基于反转法的O2 -CO2 输运性质预测

采用反转法计算得到了O₂-CO₂混合气体新的势能参数.在此基础上,根据分子动力学理论,计算了混合气体在零密度下的输运性质,包括黏度系数、热扩散系数和热扩散因子,计算的温度范围为273.15—3273.15 K.与实验值比较表明,计算结果可以满足实际工程应用.     

砾石掺量及侧限压力对黏土类土石混合体动力特性的影响分析

黏土类土石混合体常作为路基填料在工程中广泛应用,然而其在交通荷载作用下的动力特性方面研究较少。为此,本文以0.05 Lc(Lc为圆柱试样直径)为土体、块石分类阈值,根据土石混合体中砾石掺量、侧限压力的不同,采用自振柱仪对其在小应变(10^-6~10^-4)下的动剪切模量和阻尼比进行研究。结果表明:土石混合体最大动剪切模量随砾石掺量的增加而不断增大,且在20%~40%掺量区间内增幅最大,随侧限压力的增加而增大,且增幅逐渐变小;在应变幅值相同的条件下,动剪切模量衰变程度随砾石掺量的增加而不断减少,且在20%~40%掺量区间内减幅最大,随侧限压力的增加而减小,且减幅逐渐变小;最小、最大阻尼比随砾石掺量和侧限压力的增加而减少。结合试验结果分别从颗粒“骨架”结构性、动态结构稳定性、材料密实度、能量耗散等方面阐述块石掺量和侧限压力对土石混合体动剪切模量和阻尼比的影响机理。最后采用优化Hardin-Drnevich模型建立砾石掺量、侧限压力与土石混合体动力特性参数(最大动剪切模量、参考剪应变、最大阻尼比、最小阻尼比)之间的估算公式,以期为土石混合路基的动力设计和施工提供指导。     

虎跳峡龙蟠右岸土石混合体粒度分形特征研究

应用分维理论对虎跳峡龙蟠右岸分布的土石混合体粒度分布的分维规律进行了研究分析,建立了平均粒径与相应的分维数之间的定量关系模型。通过研究表明,土石混合体具有良好的统计自相似性,由于其本身为级配不良土,在分维曲线上表现为双重分形分布,这种特殊的分维分布与土石混合体的成因及形成过程有关。     

奉节白衣庵老苍屋新滑坡成因分析

通过对奉节白衣庵古滑坡体上发生在老苍屋附近的新滑坡的现场调查、地质钻孔勘探以及降雨坡面产流的调查情况,结合对滑坡边界的演化、渗入坡体水的软化作用等因素的分析,阐明了该滑坡发生的主要原因是降雨产流汇聚形成冲沟,而冲沟对坡体坡角的不断下切使其逐渐丧失了支撑。此外,降雨坡面的入渗增加了上覆荷载以及土石介质遇水软化的效应,也是滑坡发生的原因之一。滑坡前缘的冲沟坡降急剧下切也为滑动的持续提供了客观的地质条件。最后,对滑后坡体的治理方案进行出了初步地探讨。     

Recognition of mineralized belts and lithologic patterns in the Silver City-South Mountain region, Idaho, in terms of geochemical reconnaissance data

It seems unreasonable to use one population to fit the distribution of an element, and then to determine a threshold to separate anomalous data from background data in an analysis of geochemical data. Statistically, anomaly, background, and other geological categories may be represented by different component populations overlapping one another. Therefore, anomaly, background, and other geological categories should be distinguished from one another by distributions rather than by thresholds. This paper uses a method of decomposition of mixtures to identify observed distributions of five elements, obtained in a geochemical reconnaissance of the Silver City-South Mountain region, Idaho, into component populations. Observations have been assigned to populations and mapped; finally, these populations have been interpreted leading to recognition of both mineralized belts and lithologic patterns.during the period in which this study was carried out.     

Erosion rate of sand and mud mixtures

Erosion of mixed cohesive and noncohesive sediments is studied using the erosion test instrument SEDFlume. The sediment mixtures are composed of well-sorted quartz sand (0.25–0.5 mm) and one of the three used muds: kaolinite, kaolinite-bentonite and Mississippi River muds. The mud contents cover from 0 to 100%. The measured data of erosion rate and bed shear stress are used to examine the segmented linear, nonlinear, and exponential erosion models. The parameters of each erosion model are related to the physical properties of sediment mixtures, including clay fraction, mud fraction, mixture dry density, and mud dry density. It is found that the three models can fit well with the data, and their parameters have strong relations with the mud fraction and mud dry density, to a less extent with the clay fraction, but not with the mixture dry density.     

Mineral magnetic properties of mixtures of environmental and synthetic materials: linear additivity and interaction effects

Mineral magnetic properties have been used recently to classify and to attempt to quantify the sources of sediments through environmental systems. Linear modelling techniques could be used with a wide range of concentration-dependent magnetic measurements to quantify the sources of sediments. To investigate wider application of linear modelling techniques using mineral magnetic properties, research has been conducted using laboratory mixtures of up to six source materials, including both natural environmental materials and synthetic compounds. While six sources may seem ambitious, this figure was used as an absolute upper limit rather than giving a real prospect of mathematically unmixing six sources. It has been found that even with the most magnetically differentiable materials, large errors are encountered when modelling the sources of the mixtures. This paper investigates the causes of 'non-additivity' of certain magnetic measurements and the failure of the linear modelling of the sources of the mixtures. Possible reasons for this failure include source homogeneity, calibration and linearity of equipment, magnetic viscosity of materials and/or the changing physical characteristics of the source materials once mixed together (interaction effects). In testing linear additivity, low-frequency susceptibility is the most reliable mineral magnetic measurement, while remanence measurements suffer from a systematic error in the expected results. Results have shown that in the best controlled conditions where the sources are identified and are artificially mixed together, the results of linear modelling are quite poor and at best four sources can be 'unmixed' with reasonable success. It is suggested that interaction within the mixtures, especially when containing highly ferrimagnetic burnt environmental materials, causes some of the non-additivity phenomena.     

FRACTIONAL TRANSPORT OF SEDIMENT MIXTURES

A new method based on the Transport Capacity Fraction (TCF) concept is proposed to compute the fractional transport rates for nonuniform sediment mixtures in sand-bed channels. The TCF concept is derived from the understanding that the measurements and predictions of bed-material load are more accurate and reliable than the measurements and predictions of fractional loads. First the bed-material load is computed using an appropriate equation, then the fractional transport rates are determined by distributing the bed-material load into size groups through a transport capacity distribution function. For the computation of bed-material loads, the Ackers and White, Engelund and Hansen, and Yang equations are used in this study. Two new transport capacity distribution functions are developed for flows in sand-bed channels. The new expressions presented in this paper account for the sheltering and exposure effects that exist in mixtures. Comparisons with measured data show that the proposed method can signifi     

Characterization of Individual Rock Magnetic Components by Analysis of Remanence Curves, 1. Unmixing Natural Sediments

Natural sediments are a complex mixture of magnetic minerals with different origins and different geochemical history, each of which is called a magnetic component. Magnetic components practically never occur in isolated form, and their characterization using bulk magnetic measurements relies on the individuation of the systematic variation of some parameters within a large group of samples. These variations can be interpreted either as a mixing trend or as the result of natural processes, which affect the physical and chemical properties of the magnetic particles. An alternative approach is offered by the analysis of magnetization curves using model functions, which are supposed to represent the magnetic properties of individual components. The success of this approach relies on (1) the choice of model functions that can reproduce the natural properties of a component with sufficient accuracy by varying a minimum number of parameters and (2) on very precise and accurate measurements, which are necessary to overcome the extreme sensitivity of the method to noise. In this paper, the analysis of remanent magnetization curves proposed by Egli (2003) is applied to a large set of representative sediments from the most variable environments and to a set of artificial magnetite samples. Despite the variety of materials and natural processes involved in the formation of these sediments, seven groups of magnetic components with well-defined and consistent properties could be identified. It has been found that both lacustrine and marine sediments contain two magnetically distinct groups of magnetosomes, which react differently to changes of the redox potential. The effects of some natural processes, such as weathering, reductive dissolution and transport could be observed on the individual components.     

On the variability of the sediment concentration in currents on steep slopes: a simplified approach

Based on the analysis of the results of flume experiments and on a simplified theoretical approach, a formula is proposed for the evaluation of the total solid load in a water–sediment current. The obtained results show that the sediment concentration of the water–sediment currents gradually varies from the typical values of bed load to those typical of debris flows, even when the clay concentration in the whole current is not negligible in comparison with the total solid load. The proposed simplified approach confirms the theoretical results obtained by the application of more complex rheological models. Besides the proposed theoretical interpretation of the laboratory experimental results seems to confirm a unified view of the different types of solid transport, that has been presented elsewhere.