PREDICTION AND CONTROL OF ROCKBURST DURING DEEP EXCAVATION OF A GOLD MINE IN CHINA

The studies of prediction and control of rockburst are presented during deep excavation in a gold mine in China. Firstly,the stress-relief method is used to obtain a vast amount of data about initial geostress. Secondly,3D FEM analyses of large scale are performed to find out the law of geostress distribution at various excavation levels of the mining area. At the same time,as an equally important measure,six typical kinds of rock blocks are sampled for the experimental study of rockburst tendency. According to the synthesized results of the theoretical and testing results,the methods of brittleness coefficient,brittle index and stress,and so on,are adopted. Finally,the evaluation on the possibility of rockbursts is given that may take place at the deep mining area and some effective measures are put forward to prevent and control the rockburst.

Characteristics of rockburst and its mining technology in mines

In order to resolve how to mine under the condition of high stress with rockburst, this paper analyzes the law of rockburst, and considers that most of the rockbursts occur in the high stress area of stope. A method of rockburst forecast and its steps are given, and three different stages of rockburst are identified. Furthermore, this paper considers that blasting energy can effectively control rockburst by changing the characteristics of rock mass, which decreases the probability of rockburst happening. According to characteristics of rockburst, two feasible mining techniques under rockburst conditions are put forward, that is stoping and filling method, and sublevel caving method of mining without any sills in hanging wall.

Prediction and prevention of rockburst in metal mines--A case study of Sanshandao gold mine

Rockburst is a kind of artificial earthquake induced by human activities,such as mining excavations.The mechanism of rockburst induced by mining disturbance is revealed in terms of energy in this context.For understanding the rockburst mechanism,two necessary conditions for the occurrence of rockburst are presented:(1)the rock mass has the capability to store huge amount of energy and possesses a strong bumping-prone characteristic when damaged;and(2)the geological conditions in the mining area have favorable geo-stress environments that can form high-stress concentration area and accumulate huge energy.These two conditions are also the basic criteria for prediction of rockburst.In view of energy analysis,it is observed that artificial and natural earthquakes have similar regularities in many aspects,such as the relationship between the energy value and burst magnitude.By using the relationship between energy and magnitude of natural earthquake,rockburst is predicted by disturbance energy analysis.A practical example is illustrated using the above-mentioned theorem and technique to predict rockburst in a gold mine in China.Finally,the prevention and control techniques of rockburst are also provided based on the knowledge of the rockburst mechanism.

AN EXPERT SYSTEM ON ASSESSING ROCKBURST RISKS FOR SOUTH AFRICAN DEEP GOLD MINES

Expert systems are methods that can cope with rock engineer’s expertise effectively.An expert system on assessing rockburst risks for South African deep gold mines is described.Expertise was represented by rules, frames and mathematical models integratively. About 950 rules was built in the knowledge base, which can be learned by the suggested learning algorithm. A new uncertain reasoning algorithm was proposed. According to the features such as depth below surface, energy release rate (ERR), excess shear stress (ESS), geological structure, face angle with structure, distance from structure, extent of mining, mining type, width of bracket pillar, stope width, local support, regional support and gully support, rockburst risk is assessed either "Low", "Moderate", "High" or "Severe". A computer program system was developed by Turbo Prolog. The results of testing cases show its applicability of the system.

Rockburst disasters in coal mine

The ruckburst of granite from Kailuan coal mine was reproduced by a new triaxial experimental system.The experimental results show that the rockburst process can be divided into four stages including calm period,grain ejection,sheet cracking and entire collapse.The rockburst intensity is classified by the ratio of maximum principal stress to uniaxial compressive strength.Three types of rockburst for the granite have been defined as delayed rockburst,normal rockburst,and instantaneous rockburst,according to the duration from suddenly unloading to rockburst occurring.Primary mechanism for the granite was studied.

Seismological method for prediction of areal rockbursts in deep mine with seismic source mechanism and unstable failure theory

The research on the rock burst prediction was made on the basis of seismology,rock mechanics and the data from Dongguashan Copper Mine(DCM) ,the deepest metal mine in China.The seismic responses to mining in DCM were investigated through the analyses of the spatio-temporal distribution of hypocenters,apparent stress and displacement of seismic events,and the process of the generation of hazardous seismicity in DCM was studied in the framework of the theory of asperity in the seismic source mechanism.A method of locating areas with hazardous seismicity and a conceptual model of hazardous seismic nucleation in DCM were proposed.A criterion of rockburst prediction was analyzed theoretically in the framework of unstable failure theories,and consequently,the rate of change in the ratio of the seismic stiffness of rock in a seismic nucleation area to that in surrounding area,dS/dt,is defined as an index of the rockburst prediction.The possibility of a rockburst will increase if dS/dt>0,and the possibility of rock burst will decrease if dS/dt<0.The correctness of these methods is demonstrated by analyses of rock failure cases in DCM.

冲击地压煤层矿井间临近工作面相互采动影响分析

为了对冲击地压煤层矿井间临近工作面相互采动影响进行分析,以义桥煤矿3309工作面和唐阳煤矿432工作面为研究背景,采用数值模拟的研究方法,从巷道侧垂直应力和覆岩垂直位移两个方面研究了两工作面相互采动的影响。当两工作面开采时,3309工作面运输顺槽侧的应力增大了26.0%~28.0%,顶板位移增大了7.3%~10.1%,432工作面运输顺槽侧的应力增大了31.8%~48.8%,顶板位移增大了12.8%~19.2%。通过上述分析可以得出冲击地压煤层矿井间临近工作面相互采动时,对工作面应力集中分布及顶板运移规律均具有明显的影响。并在采取相应卸压措施的基础上,提出3条关于影响较大区域防冲补强措施的建议,以降低两工作面相互采动影响,确保工作面安全生产。

深部巨厚承压含水层采动疏水诱冲机理

陕蒙地区覆岩普遍赋存较厚承压含水砂岩层,工作面涌水量大、承压含水层水位显著下降,巨厚覆岩承压含水层下冲击地压和高能矿震监测表明覆岩承压水的采动疏放具有一定的诱冲效应。为揭示覆岩承压含水层采动疏水诱冲机理,开展了流固耦合数值模拟,分析了不同孔隙水压岩体力学行为及巨厚覆岩承压含水层采动疏水条件下围岩应力-能量场演化特征,揭示了覆岩承压含水砂岩层采动疏水对围岩应力场作用机制;并考虑巨厚覆岩对围岩动静载应力作用效应,提出了覆岩承压含水层采动疏水诱冲机理。研究结果表明:覆岩巨厚承压含水砂岩层下动力显现均发生在覆岩承压水位快速下降期间,覆岩承压水的采动疏放对围岩产生应力扰动;采动疏水条件下覆岩承压含水岩层孔隙水压降低,岩层强度和承载能力增大,覆岩载荷向采场两侧转移,导致围岩应力升高、能量进一步积聚,其对围岩应力场-能量场作用程度与采场尺度和疏放程度正相关,与煤层-承压含水层距离、承压含水层岩层厚度及强度负相关;巨厚覆岩承压含水层下顶板大尺度悬臂-铰接结构导致采场围岩高静载及强动载,在覆岩承压含水层采动疏水对围岩应力场作用下,煤岩体中叠加应力超过其临界载荷且释放的总能量超过其破坏所消耗能量,诱发冲击地压,其中高静载是冲击地压发生的应力基础,矿震动载和覆岩承压含水层采动疏水导致的应力扰动是重要诱因。针对覆岩承压含水层采动疏水及巨厚承压含水层覆岩结构对冲击风险的影响特征,提出了巨厚承压水含水层注浆堵水和优化盘区尺寸的防冲措施,通过地面注浆和降低采场尺寸能够降低覆岩承压含水层采动疏水对围岩应力场的作用效应、避免巨厚覆岩形成大尺度悬臂-铰接结构,从而降低巨厚承压含水层下冲击地压风险。

基于多维云模型的深井岩爆倾向综合评价

研究岩爆倾向性对深井矿山的安全开采具有十分重要的意义。以某矿山为研究对象,采用一维云模型与多维云模型结合的手段,选取岩石应力系数、岩石脆性系数及岩石弹性应变能指数构建指标体系,对不同开采中段的3种矿岩进行岩爆倾向性评价。结果表明:该矿山设计开采范围(50 m~-450 m中段)内,顶板围岩整体为弱岩爆倾向,矿体整体为中岩爆倾向,底板围岩整体为弱岩爆倾向。

BMS微震监测系统在深部岩体稳定性监测中的应用

随着矿山开采逐渐往深部延伸,出现了轻微岩爆现象,生产区域内存在由岩爆诱发的矿柱失稳和顶板冒落的危险。根据三山岛金矿深部矿体地质条件和围岩实际地质情况,研制了新一代的BMS微震监测系统,构建了矿山预警系统。该系统能有效监测到采场矿柱失稳和顶板冒落的微弱振动信号,分析微震波形,监测岩爆的发生,为深部矿体安全开采提供依据。

巨龙铜矿地应力对大断面巷道稳定性与岩爆倾向性数值模拟

分析矿山深部巷道稳定性及岩爆倾向性对于矿山安全建设具有重要意义。以巨龙铜矿大断面深埋长巷道为研究对象,利用数值模拟手段探究了青藏高原地应力影响下环形排水巷稳定性,分析了巷道掘进后岩爆倾向性。结果表明,环形排水巷道围岩内应力以水平应力为主,最大主应力为32 MPa,在16段排水巷道中,应力主要集中于巷道DE、EF、DG段。巷道围岩水平位移大于垂直位移,环形排水巷道最大位移以M点为中心向四周扩散。GM段、HL段、KN段巷道围岩均发生了较大变形,对于该区域巷道应加强支护。巷道DE、EF、DG段最大弹性应变达到1.01×10^(5) J/m^(3),呈现出岩爆倾向,可通过减小开挖进尺削弱岩体局部应力集中。现场监测表明模拟结果可靠。该研究结果为巨龙铜矿环形排水巷施工及地压灾害防控提供了理论参考。

Ground support design for dynamic loading conditions:A quantitative data-driven approach based on rockburst case studies

There are considerable challenges associated with the design of ground support for seismically-active underground mines.It is extremely difficult to establish the demand on ground support as well as the capacity of a ground support system.The resulting dynamic or impact loads caused by mining-induced seismicity are difficult to anticipate and quantify.The performance of a ground support system is defined by the load distribution and interaction between several reinforcement and surface support elements.Consequently,the design of ground support in seismically-active mines tends to evolve,or be modified based on qualitative assessments of perceived performance or response to significant seismic events or rockbursts.This research is motivated by a need to provide quantitative and data-driven design guidelines for ground support systems subjected to dynamic-loading conditions.Rockburst data were collected from three deep and seismically-active underground mines in the Sudbury basin in Canada.The constructed database comprises 209 seismic events that resulted in damage to mine excavations and ground support.These events were associated with damage at 324 locations within the three mines.The developed ground support design strategy,based on these documented case studies,identifies areas where the use of dynamic or enhanced support should be employed.The developed design methodology provides guidelines for the zoning of mine locations in which installation of enhanced support is recommended,the specifications for an optimal ground support system,and the timing or sequence of installation.

The Use of Data Mining Techniques in Rockburst Risk Assessment

目前在世界范围内的很多地下矿山,岩爆已经成为一个与矿山采矿生产密切相关的重要现象。深入理解这类现象,不仅有助于岩爆管理,而且还有可能节约采矿成本,减少人身伤亡事故。其中,实验室实验是深入研究岩爆机理的一个重要途径。在本文作者前期的研究中,已经建立了实验室岩爆实验数据库。与此同时,借助于数字采矿技术,也建立了岩爆最大应力和岩爆风险指数的预测模型。为实现基于矿山地质条件和矿山井巷建筑结构特性对岩爆类型即岩爆强度等级的准确预测,本文的重点是,基于对岩爆实例的分析来建立岩爆影响矩阵,明确岩爆现象的诱发因子,并厘清这些影响因子之间的相互关系。运用人工神经网络(ANN)和初始贝叶斯分类器等数字矿山技术,对矿山岩爆数据库进行了更深入的研究。最后给出了研究得出的各项结论。

Heavy rockbursts due to longwall mining near protective pillars:A case study

Rockburst represents a very dangerous phenomenon in deep underground mining in unfavourable conditions such as great depth, high horizontal stress, proximity of important tectonic structures, and unmined pillars. The case study describes a recorded heavy rockburst in the Czech part of the Upper Silesian Coal Basin, which occurred during longwall mining near the protective pillar. The artificial dividing of geological blocks and creation of mining protective pillars(shaft pillars, crosscut pillars etc.) is a dangerous task in light of rockbursts occurring mainly due to overstressing of remaining pillars. A simple model of this situation is presented. Natural and mining conditions are analysed and presented in detail as well as registered seismicity during longwall mining in the area. Recorded rockbursts in the area of interest are described and their causes discussed. Many rockbursts near protective pillars were recorded in this mining region. Methodical instructions for rockburst prevention in proximity of protective pillars as well as for gates driving were devised based on the evaluation of rockburst causes. The paper presents these principles for prevention.

Research on microseismic activity rules in Sanhejian Coal Mine

By the microseismic (MS) monitoring system of Sanhejian Coal Mine,the detail MS activity rules in the entire mining process of 9202 strong rockburst working face were studied,following main conclusions were obtained.(1) The strong correlation between MS activity and the region stress gradient was revealed.The higher the region stress gradient, the stronger the MS signal is,and the frequency-spectrum moves to lower frequency band the amplitude begins to add gradually.(2) The different types of MS signals have the cor- responding frequency-spectrum character.Such as relieve-shot MS signal shows the wide frequency-spectrum,multi-peak high frequency character,while rockburst omen signal shows the low frequency and amplitude,the mainshock signal has relatively higher fre- quency and amplitude.(3) To monitor and recognize rockburst dangerous region,the strong consistence between the MS signal intensity and the amplitude of electromagnetic emission (EME) signal and drilling bits measured was observed.On above,the weakening and controlling technology of MS intensity was put forward.

Numerical and Geophysical Tools Applied for the Prediction of Mine Induced Seismicity in French Coalmines

The determination of the influence of mining works and the induced seismicity is essentially obtained, separately from in-situ observations and seismic analysis, field measurements (particularly surface survey) as well as from numerical investigations. The paper presents a methodology applied for the analysis of induced seismicity due to underground coalmines based on combining numerical modelling and seismic analysis. The methodology is based on the comparing between the observations, the seismic activity and the numerical modelling for establishing a close correlation between the location of seismic activity and the induced stresses. The paper presents two case studies using seismic and geotechnical investigations, the first one concerns a fatal accident affected Lorraine coalmine (East France). The second case concerns the application of the methodology on Provence coalmines (South France). The application of the methodology shows such a coupling can be an efficient way for detecting areas subjected to rockburst hazard. This is also a powerful tool for assisting the planning of underground workings in complex geological and mining conditions. The coupling of geotechnical investigations (numerical modelling, in-situ stress measurements) and seismic analysis are strongly recommended.

Stress spatial evolution law and rockburst danger induced by coal mining in fault zone

In order to explore the influence of coal mining disturbance on the rockburst occurring in fault zone, this research constructed a mechanical model for the evolution of fault stress, and analyzed the influence of the ratio of horizontal stress to vertical stress on the stability of fault, and the spatial distribution of the stress in fault zone as well as its evolution rule. Furthermore, the rockburst danger at different spatial areas of fault zone was predicated. Results show that: when both sides of the working face are mined out, the fault zone in the working face presents greater horizontal and vertical stresses at its boundaries but exhibits smaller stresses in its middle section; however, the ratio of horizontal stress to vertical stress is found to be greater at middle section and smaller at boundaries. As the working face advances towards the fault, the horizontal and vertical stresses of the fault firstly increases and then decreases; conversely,the ratio of horizontal stress to vertical stress keeps decreasing all the time. Therefore, if the fault zones are closer to the goaf and the coal wall, the stress ratio will be smaller, and the fault slip will be more prone to occur, therefore rockburst danger will be greater. This research results provide guidance for the rockburst prevention and hazard control of the coal mining in fault zone.

我国地下金属矿山岩爆灾害发生机制及预测方法研究进展

岩爆是金属矿地下开采中难以回避的一种动力学地质灾害,其发生频率和程度将会随着金属矿山采深不断增加而愈加严重,岩爆至今仍是岩石力学领域的世界性难题。首先总结了我国金属矿山岩爆灾害的发生现状,然后重点围绕岩爆发生机制及岩爆预测两方面,探讨了我国金属矿山岩爆的研究进展,并基于能量理论提出了一种岩爆灾害预测的新方法。研究表明:①室内压缩试验是岩爆机制研究的最主要手段,根据试样受力条件可分为单轴加载、双轴加载、真三轴加载及动静组合加载;岩爆的力学机制可归纳为压致拉裂、压致剪切拉裂和弯曲鼓折3种。②指标判据法和数学模型方法是国内外学者最普遍关注的岩爆预测手段;指标判据法是针对某一工程的经验性总结,不具普遍性;数学模型方法无法获得岩爆影响因素的内在作用机制,可解释性较差。在上述分析的基础上,对岩爆机制及岩爆预测的研究方向进行了展望,供后续工作参考。

STABLE OR UNSTABLE CRACK GROWTHSIN THIN ROCK PLATE UNDER COMPRESSION FOR PREDICTING BUCKLING ROCKBURST

Underground cavern opening can cause the surrounding rock tangential compressive stress to raise rapidly. Such high compressive stress increase can result in some original pre-existing cracks growing parallelly to the free surface of the remaining rock. This paper presents a model of crack stable or unstable propagation under compressive stress in thin layers that are separated from the main rock mass due to crack growth. Based on this analysis of flat plate buckling,a rock burst mechanism is presented. Immediate and delayed rock burst mechanism are proposed to explain time dependency in brittle rock sub-critical crack growth under compression. Influence of free surface on the surface-parallel crack growth is also discussed.