生机制模型,认为目前的锚杆支护设计体系在防治巷帮煤体冲入型冲击地压存在不足,并基于其发生和破坏特征,建立了针对巷帮煤体整体滑脱型冲击地压的锚杆防冲支护设计原则,即将顶和底帮锚杆锚固端分别穿层打入稳定的顶底板内,并使用长锚索取代中部帮锚杆,提供锚杆支护的防冲作用。基于新建立的锚杆防冲支护设计方法,以大屯矿区孔庄煤矿7305工作面防冲支护为工程背景,在宽煤柱段巷帮锚杆支护采取了防冲设计,帮顶、底部锚杆及补强锚索均锚固于顶底板内部,能够有效吸收煤体滑动动能,提高安全性。

西准噶尔构造带包古图组的岩石组合及其时限

包古图组是新疆西准噶尔增生造山带西北缘石炭纪密西西比亚纪重要沉积记录。确认其完整的沉积序列、岩石组合及其与上覆和下伏地层的接触关系,对解析本区晚古生代盆地构造演化具有重要意义。本文新实测的白碱滩北红山梁剖面上,出露了岩石组合截然有别,色调区分性极强的两大套地层,上部深灰—灰黑色调“(含碳)细碎屑岩”与其下伏鲜红色调的“硅质岩-凝灰质硅质粉砂岩间夹中基性火山岩”为连续沉积(整合接触),分属包古图组和红山梁组。本文于包古图组底部和红山梁组顶部分别获得345.1 Ma和365.9 Ma的LA-ICP-MS锆石U-Pb年龄,限定其时代分别为密西西比亚纪和晚泥盆世。这一新发现,不仅确立了包古图组是区内石炭纪最老地层单位,佐证了包古图组老于希贝库拉斯组这一久争悬疑,而且使得区内密西西比亚系有了完整的地层序列,揭秘了石炭系最底部的沉积建造及其岩石组合,也为完整认识泥盆纪—石炭纪这一重要时期的盆地沉积特征及其构造演化提供了新资料。

硬岩顶板切顶留巷围岩变形分区补强控制研究

【目的】森达源煤矿传统的宽煤柱开采方式导致采掘接续紧张,并引发严重的围岩变形问题。切顶留巷技术可优化巷道支护条件,提高采煤效率,促进煤矿高效安全生产。【方法】以1号煤层的10101工作面为研究对象,运用FLAC 3D数值模拟软件,深入探究了切顶高度、切顶角度、注浆加固深度对巷道掘进、预裂切顶和切顶留巷过程中煤帮内部、采空区及顶板应力变形特性的影响。确定出最佳切顶留巷方案。在此基础上,进一步模拟分析工作面前后不同区域的围岩受力变形情况。提出回采工作面前方0~30 m内为超前补强区,采取“高预应力锚索+单体配合铰接顶梁”的联合支护。后方0~100 m内为滞后补强区,采用“工字钢+单体支柱”联合支护,同时对矸石帮实施注浆加固。通过工程应用验证了区分补强控制变形措施的有效性。【结果】结果显示:最佳切顶留巷方案为切顶高度6 m,切顶角度15°,矸石帮注浆深度1 m。此方案下,10101工作面的巷道顶底板的最终变形量为155 mm,两帮的为84 mm,均符合矿井使用要求,验证了切顶留巷技术具有良好效果。【结论】结果表明:切顶留巷技术能有效解决传统宽煤柱开采方式中存在的围岩变形问题。然而,该技术的实施受切顶高度、切顶角度和矸石帮注浆深度等因素的影响较大,需结合数值模拟和现场状况进行具体确定。总体上,切顶留巷技术和分区补强控制措施对围岩变形的控制效果显著,为类似条件下的煤矿开采提供了宝贵的经验借鉴,因而具有广阔的应用前景。

烧变作用下巷道劣化围岩破坏机制与控制技术

针对烧变岩巷道围岩力学性能显著偏低的问题,以王才伙盘煤矿烧变岩区3202工作面回风巷为研究对象,利用Hoek-Brown修正准则求解了巷道围岩各分区应力及塑性区半径解析表达式,揭示了围岩稳定性的关键影响因素;明确了烧变岩区围岩控制策略,阐述了巷道浅部注浆和主、被动支护控制原理;对无支护、锚杆(索)支护以及浅部注浆+主被动联合支护等3种支护方式的围岩应力分布、变形特征、裂隙发育以及支护系统受力特征进行了模拟。研究结果表明:巷道松动圈主要与地质强度指标、岩体破碎度等因素密切相关;综合理论计算和现场实测结果,得到松动范围为4.2 m;3种支护方式拉应力峰值分别为1.14,0.85和0.81 MPa;偏应力峰值距巷道表面的最大距离分别为2.59,1.44和0.83m;顶板最大移近量分别收敛于350,205和24 mm;采用“注浆+锚杆(索)+金属架棚”支护形式,可在围岩浅部形成稳定承载点,实现有效支撑,同时锚杆、锚索支护作用得到充分发挥。现场工程实践结果显示,采用联合支护方式,巷道顶板及两帮移近量均小于50mm,有效稳定了烧变岩区的巷道围岩。研究成果可为同类地质条件下的巷道围岩控制提供参考。

孤岛工作面开采顶板深孔预裂减冲机制及微震响应特征

孤岛工作面开采具有较高冲击风险,顶板预裂是一种有效的减冲技术。以高庄煤矿3上1105孤岛工作面为背景,通过理论分析、数值模拟和现场实测等手段,研究了孤岛工作面冲击致灾机理、顶板预裂减冲机制及其影响因素。研究结果表明,两侧采空区覆岩形成的多拱结构传递压力及“砌体梁”结构失稳诱发强动载是孤岛工作面高冲击风险主要原因;建立了局部压力拱结构力学模型,分析局部压力拱力学特性,给出了局部压力拱失稳判据;顶板预裂爆破方法减冲机制为通过破坏形成局部压力拱的“砌体梁”结构,阻断压力传递路径,降低高支承压力场,减小开采期间“砌体梁”失稳诱发强动载风险。现场微震实测数据表明,顶板预裂减冲效果较好,有效降低了冲击风险。

层状复合夹煤岩石组合体试样强度试验与破坏特征研究

针对巷道复合夹煤组合结构顶板易冒落问题,以某矿取芯和钻孔窥视探测获得的巷道层状复合夹煤顶板结构组合类型为实验背景,对砂质泥岩、中砂岩以及煤厚度为20、30、40 mm不同结构组合类型的复合试件进行了单轴压缩试验,研究了复合夹煤岩石组合体的力学特性与破坏特征。试验结果表明:复合夹煤岩石组合体的抗压强度均小于单一岩石,中砂岩夹煤厚度为30mm时抗压强度达到单一中砂岩抗压强度的85.95%,抗压强度随着煤厚变薄而下降;砂质泥岩夹煤厚度为20 mm时仅为单一砂质泥岩抗压强度的32.5%,随着夹煤厚度增加抗压强度也增大,夹煤厚度超过30mm后抗压强度增大不明显。复合夹煤岩石组合体整体呈X状共轭斜面剪切破坏、单斜面剪切破坏、部分拉伸破坏,随着复合夹煤岩石组合类型不同呈现不同的破坏特征等。