Fitting strength criteria to intact rock

Summary Rock strength data covering the full range of possible stress conditions are presented for three rocks: a granite, a limestone and a salt rock. The Hoek and Brown square root parabola and the Johnston criteria are fitted to the strength data coming from around 500 laboratory tests. The fitting procedure is facilitated by a specially built PC code, ROCKER, which is available to anyone on request.The Hoek and Brown criterion is modified through the inclusion of a third parameter to account for the low tensile strength of the salt rock. A new criterion, the Rocker function is formulated to follow strength data closely in the tension-low confining pressure region.     

Detailed comparison of nine intact rock failure criteria using polyaxial intact coal strength data obtained through PFC<Superscript>3D</Superscript> simulations

Study of intact rock failure criteria is an important topic in rock mechanics. In this study, applicability of nine different intact rock failure criteria is investigated for intact coal strength data. PFC^3D modeling was used to simulate the laboratory polyaxial tests for cubic intact coal blocks of side dimension 110 mm under different confining stress combinations. A modified grid search procedure is proposed and used to find the best-fitting parameter values and to calculate the coefficient of determination (R ²) values for each criterion. Detailed comparisons of the nine criteria are made using the following aspects: R ² values, σ ₁ ? σ ₂ plots for different σ ₃, shapes on the deviatoric plane, linearity or nonlinearity on the meridian planes. Through the comparisons of R ² values, σ ₁ ? σ ₂ plots and meridian lines, the modified Wiebols–Cook and modified Lade criteria were found to fit the intact coal strength data best. The nine failure criteria are categorized into three types based on the appearances on the deviatoric plane.     

Comparison of various pan-sharpening methods using Quickbird-2 and Landsat-8 imagery

Pan-sharpening is the process of transferring the spatial resolution of panchromatic (PAN) image to a multispectral (MS) image for producing a single image with high spatial detail and rich spectral information. In this study, PAN and MS imagery of Quickbird-2 and Landsat-8 are fused separately, using ten different pan-sharpening methods such as principal component analysis (PCA), modified-intensity hue saturation (M-IHS), multiplicative, brovey transform (BT), wavelet-principal component analysis (W-PCA), hyperspectral color space (HCS), high-pass filter (HPF), Gram-Schmidt (GS), Fuze Go, and non-subsampled contourlet transform (NSCT). The effectiveness of these techniques is assessed and compared by qualitative analysis and 14 quantitative analysis methods including bias, correlation coefficient (CC), difference in variance (DIV), relative dimensionless global error in synthesis (ERGAS), universal image quality index (Q), relative average spectral error (RASE), root mean square error (RMSE), structural similarity index method (SSIM), signal-to-noise ratio (SNR), peak SNR (PSNR), spatial correlation coefficient (SCC), image entropy (E), and gradient and quality with no reference image (QNR). The results of both analysis types show that the Fuze Go and NSCT produced the best fused image with high spatial detail and rich spectral information followed by the HPF and GS.     

Modification of rock failure criteria considering the RMR caused by joints

The aim of this study is to present a modification of the failure criteria of rock masses, separately considering the effect that the Bieniawski’s rock mass rating (RMR) has due to joints, as well as the RMR linked to compressive strength of the mass rock. This modification can be applied to three of the already existing criteria: that of Bieniawski–Yudhbir–Kalamaras, that of Sheorey, and that of Hoek–Brown, comparatively analysing the effects of the three modifications that have been proposed. The new, modified criterion will be validated with new data obtained in a marble mine exploited by means of rooms and pillars. The values observed and measured in the mine are compared to those obtained through numerical modelling of the pillars, using the Análisis Lagrangiano de Medios Continuos, Lagrangian Analysis of Continuous Media (ALMEC) program. Finally, several conclusions related to the application of these rock failure criteria to the analysis of mining excavation of rooms and pillars will be proposed.     

An analysis of failure mechanism constraints on pre-failure rock block deformation using TLS and roto-translation methods

Rockfall hazards increase the risk of train derailment along railway corridors in western Canada. In this study, repeated terrestrial laser scanning (TLS) datasets were collected every 2–3 months at three different sites along the Thompson and Fraser River corridors in British Columbia, referred to as the Goldpan, White Canyon, and Mile 109 sites. A total of 207 rockfall events occurring across all three sites between November 11, 2014 and October 18, 2016 were recorded in a database. For each of these rockfalls, pre-failure deformation was measured using a method of three-dimensional roto-translation block tracking. Each rockfall was classified by its deformation behaviour and further categorised based on failure mechanism, volume, lithology, and the roughness condition of the failure plane. Results reveal that detectable levels of deformation were measured in 33% of the total number of rockfall events using the present methods. Rotation deformation was most commonly observed in toppling failures with relatively steep joint orientations. Conversely, planar sliding blocks generally exhibited the least measurable deformation, with the majority not showing any precursory translation or rotation. It is postulated that overhanging rockfall configurations may suppress the expression of deformation in rockfall source blocks, though additional research is required to confirm this.     

Energy evolution analysis and failure criteria for rock under different stress paths

Acta Geotechnica - Triaxial loading and unloading tests on marble specimens under different stress paths were conducted to investigate the characteristics of energy evolution in rock deformation...     

Analysis of rock reinforcement using finite difference methods

Large-scale rock reinforcement offers the prospect of flexible and effective control of rock displacements aroud large open mine excavations. Although the technology of rock reinforcement is well developed, reinforcement analysis and design methods are not. Analysis is presented here for the mechanics of two models of rock reinforcement, one based on local action of a reinforcing element at a slipping joint, the other on spatially-extensive action in rock subject to diffuse deformation. The principles of some finite difference methods of analysis of stress and displacement are outlined. The performance of a code modeling spatially-extensive reinforcement is examined in a parameter study of stope hangingwall reinforcement using long, grouted cables.     

Estimation of rock physicomechanical properties using hardness methods

The purpose of this study is to investigate the statistical relationship between hardness value and physicomechanical properties of constructional and cover rocks. The definition, measurement of hardness and classification of the rocks used are very important in construction sector. From this point of view, rock hardness is one of the most important parameters for the determination of rock properties. In this study, the determination of hardness and the physicomechanical properties of constructional and cover rocks in Çukurova region was accomplished using various methods in the laboratory. Statistical relations between physicomechanical properties and hardness of rocks were also determined. High correlations were found between the hardness methods (Shore Scleroscope, Schmidt hammer hardness), which are cheap and easy to use, and other physical and mechanical properties. It was found that physicomechanical properties can be estimated using hardness methods and compared with the calculated value from different empirical equations.     

不同构造层次岩石变形准则的融合与发展

岩石变形准则对于构造地质学、工程安全等方面均具有重要的理论价值与实践意义。经典的岩石脆性变形(破裂)准则包括屈特加准则(水平直线型包络线)、库伦准则(斜直线型和抛物线型包络线)、格里菲斯准则(抛物线型包络线)等。近年来最大有效力矩准则在野外韧性剪切带观测与理论计算中都得到了广泛应用,逐渐成为岩石韧性变形的重要准则。然而,这些变形准则在应用过程中还存在一些问题,如有些准则在理论上无法解释、彼此不相协调,最大有效力矩准则在摩尔图解中尚无对应的包络线,部分准则边界条件和应用范围不清等。本文针对这些问题,结合野外实际情况和理论分析,取得了如下认识:(1)水平直线型屈特加准则在地质过程中无法实现。(2)提出了最大有效力矩准则的包络线方程为τ=-0.35(σ_n-σ_d),在摩尔图解中为一条反倾斜直线型包络线;进而将脆性变形的格里菲斯准则和库伦准则与韧性变形的最大有效力矩准则统一表述于应力摩尔图解中,使各准则彼此协调和融合。(3)初步明确了各变形准则的适用条件及所对应的构造层次:张性应力存在的构造环境(包括地壳浅表层次、水力压裂等人为张性应力环境),格里菲斯准则比较合适,以张性破裂(θ=～0°)和张剪性破裂(θ=0°～30°)为主;上地壳在一般情况下(3个主应力均为挤压应力),斜直线型库伦准则更为合适,以锐夹角共轭剪破裂(θ=～30°)为主;随着深度的增加,在中地壳,抛物线型库伦准则较合适,以锐夹角脆韧性剪切变形带(θ=30°～45°)为主;进入下地壳及以下,最大有效力矩准则更合适,以钝夹角韧性剪切变形带(θ=～55°)为主。实际地质作用过程中影响岩石变形的因素更为复杂多样,应具体问题具体分析,不能简单地对号入座。     

Groundwater classification using multivariate statistical methods: Southern Ghana

This study demonstrates the strength of R-mode factor analysis and Q-mode hierarchical cluster analysis in determining spatial groundwater salinity groups in southeastern Ghana. Three hundred and eighty three (383) groundwater samples were taken from six hydrogeological terrains and surface water bodies and analyzed for the concentrations of the major ions, electrical conductivity and pH. Q-mode hierarchical cluster analysis and R-mode factor analysis were respectively used to spatially classify groundwater samples and determine the probable sources of variation in groundwater salinity. The quality of groundwater for irrigation was then determined using three major indices. The analyses revealed two major sources of variation in groundwater salinity: silicate mineral weathering on one hand, and seawater intrusion and anthropogenic contamination on the other. A plot of the factor scores for the two major sources of variation in the salinity revealed trends which can be used in hydrogeological mapping and assist in drilling potable water boreholes in southeastern Ghana. This study also revealed four major spatial groundwater groups: low salinity, acidic groundwaters which are mainly derived from the Birimian and Togo Series aquifers; low salinity, moderate to neutral pH groundwaters which draw membership mainly from samples of the Voltaian, Buem and Cape Coast granitoids; very high salinity waters which are not suitable for most domestic and irrigation purposes and are mainly from the Keta Basin aquifers; and intermediate salinity groundwaters consisting of groundwater from the Keta basin aquifers with minor contributions from the other major terrains. The major water type identified in this study is the Ca–Mg–HCO₃ type, which degrades into predominantly Na–Cl–SO₄ more saline groundwaters towards the coast.     

Control of dynamic failure of brittle rock using expansive mortar

Acta Geotechnica - Control of rock failure under stress wave loading is challenging but important to mitigate the negative impacts of underground excavation&nbsp;on the environment (e.g., rock...     

Climatic classification of the Tibet Autonomous Region using multivariate statistical methods

A climatic regionalization of the Tibet (Xizang) Autonomous Region (TAR) is developed based on a multivariate analysis of temperature and precipitation records of two data sets from the periods 1971–1980 and 1980–1989. For these two decades 15 selected variables of the 29 meteorological stations — in total more than 50,000, partly handwritten original data — were computed. Three different statistical approaches, Cluster Analysis (CA), Factor Analysis (FA) and Discriminant Analysis (DA) were followed up. The vast expanse (1.2 million km²) and the pronounced relief of the TAR (between 500 m and 8,848 m in elevation), the low density and unequal distribution of meteorological stations, as well as uncertainties inherent in the selection of statistical methods, restricted and hampered the separation of coherent climatic subregions using multivariate statistics. However, a solution comprising of nine clusters, representing the different climatic conditions of Tibet, was found.The results of the multivariate statistical analyses were compared with traditional classification schemes published by the Chinese Academy of Sciences (CAS). The Chinese classifications from the years 1982 (CAS 82) and 1984 (CAS 84) are here presented to the scientific community of the western countries for the first time (Fig 2 and 3). The main aim of these Chinese climatic classifications in Tibet was the delineation of areas with the best climatic conditions for agricultural land-use. In comparison, the aim of this paper was to establish a new classification of Tibet's climate, mainly based on measurements of climatic elements analyzed with multivariate statistical procedures following up the approach of McGregor (1993). The Factor Analysis (FA) included the temperature factor, which explains 46% of the total variance, whereas 32% is explained by the winter moisture and 12% by the moisture factor.For temperatur zonation and, in particular, for the distribution of precipitation, the high mountain topography of Tibet is interpreted as the determining factor. The new climatic classification derived from multivariate statistics allows a more dynamic interpretation of the climatic cluster pattern. First, it shows the channelized influence of the summer monsoon along the southeast-northwest- and east-west-trending broad valleys north of the Gulf of Bengal. This is also obvious in the pattern of the temperature and moisture factors. Second, it can be supposed that a general south-trending influence of the winter monsoon, in combination with a northwest-trending influence from the Bay of Bengal leads to more irregular relief- and wind-dependent pattern, which can be estimated from the distribution of the winter moisture factor.     

基于广义Hoek-Brown强度准则的岩质边坡开挖稳定性分析

导出了广义Hoek-Brown强度准则的弹塑性矩阵计算方法,并将其用于一岩质开挖边坡施工过程模拟。同时,利用Hoek所提出的参数等效化方法对岩质开挖边坡的稳定性进行强度折减分析,揭示了开挖施工过程中边坡临界失稳模式的演变、发展过程。分析结果表明,边坡的应力-应变场、位移场、边坡的稳定性及其临界失稳模式的演变过程与采用传统的Mohr-Coulomb强度准则的发展过程是一致的,但用Hoek所提出的等效Mohr-Coulomb强度参数可能会高估边坡的稳定性。     

岩盐三轴压缩试验方法及数据处理方式的对比研究

在能源地下储存及废弃物地下处置库的设计、施工、运行中,岩盐的强度和变形特征是极为重要的参数。正确地获得岩盐的强度参数对地下储存库的设计和安全运行具有重要意义。分别选定江苏金坛和湖北江汉岩样作为试验样本,通过三轴压缩试验获得岩盐短期强度和变形的力学参数,比较并总结了以德国为代表的欧美国家与国内试验方法及数据处理方式的异同。同时介绍了德国短期强度试验确定岩盐损伤起始点的方法及其不足,提出了更为精确地确定方法并确定了金坛岩盐损伤起始点。分析发现:对于大变形岩盐,国内测量的强度数据普遍偏高,应采用横截面积修正以及科学应变代替工程应变的度量方式。     

岩石细观统计渗流模型研究(Ⅰ): 理论模型

渗流模型是岩石流固耦合研究的一个关键问题。岩石在裂纹开始产生至裂纹充分贯通前，其渗透性质受内部孔隙和不断演化的微裂纹的共同控制。目前，岩石的渗流模型一般只是针对单纯的裂隙（或裂隙网络）或孔隙建立的，因此，不能很好地描述岩石裂纹扩展演化过程中的渗透性质和现象。针对这一问题，提出了岩石细观统计渗流模型，该模型将岩石裂纹演化过程中的渗透性视为一个非线性动态过程，同时，考虑了裂纹扩展演化和孔隙渗流的共同作用。因此，该模型可用于分析岩石裂纹扩展过程中的渗透性演化。     

几种岩石强度准则的对比分析

采用常规三轴试验数据,以最小平均拟合差为评价指标定量地对比分析5种强度准则描述岩石非线性强度特征的适用性。结果表明：直线型Mohr-Coulomb准则不能描述岩石强度的非线性特征;抛物线型Mohr-Coulomb虽能描述岩石强度的非线性特征,但拟合误差较大,计算所得强度参数与事实不符,不宜使用;对于中低围压（ ）下岩石强度的非线性特征,单参数Bieniawski准则拟合精度与Hoek-Brown准则相当或稍好,拟合精度接近于指数强度准则,均优于双参数Bieniawski准则;在高围压下岩石强度非线性特征较为显著,应用单参数Bieniawski 准则或Hoek-Brown准则描述误差较大,三参数Bieniawski准则和指数强度准则拟合误差较小,可用于评价深部或特深部高应力状态下岩石的强度特征。     

多种测温方法在青海共和干热岩GR1井中的应用

干热岩钻孔温度是干热岩型地热资源评价的重要指标,目前大多数地勘工作的温度测量仪工作温度大都在180 ℃以下,然而随着干热岩钻孔深度和温度的增加,受钻孔内高温、高压的影响,出现超出仪器测温范围或测温数值不准确的情况。为此,本文利用青海共和干热岩GR1井采用BZM电子多点测温仪、MTCHT-H型测温仪以及多组温度计的方式进行了多种方法的单点测温,同时结合SKD-3000B井车测温、GRY-1型钻孔轨迹测量仪等多点连续测温方式进行对比分析。结果表明,单点测温结果更接近真实地层温度,但单点测温效率低,精度差;GRY-1型钻孔轨迹测温仪因隔热装置隔绝,温度传导效率较慢,测温结果偏低。需要进一步开发准确、有效、经济的高温井下温度测量仪器或方法。     

岩石统计渗流模型和统计损伤本构模型研究

采用Eshelby等效夹杂方法建立考虑渗流的岩石损伤本构模型是一种有效方法,但相关文献目前还极少。利用细观力学的Eshelby等效夹杂方法, 探索了考虑渗流和损伤的Helmholtz自由比能函数的确定,用连续介质损伤力学方法建立了相应的考虑渗流的岩石损伤统计本构模型,提出了考虑渗流和损伤过程的岩石破坏准则,建议了考虑损伤和应变的岩石渗透系数演化方程。与试验结果比较表明,所建立模型是合理的。