岩体节理面的力学效应研究

简易纵剖面仪和Ｒｙ—ＪＲＣ尺为定量统计研究岩体节理的表面形态和粗糙度系数提供了有效的量测工具．本文根据简易纵剖面仪在某一节理面上野外现场绘制的１０２３条不同方向、不同取样长度的节理表面轮廓曲线的实测统计资料,系统、定量地分析了节理表面形态的各质异性、各向异性和非均一性;运用ＪＲＣ—ＪＣＳ模型讨论了岩体节理力学参数的各质异性效应、各向异性效应、非均一性效应、评定长度效应、几何形状效应和法向应力效应等问题．在此基础上,提出了按岩性定向统计研究节理表面形态、估测节理粗造度系数和估算岩体节理力学参数的科学思路．文末对正确运用ＪＲＣ—ＪＣＳ模型估算岩体节理力学参数的有关注意事项作了简要说明．     

基于广义RQDt的岩石质量空间分布规律研究

自然界中的岩石通常含有大量复杂交错的结构面,造成岩石质量在三维空间中存在明显的各向异性。作为评价岩石质量的重要参数,岩石质量指标(广义RQDt)被广泛应用于岩体工程。结合三维裂隙网络模拟法和测线法,对岩体质量在三维空间不同方向上的分布规律进行研究:首先根据研究域岩体的裂隙统计参数及分布规律,利用Monte-Carlo法生成三维随机裂隙网络;然后通过在研究域内布置监测点和测线的方式来计算监测点处RQDt值随空间方位的变化,得到岩石质量空间分布图,以此来直观描述岩体质量沿空间不同方向的分布。将该法应用于某工程坝区岩体质量评估,表明该方法简单且具有较强的实用价值,可较全面描述岩体质量在空间方向上的分布规律。     

节理岩体蠕变特性研究

在已知岩石和节理蠕变规律的前提下,推导了节理岩体蠕变模型的一般表达式。假定岩石体积变形和节理法向压缩变形为弹性变形,忽略节理的剪胀现象,认为只有岩石畸变和节理剪切滑移与时间有关,从而推导了含三组相交节理的岩体蠕变模型及其参数。根据反演出的岩石和节理蠕变模型,计算了含三组相交节理的岩体在单轴应力作用下一些节理参数对岩体单轴蠕变的影响。分析表明,节理间距、剪胀系数以及节理夹角都对岩体的单轴蠕变变形有明显影响。节理间距越大,剪胀系数越大,节理夹角越小,节理岩体的单轴蠕变柔量也就越小,岩体的蠕变变形也越小。     

岩体节理体积频率的计算方法及工程应用

利用Monte-Carlo原理进行三维结构面网络模拟是研究岩体内节理面发育规律最常用的技术手段,节理体积频率(v)则是影响结构面网络模拟正确与否的关键参数之一,需要根据野外实测节理线频率()进行换算。利用三维结构面网络模拟程序,提出了基于线频率反演节理体积频率的新思路。首先赋给某组节理一个初始体积频率,利用三维结构面网络模拟程序,生成只包含该组节理的三维网络模型样本,计算此模型中该组节理在测线方向上的线频率,不同体积频率(v)对应不同线频率(),进而可建立两者的函数关系,最后将测线方向上该组节理的线频率带入该函数即可确定其体积频率。以贵州省息烽县鱼简河水库坝址区岩体为例,按照上述思路根据测线法统计数据计算了节理体积频率,结果表明v与之间呈现出高度的线性关系。当节理圆盘半径服从对数正态分布时,v与max 的比值约为0.4~1.0,而当节理圆盘半径服从负指数分布时,v与max 的比值约为1.3~3.5。最后依据《工程岩体分级标准(GB50218-94)》 表3.3.1、 表3.4.3和 表3.4.4,分别基于线频率和体积频率对鱼简河水库坝肩岩体完整性进行了评价,结果表明,后者评价结果的可信度比前者高。     

岩体强度的各向异性研究

本文运用断裂力学理论推导了含节理岩体的初裂强度公式,定量地讨论了节理方向、长度对岩石强度的影响,阐明了节理岩体强度各向异性的实质。通过证实,本文所建立的公式具有很强的适用性和较高的可靠性,可用于实际的工程岩体稳定性评价。     

岩体裂隙的空间变化性和地质统计学模型

本文运用多种地质统计学方法分析了岩石节理的空间变化性,并建立了节理方位、密度和长度参数的完整模型、通过对这些典型参数空间变化性的量测以及对交差图的分析,按无偏最小估计方差(即克立格方差)估计的克立格方法建立模型.运用普通克立格法建立局部块段节理的确定性模型以服务于某露天矿的论证,而且采用这种确定性模型能够进行边坡稳定性、块度和水力渗流系统等各种岩土工程分析.用克立格估计值和实际量测值之间的对比来检验岩体节理模型,其结果是肯定的.同时还发现节理参数的局部统计特征与其整体统计特征明显不同.由于岩体节理在任何岩土工程分析中都起重要作用,故任何岩土工程分析都必须进行局部模型分析.     

基于三维节理网络模拟的坝基岩体结构分类研究

以金沙江白鹤滩水电站左岸坝基岩体为研究对象,开展了基于三维节理网络模拟的坝基岩体结构分类研究。根据节理的分组分布和密度分布进行统计均质区分段,以分段为单位建立基于统计学和概率论的三维节理网络模型。在三维节理网络模型的模型正面、模型侧面和模型顶面上分别沿形心等角度布置模拟测线,将3个正交平面上54条模拟测线的RBI均值定义为三维等效岩体块度指数RBI3D,以RBI3D作为评价指标开展坝基岩体结构分类。结果表明：左岸第10梯段坝基岩体的完整性相对较好,其中整体块状占53.3%,块状占26.7%,次块状占20.0%,分析结果与实际地质情况相符。该方法充分考虑了节理分布的空间各向异性,并采用单一定量指标作为岩体结构的分类依据,兼顾了科学合理性和工程实用性。     

基于离散裂隙网络模型的节理岩体渗透张量及特性分析

节理岩体几何结构非常复杂,研究其渗流特性对于指导含水岩层稳定性分析具有重要价值。应用离散裂隙网络模型DFN方法,基于VC++6.0软件平台,建立了平面渗流分析方法,分析了节理岩体不同几何分布情况下的渗透率张量特征,通过定义渗流定向性系数对岩体渗流的定向性特征进行了定量分析。结果表明：单组节理岩体渗流具有明显的各向异性特征,渗流定向性随着节理角度变化显著;节理随着节理贯通性增加,节理渗透率呈现对数增加趋势;两组节理情况下,各向异性特征随着节理组间夹角变化;两组节理岩体渗流特征研究中,正交分布下,岩体仍存在各向异性,但渗流定向性系数较低;当节理倾角服从正态分布时,随着节理倾角标准差增大,渗透率增加;两组节理夹角不同时,节理渗透主方向倾角随着夹角增大而相应增大,基本沿两组节理夹角方向的角平分线方向。     

基于微结构张量理论的柱状节理岩体各向异性强度分析

复杂的结构面是控制岩体力学性质的主要因素,由结构面引起的岩体各向异性一直是岩体力学研究的热点问题。柱状节理是一类特殊的岩体地质结构面,具有强烈的各向异性特性,微结构张量理论是目前国际岩石力学领域一种较有效地探讨结构面各向异性问题的新方法。材料的微结构张量和加载向量是微结构张量法描述的两个重要参量。采用多组节理面局部坐标系与整体坐标系的投影关系,定义了材料的微结构张量计算方法,引入各向异性参数ψ表述微结构张量在加载方向的投影,将其引入Jaeger针对岩体沿节理面滑动破裂提出的基于Mohr-Coulomb强度准则,得到了多组节理岩体的各向异性强度准则。同时,结合白鹤滩坝址区的柱状节理特性,分析柱状节理引起的各向异性对坝址区稳定性的影响     

岩体工程特性研究中弹性波速参数取值方法探讨

工程岩体的各向异性特征导致了弹性波速的各向异性。因此，在岩体工程特性研究、岩体质量评价等方面，应注意合理地应用岩体弹性波速资料。笔者分析了岩体波速的各向异性特征，并指出：由于波速各向异性的存在，在岩体完整性系数计算中，岩体波速应取不同方向波速的几何平均值。当利用文中所给公式进行岩体孔隙率计算时，建议波速取最小值；在进行节理、裂隙发育的优势方向判断时，则取不同方向的波速值分别进行计算；当计算弹性模量时，必须取与岩体受力方向相一致的波速值。并给出了利用波速进行有关参数计算的实例。     

Rock quality designation-fracture intensity index method for geomechanical classification

Rock quality designation (RQD) is a simple and effective way of rock mass classification from surface scanlines or preferably borehole measurements. A major drawback in its classical use is that only one representative RQD value is obtained from the field measurements per core run. However, it is shown in this paper that the field measurements along a scanline provide detailed information about the rock quality and the fracture intensity (FI) for a given number of joints. In order to be able to extract the complete information concealed within the field data, the RQD-fracture index diagram concept is proposed and applied to actual field scanline measurements from England. The basis of the suggested procedure is to obtain a series of all possible RQD and FI values from given intact length measurements. This procedure provides additional information as to the local zones of heterogeneities within the rock mass and a new way of rock classification on the basis of the combined effects of RQD and FI. It is also possible to calculate percentages of different rock qualities within the same rock mass.     

岩体等效变形参数研究

岩体变形参数的确定对岩体稳定性模拟至关重要.提出了确定规则裂隙和不规则裂隙岩体等效变形参数的一种模型, 探讨了岩体等效变形参数的规律.通过对不考虑渗流-应力耦合时岩体等效变形性能的研究, 可以发现岩体的等效变形参数不仅与各组结构面的几何形态、结构面变形参数、岩块变形参数等有关, 而且与不同组系结构面间的交切形态有关.岩体的REVs具备以下几点规律: 首先REVs具有多尺度效应和不确定性.其次, REVs与结构面各几何形态要素之间有如下关系: 平均迹长越大, 平均间距越小, 方向角的方差越大, 结构面分布越凌乱, REVs的取值越小.REVs与岩块、结构面变形参数之间有如下关系: 结构面变形参数与岩块变形参数的差异程度对REVs的取值没有明显影响, 但是不同组系结构面或是同一组中的各条结构面, 其变形参数差异越小, REVs的取值将越小.      

Bias Correction for View-limited Lidar Scanning of Rock Outcrops for Structural Characterization

Lidar is a remote sensing technology that uses time-of-flight and line-of-sight to calculate the accurate locations of physical objects in a known space (the known space is in relation to the scanner). The resultant point-cloud data can be used to virtually identify and measure geomechanical data such as joint set orientations, spacing and roughness. The line-of-sight property of static Lidar scanners results in occluded (hidden) zones in the point-cloud and significant quantifiable bias when analyzing the data generated from a single scanning location. While the use of multiple scanning locations and orientations, with merging of aligned (registered) scans, is recommended, practical limitations often limit setup to a single location or a consistent orientation with respect to the slope and rock structure. Such setups require correction for measurement bias. Recent advancements in Lidar scanning and processing technology have facilitated the routine use of Lidar data for geotechnical investigation. Current developments in static scanning have lead to large datasets and generated the need for automated bias correction methods. In addition to the traditional bias correction due to outcrop or scanline orientation, this paper presents a methodology for correction of measurement bias due to the orientation of a discrete discontinuity surface with respect to the line-of-sight of the Lidar scanner and for occlusion. Bias can be mathematically minimized from the analyzed discontinuity orientation data.     

Rock Quality Designation Model Formulation and Simulation for Correlated Fracture Intact Lengths

An important factor in the rock quality assessment analysis from discontinuity measurements along a scanline is the correlation of intact lengths. The autorun model and first order autorun coefficient are proposed as a method for objectively quantifying intact length correlation structure and discontinuity occurrences along any scanline. Necessary definitions for the methodology are presented on a quantitative basis such as the alternative intact length percentages and experimental autorun coefficient. An expression is proposed for the number of discontinuity occurrences along a scanline depending on the scanline length, alternate intact length percentages, and the autorun coefficient. Monte Carlo simulation technique is used with a suitable autorun model to verify this expression. A mathematical expression is derived for the expected Rock Quality Designation (RQD) value by taking into account the correlation of the intact lengths. Additional simulations show the validity of the new RQD expression. With the methodology proposed much less engineering experience and judgment are required in estimating the RQD value from scanline measurements. The application of the methodology has been presented for some field data.     

Optimization of the Rock Physical Model in Tight Sandstone Reservoir

Krief model, Nur model and Pride-Lee model are usually used to calculate dry rock modulus of sandstone reservoirs, but they are not effective for tight sandstone reservoirs. Based on Krief model and Nur model, and minimizing the difference between predicted P-wave or S-wave velocities and measured velocities, we acquireed lithologic index m in Krief model and critical porosity ?_c in Nur model by Gassmann relationship. The empirical parameters used in the models are expressed as the values changing with depth, so the accuracy of Krief and Nur models to estimate the P-wave and S-wave velocities was improved, and these two models are called as the variable parameter Krief model and the variable parameter Nur model. In addition, comparing with prediction accuracy of P-wave and S-wave velocities under different constraints, we can see that the shear modulus formulas in the three models are more accurate and more suitable in the tight sandstone reservoir. Han’s relationship about K_dry and u_dry is not affected by porosity, lithology and other factors, and the paper established dry rock model by Han’s relationship and any one of the above three models. The new dry rock model was applied in the Gassmann relationship to predict S-wave velocity of H8 tight sandstone reservoir in Sulige Gas Filed, Ordos Basin, which improved the accuracy of predicting S-wave velocity. At the same time, lithology index m in Krief model, critical porosity ?_c in Nur model and consolidation parameters c in Pride-Lee model which are corresponding to each sample can be obtained. The values of these parameters can reflect lithology difference, pore structure, compaction degree and other characteristics, which indicate the geological characteristics of the reservoir.     

基于三维激光点云技术的岩体结构面智能解译

准确、高效、全面获取岩体结构面信息,对岩体的稳定性分析有着重要的意义.采用三维激光扫描设备进行岩体数据采集,基于岩体点云模型提出了结构面自动识别方法.通过对Ransac算法进行改进,引入了新的采样方法和评分准则,大大提升了Ransac算法的计算效率和提取精度,使之更好地适应粗糙不平的岩体点云数据;基于改进的Graham Scan算法可以精准描绘出结构面的凸凹边界,进而精细化计算出结构面尺寸.基于以上算法研发了结构面识别程序RDD（ransac discontinuity dtection）,并且采用了两组标准几何体数据和一组岩体数据对程序进行测试.结果表明,标准几何体产状误差在1°以内,实际岩体最大误差在6°以内,结构面尺寸最大误差率为0.278%,满足工程限定的误差要求.      

Numerical Homogenization of Jointed Rock Masses Using Wave Propagation Simulation

Homogenization in fractured rock analyses is essentially based on the calculation of equivalent elastic parameters. In this paper, a new numerical homogenization method that was programmed by means of a MATLAB code, called HLA-Dissim, is presented. The developed approach simulates a discontinuity network of real rock masses based on the International Society of Rock Mechanics (ISRM) scanline field mapping methodology. Then, it evaluates a series of classic joint parameters to characterize density (RQD, specific length of discontinuities). A pulse wave, characterized by its amplitude, central frequency, and duration, is propagated from a source point to a receiver point of the simulated jointed rock mass using a complex recursive method for evaluating the transmission and reflection coefficient for each simulated discontinuity. The seismic parameters, such as delay, velocity, and attenuation, are then calculated. Finally, the equivalent medium model parameters of the rock mass are computed numerically while taking into account the natural discontinuity distribution. This methodology was applied to 17 bench fronts from six aggregate quarries located in Tunisia, Spain, Austria, and Sweden. It allowed characterizing the rock mass discontinuity network, the resulting seismic performance, and the equivalent medium stiffness. The relationship between the equivalent Young’s modulus and rock discontinuity parameters was also analyzed. For these different bench fronts, the proposed numerical approach was also compared to several empirical formulas, based on RQD and fracture density values, published in previous research studies, showing its usefulness and efficiency in estimating rapidly the Young’s modulus of equivalent medium for wave propagation analysis.     

Regional fracture network permeability using outcrop scale measurements

Estimating the hydraulic properties of fractured aquifers is challenging due to the complexity of structural discontinuities that can generally be measured at a small scale, either in core or in outcrop, but influence groundwater flow over a range of scales. This modeling study uses fracture scanline data obtained from surface bedrock exposures to derive estimates of permeability that can be used to represent the fractured rock matrix within regional scale flow models. The model is developed using PETREL, which traditionally benefits from high resolution data sets obtained during oil and gas exploration, including for example seismic data, and borehole logging data (both lithological and geophysical). The technique consists of interpreting scanline fracture data, and using these data to generate representative Discrete Fracture Network (DFN) models for each field set. The DFN models are then upscaled to provide an effective hydraulic conductivity tensor that represents the fractured rock matrix. For each field site, the upscaled hydraulic conductivities are compared with estimates derived from pumping tests to validate the model. A hydraulic conductivity field is generated for the study region that captures the spatial variability of fracture networks in pseudo-three dimensions from scanline data. Hydraulic conductivities estimated using this approach compare well with those estimated from pumping test data. The study results suggest that such an approach may be feasible for taking small scale fracture data and upscaling these to represent the aquifer matrix hydraulic properties needed for regional groundwater modeling.     

Determination of Discontinuity Size Distributions from Scanline Data

Summary The paper outlines a new method for estimating the distribution form, and mean size, of discontinuities from scanline data. By assuming that the discontinuities are circular discs it has been possible to apply existing solutions for the distributions of censored semi-trace lengths sampled by a scanline at an exposed rock face. These solutions have been implemented by numerical quadrature in a standard Excel spreadsheet, with solution optimisation achieved with Solver. Problems caused by a singularity in the integration were overcome by applying an integration offset parameter. A trigonometrical substitution for removing this singularity is also outlined. The numerical quadrature strategy was validated by comparison with the analytical solution for the uniform distribution, and by comparison with the results of an extensive geometrical simulation of the stereological process. A new distribution, here named the Wicksell distribution, has been identified. This distribution is characterised by the fact that the distribution of disc diameters and the distribution of complete traces on a cutting plane are identical. Two examples, based on real scanline data, are presented to illustrate the practical application of the new methods.     

基于Hoek-Brown准则确定核电工程场地岩体力学参数

岩体与岩石的力学强度之间既有内在联系又存在明显的差异,场地岩石力学指标对于评价场地岩体的力学特性至关重要。以三门核电场地为研究对象,在室内岩石力学试验的基础上,结合野外地质调查,综合考虑岩体结构特征和应力分布状态等因素的影响,引入定量描述岩体结构特征和风化程度的地质强度指标（GSI）,采用Hoek Brown强度准则估计岩体力学参数,同时与岩体地质力学分类法（RMR）计算得到的岩体力学参数进行对比分析。基于GSI的Hoek-Brown法得到的中等风化凝灰质砂岩、微风化凝灰质砂岩和微风化安山玄武岩岩体的c值分别为4.03、6.20、6.10 MPa,φ值分别为31.96°、34.37°和33.87°。基于RMR评分的Hoek-Brown法得到的c值分别为4.42、6.44、7.24 MPa,φ值分别为28.92°、32.43°和34.51°。研究结果表明,采用Hoek-Brown准则确定的核电场地岩体力学强度指标比较合理,得到的岩体力学指标可以作为核电站基础设计的重要依据。