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991.
H+和有机酸对可变电荷土壤铝释放的动力学研究 总被引:4,自引:0,他引:4
利用流动搅动法研究了在模拟酸雨和低分子量有机酸条件下可变电荷土壤铝释放的动力学特征,结果表明,在pH3.5的模拟酸雨作用下,红壤和黄壤中流出液铝的浓度范围约为15~40μmol/L,铝的释放快反应来源于土壤交换性铝和有机络合态铝,铝的释放慢反应对应于含铝矿物的溶解。赤红壤和砖红壤上在0~300min内流出液铝的浓度范围约为1~5μmol/L,流出液pH值大于4.5,对H 的缓冲作用表现为阳离子交换、SO24-的专性吸附释放OH-和矿物表面的质子化;当流出液pH值小于4.5时,H 开始溶解土壤中的含铝固相,铝释放的最后浓度为20~30μmol/L。用相近pH值的有机酸溶出土壤铝的浓度比pH3.5的模拟酸雨要高,特别是在砖红壤上,开始就有大量铝的释放,其浓度为20~75μmol/L,红壤上是70~150μmol/L,随时间延长,流出液中的铝浓度分别为10~20μmol/L和20~30μmol/L。有机酸作用下铝的释放机制主要是有机酸被土壤吸附后,有机酸与位于表面晶格中的铝原子形成络合体,促进了铝的溶解;其次是有机酸的吸附掩盖了土壤表面的质子化过程,增强了酸的溶解,以及有机配体对铝的络合作用,增加了铝的释放量。不同有机酸对铝的溶出能力也有不同,其释放铝能力的大小为:柠檬酸>酒石酸>苹果酸,这取决于有机配体与铝的络合能力。 相似文献
992.
993.
现行《岩土工程勘察规范》(GB50021-2001)及《建筑地基基础设计规范》(GB50007-2002)规定,确定岩石地基承载力特征值常用方法有取岩样作室内试验和现场原位载荷试验等。软质岩的岩石试样作室内试验时,因环境条件与实地有明显的差异,试验结果多不理想,现场静载试验在实际环境条件下进行,能更好地挖掘软质岩石地基承载力特征值的潜力,减少基础工程造价。 相似文献
994.
Infiltration data were collected on two rectangular grids with 25 sampling points each. Both experimental grids were located in tropical rain forest (Guyana), the first in an Arenosol area and the second in a Ferralsol field. Four different infiltration models were evaluated based on their performance in describing the infiltration data. The model parameters were estimated using non-linear optimization techniques. The infiltration behaviour in the Ferralsol was equally well described by the equations of Philip, Green–Ampt, Kostiakov and Horton. For the Arenosol, the equations of Philip, Green–Ampt and Horton were significantly better than the Kostiakov model. Basic soil properties such as textural composition (percentage sand, silt and clay), organic carbon content, dry bulk density, porosity, initial soil water content and root content were also determined for each sampling point of the two grids. The fitted infiltration parameters were then estimated based on other soil properties using multiple regression. Prior to the regression analysis, all predictor variables were transformed to normality. The regression analysis was performed using two information levels. The first information level contained only three texture fractions for the Ferralsol (sand, silt and clay) and four fractions for the Arenosol (coarse, medium and fine sand, and silt and clay). At the first information level the regression models explained up to 60% of the variability of some of the infiltration parameters for the Ferralsol field plot. At the second information level the complete textural analysis was used (nine fractions for the Ferralsol and six for the Arenosol). At the second information level a principal components analysis (PCA) was performed prior to the regression analysis to overcome the problem of multicollinearity among the predictor variables. Regression analysis was then carried out using the orthogonally transformed soil properties as the independent variables. Results for the Ferralsol data show that the parameters of the Green–Ampt and Kostiakov model were estimated relatively accurately (maximum R2 = 0.76). For the Arenosol, use of the second information level together with PCA produced regression models with an R2 value ranging from 0.38 to 0.68. For the Ferralsol, most of the variance was explained by the root content and organic matter content. In the Arenosol plot, the fractions medium and fine sand explained most of the observed variance. 相似文献
995.
996.
A.R. Selby 《Geotechnical and Geological Engineering》1999,17(3-4):351-371
Tunnelling through soils results in ground loss, causing surface settlements and transverse movements. Where the tunnel drive passes below an existing structure, it is important to estimate the effects upon the structure. However, the free ground deformations should not simply be imposed upon a structure, because the structure contributes to stiffening of the ground. A computational soil-structure interaction analysis is required, to otain detailed stress–deformation response. First, linear finite element and Lagrangian finite difference methods are used to estimate ground movements due to a tunnel in free ground, and the results are compared with values based on empirical equations. The two linear methods and an additional hybrid FE method are then used to assess with soil-structure interaction; two cases of a typical short wall and a long wall lying across the route of tunnels of different depths. The results support the validity of the hybrid method which is used to estimate interactive ground settlements for comparison with a reported case of tunnelling below a building in central London. A more detailed case study is then undertaken to assess building damage caused by gross settlements during tunnelling in mixed soils, at a site in Workington, west Cumbria. A survey allowed estimation of free ground movements. Analysis by the hybrid method on the soils plus uncracked structures indicated intolerable horizontal stresses. Re-analysis with major cracks introduced into the structures resulted in close agreement between measured and computed settlements. 相似文献
997.
Evaluation of seismic displacement demands from the September 19, 2017 Puebla‐Morelos (Mw = 7.1) earthquake in Mexico City
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This short communication presents the assessment of seismic inelastic and elastic displacement demands computed from earthquake ground motions (EQGMs) recorded in Mexico City during the intermediate‐depth intraslab Puebla‐Morelos earthquake on 19 September 2017 (Mw = 7.1). Evaluation is conducted by means of peak elastic and inelastic displacement demand spectra, inelastic displacement ratio, CR, spectra, and generalized interstory drift spectra computed for selected recording stations located in different soil sites of Mexico City, including those located in areas of reported collapsed buildings. Results of this study confirm previous observations made from interplate (subduction) EQGMs that peak inelastic displacement demands are greater than corresponding elastic counterparts for short‐to‐medium period structures, while the opposite is true for medium‐to‐long period structures. Possible basin site effects were identified from generalized interstory drift spectra. It is also shown that an equation introduced in the literature to obtain estimates of CR developed from interplate EQGMs provides also a good estimate for mean CR computed from the intermediate‐depth intraslab EQGMs. 相似文献
998.
Evaluating spatial variation of suspended sediment rating curves in the middle Yellow River basin,China 总被引:1,自引:0,他引:1
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Abstract The suspended sediment load in the middle Yellow River basin (YRB) cannot be well predicted by capacity‐based transport formulas because a large fraction of suspended sediment load is composed of wash load. This study evaluated the spatial variations of sediment rating curves (SRCs) in the middle YRB. Both power and linear SRCs were used to fit daily flow and suspended sediment concentration (SSC) historical data at 49 gauging stations throughout the middle YRB. The spatial variation in regression coefficients was investigated, and the relationship between regression coefficients and the physical characteristics of watersheds was discussed. The results indicate that SRC regression coefficients vary with drainage area and basin slope, but their responses to these parameters are remarkably different in watersheds with different underlying surfaces, which indicates the significance of sediment availability, erodibility, and grain size distribution. For power SRCs representing sediment transport in unsaturated flows, the regression coefficients are more closely correlated with the drainage area in loess regions and with the basin slope in rock mountain regions. For linear SRCs representing sediment transport in saturated flows, saturated SSCs vary with coarse (particle size > 0.05 mm) and fine (particle size < 0.01 mm) fractions in suspended sediment. The maximum saturated SSC among the different gauging stations is associated with the optimal grain size composition of suspended sediment, which has been proposed for loess regions in previous studies. This study provides theoretical support for estimating the regression parameters for sediment transport modelling, especially in ungauged basins. 相似文献
999.
1000.
Relationships between physical‐geochemical soil properties and erodibility of streambanks among different physiographic provinces of Tennessee,USA
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Erosion of cohesive soils in fluvial environments is dependent on physical, geochemical and biological properties, which govern inter‐particle attraction forces and control detachment rates from stream beds and banks. Most erosion rate models are based on the excess shear stress equation where the soil erodibility coefficient (kd) is multiplied by the difference between the boundary hydraulic shear stress (τb) and the soil critical shear stress (τc). Both kd and τc are a function of soil properties and must be obtained through in situ field or laboratory testing. Many studies have generated predictive relationships for kd and τc derived from various soil properties. These studies typically were conducted in watersheds within a single physiographic region with a common surficial geology and/or investigated a limited number of soil properties, particularly geochemical properties. With widely reported differences in relationships between τc and soil properties, this study investigated differences in predictive relationships for τc among different physiographic provinces in Tennessee, USA. Erodibility parameters were determined in the field using a mini‐jet test device. Among these provinces, statistically four unique clusters were identified from a dataset of 128 observations and these data clusters were used to develop predictive models for τc to identify dominant properties governing erosion. In these clusters, 16 significant physical and geochemical soil properties were identified for τc prediction. Among these soil properties, water content and passing #200 sieve (percentage soil less than 75 μm) were the dominant controlling parameters to predict τc in addition to clay percentage (< 2 μm), bulk density, and soil pore water chemistry. This study suggests that unique relationships exist for physiographic provinces that are likely due to soil physical‐geochemical processes associated with surficial geology that determine minerology of the cohesive soil. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献