Caractérisation géométrique des réseaux de fracturation en carrière de roches ornementales. Application à l'optimisation de l'exploitation

The structural analysis of the rock mass at a given scale leads to the modelling of the sets of discontinuities. Several software programs created in the Centre de Géologie de l'Ingénieur, were used for the characterization of the structure of various ornamental rock deposits. This study incles: the identification of discontinuities in several quarries, statistical processing of field data, geometrical modelling of the discontinuous rock masses, analysis of the size distribution of blocks formed by the sets of discontinuities, and three-dimensional visualization of the exploitation faces and of serial cross sections simulating their inward movement.     

边坡及洞室岩体的全空间块体拓扑搜索研究

 在一定空间区域内,由三维有限长的随机结构面及确定性结构面切割形成的所有块体的搜索问题,即全空间块体搜索问题,是裂隙岩体研究中十分重要的基础性课题。在随机结构面切割下全空间块体拓扑搜索一般方法研究基础上,进行边坡及洞室岩体的全空间块体搜索问题研究。给出计算分析过程,包括三维结构面网络模拟、结构面与边界面之间的交线分析、封闭回路分析、回路空间位置分析、孤立回路删除、相关回路分析以及封闭块体搜索等,并对其中的结构面与边界面交线求解进行重点讨论。对块体切割中出现的简单凸多面体及凹多面体、坑体、环体、腔体等4种块体类型进行分析,基于单连通和复连通回路的不同特点,讨论如何统一地对4种块体类型进行搜索分析,从而实现边坡/洞室岩体的全空间块体拓扑搜索技术。在此基础上,基于经典的块体理论,实现边坡/洞室工程中的块体渐进失稳分析技术。最后,针对边坡和洞室算例进行分析和讨论。     

Stochastic analysis of progressive failure of fractured rock masses containing non-persistent joint sets using key block analysis

A stochastic key block method is developed for the analysis of complex blocky rock masses containing non-persistent joint sets. A robust block generation program is developed to model the non-persistent discontinuities. Various uncertainties of geological and geometrical parameters of the discontinuities are considered and Monte Carlo simulations of key blocks are performed. Based on the present analysis, progressive failure of a rock mass can be evaluated in a stochastic manner and the statistics of the key blocks including the total number and volume, the maximum and mean volume, shape and failure mechanism, etc. can be assessed. This approach is applied to a hypothetical horseshoe shaped tunnel in a highly fractured rock mass. Three scenarios with varying mean discontinuity size are analyzed to consider size effect on the predicted blocks and key blocks. It is shown quantitatively that a persistent discontinuity network assumption causes over-fragmentation of predicted blocks, overestimation of key blocks, and underestimation of the largest key block volume compared with non-persistent ones. More realistic representation of the discontinuities by considering the non-persistence is important to give out more reliable failure estimation of fractured rock mass. In addition, a case study application to a slope at the right bank of the Jinping I hydropower station has been conducted. Key block statistics is also helpful in support design.     

Composite wedge failure using photogrammetric measurements and DFN-DEM modelling

Analysis and prediction of structural instabilities in open pit mines are an important design and operational consideration for ensuring safety and productivity of the operation. Unstable wedges and blocks occurring at the surface of the pit walls may be identified through three-dimensional (3D) image analysis combined with the discrete fracture network (DFN) approach. Kinematic analysis based on polyhedral modelling can be used for first pass analysis but cannot capture composite failure mechanisms involving both structurally controlled and rock mass progressive failures. A methodology is proposed in this paper to overcome such limitations by coupling DFN models with geomechanical simulations based on the discrete element method (DEM). Further, high resolution photogrammetric data are used to identify valid model scenarios. An identified wedge failure that occurred in an Australian coal mine is used to validate the methodology. In this particular case, the failure surface was induced as a result of the rock mass progressive failure that developed from the toe of the structure inside the intact rock matrix. Analysis has been undertaken to determine in what scenarios the measured and predicted failure surfaces can be used to calibrate strength parameters in the model.     

Assessing the ability of rock masses to support block breakage at the TBM cutter face

In order for tunnel boring machines to efficiently cut or break rock, it is necessary that the block of rock in contact with the cutter be adequately supported by the surrounding rock mass. This support is provided by the interlocking of blocks and the friction of the surfaces. If blocks are inadequately supported or become free without breakage the result can be jamming at the TBM face. Such blocky ground conditions are typically assessed according to the spacing and orientation of discontinuities (including joints) within the rock mass, typically using a rock mass classification system. In laboratory tests on cuttability or abrasivity of rocks, test samples are typically supported securely in a frame or jig. Numerical models of rock breakage also assume boundary conditions in which the sample is completely supported. Therefore the applicability of the results from laboratory and numerical studies depends on the same degree of support of blocks in the ground. The conditions required to adequately support a block for breakage are investigated and related to rock mass parameters, in particular, the three-dimensional patterns of discontinuities. A rock mass can be capable of providing adequate support to a block of rock such that the cuttability is adequately described by conventional methods. However, there are some rock mass conditions where support of blocks is not well developed, potentially resulting in otherwise unexpected poor TBM progress or jamming of TBM with loose blocks. Three-dimensional discontinuity patterns can be assessed using stereographic methods or borehole (α–β) methods. It is proposed that problematic conditions may occur where: two or more oblique (α between 20° and 70°) discontinuity sets are present (and over-represented relative to a uniform distribution); one or more of these discontinuity sets are dipping into the opening (β = 180° ± 90°) and additional discontinuities (in sets or randomly oriented) are present to form complete tetrahedral wedge blocks.     

复杂岩石块体识别的单元重构–聚合方法

 为解决工程岩体开挖中含有复杂开挖边界时的块体识别问题,提出岩石块体识别的单元重构–聚合方法。首先,引入成熟的网格划分技术,通过建立网格模型(如有限元模型),实现对复杂开挖边界的精确模拟;其次,采用基于单元重构技术的结构面建模方法,将分布于岩体内的结构面建入网格模型;然后,提出基于单元聚合技术的块体构建方法和考虑有限性结构面时的单元组处理方法;最终可实现基于网格模型的复杂岩石块体识别。该方法识别所得的块体系统基于网格模型,块体的所有特征信息均可通过模型的单元和节点提取,块体的可视化也可在既有网格模型图形显示平台上实现。算例验证表明,当将结构面分别考虑为无限延伸和有限延展时,该方法的块体识别和稳定分析成果均与通用块体分析软件的结果一致。进一步将该方法应用于水电站大型地下洞室群的块体识别,可证明其应用于复杂岩石块体识别的有效性和优越性。因此,该方法是一种能够考虑复杂工程岩体开挖边界的岩石块体识别的新方法,其实现过程独立于基于拓扑原理的传统块体识别思路,为块体稳定分析提供了新的实现途径。     

基于激光点云数据的岩体结构面全自动模糊群聚分析及几何信息获取

 岩体结构面的优势产状和几何信息是评价岩体结构面发育的重要指标,而传统的罗盘测量方法往往无法测量高陡边坡和危险边坡,且无法精确获取岩体结构面几何信息等。三维激光测量技术可以远距离获取裸露岩体坡面的高精度三维激光点云数据,进而可获取结构面的几何信息和实现全自动模糊群聚统计分析。对高精度激光点云数据进行三角网重构,计算重构的三角网平面方程的法向向量及产状,利用模糊C平均群聚方法对结构面产状进行群聚分类,并采用不同颜色表示结构面的群聚分类结果。在此基础上应用IDL语言编制基于海量激光点云数据的岩体结构面自动统计分析软件FSS,将该方法应用于怀柔桥梓镇一裸露岩石边坡结构面优势产状的统计分析中,统计结果表明,该方法具有快速和远距离测量的优点,且结构面群聚分类结果可靠、合理。     

基于三维激光扫描技术的岩体结构面智能识别与信息提取

岩体结构面几何参数是评价岩体稳定性与渗流特征的重要研究基础。采用三维激光扫描技术,获取岩体露头点云数据,利用改进的区域生长法与解析几何理论,实现了岩体结构面智能识别与信息提取。研究结论如下:(1)通过对区域生长法进行改进,引入节点法向量判别指标,设置平整性检测阈值_1与区域生长阈值_2,可以有效地进行岩体结构面的智能识别。基于提出的信息提取算法,获取了识别结构面的产状、间距与尺寸信息;(2)选取不同的平整性检测阈值_1与区域生长阈值_2,研究了阈值对识别结果的影响规律,并提取了阈值选取的一般建议。通过规则平面与公路边坡两实例应用分析,对所提方法的可靠性进行了验证。     

岩体结构对大型地下挖掘稳定性的控制作用

岩体结构是地质年代形成和变动的结果.它反映了裂隙的密度并控制大型地下挖掘工程顶部岩体的力学性能.文章以溪洛渡水电站地下工程为例,根据断裂分布情况的研究对岩体进行分类.采用结构力学方法和UNWEDGE程序讨论了单个裂隙,成组裂隙和岩石碎块情况下顶部的稳定性来得到临界稳定厚度和可能失稳岩决的特点,可以为挖掘和支撑工作提供有益的指导.     

Rock mass characterization and assessment of block-forming geological discontinuities during caving of primary copper ore at the El Teniente mine, Chile

The primary copper ore at the El Teniente mine is very competent and massive. It is a rock with almost no open discontinuities. Nevertheless, there is a high frequency network of small scale veins coupled with widely spaced faults. A research investigation was implemented to determine what discontinuities are the most relevant in the rock mass disassembly process during cave mining. Rock mass characterization was undertaken at four different scales within the rock mass, in particular the block-forming discontinuities were characterized by studying a significant number of blocks at the caving draw points. Two relevant discontinuity characteristics have been found. The data suggest that discontinuities having approximately less than 1/3 of hard minerals as infill and thicknesses greater than or equal to 2 mm are weaker and more likely to define blocks during caving and the subsequent comminution process. The infill characteristics have been used to characterize rock mass quality in different sectors, and the results are in accordance with actual observations at the mine site.     

Correlation of the Hoek–Brown failure criterion for a sparsely jointed rock mass with an extended plane of weakness theory

An appropriate estimate of rock mass strength is necessary for the design of civil and mining structures built in or on rock. Rock mass is an inhomogeneous and anisotropic material with complex behaviour, which contains random planes of discontinuities that tend to reduce its strength. The direct estimation of this strength is practically unfeasible, due to difficulties in sampling and testing. This has led to the development of empirical failure criteria. These, express the strength of the rock mass in terms of properties of the intact rock and the discontinuities. The Hoek–Brown criterion is the most widely accepted one. However, albeit its use for many years, no experimental in situ validation with the actual rock mass strength has been demonstrated. Therefore, the Hoek–Brown criterion is investigated analytically through an extended plane of weakness theory, already validated with experimental evidence on physical specimens. Various intact rock qualities with blocky and very blocky structure are examined. The results indicate deviations in the rock mass strength predicted by the two approaches, especially when the intact rock strength is low.     

基于无人机技术获取岩体结构面信息方法研究

岩质边坡的稳定性主要取决于坡体内部结构面的发育特征和性质。获取边坡岩体内部结构面的几何信息,特别是产状数据,对于研究结构面的组合规律及进一步评价边坡的稳定性具有非常重要的意义。传统的结构面采集方法工作效率极低,且对于高陡岩质边坡,技术人员无法到达。无人机摄影测量技术具有非接触、高效率的突出优势,能够有效弥补传统方法的不足。以长春市某高陡岩质边坡为研究对象,使用无人机进行航空影像数据采集,建立边坡的三维实景模型,并提取结构面产状数据。经与现场实测代表性结构面产状数据对比可知,新方法的精度较高。该方法为快速准确评价高陡岩质边坡稳定性提供了依据。     

Simulation of cracking near a large underground cavern in a discontinuous rock mass using the expanded distinct element method

The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. A number of experimental and numerical investigations have demonstrated the significant influences of discontinuities on the mechanical, thermal and hydraulic behaviors of discontinuous rock masses, indicating that the deformation mechanism and stability of rock structures in the discontinuous rock masses depend not only on the existing discontinuities but also on the new cracks generated and thereafter keep propagating due mainly to the stress redistribution induced by excavation.In this study, an expanded distinct element method (EDEM) was developed for simulating the crack generation and propagation due to the shear and tension failures in the matrix rock blocks. Using this method, excavation simulations of deep underground caverns have been carried out on the models with differing depths of cavern and differing geometrical distributions of the existing discontinuities. Model experiments by using the base friction test apparatus were conducted to verify the proposed numerical approach. Furthermore, the support effects of rock bolts on controlling the deformations of the rock mass surrounding a cavern and movements of key blocks were evaluated by means of the EDEM approach.     

Probabilistic estimate of rock mass static and dynamic demands for underground excavation stabilisation

Excavation damage under high in situ stress depends largely upon the potential block size associated with any violent ejection. The size and shape of the dynamic instability are largely controlled by the location, orientation and extent of the pre-existing geological discontinuities. A new methodology is presented in which the rock mass demand can be expressed in terms of the mass in tonnes of unstable rock that is ejected per unit area of the excavation surface where failure occurs. A probabilistic approach has been implemented to estimate the potential rock mass instabilities and their associated static and dynamic demands. The new methodology considers that the strain energy released by the rock mass during violent stress-driven failure is largely converted into kinetic energy of ejection for blocks. The estimated dynamic demand has been favourably compared with observations of rock mass damage in a number of underground excavations.     

节理岩体结构的分形几何研究

在岩体结构宏观分区的基础上,应用分形几何的观点从三维角度对分区内的岩体结构进行了研究。应用随机不连续面三维网络模拟技术建立岩体结构统计均质区内不连续面的概化模型,借助计算机模拟再现岩体结构;从岩体结构网络图中抽取“样本”,通过计算二维、三维样本的分形维数,表明三维分形维数等于二维分形维数加1,从三维角度表明统计均质区内岩体结构具有统计自相似性。     

岩体隧洞三维快速建模及关键块体分析

是否合理考虑工程岩体结构面的特性是衡量建立数值模型计算结果的关键。本文提出利用3DMAX三维建模功能,建立岩体隧道三维数值模型,并引入到自主开发的GeoSMA-3D系统,充分挖掘GeoSMA-3D系统的非连续结构体搜索关键块体功能。成功实现3DMAX与GeoSMA-3D系统的接口,将所建立的几何模型可以准确和顺利的导入GeoSMA-3D系统。并利用GeoSMA-3D搜索节理岩体隧道中的关键块体,为工程后续施工和支护提供参考。算例表明,利用3DMAX建立工程隧道的空间几何模型,导入模拟系统后图象表征围岩块体分布情况,并搜索出相应的关键块,系统直接给出了关键块体的体积、方位等信息,对于类似和后续岩体隧道分析具有重要应用价值。     

裂隙化岩体不连续面密度的分形研究

 不连续面密度是表征岩体内部不连续面分布特征的重要参数之一,但是岩体内不连续面的分布是随机的、不规则的,要想准确获得岩体不连续面密度的真实值是不可能的。基于现场调查的岩体露头不连续面特征,借助计算机模拟技术建立岩体不连续面分布的二维、三维随机裂隙网格模型,从数理统计学的角度计算岩体不连续面密度数值。并基于分形理论计算岩体不连续面分布的二维、三维分布特征,尝试建立岩体不连续面密度与分维数的数学关系。计算结果表明,岩体不连续面密度与分维数具有相同的变化趋势,随着不连续面分维数的增大,不连续面密度增大,不连续面密度与分维数之间存在线性关系。研究结果表明,不连续面分布的体密度和三维分形维数,可以更加综合地反映岩体内部不连续面的分布特征和空间信息及对岩体强度参数的影响,对工程应用具有更好的实际作用。且在此基础上,提出基于不连续面分布的体密度和三维分形维数的岩体等效抗剪强度指标的折减计算。     

Numerical modeling of discontinuous rock slopes utilizing the 3DDGM (three-dimensional discontinuity geometrical modeling) method

The geometry of discontinuities in a rock mass is one of the most important influences on the behavior and characteristics of that rock mass. The geometry of discontinuities largely determines the stability of the rock mass, as well as appropriate methods for reinforcing and stabilizing that mass. This study introduces the 3DDGM (three-dimensional discontinuity geometrical modeling) method, which is based on the 3DGM (three-dimensional geometrical modeling) algorithm that was developed using the Mathematica software package. The 3DDGM method provides essential input data for the stability analysis of a discontinuous rock mass using block stability assessment techniques or block modeling codes. The 3DDGM method developed in the present work was designed to model discontinuities in rock masses and to provide accurate values for discontinuity parameters (i.e., location, spacing, separation, system, orientation, etc.). This algorithm was developed to increase the accuracy of the discontinuity model based on the Heliot algorithm. The 3DDGM algorithm was tested by applying it to a real case, the sloping discontinuous rock mass at the phase 7 gas flare site in the South Pars Gas Complex in Assalouyeh, Iran, and the algorithm was successful in providing a three-dimensional model of the discontinuities in the rock mass at the site.     

规则岩体结构面的蠕变特性研究

 岩体结构面的蠕变特性研究对解决岩石力学实际问题具有很重要的意义。通过规则齿型结构面在剪切应力条件下的双轴蠕变试验,研究不同爬坡角的结构面在不同法向应力时的蠕变特性,并根据蠕变试验结果,得到结构面剪切蠕变、法向蠕变随法向应力、剪应力、爬坡角的变化规律和时效性,并选取Burgers模型来描述蠕变的剪切变形特性。在模型试验的基础上采用三维有限元程序对具有锯齿状结构面的水泥砂浆块体在荷载作用下的受力性状进行模拟分析。通过有限元分析,探讨规则齿状结构面的应力分布规律。利用ANSYS计算结果,通过最大正应力理论对结构面的破坏进行判别,从而验证在剪切试验中,齿面以拉断形式破坏。     

基于三维激光扫描的高陡边坡块体稳定性研究

艰险山区工程建设中高陡边坡块体稳定性是安全与防灾的重要问题,对艰险山区高陡边坡岩体结构面的调查是分析该问题的关键。以澜沧江某重大工程高边坡为研究对象,应用三维激光扫描技术,研究了远距离调查分析岩体结构的分析方法,分析了该高陡边坡的岩体结构面空间分布状况,统计分析了结构面的优势方向和岩石块体的分布状况,以此为基础,应用极限平衡分析方法,研究了该高陡边坡的岩石块体稳定性。