无黏性土的压缩特性及模型

我国南海神狐海域海底沉积物主要由钙质砂与无黏性土组成,其力学性质对海洋工程的稳定性具有显著影响。无黏性土的压缩特性是研究其力学性能的重要内容之一,为分析不同荷载作用下土样的压缩特性,利用高压三轴仪试验系统,开展了不同砂含量及不同初始孔隙比下无黏性土样的等向压缩试验。试验结果表明：在试验采用的高有效应力下,无黏性土具有显著的过渡土性质,初始组构难以被改变;随多孔易碎钙质砂含量的增加,土样可压缩性和压缩曲线的收敛度均增加,钙质砂的破碎显著改变了初始组构。提出可以描述含砂无黏性土压缩特性的数学模型,所含参数物理意义明确且易于确定。与不同砂土压缩试验数据对比发现,该模型对其他种类土同样具有较好的拟合度,验证了本模型的广泛适用性。与已有压缩模型的对比,验证了本模型的实用性,为无黏性土应力-应变关系的理论研究提供基础。     

膨润土防水毯破损条件下渗流特性试验研究

为了从渗流量和渗透稳定角度深入研究膨润土防水毯破损处的防渗问题,开发了由压力控制系统和模型试验系统两部分组成的渗流试验装置,建立了针对坝体防渗工程中的防水毯破损情况的渗流物理试验方法,并通过膨润土防水毯不同破损工况下的渗流试验,初步探讨了影响破损防水毯与坝身土体联合抗渗的因素。结果表明,对破损防水毯和土体的综合渗透系数的影响,孔洞大小比破损率要敏感;对于孔洞修复能力,主要的敏感的因素包括孔洞直径D及防水毯规格（材料本身性能）。在工程中要做好以下两点：（1）工程中刺破孔洞直径D小于0.5 cm,超过0.5 cm的孔洞应当做修补;（2）局部刺破率不宜大于0.5%,尽量保证防水毯接触面的平整。     

混凝土构件缺陷超声无损检测的研究

对混凝土构件进行超声无损检测,超声波的振幅参数对混凝土构件中的缺陷（裂缝）最敏感,在耦合良好和测试条件基本一致时,振幅值的大幅衰减可作为判断混凝土构件存在缺陷的主要依据。超声波的速度参数对微小裂隙不敏感,缺陷较大会引起速度值的显著下降;频率参数用于检测混凝土构件缺陷不够敏感;对混凝土构件缺陷进行超声检测,速度变化和频率变化只能作为参考因素。超声波通过裂缝与未过裂缝,波形存在明显差异,通过裂缝后,有时会出现很大周期的波列,可作为判断缺陷的重要依据。综合分析超声波运动学和动力学各参数的变化,能够提高检测的准确性。     

Caractérisation par résonance paramagnétique électronique (RPE) de quartz naturels issus de différentes sources

Natural quartz crystals coming from Madagascar, Angola, Brazil, and Spain were studied by EPR after β irradiation in order to characterise the paramagnetic centres due to impurities, and examine in which way their relative proportion could constitute a useful criterion for origin researches. In all our samples, EPR experiments revealed germanium centres [GeO₄/M⁺]° with M = Li or Na, aluminium ones [AlO₄/h]° and two titanium centres ([TiO₄/H⁺]° and [TiO₄/M⁺]°) also appeared, except for samples coming from Spain. The comparison of the relative concentrations of paramagnetic species led us on to draw diagrams that allowed distinguishing the origins of the studied samples using only EPR spectra. To cite this article: M. Duttine et al., C. R. Geoscience 334 (2002) 949–955.     

Settling of Kaolinite in Different Aqueous Environment

Settling characteristics of soils carry great importance for geotechnical engineers since sediments properties are formed during the settling of soil particles in an aqueous environment. In this study, settling characteristics of kaolinite are investigated. Different ionic strengths of NaCl, CaCl₂ and AlCl₃ were considered as a function of pH in aqueous environment of varying solid concentrations. Factors affecting the settling characteristics and fabric of kaolinitic sediments have been identified. The results of the study reveal that kaolinite settles in either flocculated or dispersed forms depending on pH and ion concentration. Flocculated settling occurs in acidic pH due to formation of flocs in edge-to-face structure with increasing positive charges at the particle edges. Dispersed settling occurs in alkaline pHs when ionic strength is low. When ionic strength is increased in alkaline pHs, kaolinite particles settle in flocculated form. Furthermore, the results show that pH has a significant role on the final sediment thickness or void ratio of kaolinite. Densely packed structures in alkaline and loosely packed structures in acidic aqueous environments are formed depending on pH level. Results also show that as the solid concentration increases, the settling rate decreases due to buoyancy effect. Finally, the zeta potential of kaolinite is correlated with the final sediment thickness or void ratio of kaolinite as a function of pH. This correlation proves that there is a good agreement between zeta potential and the final sediment thickness or void ratio, especially when the soil is settled in a dispersed form.     

Point defects and cation tracer diffusion in (Ti x Fe 1?x ) 3?δ O4 1. Non-stoichiometry and point defects

 The deviation from stoichiometry, δ, in spinel solid solutions of the type (Ti _x Fe _1−x )_3−δ O₄ with x=0.1, 0.2 and 0.25 was studied thermogravimetrically as a function of oxygen activity, a _O2, at 1100, 1200 and 1300 ^∘C. The experimental results, S-shaped curves for δ vs. log a_O2, are presented and discussed with regard to the type of point defects prevailing under different conditions in the deviation from stoichiometry. It is concluded that cation vacancies are the predominant point defects at high oxygen activities, while cation interstitials prevail at low oxygen activities. The temperature and composition dependencies of point defect concentrations are also discussed. Received: 1 October 1996 / Accepted: 15 September 2002 Acknowledgements The authors thank the US Department of Energy for support of this work under Grant no. DE-FGO2–88ER45357. This work made use of the Cornell Center of Materials Shared Experimental Facilities, supported through the National Science Foundation Materials Research Science and Engineering Centers program (DMR-0079992).     

水泥土防渗墙完整性多电极电阻率法检测研究

基于不同水灰比水泥土防渗墙成墙后较短时间内的电性变化特征,沿墙体走向利用布设在墙体上方的多个电极对设有不同缺陷的防渗墙进行了电性探测试验。防渗墙施工过程中形成的深度不够、序间接缝、桩体开叉、搅拌不匀等完整性缺陷会引起探测剖面上电异常特征变化,异常区分布位置和缺陷位置具有对应关系。2.5维有限元方法数值模拟计算结果和模型试验结果具有相同的特征,并进一步表明不同缺陷的异常特征受缺陷类型、缺陷位置的电性特征、缺陷尺寸控制。     

Water diffusion in synthetic iron-free forsterite

The kinetics of hydrogenation of dry synthetic forsterite single crystals was determined by performing experiments under hydrothermal conditions. The experiments were performed at 1.5 GPa, 1000 °C for 3 h in a piston-cylinder apparatus, or at 0.2 GPa, 900–1110 °C, for 3–20 h in TZM cold-seal vessels. The oxygen fugacity was buffered using Fe–FeO or Ni–NiO powders. Polarized Fourier transform infrared spectroscopy was utilized to quantify the hydroxyl distributions in the samples after the experiments. Hydrogenation rates were measured parallel to the three crystallographic axes from profiles of water content as a function of position in the samples. The chemical diffusion coefficients are marginally slower than in natural iron-bearing olivine for the same diffusion process, but the anisotropy of diffusion is the same, with the [001] axis the fastest direction of diffusion and [100] the slowest. Fits of the diffusion data to an Arrhenius law yield similar activation energies for each of the crystallographic axes; a global fit to all the diffusion data gave 211 ± 18 kJ mol^–1, in reasonable agreement with the previous results for natural olivine. Thus hydrogenation most likely occurs by coupled diffusion of protons and octahedrally coordinated metal vacancies. The diffusion rates are fast enough to modify water contents within xenoliths ascending from the mantle, but probably too slow to permit a total equilibration of forsterite or olivine crystals.     

颗粒材料剪胀性的微观力学分析

剪胀性是颗粒材料在加载过程中表现出来的重要变形特性。以孔隙胞元描述颗粒材料内部结构的最小单元,通过对单个孔隙胞元进行剪切受力分析,探讨了剪切过程中颗粒材料体积的改变对应力比和单个孔隙胞元形状的依赖关系,解释了排列密实的颗粒材料在剪切过程中先压缩后剪胀的微观机制。用离散元数值模拟得到了在双轴剪切过程中单个孔隙胞元形状以及孔隙胞元体积变形的演化过程。离散元数值结果表明,加载过程中孔隙胞元形状由初始各向同性到沿大主应力方向变大变长、体积变形先压缩后膨胀,并且体积变形在加载过程中存在局部化现象,体积变化大的孔隙胞元在较大变形时,排列成倾斜的窄带。综合孔隙胞元的受力分析和离散元数值结果表明,致密排列颗粒材料的剪胀性与微观尺度上孔隙胞元的几何结构及其内部的力链传递方式密切相关。     

Undrained monotonic response of sand–silt mixtures: effect of nonplastic fines

The effect of non-plastic fines (silt) on the undrained monotonic response of saturated and isotropically consolidated sand specimens prepared to various measures of their density was studied in detail through various approaches namely gross void ratio approach, relative density approach, sand skeleton void ratio approach, and interfine void ratio approach. Specimens of 50 mm in diameter and 100 mm in height were tested at a rate of loading of 0.6 mm/min for this purpose. The limiting silt content and the relative density of a specimen were found to influence the undrained monotonic response of sand–silt mixtures to a great extent. Undrained monotonic response was observed to be independent of silt content at very high relative densities; however the presence of fines significantly influenced this response of loose to medium dense specimens. Individual and combined analyses of undrained monotonic peak strengths which are closely related to the liquefaction related problems have been done in this paper to assess the variation patterns.