Characteristics of evolution of mining-induced stress field in the longwall panel:insights from physical modeling

The evolution of mining-induced stress field in longwall panel is closely related to the fracture field and the breaking characteristics of strata.Few laboratory experiments have been conducted to investigate the stress field.This study investigated its evolution by constructing a large-scale physical model according to the in situ conditions of the longwall panel.Theoretical analysis was used to reveal the mechanism of stress distribution in the overburden.The modelling results showed that:(1)The major principal stress field is arch-shaped,and the strata overlying both the solid zones and gob constitute a series of coordinated load-bearing structures.The stress increasing zone is like a macro stress arch.High stress is especially concentrated on both shoulders of the arch-shaped structure.The stress concentration of the solid zone in front of the gob is higher than the rear solid zone.(2)The characteristics of the vertical stress field in different regions are significantly different.Stress decreases in the zone above the gob and increases in solid zones on both sides of it.The mechanical analysis show that for a given stratum,the trajectories of principal stress are arch-shaped or inverselyarched,referred to as the‘‘principal stress arch’’,irrespective of its initial breaking or periodic breaking,and determines the fracture morphology.That is,the trajectories of tensile principal stress are inversely arched before the first breaking of the strata,and cause the breaking lines to resemble an inverted funnel.In case of periodic breaking,the breaking line forms an obtuse angle with the advancing direction of the panel.Good agreement was obtained between the results of physical modeling and the theoretical analysis.

Numerical simulation of spatial distributions of mining-induced stress and fracture fields for three coal mining layouts

In this study, the spatial distributions of stress and fracture fields for three typical underground coal mining layouts, Le, non-pillar mining （NM）, top-coal caving mining （TCM） and protective coal-seam mining （PCM）, are modeled using discrete element software UDEC, The numerical results show that different mining layouts can lead to different mining-induced stress fields, resulting in diverse fracture fields, For the PCM, the mining influenced area in front of the mining faces is the largest, and the stress concentration factor in front of the mining faces is the lowest, The spatial shapes of the mining-induced fracture fields under NM, TCM and PCM differ, and they are characterized by trapezoidal, triangular and tower shapes, respectively, The fractal dimensions of mining-induced fractures of the three mining layouts decrease in the order of PCM, TCM and NM, It is also shown that the PCM can result in a better gas control effect in coal mines with high outburst potential, The numerical results are expected to provide a basis for understanding of mining-induced gas seepage fields and provide a reference for high- efficiency coal mining,

Coal and rock fissure evolution and distribution characteristics of multi-seam mining

Henan Pingdingshan No.10 mine is prone to both coal and gas outbursts.The E_(9-10)coal seam is the main coal-producing seam but has poor quality ventilation,thus making it relatively difficult for gas extraction.The F_(15)coal seam,at its lower section,is not prone to coal and gas outbursts.The average seam separation distance of 150 m is greater than the upper limit for underside protective seam mining.Based on borehole imaging technology for field exploration of coal and rock fracture characteristics and discrete element numerical simulation,we have studied the evolution laws and distribution characteristics of the coal and rock fissure field between these two coal seams.By analysis of the influential effect of group F coal mining on the E_(9-10)coal seam,we have shown that a number of small fissures also develop in the area some 150 m above the overlying strata.The width and number of the fissures also increase with the extent of mining activity.Most of the fissures develop at a low angle or even parallel to the strata.The results show that the mining of the F_(15)coal seam has the effect of improving the permeability of the E_(9-10)coal seam.

Deformation characteristics and reinforcement technology for entry subjected to mining-induced stresses

The entry at Zhangcun coal mine in Lu＇an coal mining area in Shanxi Province suffered from severe mining-induced stresses with the heading face driven oppositely to an adjacent working face. In this paper, the characteristics of deformation and failure of the entry were investigated in terms of the tempo-spatial relations between heading and working faces through field study and numerical modeling. The three-dimensional （3D） finite difference models were built to investigate stresses, displacements and damages in the surrounding rocks of the entry and the working face. The field study includes selection of reinforcing methods and materials, design parameters, and determination of cable prestress. The monitoring data of entry deformation and stress along the cables during every stage were presented. The state of the reinforced entry was evaluated based on the monitoring data. The results demonstrate that before the heading face of the entry crosses the adjacent working face, the influence of advanced abutment pressure caused by adjacent working face upon the entry is not significant. After they cross each other, however, the lateral abutment pressure will have an evident impact on the entry. The displacement rate of the entry will be greatly increased and reaches a certain value within a certain distance between the heading face and the working face. Then, it will increase again with the presence of secondary mining-induced pressure on the entry when the present working face advances. The fully-grouted cable with short length, high strength and high prestress is an effective way to reinforce the entry suffering from severe mining-induced stresses, which greatly reduces the displacement and failure possibility of the entry. Finally, the principles and recommendations for reinforcing design of entries suffering from severe mining-induced stresses were proposed according to field study, numerical modeling and experiences from other coal mines. Problems encountered in field study and suggestions for reinforcement were also discussed.

深部煤层开采导水裂隙发育规律研究

导水裂隙发育规律是深部煤层安全开采的一个重要参数,以孔庄煤矿7303工作面为依托,采用相似模拟实验、钻孔注水漏失量探测和钻孔窥视相结合的方法,对工作面导水裂隙发育特征进行研究。结果表明:相似模拟实验表明工作面平均周期来压步距19.5 m,垮落带呈梯形,随着工作面推进,离层裂隙被压实,导水裂隙发育由低速向高速转变,导水裂隙最大发育高度69.8 m,裂采比21.8。通过现场实测得到导水裂隙最大发育高度65.27 m,裂采比18.13,与浅部煤层工作面裂隙发育特征进行对比分析,裂采比与煤层埋深呈正相关。该研究成果对孔庄煤矿防治水害具有重要的指导意义。

养护方式对混凝土结构温度场及裂缝影响分析

为了探究养护方式对混凝土结构温度场演化规律的影响,依托松江污水池改造工程,设置恒定喷淋、定时喷淋、自然养护、潮湿遮挡养护4种养护方式,研究4种方式下混凝土温度场演化规律,并深入分析温度应力规律及对裂缝产生的影响,指导工程实践。试验结果表明:大气温度及养护条件对结构表面温度有显著影响,自然养护条件下结构表面温度与大气温度数值方面比较接近,其余3种养护条件可显著减缓结构表面温度的变化,并且使最高温度下降了1.5~4.8℃;但对混凝土结构深部温度无明显影响,内部温差在1.5℃以内。自然养护区域温度应力最大,其余3种养护方式(恒定喷淋、定时喷淋、潮湿遮挡养护)最大温度应力分别降低了13.5%、12.9%、13.3%,进而降低了裂缝的产生机率。

基于流-固-损伤全耦合模型的裂隙型岩溶突涌水数值模拟

岩溶地区隧道建设频遇突涌水灾害,裂隙型突涌水勘察与预测难度极大、致灾风险高。为揭示裂隙型岩溶突涌水机理与明确前兆信息,基于流-固-损伤耦合模型对裂隙型岩溶突涌水致灾机理与临界条件展开研究。通过公式推演与多场耦合数值分析得到以下结论:建立了完整的流-固-损伤耦合裂隙型岩溶突涌水致灾机理数学模型,并论证其可行性与合理性;分析了不同溶腔水压工况下,隧道拱顶围岩位移演化规律。结果表明,裂隙型岩溶突涌水与富水溶腔水压高度相关;分析了临界突水条件下围岩特性,提出了缓慢增长段-快速增长段-位移失控段的三阶段裂隙型岩溶突涌水围岩位移演化规律。

安山煤矿浅埋煤层覆岩导水裂隙带发育高度实测研究

为了研究庙哈孤矿区浅埋煤层开采导水覆岩裂隙带发育规律,以安山煤矿133103工作面为研究背景,采用理论分析与现场实测相结合的手段对3-1煤层开采后覆岩裂隙发育规律进行研究。结果表明,133103工作面垮落带高度10.69~15.88 m,垮采比为4.86~5.73,导水裂隙带发育范围52.33~62.52 m,裂采比为23.8~28.4。研究成果为庙哈孤矿区类似条件下工作面开采顶板水灾害防治提供参考。

基于相场法的水-力耦合作用下裂隙岩体变形破坏机理

探究水-力耦合作用下裂隙岩体的力学响应和破坏机制,对解决水-力耦合工况下岩体工程安全与稳定问题具有重要意义。基于Biot多孔介质理论及弹性理论,提出一种水-力耦合相场数值模拟方法,提出交错时间积分方案来获得流体压力和固体变形的稳定解,得到的控制方程式采用全饱和多孔介质弹性理论的体积应变分离和偏应变分离。通过模拟水力压裂与天然裂隙相互作用等数值算例验证了数值模型的有效性和正确性。此外,为探究实际工程开挖过程中的卸载破坏机理,结合钻孔注液试验数值实例,建立一个裂隙岩体水-力耦合卸载破坏模型,模拟水-力耦合条件下裂隙岩体卸荷破坏全过程。结果表明:在水-力耦合卸载破坏过程中,混合拉-剪裂纹的扩展和连接主导了最终破坏模式;初始围压、初始卸荷应力状态对剪切裂纹的发育具有促进作用,水压则反之。

近距离煤层群隔层“探、治”瓦斯技术体系研究及应用

为解决贵州地区近距离复杂群层群采掘过程中邻近煤层瓦斯防治难题,提出了包括邻近煤层瓦斯参数探查技术、保护层开采上覆岩层“三带”范围考察技术和邻近煤层瓦斯抽采防治技术的隔层“探、治”瓦斯技术体系。该技术体系在安顺煤矿的应用结果表明:M9煤层工作面采空区冒落带和裂隙带高度分别约为3.8 m和15.7 m,能够有效增益上覆M8煤层瓦斯治理;临近煤层瓦斯抽采效果受到抽采孔空间位置、长度和工作面推进情况影响,高位钻场、高位巷、高位定向长钻孔和密集穿层高位钻孔抽采方式的抽采纯量分别能达到12、37.7、10.0、40.1 m^(3)/min,高位巷和密集穿层高位钻孔抽采效果更优。研究成果为贵州地区煤层群瓦斯高效治理提供了理论和工程实践基础。

坚硬顶板预裂弱化后应力场及裂隙场演化特征数值模拟研究

工作面上覆坚硬顶板,开采过程不易垮落,采场周围形成高应力场,易引发冲击地压与瓦斯异常涌出灾害事故。为确保安全生产,工作面回采过程中,需对坚硬顶板进行弱化处理,弱化后煤、岩层应力场、裂隙场演化特征是工作面灾害治理的依据和关键,通过理论分析获得顶板的初次来压步距和坚硬顶板分类,以宽沟煤矿I010202工作面为工程背景,利用UDEC数值模拟软件,结合矿井实际地质资料及相关煤岩力学参数,建立平面数值模型,对工作面开采过程中应力场及裂隙场演化特征进行模拟。模拟计算得出顶板弱化后应力场、裂隙场分布特征,为工作面冲击地压及瓦斯灾害治理提供了理论依据。

重复压裂造缝的应力场分析

通过对重复压裂造缝的应力场进行分析,推导出满足重复压裂产生新裂缝的条件。主要分析了一次压裂的 裂缝、储层压力等多种因素对当前地应力场的影响,可以看出诱导应力改变了原地应力场,当原应力场最小水平主 应力大于原最大水平主应力时,重复压裂裂缝可能重新定向。

巨厚火成岩下采动裂隙场与瓦斯流动场耦合规律研究

为考察巨厚火成岩下远程下保护层开采覆岩采动裂隙场与瓦斯流动场耦合规律,通过采用理论分析、相似模拟试验、数值模拟实验及现场观测的方法,分析了覆岩垮落变形和裂隙发育规律,研究了巨厚火成岩下瓦斯储运规律。结果表明:巨厚火成岩控制着其上覆岩层的全部运动,弯曲带内存在裂隙与离层长期不闭合的区域,即离层区;弯曲带内离层区存在大量离层裂隙和少数穿层裂隙,其中裂隙成为瓦斯运移的通道,离层成为瓦斯的富集区;巨厚火成岩下断裂带与离层区内气体运移与煤岩体变形之间存在着复杂的相互作用,它是渗流场、浓度场和裂隙场(包括离层)之间耦合的一个动态平衡体系。

渭河盆地地裂缝群发机理及东、西部地裂缝分布不均衡构造成因研究

利用渭河盆地2001—2008年高精度GPS监测资料,结合区域构造特点建立了渭河盆地有限元动力学模型,基于此研究了区域现今地壳应力场特征,深入分析了构造应力场与盆地内地裂缝群发之间的内在关系,首次基于空间大地测量定量的揭示出了区域构造应力场与盆地内地裂缝群发的内在动力学联系,及盆地东、西部地裂缝分布不均衡的根本成因.研究结果表明:渭河盆地现今地壳应力场差异性显著,主要呈现出中、东部以NW-SE向拉张为主,西部则以NW-SE向压缩应力为主,整体具有相对左旋运动趋势,与区域以往长期构造变形具有较好的继承性;分析揭示出区域NW-SE向拉张构造应力正是盆地内中、东部地裂缝群发的力源机制,而盆地内差异性构造应力场也正是导致盆地东、西部地裂缝发育不均衡的根本原因所在,由此进一步证实了渭河盆地地裂缝的强构造属性,其是由活断层在上述力源机制作用下,以蠕滑形式错断地层使土层破裂而形成的.本文研究结果为盆地地裂缝灾害防治、城市安全建设提供了重要信息.

覆岩及采动岩体裂隙场分布特征的可视化探测

利用钻孔彩色电视系统观测了大量钻孔内部原生裂隙以及采动岩体裂隙的分布及其发育特点.研究得出原生裂隙场具有绝大多数发育横向微裂隙,裂隙被充填物所充填以及部分发育纵向裂隙,较破碎的特点;采动岩体裂隙则具有发育纵横交错的相交裂缝,以高角度纵向裂缝为主,且随着离煤层顶板距离减小,并逐步向破碎型裂缝发展的特点.

从岩石露头裂隙迹线估算裂隙三维空间方向

通过提取岩石露头数字影像中裂隙痕迹分布的二维信息,研究岩石内部裂隙面产状特征,进而模拟岩石裂隙网络空间分布,在地下资源(尤其是流体资源)的预测和地下空间稳定性评价等领域具有重要的意义。根据岩石中裂隙分布多表现出丛聚规律的特征,将裂隙分为若干个组;假设每个组内部的裂隙围绕一个中心值分布,考虑镜头方向与岩墙面法线夹角,从裂隙面、岩墙面产状以及裂隙痕迹倾角三者关系入手,估算得到已知裂隙面产状。根据Fisher分布,利用随机函数产生裂隙分布,由裂隙痕迹倾角求得裂隙面三维空间分布,并利用模拟退火法对原问题求逆,误差控制在5%。根据个旧锡矿高松矿田岩石露头裂隙的特征,将岩体裂隙分为两组,平均倾角分别为49.0°和128.2°,倾角的标准方差为0.38和0.32,最后估算出Fisher分布常数K=200时裂隙面产状分别为171.1°∠75.1°和338.3°∠3.9°,与现场调查数据吻合。据此对裂隙网络进行了模拟,取得了很好的预测效果,其结果对于根据岩石露头迹线方向直接估算裂隙的三维空间分布具有重要意义。

煤储层孔隙系统发育特征与煤层气可采性研究

借助于低温氮等温吸附试验和压汞孔隙分析,研究了河南煤田主要矿区煤储层孔隙系统发育特征。研究发现河南煤储层孔隙系统具有如下特征:①煤储层的孔比表面及总孔体积均较大;②压汞孔隙度较大,孔隙结构以吸附孔占绝对优势,约占总孔隙含量的78%;③孔隙类型主要为细孔细喉型,渗流孔内部的连通性较好但渗流孔和吸附孔之间的连通性较差;④研究区的这种孔隙系统对煤层气的储集非常有利,但对煤层气的解吸和开发较为不利。

充填法开采引起的地裂缝分布特征与现场监测分析

通过对金川二矿区地裂缝的现场调查和槽探揭示,分析地裂缝的分布特征及其与地下采矿的关系。利用自行研制的IGG–1型裂缝计对地裂缝的发展变化进行监测。结果表明,金川二矿区的地裂缝两侧位移具有明显的三维特征。在此基础上,讨论充填法开采引起的岩体移动和地表裂缝的形成条件、成因机制及影响因素。研究结果表明,采充效应造成的围岩应力重分布、充填体刚度低、地下未充填空区的存在以及重复性的采动影响是金川二矿区地裂缝产生的主要原因。

动压巷道围岩渗流场的空间分布特征

采用原位窥视仪观测实验与理论分析,根据围岩不同的渗流特性,沿巷道径向将巷道围岩空间划分成完全渗流区、定向渗流区、渗流屏蔽区、原岩渗流区;沿巷道轴向岩体渗透性呈现负指数规律逐渐增加达到极值,随后趋向减少;沿巷道环向渗透性能受层状沉积的缘故,不同部位渗透性差异很大,层内的渗流,往往在层理面发生隔断.

大港探区千米桥奥陶系潜山裂缝分布预测

依据大港千米桥地区大量静、动态资料,在储层特征、产层分布规律研究的基础上,总结出裂缝是影响储层品质及产能的主要因素,储集类型主要为微裂缝—孔隙型。研究区裂缝主要发育构造(溶蚀)缝、压溶缝及节理缝等。将裂缝分为大尺度裂缝和小尺度裂缝并建立裂缝模型,显示裂缝密度高值区的发育主要集中在不整合下的表层岩溶带内且以奥陶系潜山面下20～80m范围内最为集中,裂缝密度高值区具有成层分布、局部富集、各井之间裂缝发育差异明显的特点。