Structure and deformation measurements of shallow overburden during top coal caving longwall mining

Mining induced pressures are strong and overburden failure areas are large in top coal caving longwall mining, which constrains high production and safety mining. By employing the combination of the full view borehole photography technique and the seismic CT scanner technique, the deformation and failure of overlying strata of fully mechanized caving face in shallow coal seam were studied and the failure development of overburden was determined. Results show that the full view borehole photography can reveal the characteristics of strata, and the seismic CT scanner can reflect the characteristics of strata between the boreholes. The combined measurement technique can effectively determine the height of fractured and caved zones. The top end of the caved zone in Yangwangou coal mine employing the top coal caving longwall mining was at the depth of 171 m and fractured zone was at the depth of 106-110 m. The results provide a theoretic foundation for controlling the overburden strata in the shallow buried top coal caving panel.

Experimental study on the deformation behaviour,energy evolution law and failure mechanism of tectonic coal subjected to cyclic loads

Compared to intact coal,tectonic coal exhibits unique characteristics.The deformation behaviours under cyclic loading with different confining pressures and loading rates are monitored by MTS815 test system,and the mechanical and energy properties are analysed using experimental data.The results show that the stress-strain curve could be divided into four stages in a single cycle.The elastic strain and elastic energy density increase linearly with deviatoric stress and are proportional to the confining pressure and loading rate;irreversible strain and dissipated energy density increase exponentially with deviatoric stress,inversely proportional to the confining pressure and loading rate.The internal structure of tectonic coal is divided into three types,all of which are damaged under different deviatoric stress levels,thereby explaining the segmentation phenomenon of stress-strain curve of tectonic coal in the cyclic loading process.Tectonic coal exhibits nonlinear energy storage characteristics,which verifies why the tectonic coal is prone to coal and gas outburst from the principle of energy dissipation.In addition,the damage mechanism of tectonic coal is described from the point of energy distribution by introducing the concepts of crushing energy and friction energy.

Experimental study on the deformation and failure mechanism of overburden rock during coal mining using a comprehensive intelligent sensing method

Understanding the spatiotemporal evolution of overburden deformation during coal mining is still a challenge in engineering practice due to the limitation of monitoring techniques. Taking the Yangliu Coal Mine as an example, a similarity model test was designed and conducted to investigate the deformation and failure mechanism of overlying rocks in this study. Distributed fiber optic sensing(DFOS), highdensity electrical resistivity tomography(HD-ERT) and close-range photogrammetry(CRP) technologies were used in the test for comprehensive analyses. The combined use of the three methods facilitates the investigation of the spatiotemporal evolution characteristics of overburden deformation, showing that the mining-induced deformation of overburden strata was a dynamic evolution process. This process was accompanied by the formation, propagation, closure and redevelopment of separation cracks.Moreover, the key rock stratum with high strength and high-quality lithology played a crucial role in the whole process of overburden deformation. There were generally three failure modes of overburden rock layers, including bending and tension, overall shearing, and shearing and sliding. Shear failure often leads to overburden falling off in blocks, which poses a serious threat to mining safety. Therefore, realtime and accurate monitoring of overburden deformation is of great significance for the safe mining of underground coal seams.

Theoretical analysis on the deformation characteristics of coal wall in a longwall top coal caving face

Against the background of analyzing coal wall stability in 14101 fully mechanized longwall top coal caving face in Majialiang coal mine,based on the torque equilibrium of the coal wall,shield support and the roof strata,an elastic mechanics model was established to calculate the stress applied on the coal wall.The displacement method was used to obtain the stress and deformation distributions of the coal wall.This study also researched the influence of support resistance,protective pressure to the coal wall,fracture position of the main roof and mining height on the coal wall deformation.The following conclusions are drawn:(1) The shorter the distance from the longwall face,the greater the vertical compressive stress and horizontal tensile stress borne by the coal wall.The coal wall is prone to failure in the form of compressive-shear and tension;(2) With increasing support resistance,the revolution angle of the main roof decreases linearly.As the support resistance and protective force supplied by the face guard increases,the maximum deformation of the coal wall decreases linearly;(3) As the face approaches the fracture position of the main roof,coal wall horizontal deformation increases significantly,and the coal wall is prone to instability;and(4) The best mining height of 14101 longwall face is 3.0 m.

Roadway failure and support in a coal seam underlying a previously mined coal seam

The influence of an upper,mined coal seam on the stability of rock surrounding a roadway in a lower coal seam is examined.The technical problems of roadway control are discussed based on the geological conditions existing in the Liyazhuang Mine No.2 coal seam.The stress distribution and floor failure in the lower works after mining the upper coal is studied through numerical simulations.The failure mechanism of the roof and walls of a roadway located in the lower coal seam is described.The predicted deformation and failure of the roadway for different distances between the two coal seams are used to design two ways of supporting the lower structure.One is a combined support consisting of anchors with a joist steel tent and a combined anchor truss.A field test of the design was performed to good effect.The results have significance for the design of supports for roadways located in similar conditions.

Study on gob-side entry retaining in fully-mechanized longwall with top-coal caving and its application

Based on the engineering background of gob-side entry retaining in fully-mechanized longwall with top coal caving(GER-FLTC) on N2105 working face of Yuwu coal mine, by adopting the methods of theoretical analysis and numerical calculation, the control techniques of surrounding rocks in GER-FLTC working face are studied in this paper. The two main difficulties of stability of surrounding rocks at gob-side retained entry in fully-mechanized longwall working face are the stability control of top coal and control of large deformation of GER-FLTC working face. Interaction mechanical model between roofing and roadside backfilling in GER-FLTC is established and the equations for the calculation of roof-cutting resistance of roadside backfilling are derived. Results of numerical calculation show that the damage zones of top coal can be categorized into the delaminating zone of top coal above the backfilling, tensile damage zone of top coal above the retained roadway and shear damage zone of the upper rib of the solid coal. Stability control of top coal is the critical part to success of GER-FLTC. With consideration of large deformation of surrounding rocks of gob-side retained entry in fully-mechanized longwall, the support technique of‘‘roofing control and wall strengthening'' is proposed where high strength and highly prestressed anchor rods and diagonal tensile anchor cables support are used for top coal, high strength and highly prestressed yielding anchor rod support is used for solid coal and roadside prestressed load-carrying backfilling is constructed by high-water material, in order to maintain the integrity of the top coal, transfer load, high resistance yielding load-carrying of solid coal, roof-cutting of roadside backfilling and support,and to achieve GER-FLTC. Results from this study are successfully applied in engineering practice.

Ground stability of underground gateroad with 1 km burial depth： A case study from Xingdong coal mine, China

本文采用数值模拟、案例分析、现场试验相结合的综合研究方法分析千米埋深煤矿巷道围岩稳定性。首先,在试验巷道进行了地应力监测与煤岩体力学性能测试;然后,通过FLAC^(3D)数值模拟软件分析了试验巷道围岩位移场、应力场、塑性区与锚杆受力特征。研究结果表明,软岩特性与高地应力是深部巷道失稳的主要因素,高应力引起的剪切滑移破坏是深部巷道围岩的主要破坏模式;不合理的支护方式,特别是锚杆索长度短且预紧力低、缺少高强二次支护、底板无支护等亦是巷道失稳的原因。基于上述研究,提出了集长锚杆索、可缩性环形支架、注浆加固于一体的联合加固措施,并通过现场监测验证了支护方案的合理性。本文研究成果为深入理解千米深井巷道破坏机制提供了借鉴。

多源煤基固废胶结充填体力学及变形破坏特征试验研究

【目的】为研究多源煤基固废胶结充填体的力学特性及变形破坏规律,选择5种典型煤基固废,开展了煤基固废胶结充填体(Coal-Based Solid Waste Cemented Backfill,CBSWCB)的单轴压缩、声发射响应及微观结构测试试验。【方法】分析了CBSWCB单轴抗压强度的影响因素和交互作用,建立了基于交互作用的抗压强度影响因素四维空间可视化模型,结合CBSWCB的声发射及微观结构特征,阐明了单轴压缩条件下的力学演化特征及宏观变形破坏规律,从微观角度进一步论证了CBSWCB承载过程中水化反应机理及宏细观联系。【结果和结论】试验结果表明:(1)单轴抗压强度的主要影响因素是质量分数,而炉底渣掺量的影响程度最小。(2)单轴压缩下CBSWCB的宏观变形破坏由塑性、弱劈裂破坏逐渐向脆性、剪切破坏转化。(3) CBSWCB试件声发射参数演化可以分为上升期、平静期、活跃期、稳定期,声发射累计振铃计数曲线呈现明显的“阶梯状”增长,累计振铃计数在上升期和平稳期内缓慢增加,在活跃期急剧增加,在稳定期逐渐趋于平缓。(4)水泥掺量偏低以及多源煤基固废充填材料属性差异导致水化反应程度有限,水化产物数量较少是CBSWCB单轴抗压强度普遍偏低的主要原因。研究结果可为多源煤基固废用于充填开采提供一定参考依据。

循环梯度加载下煤岩损伤破坏特性及能量演化规律研究

煤矿开采中岩体受开挖卸荷因素的影响常处于反复的循环加载过程,为研究循环梯度加载作用下煤岩的损伤破坏特性和能量演化规律,对煤样进行单轴循环梯度加载实验,对比分析煤岩在不同循环梯度加载下的变形破坏特性、输入能量密度、耗散能密度和损伤变量的规律。结果表明:随着循环梯度应力的递增,煤岩试样所承受的循环次数递减、峰值强度降低,分别为17.97、14.86、11.23、10.53 MPa;在循环梯度加载中,输入能量密度绝大部分以弹性应变能的形式储存于岩样内部,耗散能在单次循环输入总能量的0.2%~40%之间递增。选用累积耗散作为煤岩损伤破坏全过程的量化指标,并通过Logistic方程对煤岩损伤进行了拟合,得到了煤岩损伤的演化模型。

倾斜煤系地层大断面客专隧道大变形原因分析及处置

针对沪昆铁路刘家庄隧道穿越煤系地层施工中发生的大变形现象,基于理论分析、数值模拟和现场监测方法,分析隧道发生大变形的原因,推导并验证了产生大变形的起始位置,得到了掌子面上方煤层单元体沿倾斜面方向的应力状态与隧道进入含倾斜煤系地层水平距离之间的变化规律,对倾斜煤层单元体与初期支护结构的应力与变形进行了分析。结果表明:掌子面上方煤体单元应力状态变化随掌子面进入倾斜煤层下方水平距离的增加,围岩经历挤压、压剪和剪切滑移3个变形阶段。围岩大变形与初期支护结构破坏均发生在剪切滑移阶段的初期,应在压剪变形阶段结合现场监测数据对掌子面进行喷射混凝土封闭、注浆加固掌子面上方松散煤层和加强初期支护结构刚度等措施以预防隧道产生大变形。

深部顶板夹煤层巷道变形破坏分析及其控制

为了探究深部顶板夹煤层软岩巷道大变形破坏问题,以平煤六矿三水平戊二胶带运输巷为工程背景,开展夹煤层巷道围岩破坏分析及控制对策的研究。首先,构建原支护体系组合拱力学模型,推导出直墙半圆拱形巷道稳定判别式;其次,提出“锚网索-梁-注浆-组合砂浆锚索”联合返修控制对策,即沿戊8煤层顶板进行巷道扩刷,采用锚网索、梯子梁完成基本支护,对围岩进行深浅孔注浆加固、顶板及两帮关键部位布置组合砂浆锚索等加强支护,并通过数值模拟分析返修前后应力、位移场分布特征;最后,开展工业性试验,并监测矿压。结果表明:两帮及顶底板最大收敛量分别为93、112 mm,后期变形速率均低于1 mm/d,围岩变形得到有效控制,返修效果良好。

考虑侧壁阻力的顺层边坡失稳机制及稳定性评价

侧壁阻力作用下,顺层边坡主滑方向将偏离岩层倾向,其变形及失稳机制具有典型特征。以四川盆地马边河流域某顺层边坡为例,基于其工程地质条件,总结顺层边坡不同变形区域的特征,结合失稳边界条件研究了考虑侧壁阻力的顺层边坡失稳演化机制;最后,对比主滑方向偏离岩层倾向与否的受力差异,分析考虑侧壁阻力的顺层边坡三维稳定性,并研究了各影响因素的作用效应。结果表明:(1)考虑侧壁阻力的顺层边坡变形可划为失稳滑走区、滑坡区和稳定区,滑坡区包含滑动区和蠕滑变形区,滑动区岩体滑动后解体风化为碎、块石土,蠕滑变形区受侧壁阻力影响岩体仅变形拉裂;(2)顺层边坡经岩体劣化和前缘临空后,总体呈下部滑动、中部蠕滑拉裂的顺层临空-后退式破坏;滑动区边界受前缘及侧壁临空控制,长度与侧壁冲沟下切段长度相近;蠕滑变形区部分侧壁由节理面转化为挤压带,侧壁阻力增大,稳定性高于临界失稳状态;受侧壁阻力及滑体厚度控制,蠕滑变形区与稳定区界限处因滑体厚度削薄而拉裂;(3)建立了考虑侧壁阻力的顺层边坡稳定性系数计算式,以及岩层倾角δ、滑面倾角α、主滑方向偏离岩层倾向夹角β三角度间的换算关系式,侧壁摩擦系数和β越大,侧壁阻力越利于顺层边坡稳定。

应力扰动路径对煤岩力学性能的影响试验研究

在利用废弃矿井抽水蓄能过程中,煤柱不仅受到单调荷载的影响,而且会遭受频繁的应力扰动。以陕西省河畔煤矿煤岩为研究对象,研究了单调荷载(路径1)、多级等幅循环荷载(路径2)、多级增幅循环荷载(路径3)影响下试样的强度、变形特征以及破坏模式。试验结果表明:循环荷载作用下,试样的应力-应变曲线形成了明显的滞回环,且随着应力水平增加,滞回环面积显著增加;与轴向应变相比,环向应变对应力路径的敏感性更强;单调荷载作用下煤样的峰值强度和峰值应变最大,多级循环荷载作用下试样的强度和峰值轴向应变分别降低了22.12%、18.35%(路径2)、5.30%、10.34%(路径3);应力路径2作用下的试样割线模量明显高于其他应力路径;应力路径对试样宏观破坏模式的影响甚微,但多级循环荷载使得试样表面裂纹数量和尺寸变大。

煤柱-顶板结构能量演化特征及稳定性研究

煤矿事故的发生大多是由煤柱及其上覆顶板岩层失稳破坏引起的。为了研究不同煤-岩高度比对煤柱-顶板结构变形破坏及能量演化机制的影响,对煤-岩高度比分别为1∶3、1∶2、1∶1、2∶1及3∶1的煤-岩组合体进行了单轴加载及循环加卸载试验,研究了煤-岩结构体变形与能量演化之间的变化关系,利用加卸载响应比对煤-岩组合体的稳定性进行分析,对煤-岩组合体稳定性进行定量评价。结果表明:煤-岩组合体在单轴加载及循环加卸载作用下的峰值强度均随着煤-岩高度比的增加而逐渐降低,煤-岩组合体在循环加卸载作用下的峰值强度均低于单轴加载试验中的峰值强度,煤-岩高度比越大,循环载荷作用下组合体峰值强度降低率越小;组合体输入能、弹性能和耗散能随应力增加呈非线性增加,煤-岩高度比与组合体循环载荷过程中产生的平均弹性应变、平均弹性能、平均残余应变、平均耗散能、总残余应变和加卸载响应呈正比关系,与总弹性应变、总弹性能和总耗散能呈反比关系。

煤柱应力区的巷道破坏特征及控制技术研究

在连续煤层开采过程中,上部采空区残余煤柱常导致下伏长壁开采工作面产生强应力,应力积累会造成回采巷道严重破坏变形。为此,以隆泰煤矿巷道的应力破坏变形过程为例进行了研究,分析了采矿巷道围岩的破坏变形过程,运用FLAC3D模拟了应力分布特征以及巷道周围垂直应力和破坏带的演化过程。结果表明,支护煤柱以下工作阻力普遍较高,平均值为9726.6kN,采空区以下普遍较低,平均值为7 655.5 k N;受影响,回采巷道在距工作面30 m以外变形破坏程度相对中等,在距9+10号工作面30 m以内变形破坏程度相对严重;基于残留煤柱集中应力分布特征,采用水力压裂控制其力学特性,改善了回采巷道应力环境。

浅埋近距离煤层开采超前煤柱群冲击失稳机制

工作面前方遗留煤柱群(后文简称“超前煤柱群”)在采动影响下会发生链式冲击失稳,诱发动载矿压灾害并影响下伏煤层的安全高效开采。揭示超前煤柱群链式冲击失稳机制是浅埋近距离煤层安全开采的根本前提。本文实测分析了元宝湾煤矿房式采空区下伏6107工作面开采的覆岩移动规律,发现了超前煤柱群的回弹变形现象,开展了房式采空区下伏煤层开采的物理模拟实验,研究了房采煤柱群-覆岩的变形破坏特征,分析了采动影响下超前煤柱群回弹冲击失稳的动态过程,揭示了浅埋近距离煤层开采超前煤柱群的冲击失稳机制。结果表明:(1)浅埋柱采区近距离下伏煤层开采过程中工作面前方覆岩呈现出“先短暂回弹后剧烈下沉”的运动特征,即首先存在极短时间的覆岩回弹变形现象,之后出现了部分覆岩的整体破断与垮塌。由此,反推出采动影响下超前煤柱群也发生了回弹变形。(2)柱式采空区下伏煤层开采过程中关键柱在覆岩沉降和超前支承压力的作用下最早出现斜切破坏,引起载荷的转移,加剧邻近部分房采煤柱群的应力集中程度,进而发生链式斜切破坏。在此过程中,覆岩持续沉降,裂隙也不断发育,形成剪切贯通断裂面,发生破断回转,促使超前煤柱群回弹变形与冲击失稳,引发层间岩层的全厚切落,带动更大规模房采煤柱群的链式失稳,并造成下伏工作面动压灾害的发生。(3)浅埋近距离下伏煤层开采“煤柱群-覆岩”的失稳垮塌过程可以细分为:关键柱斜切破坏阶段、关键柱邻近部分煤柱群破坏阶段、超前煤柱群回弹冲击失稳阶段、覆岩垮塌与层间岩层切落致灾阶段。(4)浅埋近距离煤层开采超前煤柱群冲击失稳是“煤柱群回弹变形”与“覆岩联动垮塌”共同作用且互馈影响的动态过程。该研究可以解释柱式采空区下伏近距离煤层开采超前动载矿压的显现原因,有望为超前动载矿压的预测和控制提供理论指导,并进一步保障近距离煤层群的安全绿色高回收率开采。

不同覆岩地层正断层下盘煤层开采地表下沉规律

断层破坏覆岩地层的整体性,影响岩土体的强度特性和变形性质,导致开采沉陷规律更为复杂。为研究不同覆岩地层与正断层共同影响下煤层开采地表沉陷规律,构建不同覆岩地层正断层下盘煤层开采覆岩运动与地表变形的理论模型,数值模拟分析不同覆岩地层正断层下盘煤层开采地表下沉规律与特征,结合实例进行了对比分析。结果表明:地表移动变形范围与松散层厚度密切相关,随松散层厚度的增加,相较于无断层一侧,地表下沉盆地在断层一侧的移动变形范围先减小后扩大再减小,最终与无断层一侧相同;厚基岩地质条件下,随松散层厚度增加,地表产生裂缝的位置由断层露头先向采空区偏移后向断层上盘偏移;厚松散层地质条件下,松散层吸收了断层诱发的非连续变形,随松散层厚度增加,地表由偏态下沉盆地逐渐变为对称的下沉盆地。

不同高比灰岩-煤组合体变形破坏特征实验研究

为探究不同岩煤(高度)比的灰岩-煤组合体试样变形破坏特征,首先,对5组组合体试样进行了单轴压缩试验;其次,基于声发射系统和XTDIC三维全场应变测量系统,采集了加载全程试样声发射信号及其表面应变信息;最后,从变形场演化、回弹变形、能量耗散和声发射特征等方面,定量揭示了组合体试样的变形破坏特征。研究结果表明:随着岩煤高比增大,组合体试样单轴压缩强度和弹性模量均呈增大趋势,其破坏均发生在煤样内,由张拉破坏向拉-剪混合破坏转变,塑性破坏增强;变形局部化带首先出现在煤样原生裂纹区域,且随着裂纹的起裂、扩展而发生交汇,进而诱发煤样破坏;同时,煤样破坏导致灰岩回弹变形,随着岩煤高比增大,灰岩回弹变形量由0.042 mm递减至0.008 mm,回弹变形率由0.210%递减至0.010%,回弹变形量和回弹变形率整体呈递减趋势。随着岩煤高比增大,组合体试样峰前弹性能密度占比由98.56%递增至99.86%,外界能量转化为弹性能的能力增大,峰后弹性能转化为峰后释放能和剩余弹性能的能力增大,破坏后宏观裂纹增多且动力显现程度增大。组合体试样声发射能量率信号具有明显的时效特征,分为波动、静寂、活跃和骤增4个阶段,当组合体试样发生整体破坏时,声发射能量率信号达到最大值。

深部留底煤回采巷道变形破坏及支护策略研究

为揭示深部留底煤回采巷道围岩变形破坏规律、提出有效支护策略,以青云煤矿020202工作面轨道巷为研究对象,通过建立深部巷道力学模型,引入无量纲形式的敏感度因子,研究埋深、围岩强度、采动应力和支护阻力对围岩变形破坏的影响规律,基于此提出新支护策略,并采用数值模拟和现场实测验证。研究结果表明:围岩表面位移量和塑性区半径各影响因素按影响程度排序为埋深>围岩强度>采动应力>支护阻力;“去底煤注浆加固+高预应力强力锚杆锚索及时支护”策略可有效抑制巷道围岩塑性区发育,使围岩变形量减少约50%,无需返修。研究成果可为深部留底煤巷道支护设计提供借鉴参考。

含矸煤层煤壁稳定性夹矸厚度效应研究

为了解夹矸厚度对含矸煤层煤壁稳定性的影响,采用理论分析与数值模拟相结合的方法,推导出夹矸层剪切破坏力学模型,进而建立含矸煤层煤壁稳定性数值模型,分析不同夹矸厚度下的煤壁前方水平位移、垂直应力的空间分布特征。结果表明:煤壁前方产生失稳影响区主要位于夹矸层周围,形成以夹矸层为中心的凸出区域;夹矸厚度较小时,夹矸层呈现出多块体联合破坏形态,而夹矸厚度较大时,夹矸层出现单块体逐个破断现象;力学分析得知:夹矸层破坏面发生剪切破坏的危险系数随着夹矸厚度的增大而逐渐减小,数值模拟结果与理论分析一致。