Frequency spectrum analysis on micro-seismic signal of rock bursts induced by dynamic disturbance

Blasting and breaking of hard roof are main inducing causes of rock bursts in coal mines with danger of rock burst,and it is important to find out the frequency spectrum distribution laws of these dynamic stress waves and rock burst waves for researching the mechanism of rock burst.In this paper,Fourier transform as a micro-seismic signal conversion method of amplitude-time character to amplitude-frequency character is used to analyze the frequency spectrum characters of micro-seismic signal of blasting,hard roof breaking and rock bursts induced by the dynamic disturbance in order to find out the difference and relativity of different signals.The results indicate that blasting and breaking of hard roof are high frequency signals,and the peak values of dominant frequency of the signals are single.However,the results indicate that the rock bursts induced by the dynamic disturbance are low frequency signals,and there are two obvious peak values in the amplitude-frequency curve witch shows that the signals of rock bursts are superposition of low frequency signals and high frequency signals.The research conclusions prove that dynamic disturbance is necessary condition for rock bursts,and the conclusions provide a new way to research the mechanism of rock bursts.

Theoretical Study of Coupling Mechanism between FBG and Shock Waves of Rock Burst

To achieve the monitor of rock burst in coal mine with fiber Bragg grating (FBG) sensing, the coupling mechanism between FBG and shock waves was theoretically analyzed. Based on Housner’s random shock model, the coupling mechanism between shock waves and FBG was theoretically analyzed. The result shows that the wave will change the period Ʌ and effective refractive index n of FBG, and further affect the initial wavelength value. The amplitude, phase and frequency of shock wave are directly related to the wavelength drifts of FBG. The transmitting velocity of shock wave in rock is affected by lithologic characteristics. The Elastic modulus, density and Poisson’s ratio of rock influence the initial wavelength value of FBG. This study provided a theoretical basis and practical application guidance for coal or rock burst monitoring with FBG sensing.

Spatial gradient distributions of thermal shock-induced damage to granite

In this study,we attempted to investigate the spatial gradient distributions of thermal shock-induced damage to granite with respect to associated deterioration mechanisms.First,thermal shock experiments were conducted on granite specimens by slowly preheating the specimens to high temperatures,followed by rapid cooling in tap water.Then,the spatial gradient distributions of thermal shock-induced damage were investigated by computed tomography(CT)and image analysis techniques.Finally,the influence of the preheating temperature on the spatial gradients of the damage was discussed.The results show that the thermal shock induced by rapid cooling can cause more damage to granite than that induced by slow cooling.The thermal shock induced by rapid cooling can cause spatial gradient distributions of the damage to granite.The damage near the specimen surface was at a maximum,while the damage inside the specimen was at a minimum.In addition,the preheating temperature can significantly influence the spatial gradient distributions of the thermal shock-induced damage.The spatial gradient distribution of damage increased as the preheating temperature increased and then decreased significantly over 600
C.When the preheating temperature was sufficiently high(e.g.800
C),the gradient can be ignored.

Comprehensive use of the Gutenberg–Richter law and geotomography for improving seismic hazard evaluation in hard coal mines

Mining-induced seismicity occurs in numerous underground mines worldwide where extraction is conducted at great depths or in areas characterised by complex tectonic structure.It is accompanied by rock bursts,which result in the loss of working functionality and the possibility of accidents among personnel.The issue of a constant and reliable seismic hazard evaluation is of key signifcance for both the safety of miners and the stability of production.Research on its improvement is directed at developing new interpretive solutions and methods.The nature of the presented solution is the complex interpretation of seismological data that characterise rock mass seismicity and of underground measurement results in the form of a map presenting the longitudinal wave propagation velocity distribution in the rock surrounding the mined coal seam.The solution was tested in hard coal mines located in the Upper Silesian Coal Basin.The mines are equipped with a modern seismological system enabling the constant monitoring of seismicity together with hazard level evaluation as well as with seismic apparatus for conducting periodic measurements of the seismic wave propagation velocity before the mining face.Comprehensive seismic hazard evaluation criteria were determined based on the obtained results,involving the anomaly of the Gutenberg–Richter law“b”value and the maximum longitudinal seismic wave propagation velocity in the roof rock.The obtained experience and the result validation of this new comprehensive hazard evaluation method confrm its practical usefulness and indicate the directions of improvement for the solution in question.

A proposed classification of the Earth’s crustal areas by the level of geodynamic threat

It is accepted as a well-known fact that in different places on the Earth’s crust,a similar anthropogenic impact causes a dissimilar response.Seismic zoning maps are not designed to predict such geodynamic hazards as rock bursts,induced earthquakes,reactivation of tectonic faults,etc.,and therefore require careful adjustments in places of intense impact on the subsurface strata.In this regard,we consider the classification of the Earth’s crustal areas according to the degree of geodynamic hazard,i.e.its potential geodynamic response to anthropogenic intervention.This classification is based on the concept that there exists a critically stressed layer within the Earth’s crust.It is believed that such a critically stressed layer within the Earth’s crust extends from the Earth’s surface to a certain depth,and each point depends on the nature of the interaction between crustal blocks of different hierarchical levels.From this perspective,anthropogenic impact,such as mining operations,represents a direct impact upon the critically stressed zone.We recognize the hypothesis that the thicker the critical stressed rock layer,the stronger the response might be to anthropogenic intervention,as it has more accumulated energy.Four categories of geodynamic threat have been found and mapped.To verify this classification,the manifestations of the geodynamic hazards were studied.The intensity of geodynamic hazard increased from the first area to the fourth area.The phenomenon of large induced seismic events with hypocenters at great depths is explained on the basis of this theory,and could be associated with anthropogenic impacts from the surface directly on the regional zone of the critically stressed rock massif.The approach can be used to assess the geodynamic consequences of human exposure to the Earth’s crust.

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。

微波热力冲击下硬脆砂岩冲击倾向性演化规律试验研究

冲击地压是深部资源开采的主要灾害类型,冲击倾向性是表征冲击地压风险的重要指标。为了探索微波热力冲击对岩石冲击倾向性的影响,本文对典型强冲击倾向性硬脆砂岩开展了微波热力冲击和单轴压缩试验,分析了微波热力冲击后砂岩的物理力学性质和冲击倾向性指标响应规律。研究结果表明:(1)微波作用后,砂岩表面温度随着热力冲击时间增加持续升高,直至150 s发生热破断;(2)微波热力冲击120 s后,砂岩内部结构发生微破裂,岩石冲击倾向性明显减弱,纵波波速与弹性模量分别下降了15.12%、8%;(3)单轴压缩变形破坏过程各阶段声发射信号密度增大,砂岩最终破坏时的绝对能量最大值下降42.3%;(4)岩石动态破坏时间增长了259%,冲击能量指数减小95%,弹性能量指数下降92%,砂岩由强冲击性岩石变为弱冲击性岩石。研究结果为煤炭深部开采冲击地压防治和深地工程高效破岩具有参考价值。

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。

岩性特征对冲击地压震动波光栅监测影响机理研究

为了得出冲击地压震动波在岩石中传播时岩性特征的影响机理,借助光纤光栅对不同岩石载体中的震动波进行了监测,并从理论上分析了二者之间的耦合关系。以Housner的随机震动模型为基础,对震动波与光纤光栅之间的耦合机理进行了理论分析,结果表明,震动波可以改变光栅的周期Λ和有效折射率n eff,进而影响其初始波长,震动波幅值、相位及频率等参数与波长变化直接相关;震动波在岩石中传播的波速受岩性特征参数的影响,岩石的弹性模量、密度和泊松比以特定的形式影响光纤光栅的初始波长,且与波长变化呈余弦相关;对砂岩、石灰岩及大理石板分别进行了震动波传感监测实验,结果表明,3种岩石的岩性参数I与光纤光栅的初始波长值具有余弦函数对应关系,与理论分析的结果相一致。研究为煤岩冲击地压光纤光栅传感监测提供了理论依据及实践应用指导。

基于三维负泊松比蜂窝结构的防冲支架性能研究

提出一种应用于支架顶梁上方的吸能缓冲装置,该缓冲装置采用轻质、吸能量高的负泊松比材料,旨在将冲击地压带来的能量快速让位、缓冲吸收。对缓冲装置的构型进行设计并进行准静态压缩仿真;对缓冲装置施加低速、中速、高速进行抗冲击特性研究。结果表明:胞元角度为θ=70°的胞元具有良好的负泊松比效应、更长的压缩行程、更高的吸能量,适宜于做缓冲结构的胞元结构。对缓冲结构施加不同的速度,得到随着冲击速度的增大,缓冲结构的比吸能越大。

矿震诱发冲击地压机理研究

根据弹性波理论推导出矿震产生的应力波诱发动力扰动的公式,建立冲击地压理论模型从而推导出冲击地压发生的发生理论;并利用ABAQUS数值模拟技术模拟了矿震诱发冲击地压的过程;并探究围岩巷道受到静—动荷载叠加作用时,冲击地压的发生条件;根据现实中某矿矿震引发的冲击地压测得的数据,验证了矿震诱发冲击地压这一理论。模拟结果表明,当围岩巷道受到的地应力静载过大,达到临界塑性区时,微小的矿震会引发围岩巷道出现冲击地压现象。

覆岩关键层运动诱发冲击的规律研究

基于岩层运动关键层理论,研究了覆岩关键层破断规律,从力学机理上分析了覆岩关键层正"O-X"型破断时,矿山压力达到最大值,极易导致强矿震、冲击矿压的发生。利用微震监测系统,对关键层破断诱发冲击矿压进行定位分析,证明了高能量级别的矿震大多数发生在工作面推进过程中覆岩关键层处于正"O-X"型破断位置。研究表明由关键层运动破断诱发冲击矿压前后,微震事件的时空演化规律、前兆信息显著。研究结果为利用岩层运动理论与微震监测相结合的方法预测冲击矿压奠定了基础。

复合型厚煤层“震-冲”型动力灾害机理、预测与控制

针对软硬分层相间的复合型厚煤层综放工作面发生的动力灾害事故,提出了复合型厚煤层综放工作面"震-冲"型动力灾害的概念.通过理论和实践研究,初步建立了复合型厚煤层"震-冲"型动力灾害的力学模型,研究了其发生的机理,分析了矿震和冲击地压发生的力学条件和相互关系.研究成果在兖州矿业集团公司南屯煤矿得到应用,成功预测了动力灾害发生位置,并做好了预先卸压、监测和防护,实现了"有震无灾"的控制目标.

矿震动载对围岩的冲击破坏效应

分析了矿震激发震动波能量的传播模式、衰减特征及动态应力降大小,并基于能量和刚度理论,分析了动静载组合作用下巷道煤体的冲击破坏机理。研究表明,矿震震动能量的传播衰减特征主要依赖于能量几何扩散、传播岩体介质的阻尼衰减,以及矿震震源的震动位移场和能量辐射特征的综合影响。矿震动载传播至采场或巷道围岩时,分别与煤岩系统的静态应力(能量)场进行能量标量和应力矢量叠加。矿震动载的能量叠加可使煤岩系统聚集的能量增加,而应力叠加使系统内煤体变形破坏做功所消耗的能量减小,从而使系统聚集和消耗的"差能"增加。系统可释放的"差能"越多,煤体失稳的可能性越大,当动静载组合作用下煤岩系统同时满足冲击矿压发生的能量和刚度条件时,煤层发生动态冲击破坏。

硬岩金属矿山深部开采中的动力学问题

从深部开采环境阐述了金属矿硬岩在高地应力作用下的储能特征,并从深部开采工艺方面分析了随着金属矿山开采深度的不断增加,连续采矿方法已经成为未来深部开采的必然趋势。通过分析,认为处于高应力下的硬岩矿体在承受连续采矿法带来的动力扰动时,可以认为是岩石动静组合的受力问题。在此基础上,利用岩石动静组合加载理论分析了硬岩矿山在深部开采中的几个关键动力学问题,主要包括:硬岩矿山深部开采中的系统扰动和岩爆、深部开采中爆破引发的矿震及巷道失稳现象、深部硬岩开采中的能量释放与有序调控。理论分析和工程实践证明,硬岩金属矿山深部开采中存在的很多动力学问题可以利用岩石动静组合加载理论进行科学论证和分析,这对深部采矿的工程实践有较好的指导意义。

高应力硬岩地区岩体结构对地下洞室围岩稳定的控制效应研究

官地水电站地下厂房属典型的硬岩地区深埋大型地下洞室群,其重要特点是同时面临高地应力和结构面发育这2个不利条件,实测最大主应力为25～35 MPa,厂区无大的断层和软弱结构面,但错动带和裂隙十分发育。通过对地下洞室群施工过程中出现的围岩局部失稳破坏现象进行全面的分析整理,对三大洞室的岩体结构特征和围岩变形破坏模式进行系统的分析、比较和总结,从而对影响围岩稳定的两大控制因素——地应力和岩体结构对官地地下厂房洞室群围岩稳定的影响程度和方式进行分析和对比。研究表明,由于三大洞室围岩类别以II类为主,岩体结构以块状～次块状结构为主,围岩具有较高的力学强度和强度应力比,从而具有较强的抵抗应力破坏的能力;岩体结构对地下厂房围岩变形与稳定的控制作用较地应力则更为明显,地下洞室群开挖过程中出现的局部失稳或较大变形多与不利方位的结构面直接相关。三大洞室围岩岩体结构特征总体上的相似性非常明确,反映在三大洞室围岩的变形特征和破坏模式上具有很好的统一性。然而,三大洞室的岩体结构特征也存在一定的差异,导致岩体结构影响围岩稳定的方式和程度有所不同。结构面发育造成的另一个不利影响是为坚硬岩体在高地应力条件下产生卸荷时效变形提供了内部条件。因此,在强度应力比较高的硬岩地区,应充分重视岩体结构及其演化对围岩变形和稳定的控制效应。

震源扰动型巷道冲击矿压破坏力能准则及实践

针对震源扰动型巷道冲击矿压破坏机理进行研究,建立了巷道围岩冲击震源扰动型冲击破坏的动力分析模型,推导了巷道围岩承载结构在"静载+动载"组合作用下动力破坏的应力判据和能量准则。基于该力学模型及其机理分析,提出合理设置弱结构消波吸能的防冲理念,并从理论角度分析了弱结构消波吸能的作用机理。最后通过工程实例,应用能量准则进行了冲击煤层巷道的支护设计及其防冲性能核算,理论研究成果初步得到了应用和检验。

薄煤层冲击矿压特征及防治研究

统计了桃山矿薄煤层冲击矿压强度、显现位置、诱发因素等特征,试验研究了煤岩组合试样单轴抗压强度、冲击能指数与煤岩高度比的关系,分析了薄煤层应力分布及转移规律和冲击矿压机理,探讨了薄煤层工作面冲击矿压防治技术。研究表明:薄煤层冲击矿压强度小,发生在工作面的比例高,工作面距上端头5 m附近冲击显现最为频繁,爆破、割煤等动力扰动是其主要诱因;随着煤岩高度比减小,组合煤岩单轴抗压强度、冲击能指数均增大,煤层越薄,煤体承载能力越强,越不容易产生应力转移,爆破、割煤等剥离或松动煤壁处煤体,引起峰值应力区垂直应力升高,水平应力对煤体约束减小,导致冲击矿压。薄煤层冲击矿压防治应使高应力区向煤体深部转移,使工作面前方有足够卸压保护带。

一维动静组合加载下砂岩动力学特性的试验研究

基于对深部岩石承受高地应力并在动力开挖扰动下发生破坏这一问题的科学认识,利用改造的劈裂霍普金森压杆动静组合加载试验装置,开展一维动静组合加载下砂岩的动力学特性试验研究。选取无轴压和3个典型轴压水平4种情形,开展不同应变率下的冲击试验。研究结果表明,相同应变率下岩石对外界冲击的响应受轴压比影响很大,冲击强度会随着轴压比的增加出现先增加后减小的趋势,在轴压比为0.6～0.7时达到最大值。相同轴压下,冲击强度会随着应变率的增加而增加,呈现指数函数关系。在一定的轴压比范围内,随着入射能的递增,岩石在加载破坏试验中先后会经历"吸收能量-释放能量-吸收能量"3个阶段。这3个阶段可以较好的解释高应力下岩石的动态强度递增、岩爆发生和诱导致裂三者之间的互相转化机制,对深部岩石工程的实践可以提供理论上的指导。

深部下山煤柱区矿震规律研究

针对某矿-1 025 m西一下山采区9煤回风下山发生的多次冲击矿压显现,利用SOS微震监测系统,研究分析深部下山煤柱区域矿震活动规律。结果表明:冲击矿压发生前,矿震能量持续上升,频次亦持续增加或维持在较高水平;矿震沿下山集中明显,主要位于2个覆岩关键层内,高静载加强矿震扰动是诱发巷道冲击破坏的主要原因;冲击前兆强矿震信号呈现低频率、高振幅特征。根据监测结果实施煤体大直径钻孔、顶板预裂爆破以及优化支护等矿震弱化控制技术,现场效果良好。