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.

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。

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。

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。

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。

冲击地压矿井充填工作面超前采动应力对充填体充实率的反馈机制

高应力是深部矿井冲击地压灾变频率走高的主要原因,充填开采则是控制岩层运动,缓解采动应力集中程度,降低围岩破坏和冲击风险的有效手段。为研究采空区充填体对超前采动应力的控制能力,以山东古城煤矿1123充填工作面为工程背景,采用理论分析、室内试验、现场实测手段探究充填开采工作面采动应力分布规律,揭示超前采动应力对充填体充实率的反馈机制,指导冲击地压矿井充实率确定。结果表明:工作面开采初期充填体充实率低于80%,坚硬顶板下沉量大,超前采动影响范围大于30 m,应力集中系数达到1.5,断层影响区采动应力影响范围和集中系数分别增至60 m和1.65,片帮冒顶等围岩失稳现象增多;实测了采空区充填体承载应力全程动态演化特征,承载应力分布曲线划分为“快速降低—短暂稳定—快速升高—缓慢降低—二次稳定”5个阶段,低充实率条件下采空区上、中、下3个区域承载应力稳定值分别为1.9、5.2、2.8 MPa;将采空区充填体划分为非充分压实区和充分压实区,构建了充填体支撑作用下坚硬顶板连续沉降模型,得到了坚硬顶板“ʅ”型沉降曲线,非充分压实区范围随充实率近似呈线性减小;试验得到充填体弹性模量和单轴抗压强度随凝固时间的演化曲线,结合顶板沉降曲线和推进速度得到工作面前后采动应力全区域分布曲线;建立了超前采动应力集中程度与充填体承载能力的负指数函数关系,揭示了超前采动应力对充填体充实率的负向反馈机制,实现充填开采降载防冲效果的定量评价;提出了充填体充实率“三位一体”协同提升措施,将1123工作面充实率升高至90%,增强了充填体承载能力,超前采动应力集中系数降至1.3,厚顶煤膨胀变形量减少至50 mm,坚硬顶板破断致冲风险显著降低。

工作面单双巷顶板爆破应力演化规律研究

坚硬顶板是影响工作面冲击危险的重要因素,实践中常采用爆破技术对工作面顶板进行预裂和卸压。以田陈煤矿3煤层上方存在坚硬顶板的7202工作面为对象,采用理论分析、数值模拟、工业试验等方法,研究了不同爆破高度、工作面单巷和双巷顶板爆破下围岩应力演化及微震规律。结果表明:针对低位亚关键层采用单巷和双巷爆破时,爆破高度越大,巷道围岩峰值应力越低,卸压效果与爆破高度呈正相关关系;但采用双巷爆破时,当爆破高度增加至6倍采高(亚关键层中部位置)以上时,工作面中部区域会出现应力升高现象,且工作面越短应力升高越明显;在7202工作面初采阶段进行高度为3倍采高的单巷顶板爆破时,微震多集中在巷道区域,卸压效果一般,改为双巷顶板爆破并提高爆破高度至6倍采高后,微震多集中到工作面中部区域,无大能量微震事件发生,应力监测预警次数也大幅降低,巷道区域卸压效果较好。

深部采煤深孔爆破技术防控强矿震机制研究

中国华东、东北、华北大部分煤矿已进入600 m以下深度开采,矿震等动力灾害屡有发生,严重制约了煤矿安全、绿色、高效生产。针对中国深部煤矿厚硬顶板下开采矿震频发问题,以东滩煤矿为例,采用现场监测、理论分析和数值模拟等方法,详细阐述了深孔爆破顶板卸压前后强矿震空间分布特征,研究了深孔爆破技术预裂顶板机制、对采动中覆岩活动影响及防控矿震的效果。研究发现深孔爆破技术可有效弱化或断裂上覆厚硬岩层,释放上覆岩层积聚的应变能,减少大能量矿震的风险。基于爆炸荷载作用下岩石破坏区理论分析计算出了深孔爆破岩石破碎区、裂隙区和有效破坏范围,并结合工作面支架阻力监测,发现深孔爆破技术可主动调控矿山压力,避免了强矿压显现。建立了含四次深孔爆破的煤层开采全过程数值模型,分析了深孔爆破前后覆岩应力及位移演化特征,揭示了深孔爆破对采动中覆岩活动影响机制。深孔爆破断顶卸压技术能够有效弱化煤层顶板、降低顶板来压强度、增大覆岩的碎胀系数,能够用于防控深部采煤强矿震的发生。

新街矿区厚硬顶板条件邻空巷道冲击地压机理与控制

【目的和方法】针对厚硬顶板条件下深部矿井回采巷道冲击地压严重威胁工作面安全生产的问题,以内蒙古新街矿区典型深采矿井3-1103工作面辅运巷为工程研究背景,分析邻空巷道冲击地压频发区域外在主控因素和内在驱动力源;构建基于软化地基与弹性地基假定“岩梁-地基”系统力学特性的顶板断裂前受载力学模型,解析采场覆岩结构演化过程厚硬顶板岩梁能量演化规律及其主控因素;运用FLAC3D模拟并探查邻空巷道冲击失稳高风险区域位置与特征;研究采场覆岩结构优化与围岩应力能量控制方案,制定厚硬顶板破断诱发邻空巷道冲击地压控制方法。【结果和结论】结果表明:(1)邻空巷道冲击地压频发区域易发生以高静载或高静载叠加动载为主导灾变力源的失稳破坏,影响因素主要为顶板厚硬岩层、邻近采空区、区段煤柱。(2)顶板储能总量与覆岩载荷、软化地基系数、顶板岩梁弹性模量及惯性矩、采空区顶板极限跨距、工作面支架参数等有关。其中,覆岩载荷、软化地基系数和采空区顶板极限跨距与岩梁应变能密度呈正相关,顶板岩梁弹性模量及惯性矩、工作面支护参数与岩梁应变能密度呈负相关。(3)回采期间3-1103工作面超前支承压力区及其影响区域内区段煤柱和回采巷道煤体呈现多因素叠加影响,发生应力集中和能量积聚,是冲击失稳高风险区域;该区域较3-1101综采面其围岩应力与能量集中度进一步加剧增大。其中,工作面前方应力和应变能密度峰值增幅最大分别为6.61%、12.04%,区段煤柱应力和应变能密度峰值增幅最大分别为29.06%、65.14%。(4)提出了“卸压爆破预处理高静载区域+深孔爆破或水力致裂预裂厚硬顶板+强化巷道吸能防冲支护”的解决方案,现场应用效果明显。

非均厚“弓形”巨厚关键层动静载作用机制

巨厚关键层破裂运动是诱发矿山动力灾害的重要因素,探究其厚度变化对采动应力分布及破裂动载的影响,对明确巨厚关键层采场动、静载来源及冲击矿压孕育机制具有重要意义,是冲击矿压风险预测及灾害防控的理论基础。以陕西彬长矿区某矿非均厚“弓形”巨厚关键层为研究对象,综合理论分析与数值仿真计算,剖析了巨厚关键层“弓形”形态下伏煤岩体采动应力异常集中的力学原理,探明了“弓形”形态对巨厚关键层破裂特征的影响规律,揭示了“弓形”形态下伏区域动静载叠加致灾机制,据此提出了“弓形”巨厚关键层破裂致灾风险预测方法。结果表明,“弓形”巨厚关键层底部凸起导致下伏煤岩体垂直应力异常集中,相较于均匀厚度巨厚关键层,该区域煤岩体垂直应力额外增加22.1 MPa,增幅比例高达56%,此为下伏煤岩体高静载形成的根本原因。同时,伴随着开采范围的扩大以及非均厚“弓形”巨厚关键层运动,造成其底部内凹拐角区出现显著的高应力集中现象,导致该区域岩石发生破裂及弹性能快速释放,此为强动载形成主要原因。在上述非均厚“弓形”巨厚关键层动静载叠加作用下,煤柱大巷区域极易出现冲击矿压。基于此,准确识别并定位了非均厚“弓形”巨厚关键层影响下采动覆岩动载形成来源及发生区位,结合巨厚关键层分布式光纤原位监测结果,以光纤断裂高度为监测指标,验证了巨厚关键层破裂及动载荷形成之间的内在联系。

托顶煤切顶留巷围岩控制技术研究

为了解决托顶煤巷道围岩变形难以控制的问题,运用理论分析、离散元数值模拟及现场工业试验相结合的方法对义棠煤业100602工作面切顶成巷围岩控制技术进行研究,分析了不同切顶高度、采高对留巷围岩变形影响规律。研究发现,适当增加切顶高度并降低采高有利于巷道围岩稳定,并确定开采技术参数为切顶高度24 m、采高6 m。现场监测结果显示,在合理的支护策略及开采工艺参数下,托顶煤切顶留巷围岩变形控制效果良好。

膨胀应力作用下复合顶板巷道围岩支护研究

针对澄合矿区复合顶板管理难度大,巷道支护困难,严重制约矿井安全开采这一问题,以山阳煤矿5号煤层1501回风巷为工程背景,对复合顶板软岩巷道的破坏机理及支护问题展开了研究。首先通过物理力学试验,得到顶板各岩层的物理参数,然后采用现场实测和理论分析的方法,分析复合顶板的应力分布特征,从而构建山阳煤矿巷道的复合顶板力学模型,最后运用数值模拟和现场实测的方法验证支护方案的可行性。研究结果表明,矿井复合顶板上部砂质泥岩为膨胀岩,最大膨胀率为42.3%,最大膨胀应力为198.2k Pa;中粒砂岩层K4为关键岩层;提出的顶板采用全锚索支护,巷帮采用金属网+钢带+锚杆支护的支护方案,经过数值模拟和现场实测的验证,该方案可满足现场生产需求。研究成果可为类似地质条件的巷道支护提供参考。

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.