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.

Rockburst management in Canadian hard rock mines

Rockburst is a complex mining-induced phenomenon that remains difficult to be quantified.In particular,geological conditions contributing to rockbursts are more variable than those in many conventional engineering approaches.Faults,intact rock properties,and other rock mass conditions vary,sometimes,within small distance.Stress levels that store energy or drive structures can change with geological complications.For example,faults may channel stress between the void and the discontinuity,and/or alter the local stress direction.High-strength rock masses may be very massive at shallow depth,allowing for large/stable excavations.The same rock type may store excessive strain energy at depth or high mineral extraction,and lead to rockbursts.More robust ground support systems that can bear dynamic loading are now commonplace in mining industry.A typical approach would be able to evaluate rockburst potential,and selectively deploy more robust ground support systems.Rockburst resistant support is more expensive in installation than most support systems designed for gravity loading.Thus,an excessively conservative risk assessment can affect both direct support costs and productivity.As mines continue to go deeper,selective use of burst-prone support may not be an optimal choice,and pervasive installation may become necessary.This implies a need to maintain a reasonable installation speed,and the time to get to deep orebodies is a major economic factor.This paper shows field examples of rockbursts to highlight some of the complex issues related to the rockburst.A multi-tiered risk mitigation approach is used for rockburst conditions.Examples of risk reduction strategies are given and some examples from a deep hard rock mine are used to illustrate the relative success of the strategies.Given that some residual risks to worker safety remain,discussion is presented on where more research or process improvements would be beneficial.

Discussions on rockburst and dynamic ground support in deep mines

The paper is a summary of discussions on four topics in rockburst and dynamic ground support.Topic 1 is the mechanisms of rockburst.Rockburst events are classified into two categories in accordance with the triggering mechanisms,i.e.strain burst and fault-slip burst.Strain burst occurs on rock surfaces when the tangential stress exceeds the rock strength in hard and brittle rocks.Fault-slip burst is triggered by fault-slip induced seismicity.Topic 2 is prediction and forecasting of rockburst events.Prediction for a rockburst event must tell the location,timing and magnitude of the event.Forecasting could simply foresee the probability of some of the three parameters.It is extremely challenging to predict rockbursts and large seismic events with current knowledge and technologies,but forecasting is possible,for example the possible locations of strain burst in an underground opening.At present,the approach using seismic monitoring and numerical modelling is a promising forecasting method.Topic 3 is preconditioning methods.The current preconditioning methods are blasting,relief-hole drilling and hydrofracturing.Defusing fault-slip seismicity is difficult and challenging but has been achieved.In very deep locations(>3000 m),the fracturing could extend from the excavation face to a deep location ahead of the face and therefore preconditioning is usually not required.Topic 4 is dynamic ground support against rockburst.Dynamic ground support requires that the support system be strong enough to sustain the momentum of the ejecting rock on one hand and tough enough on the other hand to absorb the strain and seismic energies released from the rock mass.The current dynamic support systems in underground mining are composed of yielding tendons and flexible surface retaining elements like mesh/screen and straps.Yielding props and engineered timber props are also used for dynamic support.

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.

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.

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.

Effects of torpedo blasting on rockburst prevention during deep coal seam mining in the Upper Silesian Coal Basin

In the Upper Silesian Coal Basin(USCB),coal seams are exploited under progressively more difficult geological and mining conditions(greater depth,higher horizontal stress,more frequent occurrence of competent rock layers,etc.).Mining depth,dislocations and mining remnants in coal seams are the most important factors responsible for the occurrence of rockburst hazards.Longwall mining next to the mining edges of neighbouring coal seams is particularly disadvantageous.The levels of rockburst hazards are minimised via the use of rockburst prevention methods.One active prevention method is torpedo blasting in roof rocks.Torpedo blastings are performed in order to decrease local stress concentrations in rock masses and to fracture the roof rocks to prevent or minimise the impact of high-energy tremors on excavations.The estimation of the effectiveness of torpedo blasting is particularly important when mining is under difficult geological and mining conditions.Torpedo blasting is the main form of active rockburst prevention in the assigned colliery in the Polish part of the USCB.The effectiveness of blasting can be estimated using the seismic effect method,in which the seismic monitoring data and the mass of explosives are taken into consideration.The seismic effect method was developed in the Czech Republic and is always being used in collieries in the Czech part of the coal basin.Now,this method has been widely adopted for our selected colliery in the Polish part of the coal basin.The effectiveness of torpedo blastings in the faces and galleries of the assigned longwall in coal seam 506 has been estimated.The results show that the effectiveness of torpedo blastings for this longwall was significant in light of the seismic effect method,which corresponds to the in situ observations.The seismic effect method is regularly applied to estimating the blasting effectiveness in the selected colliery.

深部复杂覆岩结构煤层开采冲击地压致灾层位判识研究

以孟村煤矿401102工作面为研究对象,系统开展深部复杂覆岩结构煤层开采冲击地压致灾层位判识数值模拟研究,建立覆岩冲击地压致灾影响系数Wrb,揭示工作面不同覆岩条件下各岩层致灾影响程度特征与致灾关键岩层分布规律。研究表明:(1)401102工作面煤层上方100 m范围亚关键层均为致灾影响程度较大岩层,同时非关键层运动破断的冲击致灾作用也不可忽视;(2)401102工作面基本顶为最主要冲击致灾岩层;(3)当对401102工作面内Wrb较高岩层采取地面水平井压裂后,冲击地压治理效果较好。研究成果可为深部煤层开采顶板灾源准确识别与冲击地压精准防控提供借鉴与指导。

深埋隧洞强岩爆微震活动特征分析及多元信息预警

岩爆的监测和预警一直是岩石工程领域的挑战,如何有效预测和动态防治岩爆灾害已成为深部地下工程亟待解决的问题.以雅砻江锦屏二级水电站隧洞岩爆高风险区为研究对象,采用地震学原理将定性分析与定量计算相结合,基于微震时、空、强分布特征及演化规律,揭示岩爆孕育发展过程中各震源参数的演化特征及规律.微震监测和研究结果表明,开挖卸荷下的微震时空活动是由空间分散无序向集中有序的自组织演化过程,震源参数如微震事件密度、能量密度、视体积、能量指数及b值随时间突增或骤降等异常变化可视为岩爆征兆响应的预警指标.基于震源参数的时空演化特征,提出深埋隧洞岩爆多元信息预警方法和预警流程,该方法可为深部隧道工程的岩爆监测预警和顺利施工提供借鉴.

采矿诱发地震分类的探讨

为有利于矿震灾害的预测、预防和治理,针对目前矿震各种分类间尚未建立起相互联系体系的现状,应用该灾害机制的最新研究成果,按照有利于对症治理灾害的原则,照顾到已被普通接受的习惯,提出矿震层级分类的概念、原则和优越性。按照矿震发生受原生构造应力场作用方式、岩石介质物理力学性质及岩层力学结构对矿震的控制作用、矿震与采矿活动的相关性、次生应力场动力来源和矿震发生及破坏的部位分出5个层级16种矿震类型,强调区域构造应力场和开挖造成的岩体应力状态改变在矿震分类、研究和治理中作用的重要。

基于地震CT技术的冲击地压危险性评价模型

运用地震波运动学理论,分析了地震波在"岩-煤-岩"特殊结构中的传播路径特征,结合现场实测数据统计结果,得出通过地震波走时CT技术,可利用回采工作面煤岩交界面的折射波对顶(底)板纵波波速进行成像,进而间接反映煤层性质。深入分析了地震波波速和地震波波速梯度与冲击地压危险性的相关性,以此为基础,初步建立了以地震波波速异常系数和地震波波速梯度系数为主要因子的冲击地压危险性评价模型。该模型基于地震CT技术对煤岩体纵波波速的成像数据,评价结论以二维图像形式表现。将该模型应用于新疆宽沟煤矿冲击地压工作面,评价结论与现场实际情况吻合性较好。

大规模开采矿山地震视应力和变形与区域性危险地震预测

大规模开采的矿山存在复杂的诱导地震活动,在高应力硬岩条件下具有产生区域性危险地震和岩爆灾害的可能性,震源的地震视应力和变形参数是地震机制和地震活动性预测研究的重要参数,对此开展研究具有重要意义。针对冬瓜山铜矿深井开采诱导地震活动,对地震视应力和位移在矿区开采过程中的时空特征开展研究,发现地震活动具有区域性分布特征,其时空分布与开采活动及矿区矿柱分布具有较强的对应关系。以此为依据,结合矿区地质构造和地应力状态,研究该矿区区域性地震机制,指出可以利用天然地震复杂震源的凹凸体理论来解释该矿区区域性地震成核机制,从而提出该矿区区域性危险性地震成核概念模型,并针对该矿地震活动的特征讨论识别成核区的方法。针对该矿区域性岩体破坏实例,分析地震视应力和变形参数时间序列特征,讨论潜在区域性地震成核区的地震活动危险性和岩体破坏性态的评价与预测。研究结果在工程实践中得到实际应用。

深埋隧洞不同开挖方式下即时型岩爆微震信息特征及能量分形研究

基于锦屏二级水电站深埋隧洞钻爆法及隧道掘进机(TBM)开挖过程中大量微震监测数据及不同等级的岩爆案例,对不同开挖方式下即时型岩爆的孕育及发生过程的能量释放展开研究,并运用分形几何原理研究微震能量分布的变化规律,得到以下结论:(1)即时型岩爆的孕育及发生过程中,岩爆区围岩岩体处于破坏加速集聚并不断扩展的过程;(2)钻爆法开挖过程中储存在岩体内的弹性应变能消耗于岩体破裂过程大于TBM开挖,而转化为岩体动能小于TBM开挖;(3)钻爆法开挖微震能量分形维度在即时型岩爆的孕育过程不断增加,岩爆临近前会增加到某个临界值以上;(4)TBM开挖即时型高等级岩爆能量分形维度值大于钻爆法开挖,并且其分形维度值可以反映低等级岩爆伴随发生的特征。

节理岩体中隧洞围岩的损伤破坏机理

结合细观节理形态的变化,在二轴围压条件下,数值模拟了节理岩体中隧洞围岩损伤破坏过程,研究了节理岩体中隧洞围岩体的破坏机理,分析了岩体中节理倾角对隧洞围岩稳定性的影响规律.结果表明:裂隙的产生和发展延伸主要是拉应力的作用,裂隙延伸方向大致与节理面垂直;节理倾角较小时,岩体中破裂以垂直于节理面的拉裂隙为主;节理倾角较大时,岩体裂隙以沿节理面的滑动裂隙为主;不同倾角的节理面对岩体破坏的脆性也有较大影响;岩体破坏前有大量微裂隙产生,同时伴随着声发射能量的释放,利用微震监测技术抓住这些微破裂前兆信息,能够较好地进行隧洞塌方、冒顶、岩爆等灾害预测,提前做好支护等应对措施,以保障人员、设备安全.

深井矿山微震事件波形研究

介绍了冬瓜山铜矿引进的南非ISSI公司微震监测系统的软硬件组成;对记录地震事件波形的处理方法开展了深入研究,并对比了手动处理与系统自动处理的区别,提高了事件定位的精度,为震源参数的精确计算奠定了基础;基于波形与生产活动的对应关系,对波形所做的分类研究可确保能够快速识别各类事件;通过对测试爆破和矿山发生的地压活动事件的分析,验证了波形分析方法的可行性;为圈定岩体稳定性危险区并判断其发展趋势,及保证生产安全提供了依据。

爆孕育过程的微震源事件空间分形行为

为了分析岩爆过程中微破裂事件的自相似特征,提出微震源事件空间分形计算方法.运用该方法,针对锦屏山水电站TBM及钻爆法2种不同开挖方式下,岩爆灾害孕育及发生所获得的微震信息进行研究.结果表明:对于深部岩体隧洞施工过程中发生的岩爆灾害,微震事件的空间分布是具有分形结构的;微震事件空间分形维数具有随着岩爆的孕育过程不断减小,当岩爆发生时达到最小值的特征;TBM开挖方式下的微震事件空间分形维数分布在0.6~1.8的范围内,钻爆法开挖方式下分布在1.2~2.0的范围内;微震事件空间分形维数与微震能量释放之间表现出明显的反比例关系.

深井矿山岩爆控制体系构建

随着矿山开采深度的增加,原岩应力水平大大提高,导致岩爆等灾害发生频率提高,矿山生产的安全性下降。以微震监测技术为中心构建深井采矿岩爆控制体系,可以提高有岩爆危险和/或危害矿山采矿的安全性。以微震监测系统为中心的岩爆控制体系主要包括:微震监测网络的建立、微震事件波形的处理、微震事件震源参数的量化、回采过程中微震震源参数变化的规律分析、危险区域的识别、危险震级的有效预测、采矿策略的调整和最佳策略的确定。

深井大规模矿床开采岩爆控制策略研究

随着大规模矿床的开采,在高应力作用下,不断的产生破坏性岩爆等灾害,严重制约着这些矿床的正常生产。针对国内矿山即将进入1500m深度的千万吨级生产规模,本文对深井大规模矿山的采矿战略进行了研究,制定了深埋大规模硬岩矿床采矿的工作程序。设计阶段要遵守原则,如井下工程布置,采矿方法选择,实时监测系统布置等;生产阶段主要致力于日常矿山微震风险的管理工作,建立微震监测系统,调查破坏事件,分析应力场变化规律与预测风险区域,最终采取针对性的支护技术,合理安排出矿计划和特定工作环境下作业人员技能的培训等应对策略。

深部开采岩爆机理数值分析方法与应用

应用自行开发的岩石破裂与失稳分析数值工具(RFPA系统),模拟了深部开采中岩爆的发生、发展全过程,用应力场分布再现了岩爆和破坏失稳的机理。并结合辽宁抚顺红透山铜矿深部开采及其岩爆问题,进行数值模拟,结果表明,岩爆的发生是可以预测的,并提出了岩爆预测新方法。

基于微震监测技术的深部采场采动规律研究

冬瓜山铜矿是目前国内开采最深的金属矿山之一,岩石具有典型的岩爆倾向性。为了掌握岩爆发生规律,并及时采取有效安全控制措施指导矿山安全生产,矿山引进了南非ISS公司的微震监测系统,实现了对采矿引起的岩体应力、应变状态的实时监测。本文简单介绍了冬瓜山铜矿首采区的地质条件、采场结构及微震传感器的空间布置。在前期处理波形和事件聚类分析研究基础上,与生产活动相对应,采用地震参数对采场开采过程中不同阶段的应力变化规律进行了对比分析研究,并结合矿山实际的破坏事件,进行了针对性分析研究。研究成果为后续相邻采场开采及隔离矿柱稳定性的控制策略等提供依据。