Determination of Joint Roughness Coefficients Using Roughness Parameters

This study used precisely digitized standard roughness profiles to determine roughness parameters such as statistical and 2D discontinuity roughness, and fractal dimensions. Our methods were based on the relationship between the joint roughness coefficient (JRC) values and roughness parameters calculated using power law equations. Statistical and 2D roughness parameters, and fractal dimensions correlated well with JRC values, and had correlation coefficients of over 0.96. However, all of these relationships have a 4th profile (JRC 6–8) that deviates by more than ±5 % from the JRC values given in the standard roughness profiles. This indicates that this profile is statistically different than the others. We suggest that fractal dimensions should be measured within the entire range of the divider, instead of merely measuring values within a suitable range. Normalized intercept values also correlated with the JRC values, similarly to the fractal dimension values discussed above. The root mean square first derivative values, roughness profile indexes, 2D roughness parameter, and fractal dimension values decreased as the sampling interval increased. However, the structure function values increased very rapidly with increasing sampling intervals. This indicates that the roughness parameters are not independent of the sampling interval, and that the different relationships between the JRC values and these roughness parameters are dependent on the sampling interval.     

岩体节理表面形貌的各向异性研究

本文根据激光表面仪测量的节理表面形貌数据,通过将高度分布转化为斜率分布、并对斜率分布采用频谱分析的方法,研究了节理表面形貌的各向异性特征。一般的统计参数只能给出节理表面剖线某种性质的平均测度,很难捕捉节理表面的各向异性性质。而功率谱密度全面反映了节理表面形貌中大尺度上的起伏和小尺度上的涨落,具有一般统计参数不可比拟的优越性,通过定义累计功率谱密度指数psd*的方法,定量地表征了岩体节理表面的各向异性。      

结构面粗糙度系数与采样精度的关系研究

结构面粗糙度系数（JRC）的获取过程中存在采样精度问题,为了获取合理的JRC值,本文开展了JRC剖面线采样点精度研究。选取3种岩石,每种取10个具有一定粗糙程度的结构面为研究对象,运用三维激光扫描技术获取结构面几何形貌特征并进行数字化处理。在此基础上,提取结构面选定剖面线的起伏信息,利用分形理论计算不同采样点间隔条件下剖面线的JRC值,分析JRC取值中存在的采样点间隔效应,并研究其影响因素。结果发现:JRC值受剖面线采样点间隔影响,当采样点间隔小于临界间隔值时,JRC值基本保持不变;当间隔大于临界间隔值时JRC值出现波动。采样点临界间隔值与结构面粗糙程度相关,与JRC值呈负指数函数关系,并且其关系受岩石类型影响,岩石颗粒越小两者拟合度越高。综合3种岩石得到JRC值与采样点临界间隔值关系服从y=1.8314e-0.067x的函数分布,可以此为依据进行采样点临界间隔定量取值,来消除间隔效应对JRC值的影响。该项研究成果可为结构面粗糙信息采集提供科学的方法,通过选取合理的采样点数量,保证结构面信息采集工作效率和JRC值计算精度。     

Spatial variability of flow parameters in a stratified sand

The spatial variability in porosity, hydraulic conductivity, compressibility, and various grain size fractions is analyzed for several sets of samples from the Quadra Sand. This unit is a well-sorted, medium grained, horizontally stratified sand with relatively few silt or gravel interbeds. Both random and uniformly spaced sample plans are used. The heterogeneity of the flow parameters is characterized by frequency histograms and their estimated moments, by their sample autocorrelation functions, and the estimated power spectra. Emphasis is placed on the nature of the spatial dependence between neighboring values of the flow parameters. A nearest neighbor stochastic process model is fit to the data to consider its adequacy in describing the spatial dependence within the porosity and hydraulic conductivity sequences. Even though the Quadra Sand is relatively uniform, a fairly complex spatial structure is observed. A simple monotonically decaying autocorrelation function may not adequately represent the spatial continuity. Statistical anisotropy is observed in both the extent of the spatial autocorrelation and in its functional form. Results show the importance of scale in constructing a probability model to describe the spatial variability.     

北京典型土层抗剪强度的相关性及变异性分析

新近沉积层是北京地区典型的浅部相对软弱土层,土层力学指标变异性较大.依据北京地区大量实际工程的勘察资料,采用土层分布随机场模型,对北京地区新近沉积典型地层的抗剪强度指标的空间概率特征进行统计分析,北京地区新近沉积土层的自相关距离一般为3～4 m,是比较合适的取样间距.     

基于改进遗传算法的岩体结构面幂函数模型参数辨识

沿结构面的剪切滑移是工程岩体主要的破坏模式之一,选择恰当的岩体结构面本构模型是分析岩体结构面破坏的重要一环。当前常用的结构面本构模型有指数型模型、曲线型模型和幂函数型模型,其模型参数都是根据工程实际经验或室内试验所得,不能很好的模拟实际变形情况。指数型模型得出的模拟值偏大,曲线型模型得出的模拟值偏小,幂函数型模型在较低的法向应力下能较好的模拟剪切变形过程,但在较高的法向应力下得出的模拟值偏小。为此,通过改进的遗传算法对岩体结构面幂函数模型参数进行辨识,得出由"等效参数"构成的幂函数模型。实例验证结果说明,通过改进的遗传算法辨识出的由"等效参数"构成的幂函数模型能够很好的模拟实际变形情况,能够很好的适应于不同的工程实际应用。      

Random field characterization of uniaxial compressive strength and elastic modulus for intact rocks

Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework.     

不同充填度岩石分形节理抗剪强度的数值模拟

在对岩石节理进行分形模拟的基础上,建立了岩石分形充填节理直剪试验数值分析模型,采用数值模拟方法,研究了充填度与岩石分形充填节理抗剪强度之间的关系。结果表明,随着充填度的增大,分形节理抗剪强度总体上呈非线性减小。当充填度小于1时,随着充填度的增大,分形节理抗剪强度迅速减小,节理抗剪强度受节理表面形态、充填物力学性质以及壁岩力学性质的共同影响;当充填度大于1时,节理抗剪强度主要受充填物力学性质的控制,强度参数接近于节理充填物的强度参数。      

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。     

Modelling the effect of climate change induced soil settling on jointed drinking water distribution pipes

Soil settlements related to groundwater lowering are expected to be accelerated by climate change and may damage underground infrastructure networks. A 1D mechanical model, previously developed for continuous pipelines, has been extended towards jointed pipelines to calculate the stresses and joint rotations induced by the soil settlements. From the mechanical model, curve fits were acquired that can be used to estimate the bending moments and joint rotation. The curve fits differ per soil type, joint stiffness, joint position and joint distance. The stresses calculated by the 1D mechanical model and curve fits were validated by means of 3D finite element modelling. Using the curve fits, a probabilistic approach was followed by means of a Monte Carlo method to calculate the probability of failure of the pipeline system. The effect of joints is that the pipe stresses are reduced as the joints absorb a part of the soil displacement. For the probability of failure, the pipe stresses have a larger contribution than the joint rotation, as the joint rotation remains small compared to the maximum allowable joint rotation.     

含两组交叉贯通节理岩体的强度及破坏特征分析

天然岩体中常含有多组相互交叉的贯通节理,它们的存在极大地削弱了岩体的力学性质。为了研究含两组交叉贯通节理岩体的强度及破坏特征,基于弹塑性数值流形方法,对不同应力状态下,节理倾角和节理间距不同的岩体压缩试验进行数值模拟。结果表明：岩体强度随节理倾角的变化曲线呈现出多波峰、多波谷特点,岩体强度随节理间距变化曲线符合负指数函数形式。根据节理状态,两组节理岩体的破坏模式可以分为3种：岩块破坏、沿一组节理滑移和沿两组节理滑移。两组节理均会影响岩体强度,一组起主要作用,另一组起次要作用,并且节理组之间存在相互影响。通过对数值计算结果进行回归分析,基于一组节理岩体强度预测模型,量化节理组之间的相互影响,提出适用于含两组交叉贯通节理岩体的强度预测模型。模型形式简单,使用方便,可为实际工程中正确评估岩体强度提供指导性意见。     

Ground-penetrating radar detection of small-scale channels,joints and faults in the unconsolidated sediments of the Atlantic Coastal Plain

The geological characterization of the shallow subsurface in the unconsolidated sediments of the Atlantic Coastal Plain, and other unconsolidated sediment regimes, may involve jointing, faulting, and channeling not readily detectable by conventional drilling and mapping. A knowledge of these features is required in environmental, geotechnical, and geomorphological studies. Ground-penetrating radar (GPR) may be used to routinely map these structures. Three principal shallow subsurface features are readily detectable using GPR: paleochannels, joints or fractures, and faults. The detection of paleochannels is dependent on the scale of the GPR survey and the attitude of the channel within the survey area. Channel morphological features such as scour surfaces, point bars, and thalwegs are observable. Joints and fractures are more difficult to detect depending upon size, patterns, orientation, and fill material. Vertical joints may not be visible to radar unless they are wider than the sampling interval or are filled with radar-opaque materials such as limonite. Angled joints or fractures may be distinguished by an apparent continuous reflector on the radar profile. Faulting on radar profiles may be observed by the offset of reflectors, the image of the fault plane, or the coherent interpretation of a fault system.     

Estimation of joint trace length probability distribution function in igneous,sedimentary, and metamorphic rocks

To predict the behavior of structures in and on jointed rock masses, it is necessary to characterize the geomechanical properties of joints and intact rock. Among geometry properties of joints, trace length has a vital importance, because it affects rock mass strength and controls the stability of the rock structures in jointed rock masses. Since joint length has a range of values, it is useful to have an understanding of the distribution of these values in order to predict how the extreme values may be compared to the values obtained from a small sample. For this purpose, three datasets of joint systems from nine exposures of igneous, metamorphic, and sedimentary rocks are studied. Joint trace length is one of the most difficult properties to measure accurately, but it may be possible to record other geometrical properties of exposed joints accurately; thereby, support vector machine (SVM) model is used to predict the joint trace length. SVM is a novel machine learning method, which is a powerful tool used to solve the problem characterized by small sample and non-linearity with a good generalization performance. Consequently, goodness-of-fit (GOF) tests were applied on these data. According to these GOF tests, the lognormal distribution was found to be the best probability distribution function for representing a joint trace length distribution.     

Underestimation of roughness in rough rock joints

Numerous studies have been made to improve Barton's shear strength model for the quantification of rock joints. However, in these previous studies, the roughness and shear strength of the rock joint have been underestimated especially for relatively high undulated profiles (joint roughness coefficient (JRC) >14). The main factors of roughness underestimation in rough rock joints are investigated for the proper quantification of rock joint roughness. The aliasing effect and the roughness characteristics are analyzed by using artificial joint profiles and natural rock joint profiles. A 3D camera scanner is adopted to verify the main source of underestimation when using conventional measurement methods. Shear strength tests are carried out by using two types of shear apparatus to study the roughness mobilization characteristics, which may also affect the roughness underestimation. The results of joint roughness assessment, such as aliasing and undulation of waviness, show that the roughness can be underestimated in relatively rough joint profiles (JRC>14). At least two components of roughness parameters are needed to properly represent the joint roughness, for example, the amplitude and the inclination angle of joint asperity. Roughness mobilization is affected by both the normal stress and the asperity scale. Copyright © 2008 John Wiley & Sons, Ltd.     

位移不连续模型在黏弹性节理刚度计算的应用

考虑节理质量对应力波传播的影响,运用波的位移位函数推导了谐波在厚黏弹性节理的透、反射系数计算公式,采用波形相关系数描述子波穿过黏弹性节理的波形变化,讨论具有一定厚度的黏弹性节理简化位移不连续模型的适用条件。设厚黏弹性节理模型和位移不连续模型的透射波波形相关系数为0.9时对应的节理厚度为临界厚度,岩体与节理的阻抗比对临界厚度的影响很小;临界厚度随子波中心频率增大呈负指数减小,入射角越大,临界厚度随中心频率减小得越慢。试验数据分析表明：当节理厚度为0.03 m时,采用位移不连续模型和厚黏弹性模型计算得到的节理力学参数非常接近,随节理厚度和子波中心频率增加,运用位移不连续模型的计算结果偏差越大,试验结果与理论分析是一致的。     

岩石结构面粗糙度系数尺寸效应的推拉试验研究

粗糙度系数是结构面抗剪强度的主要影响因素,然而由于结构面表面形态的复杂性,粗糙度系数尺寸效应研究并未获得较大进展。总结了结构面粗糙度系数的3种获取手段：标准剖面对比法、理论公式法、试验反分析法。在此基础上分析了3种方法在研究粗糙度系数尺寸效应方面存在的问题和困难。为了研究结构面粗糙度系数与试样尺寸的相关度,对中砂、硅粉、水泥、非引气型萘系减水剂等原材料的配比进行了研究,获得了与天然钙质板岩物理力学特性相类似的岩石模型材料,然后采用研发的结构面制作模具及其制备工艺制作了8组共176对具有不同尺寸和表面起伏粗糙程度的结构面,并利用改进的高精度岩石结构面推拉仪对结构面粗糙度系数进行了推拉试验研究和数据统计分析,结果表明：模型结构面粗糙度系数的统计均值随试样尺寸的增加而降低,但特定结构面粗糙度系数的尺寸效应规律需要根据结构面的具体表面形貌进行测试;Barton理论公式计算的结构面粗糙度系数尺寸效应变化规律与推拉试验测试规律总体上一致,但试验值与理论值有差异,且结构面试样尺寸越小,二者的差异就越大;具有特定表面形貌的模型结构面粗糙度系数也有差异,工程大尺寸岩体结构面粗糙度系数需要根据表面形貌和分布特征进行综合判定。     

岩体结构面各向异性变异系数的尺寸效应研究

岩体结构面的各向异性与尺寸效应特征对其力学性质影响较大,综合考虑两者之间的相互关系对工程岩体稳定性评价具有重要意义。全面分析不同尺度结构面的各向异性分布,提出考虑正交方向三维形貌参数的各向异性变异系数AVC3D。通过渐进覆盖法统计4组天然岩体结构面10种不同采样尺寸的各向异性变异系数及其尺寸效应规律。结果表明：各向异性变异系数均随结构面尺寸增大而减小至定值,其与结构面尺寸具有较好的负对数函数关系;通过归一化处理,各向异性变异系数与结构面尺寸呈现较好的线性函数关系,表明各向异性变异系数具有分形结构,分维数D可以实现其尺寸效应的规律统计。该方法揭示了影响结构面形貌特征方向性变化的最大有效倾角 和粗糙系数C的增长幅度会随采样尺寸增大趋于稳定的变化机制,体现了当结构面达到各向异性尺寸效应的阈值后,会呈现出稳定的各向异性规律。     

节理面按产状的模糊聚类及其优势方位的确定

分析了已有的几种对节理面按产状分组方法的不足，指出应用模糊聚类对节理进行分组的原由。为了构造模糊矩阵，矩阵中的元素取为两节理面锐夹角的余弦，即两节理面向上的单位法向矢量点积的绝对值。对某组节理面向上的单位法向量进行部分反向后，其矢量之和对应的产状即为该组节理面的优势方位。     

斜入射线弹性节理应力波传播特征的数值模拟

依据弹性波理论,应力波斜入射线弹性节理时会发生波场分解。根据入射、透射及反射各波形的不同到时,运用离散元软件UDEC模拟应力波在含倾斜节理岩体中的传播并计算其透射、反射系数,并分析其波型转换规律。应力波斜入射单节理时,模拟得到的透射、反射系数随节理刚度、入射角度的变化规律,与已有的理论解是吻合的。应力波斜入射一组平行节理时,随着节理间距的增大,其同类波的透射系数Tpp、Tss先增大后减小,最后趋于稳定值;节理条数越多,Tpp、Tss越小。此外,不同条数的节理,透射系数达到最大值的临界节理间距值基本一致,但趋于稳定时的节理间距值随节理条数的增加而逐渐增大。