Box fractal dimension as a measure of statistical homogeneity of jointed rock masses

A written computer programme to estimate the box fractal dimension (D_B) is verified by estimating D_B of the triadic Koch curve for which the theoretical D is known. The influence of a number of input parameters of the box-counting method on the accuracy of estimated D_B is evaluated using the same Koch curve. The employed size range of the applied box networks was found to be the parameter which has the strongest influence on the accuracy of estimated D_B. This indicated the importance of finding the range of self-similarity or self-affinity for the object considered to select the proper range for the box sizes and, in turn, to obtain accurate estimates of D_B. By calculating D_B for different block sizes sampled from three generated two-dimensional joint patterns, it is shown that D_B can capture the combined effect of joint-size distribution and joint density on the statistical homogeneity of rock masses. The spatial variation of D_B along a 350 m stretch of a tunnel in the shiplock area of the Three Gorges dam site is computed using the joint data mapped on the walls and the roof of the tunnel. This spatial variation of D_B is used, along with the visual geological evaluation of the joint trace maps of the tunnel, in making decisions about statistical homogeneity of the rock mass around the tunnel. The results obtained on statistically homogeneous regions were found to be quite similar to the results obtained from a previous statistical homogeneity investigation which incorporated the effect of number of joint sets and their orientation distributions, but not the spatial variation of D_B. It is recommended that the spatial variation of D_B is used, along with the results of other methods such as contingency table analysis and equal area plots, which incorporate the effect of joint orientation distribution, in addition to the geology of the site, in determining the statistically homogeneous regions of jointed rock masses.     

两种地幔对流模式下俯冲带的热结构

根据准动力学计算方案，通过采用等效热源和等效热传导系数的方法，用有限元法计算了不同俯冲角度，而俯冲速度为８ｃｍ／ａ、年龄为１００Ｍａ的俯冲带在稳定俯冲状态的热结构．计算结果表明俯冲带在接近６７０ｋｍ间断面的最低温度可达到１１００℃．全地幔对流模式热结构的计算结果表明６７０ｋｍ间断面以下可存在最低温度达１０００℃的低温区，相应于有０．７％-３．０％的Ｐ波低速异常存在．双层地幔对流模式表明，在６７０ｋｍ间断面以上可有与周围地幔相差约４００℃的水平舌状低温区存在，相应于０．５％-１．４％的Ｐ波低速异常．     

工程岩体结构面间距空间分布的ARIMA模型及应用

结构面间距是反映结构面分布特征的重要指标之一,也是工程岩体质量级别划分的重要指标之一。与传统的结构面间距定义不同,本文认为只需按组测量结构面之间的间距同样可以分析结构面分布特征,并给出了结构面类型的4类划分法,依此建立结构面序列,利用时间序列的自回归滑动平均模型建立节理间距的AR IMA模型,提出了间距序列建模和模型检验方法,并以实例印证了AR IMA模型表示间距序列是合适的。     

Comparison of rock discontinuity mean trace length and density estimation methods using discontinuity data from an outcrop in Wenchuan area,China

The equations that exist in the literature to estimate corrected mean trace length and corrected two-dimensional density of a rock discontinuity set using area sampling technique are critically reviewed. The discontinuity traces appearing in an outcrop in Yingxiu area in China are used along with rectangular windows to calculate the corrected mean trace length and two-dimensional density using Kulatilake and Wu’s equations. Similarly, circular windows are used along with Mauldon’s and Zhang and Einstein’s equation to calculate the mean trace length and Mauldon’s equation to calculate the two-dimensional density for the same discontinuity sets using the same outcrop discontinuity trace data. For both parameters, the predictions based on the rectangular window methods were found to be more accurate than that based on the circular window methods.     

Indirect determination of weighted joint density (wJd) by empirical and fuzzy models: Supren (Eskisehir, Turkey) marbles

Correct block size assessment is the most important stage for rock quarry management. Although volumetric joint count (J_v) and weighted joint density (wJd) were proposed for this purpose, simple prediction method for these indices is not encountered in literature. Due to the fact that some rock masses such as marbles contain less discontinuity, collection of representative amount of data from in situ line surveys for statistical assessments is highly difficult. For this reason, the main targets of the present paper are to apply photoanalysis approach for collecting additional discontinuity data and to obtain some simple statistical and fuzzy models for predicting weighted joint density to evaluate block size in engineering practice for marbles around Supren (Eskisehir, Turkey). In addition, a new and simple approach to predict volumetric decrease caused by chemical weathering is introduced. For these purposes, extensive field and photoanalysis studies were performed and the data obtained from both field and photoanalysis studies were assessed by regression and fuzzy approaches. The results revealed that the prediction performance of the fuzzy inference system is higher than that of the regression equation.     

Permeability of 3D discontinuity networks: New tensors from boundary-conditioned homogenisation

Two equivalent permeability tensors are defined for 3D heterogeneous media, K^p${\mathbf{K}}^p$ and K^q${\mathbf{K}}^q$, valid respectively for linear pressure and constant flux conditions at the block boundary. Both tensors are symmetric and positive-definite and the second one produces lower magnitude of directional permeability than the first one. These tensors only depends upon the internal block structure and 3D distribution of the local permeability values. On this basis, we develop first a straightforward method for evaluating the coefficients of the 2D tensor for the problem of flow through fracture traces in a cross-section, subject to linear pressure conditions. A quartzite rock mass is used as an example to illustrate this method. Then, an approximated method is proposed to build up the 3D permeability tensor of the fractured block from the ellipses within cross-sections in varied orientations.     

花岗岩中结构面分布及其在岩体质量评价中的意义

花岗岩这样的硬质岩石,其岩体质量与结构面关系极为密切。本文列举了3个建于花岗岩体的工程项目实例,主要研究其结构面的分布特征,采用的方法有现场勘查、赤平投影、结构面统计法和地应力等。结构面主要指不同规模和成因的断层、节理、岩脉、接触面和裂隙,节理为最普遍的结构面,可以用来推测地应力的方向。对通用的围岩分类指标RMR, Q, BQ和T进行了比较,利用关系矩阵发现RMR和BQ的相关性最大,其次是T值,相关性最差的是Q值。结构面的密度、方向和强度是隧道工程项目选址和设计阶段岩体分类的主要指标。     

广西龙州县金龙铝土矿地质特征及成因初探

广西龙州县金龙铝土矿是近年新发现的迭大型以上规模的堆积型一水铝土矿床.文章在分析研究区域成矿地质背景、矿床地质特征的基础上,对矿床成因及控矿因素进行了初步探讨,总结了找矿标志,认为矿源层来自晚泥盆世与早石炭世之间古侵蚀间断面上的原生铁铝岩(铝土矿);成矿经历了矿源层的形成、表生的风化岩溶作用和改造富集三个阶段;矿区外围...     

白鹤滩水电站冬春季两次极端强风天气的对比分析

利用FNL 1°×1°再分析资料和常规气象观测资料从时空上统计分析了白鹤滩水电站大风天气过程,选取2个冬春季11级极端强风个例进行对比分析,从环流形势、天气系统、地形作用、物理量场、斜温图等方面揭示了大风形成、发展的原因。结果表明:白鹤滩水电站受大风天气影响巨大,特别是冬春季,且存在明显季节差异;电站地形复杂,狭管效应显著,冷空气南下、山谷风活动、河谷狭管效应及下垫面摩擦力共同作用,导致了大风天气的发生。"2.21"过程与"3.10"过程大尺度环流形势基本一致,但冷空气位置、强度及影响时间不同,散度涡度场、水汽通量散度场及垂直速度场的分布对大风天气有较好的指示作用,强风区对应垂直螺旋度上负下正的垂直结构;还总结了斜温图中大风天气的预报指标,为预报大风天气提供了经验。