Microcrack analysis of Sanya grantite fragments from rockburst tests

Fractures running along a plane reflect the cracking progress.In this paper uniaxial and rockburst tests on a group of granite specimens from Sanya province are described.Scanning electron microscopic imaging was used to characterize the fragments.Fractal fracture mechanics were used to analyze the microcracks in terms of both the crack type and the mineral constituent.A statistical analysis showed that the area of inter-granular cracking exceeds that of intra-granular cracking.Several types of crack were observed in the cracked areas.The percentage of intra-granular cracks in fragments from rockburst tests exceeds that from uniaxial compression tests.The results also showed that feldspar deformation was the main cause of fracture and that the consolidation along quartz grain boundaries was another weak area in the granite.Cracking along quartz grains had enough energy to enter the quartz crystal in the rockburst samples.All these results contribute to further research on rockburst mechanics.

Dynamic analysis of granite rockburst based on the PIV technique

This paper describes the deep rockburst simulation system to reproduce the granite instantaneous rockburst process.Based on the PIV(Particle Image Velocimetry)technique,quantitative analysis of a rockburst,the images of tracer particle,displacement and strain fields can be obtained,and the debris trajectory described.According to the observation of on-site tests,the dynamic rockburst is actually a gas–solid high speed flow process,which is caused by the interaction of rock fragments and surrounding air.With the help of analysis on high speed video and PIV images,the granite rockburst failure process is composed of six stages of platey fragment spalling and debris ejection.Meanwhile,the elastic energy for these six stages has been calculated to study the energy variation.The results indicate that the rockburst process can be summarized as:an initiating stage,intensive developing stage and gradual decay stage.This research will be helpful for our further understanding of the rockburst mechanism.

PREDICTION OF ROCKBURST BY ARTIFICIAL NEURAL NETWORK

Based on the analysis of main causes of rockburst,the compressive strength,tensile strength,elastic energy index of rock and the maximum tangential stress of the cavern wall are chosen as the criterion indexes for rockburst prediction.A new approach using neural method is proposed to predict rockburst occurrence and its intensity.The prediction results show that it is feasible and appropriate to use artificial neural network model for rockburst prediction.

Rockburst proneness criteria for rock materials:Review and new insights

To review the rockburst proneness(or tendency)criteria of rock materials and compare the judgment accuracy of them,twenty criteria were summarized,and their judgment accuracy was evaluated and compared based on the laboratory tests on fourteen types of rocks.This study begins firstly by introducing the twenty rockburst proneness criteria,and their origins,definitions,calculation methods and grading standards were summarized in detail.Subsequently,to evaluate and compare the judgment accuracy of the twenty criteria,a series of laboratory tests were carried out on fourteen types of rocks,and the rockburst proneness judgment results of the twenty criteria for the fourteen types of rocks were obtained accordingly.Moreover,to provide a unified basis for the judgment accuracy evaluation of above criteria,a classification standard(obtained according to the actual failure results and phenomena of rock specimen)of rockburst proneness in laboratory tests was introduced.The judgment results of the twenty criteria were compared with the judgment results of this classification standard.The results show that the judgment results of the criterion based on residual elastic energy(REE)index are completely consistent with the actual rockburst proneness,and the other criteria have some inconsistent situations more or less.Moreover,the REE index is based on the linear energy storage law and defined in form of a difference value and considered the whole failure process,and these superior characteristics ensure its accuracy.It is believed that the criterion based on REE index is comparatively more accurate and scientific than other criteria,and it can be recommended to be applied to judge the rockburst proneness of rock materials.

Dynamic buckling mechanism of pillar rockbursts induced by stress waves

Rockbursts are sudden and violent rock failures that can lead to huge production and equipment losses,injury or death of mining workers.Buckling has been regarded as one of the key mechanisms of rockbursts,which are often induced by dynamic loads from mining excavations,such as drilling and blasting in underground mining.The paper attempts to investigate the dynamic buckling mechanism of pillar rockbursts in underground mining,by considering rockbursts as a dynamic stability problem of underground rock structures.The results include:(1)A new explanation of the“sudden and violent”phenomenon of rockbursts,characterized by exponential growth of the amplitudes of transverse displacement responses,even in the presence of rock damping;(2)Identification of the critical role in inducing rockbursts of dynamic loads that bear frequencies approximately double the natural pillar frequency;(3)The greater influence on rockburst occurrence of the amplitude of dynamic component relative to the static component of loads;and(4)Quantification of the relative effects of stress waveform of dynamic loads on pillar rockbursts,which are in decreasing order if other parameters remain constant:rectangular,sinusoidal,and exponential waveforms.Application examples are provided and limitations of the approach are discussed.This research is motivated by the on-going and ubiquitous occurrence of rockbursts in underground excavations all around the world.In contrast to conventional methods that use rock specimens or rock materials to study rockbursts,this investigation emphasizes the structural effects on rockbursts,which has potential applications in hard rock mining engineering.

基于D-S证据理论的岩爆预测方法研究

为了有效预测岩爆,提出基于D-S证据理论的岩爆预测方法.首先,选取与岩爆发生相关的6个指标因素作为证据体,并通过模糊物元框架和正态型隶属度函数构建证据体的基本概率分配.然后,利用K均值将证据体分类,并提出簇内证据用传统方式融合而簇间证据用权重方式融合的组合融合规则,以减轻高冲突证据融合的不利影响.最后,将模型应用在秦岭终南山公路隧道2号竖井工程,且与经验方法对比.为了分析预测过程的不确定性和估计岩爆发生概率,采用蒙特卡洛模拟进行抽样仿真,并通过Spearman秩相关系数衡量输入指标的全局敏感性.研究结果表明:输入指标在不同的岩爆案例的影响程度差异较大且方向不同;5个岩爆案例的发生概率在40.8%~70.1%之间.该模型表现出优异的预测分类性能,可为深埋地下工程岩爆预测提供参考.

深部极高地应力花岗岩隧道岩爆破坏特征及成因机理研究

深部极高地应力花岗岩隧道施工过程中,岩爆灾害异常突出,硬岩岩爆不同程度地造成岩体片状剥落、棱板状破裂、岩块抛掷及强烈弹射等。为了揭示花岗岩隧道岩爆成因机制,综合地质调绘、监控量测、岩爆实录统计、室内岩石力学试验、微观分析和数值模拟分析等方法对隧道高地应力及岩爆的形成、破坏特征及影响因素进行探讨分析。根据现场岩爆实录统计分析,花岗岩隧道岩爆破坏特征复杂多样,发生时间集中,高水平构造应力使靠近雅鲁藏布江河谷一侧岩爆烈度显著增大,大埋深高自重应力导致岩爆主要分布在隧道掌子面和拱顶。基于钻孔实测地应力数据和初始地应力场反演分析,发现花岗岩隧道地应力场由构造应力和自重应力共同主导,隧道沿线82.0%的区段处于高到极高地应力状态,为岩爆的发生提供内动力地质条件。室内岩石力学试验表明二长花岗岩和花岗闪长岩均具有中等岩爆倾向性,厚层状、强度大、刚度高、完整性好的岩体为岩爆提供充足的物源条件。受控于雅鲁藏布江缝合带地质构造作用以及新生代岩浆活动作用影响,花岗岩隧道呈现高地温特征,地温梯度为5.5℃/100 m,最高实测地温达到89.6℃,高温热力耦合作用加速岩爆发生并提高岩爆危险性等级。隧道施工工艺会改变围岩应力重分布,影响围岩的应力集中,造成一定的尺寸效应,影响岩爆发生的烈度等级、时间和空间分布。

某深埋TBM隧洞围岩地质变化区破坏特征与类型判别方法

某深埋TBM隧洞地质变化区开挖过程中岩爆和塌方交替发生,导致工期严重延误,严重威胁现场人员及施工安全。通过现场地质踏勘、微震监测和结构面统计,研究现场工程地质灾害与围岩岩性、地质条件的关系,建立基于岩性、地质及微震活动特征的地质灾害类型判别方法。结果表明,该隧洞破坏类型与围岩岩性有显著相关性,黑云母花岗岩洞段岩爆风险最高,混合花岗岩洞段次之,钾长石花岗岩与黑云母花岗岩围岩蚀变的洞段易发生塌方;岩性变化的交界面位置,破坏规模明显增大;破坏类型还与结构面密度相关,随着结构面密度减小,破坏类型由塌方转变为中等岩爆,进一步等级降低为轻微岩爆;微震特征分析表明,岩爆区域微震活动远大于塌方区域微震活动。当微震活动较低时,围岩破坏以塌方为主;当微震事件数>15,微震释放能>1000 J,围岩破坏以岩爆为主;当微震事件数>20,微震释放能>20000 J时,围岩可能发生中等岩爆。现场应用表明,该方法可准确预测掌子面前方潜在破坏类型,为类似工程灾害交替发生洞段的安全、高效施工提供参考。

高地应力水平岩层隧道滞后型岩爆时空倾向性机制分析

浙江杭温水平岩层隧道内滞后型岩爆频发,但目前对于其孕育机理和时空倾向性研究不足。故采用有限差分软件,通过地应力测试和统计现场岩爆资料的方法,研究分析滞后型岩爆时空特征机制。结果表明:①滞后型岩爆具有明显的时空倾向性特征。近70%的滞后型岩爆时间上发生在该区开挖6~30 d,空间上滞后于掌子面30~100 m之间;且多发生中等岩爆,岩爆等级及可能性随时空变化呈现倒“V”形趋势。②硬岩在高地应力环境中具有明显的延性与时效变形特征;在卸荷条件下,应力释放率的逐渐增加是诱发滞后型岩爆的最主要因素。③开挖一定距离后,隧道周边不同位置处都出现应变能突变,且保持较高的应变能密度,易发生等级较高的岩爆。上述结果为以后预测滞后型岩爆和施加相应支护措施提供了依据。

Failure mechanism and coupled static-dynamic loading theory in deep hard rock mining: A review

Rock failure phenomena,such as rockburst,slabbing(or spalling) and zonal disintegration,related to deep underground excavation of hard rocks are frequently reported and pose a great threat to deep mining.Currently,the explanation for these failure phenomena using existing dynamic or static rock mechanics theory is not straightforward.In this study,new theory and testing method for deep underground rock mass under coupled static-dynamic loading are introduced.Two types of coupled loading modes,i.e.'critical static stress + slight disturbance' and 'elastic static stress + impact disturbance',are proposed,and associated test devices are developed.Rockburst phenomena of hard rocks under coupled static-dynamic loading are successfully reproduced in the laboratory,and the rockburst mechanism and related criteria are demonstrated.The results of true triaxial unloading compression tests on granite and red sandstone indicate that the unloading can induce slabbing when the confining pressure exceeds a certain threshold,and the slabbing failure strength is lower than the shear failure strength according to the conventional Mohr-Column criterion.Numerical results indicate that the rock unloading failure response under different in situ stresses and unloading rates can be characterized by an equivalent strain energy density.In addition,we present a new microseismic source location method without premeasuring the sound wave velocity in rock mass,which can efficiently and accurately locate the rock failure in hard rock mines.Also,a new idea for deep hard rock mining using a non-explosive continuous mining method is briefly introduced.

Rock brittleness indices and their applications to different fields of rock engineering:A review

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst proneness.As such,it is of high practical value to correctly evaluate rock brittleness.However,the definition and measurement method of rock brittleness have been very diverse and not yet been standardized.In this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly discussed.The development and role of rock brittleness in different fields of rock engineering are also studied.Eighty brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are discussed.The results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock brittleness.On the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness.It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness.This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.

基于岩爆碎屑研究的高楼山隧道岩爆机理分析与类型判定

在建高楼山隧道是通达陇南市及四川省九寨沟的控制性工程,项目具有“三高一大”的特点,是复杂地质条件下深埋特长公路隧道的典型代表.以现场两种岩爆类型为研究对象,通过冲击岩爆实验系统并设定不同应力路径,首先进行了岩爆实验全过程分析,而后对比研究了板裂屈曲型岩爆实验碎屑(岩爆碎屑1)、爆破冲击型岩爆实验碎屑(岩爆碎屑2)和现场收集的不知类型的岩爆碎屑(岩爆碎屑3)的质量、尺度分布及形状分形维数特征.在此基础上,结合岩爆实验图像变化过程,深化了对不同类型岩爆碎屑成因及岩爆机理的认识.结果表明:(1)板裂屈曲型岩爆和爆破冲击型岩爆区别在于破坏主导机制不同,一种为张拉破坏主导,另一种为张剪破坏主导.(2)岩爆碎屑1以中粒、条板状碎屑为主,在长度方向上更容易破碎,且质量远大于岩爆碎屑2,这与竖向应力集中形成板裂化结构的板裂屈曲型岩爆孕育机制密不可分.(3)动载的介入使得岩爆碎屑2受剪切作用明显,因而在厚度方向的破碎更容易且破碎程度更高,形成以粗粒、片状碎屑为主的碎屑,该类型碎屑在现场岩爆中由于质量较大、体积较大、弹射距离较远,因此危害性可能更大.(4)通过上述比对分析,可基本判定岩爆碎屑3对应的岩爆类型为爆破冲击型,且片状、“V”形特征碎屑为该类型岩爆特有的碎屑类型.

基于侵入试验的单齿破岩机理及齿形优化研究

齿形是影响镶齿滚刀破岩效率的关键因素。本文通过单齿侵入破岩试验对4种刀齿(镐形齿、锥形齿、楔形齿和球形齿)的破岩机理及硬岩破岩齿形优化等相关问题进行探讨,研究不同齿形侵入岩体过程中的破岩特征、加载力侵深曲线特征以及对侵深、破碎体积、破碎坑半径、破岩岩屑分布特征的影响规律。通过分形理论评估破岩效果,从而达到优化齿形及加载力的目的。结果表明:随加载力增大,齿形对侵深、破碎体积、破碎坑半径等破岩效果指标的影响差异随之增大;破碎岩屑在粒度上具有分形特征,通过破碎分形维数并结合破碎体积等指标可以评估破碎效果,优化齿形及加载力;针对花岗岩类岩石,镐形齿所获得的破碎分形维数最低,破碎体积、破碎坑半径、侵深最大,可优选为花岗岩类硬岩中镶齿滚刀的齿形,并推荐100 kN为镐形齿优化加载力。

恒阻吸能锚固岩体动力特性及控制机制

深部围岩动力灾害发生的本质在于围岩积聚能量的突然释放,通过锚固支护实现能量的有效吸收是围岩控制的常用手段,也是围岩动力灾害控制的关键。锚固岩体动力特性及控制机制研究是锚固支护合理设计的前提。基于此,研发了新型高强、高延伸率、高吸能特性恒阻吸能支护材料,开展了恒阻吸能锚固岩体动力试验,分析了锚固岩体的动力学响应特征与能量演化规律。结果表明,与无锚岩体相比,恒阻吸能锚固岩体表面损伤率和体积损伤率分别降低了62.1%和93.1%,中粒、细粒和微粒岩爆碎屑质量减少均在90%以上,总能量、平均能量和最大能量分别降低了87.6%、82.9%、80.3%,岩爆峰值应力增加了54.2%,岩爆时间延后了140.2%。同时对恒阻吸能支护构件的强度、吸能能力、剪切偏移等特征进行了分析,恒阻吸能材料的强度、形变和吸能安全储备率分别为38.8%、94.0%、97.9%,安全性好。试件上端和下端支护构件的上下总偏移量分别为0.886、0.403 mm,岩爆锚固控制应考虑围岩的剪切作用。基于岩爆能量计算模型,研究了岩爆峰值应力与能量释放的规律,明确了预应力锚固支护对岩爆的控制机制。恒阻吸能锚固使岩体岩爆的峰值应力从单轴抗压强度的1.6倍增加到2.5倍,加锚岩体岩爆所需能量是无锚岩体的2.3倍,预应力锚固支护有效降低了岩爆发生的风险。在上述研究基础上,从监测预警、控制方法、支护设计、效果评价等方面提出了岩爆防控的工程建议。

基于机器学习可解释性算法的岩爆指标分析

为探究弹性能指数、应力系数、脆性系数、埋深4种岩爆指标与岩爆等级之间的相关关系,解决复杂机器学习算法的黑盒问题。引入LIME(local interpretable model agnostic explanations)算法,完善岩爆机器学习预测过程中的可解释性。搜集了中外190组岩爆实例工程构建数据集经过预处理后,通过9种机器学习算法比较获得最优算法并采用贝叶斯优化获得算法最优参数,建立岩爆预测模型。基于LIME可解释性算法,对4种岩爆指标进行相关、回归及阈值分析,最后采用弹性能指数及应力系数两种指标阈值对终南山隧道竖井工程进行岩爆预测。研究结果表明:岩爆等级与弹性能指数、应力系数呈线性相关,且弹性能指数线性关系更明显;岩爆等级与脆性系数、埋深呈非线性相关,且脆性系数非线性关系更明显;4个岩爆指标对岩爆等级影响程度依次为:弹性能指数、应力系数、埋深、脆性系数;LIME算法可以准确地表达岩爆等级与岩爆指标之间的相关关系且得到的两种指标阈值与终南山隧道竖井工程实例具有一致性。

基于集成算法和普通机器学习算法的岩爆分级预测及选择

岩爆是国内外深部地下工程面临的巨大灾害,岩爆预测具有显著的现实意义。现阶段单一的机器学习算法准确率较低、泛化性不足,难以发挥各个算法优点。为满足岩爆预测与工程实际需要,提出基于集成算法和普通机器学习算法相互结合预测岩爆各个等级,充分发挥不同算法在某一岩爆等级预测的优势并形成互补。提出改进的Boosting、Bagging集成预测算法,与Stacking、Random Forest、Random Subspace集成算法和普通学习算法诸如BP、贝叶斯算法(bayes)、k最近邻(KNN)、支持向量机(SVM)等在内的14种预测算法进行相互结合验证。基于国内外地下工程165组岩爆实例,选取围岩最大切向应力(MTS)、岩石单轴抗压强度(UCS)、岩石单轴抗拉强度(UTS)、岩石弹性能量指数(W et)构建岩爆预测体系,引入T-分布邻域嵌入(T-SNE),对数据进行降维可视化。为避免算法预测岩爆过程中预测结果的偶然性,即出现预测准确率过高或过低的现象,采用在各个岩爆等级按照比例随机筛选训练集和测试集,确保数据集分类的严谨性;每次机器学习过程的数据都具有随机性,在采用10次运行结果后取各项预测平均值,评价算法在各个等级的准确率和算法整体的预测稳定性。结果表明:LDA对Ⅱ级岩爆有更高的准确率,Bayes分类Ⅳ级岩爆效果最好,Adaboost.M1对Ⅰ级和Ⅲ级有最高的准确率。整体预测效果基于决策树的Bagging预测稳定性更好,预测精确率高。最后引入终南山隧道竖井工程案例,预测结果与现场实际工况较为一致,表明本文所建立算法的可靠性。

Sliding modes of fault activation under constant normal stiffness conditions

Fault activation has been the focus of research community for years.However,the studies of fault activation remain immature,such as the fault activation mode and its major factors under constant normal stiffness(CNS)conditions associated with large thickness of fault surrounding rock mass.In this study,the rock friction experiments were conducted to understand the fault activation modes under the CNS conditions.Two major parameters,i.e.the initial normal stress and loading rate,were considered and calibrated in the tests.To reveal the response mechanism of fault activation,the local strains near the fault plane were recorded,and the macroscopic stresses and displacements were analyzed.The testing results show that the effect of displacement-controlled loading rate is more pronounced under the CNS conditions than that under constant normal load(CNL)conditions.Both the normal and shear stresses drop suddenly when the stick-slip occurs.The decrease and increase of the normal stress are synchronous with the shear stress in the regular stick-slip scenario,but mismatch with the shear stress during the chaotic stick-slip process.The results are helpful for understanding the fault sliding mode and the prediction and prevention of fault slip.

基于3种机器学习模型的岩爆类型预测

基于国内外397组岩爆案例数据,采用模型参数优化及交叉验证技术获得最近邻、支持向量机与决策树模型最佳参数;对比主成分分析(PCA)与过采样SMOTE(synthetic minority oversampling technique)算法对3种机器学习算法预测准确率的影响,并对模型预测性能进行评估.结果表明:主成分分析对3种机器学习模型的预测准确率并无提升,不同岩爆类型的样本之间不具有较为明显的分类边界;过采样SMOTE算法仅对决策树模型有明显的提升,基于过采样建立的SMOTE-DT模型预测准确率为77.50%,高于仅对原始数据集进行标准化处理的K-最邻近(KNN)和支持向量机(SVM)模型的68.75%与57.50%;SMOTE-DT在避免高估与低估岩爆类型表现优于KNN与SVM模型,对于4种岩爆类型的F_1值均大于0.7,岩爆预测性能稳定可靠.此外,采用本文构建的3种机器学习模型对山西紫金金矿进行岩爆类型预测,模型预测结果与现场观测结果相一致.

Fan‐hinged shear instead of frictional stick–slip as the main and most dangerous mechanism of natural,induced,and volcanic earthquakes in the earth's crust

Frictional stick–slip instability along pre‐existing faults has been accepted as the main mechanism of earthquakes for about 60 years,since it is believed that fracture of intact rocks cannot reflect such features inherent in earthquakes as low shear stresses activating instability,low stress drop,repetitive dynamic instability,and connection with pre‐existing faults.This paper demonstrates that all these features can be induced by a recently discovered shear rupture mechanism(fan‐hinged),which creates dynamic ruptures in intact rocks under stress conditions corresponding to seismogenic depths.The key element of this mechanism is the fan‐shaped structure of the head of extreme ruptures,which is formed as a result of an intense tensile cracking process,with the creation of inter‐crack slabs that act as hinges between the shearing rupture faces.The preference of the fan mechanism over the stick–slip mechanism is clear due to the extraordinary properties of the fan structure,which include the ability to generate new faults in intact dry rocks even at shear stresses that are an order of magnitude lower than the frictional strength;to provide shear resistance close to zero and abnormally large energy release;to cause a low stress drop;to use a new physics of energy supply to the rupture tip,providing supersonic rupture velocity;and to provide a previously unknown interrelation between earthquakes and volcanoes.All these properties make the fan mechanism the most dangerous rupture mechanism at the seismogenic depths of the earth's crust,generating the vast majority of earthquakes.The detailed analysis of the fan mechanism is presented in the companion paper“New physics of supersonic ruptures”published in DUSE.Further study of this subject is a major challenge for deep underground science,earthquake and fracture mechanics,volcanoes,physics,and tribology.

深埋隧洞岩爆孕育规律与机制:即时型岩爆

论述深埋隧洞岩爆孕育过程的现场原位综合观测试验思路和方法,给出利用该方法观测到的岩爆孕育时空演化规律以及基于观测结果的关于岩爆孕育机制的认知成果。通过一系列现场深埋隧洞开挖过程中的多元信息综合观测试验,揭示深埋隧洞的即时型岩爆(隧洞开挖卸荷效应影响过程中的隧洞掌子面及其附近的围岩,开挖后几小时到几天内发生)的裂纹(萌生、扩展、张开和闭合过程)、变形、弹性波、声发射和微震时空演化规律及其在时空上的分布特征。通过对监测的微震信息进行矩张量分析,认识即时型岩爆中应变型和应变–结构面滑移型2类岩爆的孕育机制差异性:前者主要是拉张破裂引起,后者主要是拉张破坏、剪切破裂与拉剪–压剪破裂引起,剪切破裂主要沿着硬性结构面发生,形成爆坑边界。该研究成果为针对时空演化规律的深埋隧洞岩爆的预测和动态调控提供了重要基础。