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91.
从水泥在水泥-水-粘土系统中水化的特点出发,阐述了湿塑性水泥土的强度形成过程,主要是依赖于水泥石的强度骨架与粘土之间的结构连接。通过实验,研究了几种外加剂对湿塑性水泥土的增强作用及其增强机理,结果表明,外加剂能改善水泥土的水化介质环境和结构粘接,可改善水泥土的稠度和强度。  相似文献   
92.
通过渗析法和水汽平衡法研究不同温度控制下干密度1.7 g/cm~3压实红粘土持水特性(SWRC:soil water retention characteristics)。试验结果表明:20℃下干密度1.7 g/cm~3压实红粘土进气值约为110 k Pa;试样控制的温度越高,压实红粘土样持水能力越低,土样进气值随着温度升高而减小,且呈线性关系;Van Genuchten(1980年)土水特征模型能很好的描述干密度1.7 g/cm~3压实红粘土持水特性曲线。  相似文献   
93.
花岗岩残积土在华南、东南沿海、南岳、新疆等地区广泛分布,前人的研究多集中在结构性及微观特性上,后循环加载、位移演化、土壤密度等因素对筋-土界面的剪切特性及加筋作用效果的影响评估研究较少。从循环试验剪切刚度这一重要参数入手,以加载次数、加载频率值、位移振幅值、土壤重度值为自变量,应用控制变量法,通过设计循环直剪试验,得到加筋花岗岩残积土的剪切应力与剪切位移、垂直位移与剪切位移关系曲线进行观察对比,结果表明:花岗岩残积土土工格栅界面剪切刚度受位移半振幅、土壤干重度影响很大,受加载频率影响很小,循环加载并没有弱化后循环界面剪切强度,剪切位移与位移半振幅呈负相关关系。  相似文献   
94.
针对上海地区软土地基特点,利用工业废渣为主要原料配制成新型土体固结材料——土体固结粉。通过室内的无侧限抗压强度及XRD试验得出其固化土的强度性能及加固机理;再通过室外原位搅拌桩施工及芯样试验进行分析,研究了土体固结粉在软土地基加固实际工程中的适用性。  相似文献   
95.
Nitrogen transformations occurring in ten soils fertilized with urea were determined during incubation in the laboratory for four weeks. Urea was applied at one rate, but with different placement methods. Urea was applied in solution, as prills with a 1 cm grid spacing and as prills with no spacing. Unfertilized soils and soils amended with KNO3 solution were included as controls.Nitrite accumulated in the majority of soils treated with urea, and the maximum nitrite concentration measured was directly related to initial soil pH. Cumulative gaseous N losses as percentages of applied N were: NH3, 0-59.6; N2, 0-4.9; N2O, 0-9.9; KMnO4-N, 0-1.3; CH3ONO, 0-<0.1. No gaseous N evolution was detected in control treatments. Gaseous N losses were correlated with soil pH (NH3) maximum NO 2 - concentration (N2, N2O, KMnO4-N) and organic C content (N2, N2O). Fertilizer placement effects were generally not significant and were small in comparison with differences between soils.
Resumo Foram determinadas, durante incubação em laboratório por quatro semanas, as transformações do nitrogênio ocorridas em dez solos fertilizados com uréia. A uréia foi aplicada a um só nivel, mas com diferentes métodos de aplicação: em solução e em grânulos com 1 cm de espaçamento de grade e em grânulos sem espaçamento. Solos não fertilizados e solos corrigidos com solução de KNO3 foram incluidos como controles.O nitrito acumulado na maioria dos solos tratados com uréia e a concentração máxima de nitrito medido foram diretamente relacionados ao pH inicial do solo. As perdas cumulativas de N gasoso tomadas em percentagens de N aplicado foram: NH3, 0-59.6; N2, 0-4.9; N2O; 0-9.9; KMnO4-N, 0-1.3; CH3ONO, 0-<0.1. Não foi detectada liberação de N gasoso nos tratamentos de controle. As perdas de N gasoso foram relacionadas com o pH do solo (NH3), concentração máxima de NO 2 - (N2, N2O, KMnO4-N) e teor de C orgânico (N2, N2O). Efeitos da aplicação de fertilizante não foram de um modo geral significativos e foram pequenos em comparação com as diferenças entre os solos.
  相似文献   
96.
Effects of soil solution on the dynamics of N2O emissions: a review   总被引:5,自引:0,他引:5  
In this review, which consists of two parts, major interactions between nitrous oxide (N2>O) and soil solution are described. In the first part, as an introduction, concentrations of dissolved N2>O in different aqueous systems are summarized. An inventory of data on maximal N2>O concentrations in soil solution (up to 9984 g N2>O-N l–1>) and in soil air (up to 8300 ppm) from literature is presented. The peak N2>O concentrations represent a N2>O supersaturation in the soil solution up to 30000 times with respect to ambient air and a soil air N2>O concentration about 25000 times higher than in the atmosphere. The main physico–chemical parameters (solubility, diffusion) controlling N2>O distribution between soil solution and soil air are outlined. The influences of cultivation practice, nitrogen turnover, water content and temperature on N2>O a ccumulation in soil solution and soil air are reviewed. In the second part some models of N2>O dynamics in soils are discussed with emphasis on N2>O transport processes. A simple qualitative scheme is developed to categorize the effects of the soil solution on N2>O dynamics in soils. In this scheme the temporary, intensive N2>O oversaturation of the soil solution is interpreted as a result of gas diffusion inhibition by water (barrier function of soil solution) resulting in an accumulation of N2>O. In addition, N2>O supersaturation is an indication that transitory much N2>O can be stored in the soil solution (storage function of soil solution). Where the soil solution flows up-, down- or sidewards it can act as a relevant transport medium for dissolved N2>O (transport function of soil solution). This scheme is applied to examples from the literature.  相似文献   
97.
In this paper efficiency of applied fertilizers under tropical conditions is examined. Understanding of the fertilizer efficiency is particularly important for the developing countries mainly because there is need for enhancement of crop yields at a reduced cost. Many of the soil, plant and climatic factors of the tropical regions that contribute to the efficiency of the applied fertilizers have been discussed. Many of the tropical soils are acidic in nature and in these soils efficiency of applied fertilizer is relatively poor, mainly because plant roots are unable to grow and function to their fullest extent in utilizing the soils available nutrients. To enhance yield potentials there is need for understanding of interaction between crop species and soil and climatic variables. Incorporation and adoptation of a suitable application time can greatly enhance efficiency of urea form of nitrogen. Research findings in tropical soils have shown that an initial broadcast application of P and subsequent band treatment is more effective than either method of application alone. Current crop yields in tropical countries are far below the known yield potentials. Such low production potentials are attributed to the lack of suitable crop germplasms and understanding of improved agronomic practices. Intensification of research activities in fertilizer use efficiency in tropical countries is suggested.Senior author formerly was a Research Advisor to EMBRAPA/IICA/World Bank Program in Brazil.  相似文献   
98.
A pot incubation method for measuring mineralization dynamics from fresh plant material was tested. The aim was to develop a method which under well-defined conditions could produce mineralization data suited for estimating model input parameters for nitrogen prediction models. The results showed that the water tension of the soil could be controlled easily and precisely by diffusion through porous ceramic cups, and that nitrogen mineralization or immobilization could be measured already after 15 days at 15°C. The results showed that for the incubated catch crop residues carbon, nitrogen and nitrate-N contents were the most important factors determining mineralization. No significant effects ould be ascribed to other parameters measured.  相似文献   
99.
被动桩中土拱形成机理的平面有限元分析   总被引:2,自引:0,他引:2  
国内外对被动桩中土拱形成机理的研究比较少,尤其针对不同土性土体中这类问题的对比研究更是少见。借助平面有限元数值方法,对粘性土与无粘性土中被动桩间的土拱形成机理作了研究和对比分析,并讨论了土拱形成过程与土拱效应随土体参数如粘聚力、内摩擦角、弹性模量、剪胀角、泊松比、桩土接触特征的变化规律。研究表明:土性不同时,土拱形成过程中桩周土体的受力和破坏形式不同;剪胀角、泊松比、桩土接触特征对桩间土拱形成机理和效应影响明显。  相似文献   
100.
The main objective of this field study was to estimate the total plant uptake of soil mineral N in maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) grown in crop rotations under different N content in Nicaragua. Secondary objectives were to estimate the fraction of the measured soil mineral N content taken up in this way, and to determine how the measured N in plant aboveground parts was related to the total mineral N uptake. A large variation in N content was obtained by using data from fertilisation experiments. Plant total N uptake was estimated as the residual N in a mass balance calculation of soil mineral N. Mineral N content in the top 0–0.3 m soil layer in the field cultivations and in tubes isolated from root uptake, and N content in aboveground plant parts were measured every 30 days. Estimated plant total uptake of soil mineral N varied considerably (2.5–14 g N m−2 30 day−1) over periods and N treatments. The range of variation was similar for maize and bean. The fraction of the soil mineral N that was taken up by the plant daily varied more in maize (about 0.03–0.12 day−1) than in bean (about 0.05–0.08 day−1). Our results suggest that monthly changes in N in aboveground plant parts were linearly related to plant total N uptake during the same period. Aboveground plant N constituted between about 55% and 80% of total uptake of soil mineral N in maize depending on period within season, whereas for bean it was more constant and smaller (about 40%).  相似文献   
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