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971.
972.
973.
除饱和砂土液化外,饱和粉土地震液化问题也是岩土地震工程中一个重要的研究课题。饱和粉土地基的地震液化及变形可以采用多种地基加固方法防治,碎石桩技术是常用方法之一。碎石桩复合地基的抗液化效应,主要是增加桩周土体的密度、利于桩体的排水以及由桩体分担地震水平剪应力(桩体减震作用)。但由于粉土的土质特性,粉土-碎石桩复合地基的抗液化特性与砂土有着明显的差异。本文结合目前国内外碎石桩复合地基抗液化研究的最新进展,对粉土-碎石桩的密实、排水减压和减震作用做了较详细的评述,最后提出了关于碎石柱复合地基抗液化特性需要进一步研究的问题。 相似文献
974.
975.
The behaviour of an embankment built on normally consolidated soft soil reinforced with deep mixing columns is studied using a coupled soil–water formulation. The numerical predictions are analysed in terms of settlements, increments in vertical effective stresses and excess pore pressures. Firstly, the effectiveness of the use of deep mixing columns is studied. Afterwards, a parametric analysis is performed to study the influence on the soil-columns system of the replacement ratio (columns’ spacing), the deformability of the embankment and columns, and the coefficient of vertical permeability of the columns. 相似文献
976.
This paper investigates two aspect of the direct simple shear (DSS) using three-dimensional finite element analysis. Firstly, the different total stress paths followed by DDS devices that impose constant cross-sectional area using a stiff external boundary, and those that use a constant total stress lateral boundary condition are explored. This is done by conducting finite element analysis of a single cubic element. It is shown that this element may be subjected to perfect simple shear using four different boundary condition types. Each boundary condition type results in the same effective stress path, but different total stress paths and excess pore pressures. The boundary condition types are related to DSS devices in use. The second aspect investigated is the fact that no DSS device can impose true simple shear conditions, as they are unable to generate the required complementary shear stress on the vertical boundaries. Full three-dimensional finite element analysis of a UWA/Berkeley type simple shear device, which has a constant total stress lateral boundary, is then presented. The results are compared to the ideal solution and effects of stress non-homogeneity on the friction angle and undrained shear strength, deduced from a standard interpretation, are established. 相似文献
977.
Industrial emissions are the major sources of heavy metal pollutions. This study investigates the anthropogenic contribution of heavy metal accumulation surrounding an industrial town in China, using the component partition method. Results show that Cu, Ni, Pb, and As have higher concentrations compared with their background levels and the industrial town has a significant impact on heavy metal accumulations in its surrounding agricultural soil. Prevailing wind direction may explain the difference of heavy metal concentration in different directions. Anthropogenic components of Cu, Ni, Pb and As, which decrease with distance following exponential functions, account for 11.4%, 6.2%, 18.5% and 7.9% of their total concentrations, respectively. The natural components are modeled as the functions of physico-chemical variables through multiple regressions. The accumulating processes of heavy metals affected by industrial activities could be explained by anthropogenic and natural components, and thus, it could provide basic information for further simulation of heavy metal accumulations. 相似文献
978.
In the initial period of mining activities in the Idrija basin (the16th and the first half of the17th centuries), Hg ore processing was performed at various small-scale roasting sites in the woods surrounding Idrija, by roasting ore in earthen vessels. The recovery rate of this method was very low; about half of Hg was lost, causing soil contamination and considerable amounts of waste material that could potentially leach Hg into the surrounding environment. The main aims of present geochemical study were to determine the contents, vertical distribution and speciation of Hg in soils at the roasting site at Frbej?ene trate in order to verify the extreme pollution of ancient Hg ore roasting sites in the Idrija area and to establish their significance in the wider spatial contamination of soils and aquatic systems. Soil sampling was performed at the area of the former roasting site. The organic matter-rich surface soil layer (SOM) and underlying mineral soil were sampled at 63 sampling locations. Mercury speciation was performed using Hg thermo-desorption-AAS to distinguish cinnabar from potentially bioavailable forms. The results indicate extremely high Hg concentrations with a maximum of 37,000 mg/kg in SOM and 19,900 mg/kg in mineral soil. The established Hg median in soil was 370 mg/kg and in SOM 96.3 mg/kg. Spatial distributions of Hg in SOM and soil showed very high Hg contents in the central area and decreased rapidly with distance. The results of Hg thermo-desorption measurements indicated the presence of cinnabar (HgS) and Hg bound to organic or mineral soil matter. A significant portion (35–40%) of Hg in the investigated soil and SOM samples was comprised of non-cinnabar compounds, which are potentially bioavailable. It has been shown that soils contain high amounts of potentially transformable non-cinnabar Hg, which is available for surface leaching and runoff into the surrounding environment. Therefore, contaminated soils and roasted residues at the studied area are important for persistent Hg release into the aquatic ecosystem. 相似文献
979.
通过现场标准贯入试验,对国道317线K205+700~K207+100段路基填方段中的淤泥质粉细砂层进行了液化判别.<公路工程抗震设计规范>(JTJ004-89)和<建筑抗震设计规范>(GB5001-2001)的计算结果均表明该砂层会产生液化.但前一规范的计算值偏大,在工程中建议使用后一规范,并以振冲密实法进行预防. 相似文献
980.