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利用不同浓度NaCl溶液饱和黏土,进行等向压缩试验并分析渗透吸力对等向压缩特性的影响规律。试验结果表明：渗透吸力对于黏土的等向压缩行为存在明显影响,主要体现在对初始弹性压缩线斜率、初始屈服应力的影响上。随着渗透吸力的增大,初始弹性压缩线斜率增大、初始屈服应力逐渐减小;而渗透吸力对弹塑段压缩线斜率和卸荷回弹线斜率影响不大。基于等向压缩试验结果,建立了盐溶液饱和黏土的本构模型,经过验证该模型能有效地模拟盐溶液饱和黏土的等向压缩特性。此外,该模型还可以模拟恒定等向压力下渗透吸力改变引起的试样变形。该等向压缩试验结果及所建立的模型为进一步分析及模拟化学-力学耦合行为提供了数据支持和理论基础。 相似文献
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采用滤纸法和压力板法测定不同含盐量盐渍土的土-水特征曲线（SWCC）,探讨土中含盐量对盐渍土土-水特征曲线的影响。试验结果表明,粉土中含盐量对基质吸力土-水特征曲线的影响不大。采用滤纸法测得的总吸力与基质吸力之间的差值随着土中盐溶液浓度的增加而增加,且该差值要大于相同浓度纯盐溶液的渗透吸力,其原因是由于土颗粒表面对溶液吸附作用引起的,用滤纸法测得的基质吸力土-水特征曲线处于脱湿曲线和吸湿曲线之间。采用蒸汽平衡法测定Whatman 42号滤纸在高吸力阶段的总吸力的率定曲线,使得高吸力时用滤纸法测定吸力更为精确。 相似文献
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非饱和膨胀土的土-水特征曲线研究 总被引：9，自引：2，他引：9
在干旱和半干旱地区 ,土体中含水量的变化常会引发各种工程问题。研究表明 ,非饱和土的工程性质不仅取决于土的组成、结构和应力状态 ,还与土中的吸力密切相关。非饱和土的土 -水特征曲线表达了土体中含水量与吸力的关系 ,是非饱和土研究的重要内容之一。 相似文献
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莫高窟气候干燥,窟内壁画地仗层常处于低含水率、高吸力的状态,受到洞窟环境湿度波动的影响较大。为了进一步了解湿度影响下地仗层土体中吸附水以及吸力变化特征,本文通过蒸汽吸附法测试莫高窟不同地仗层高吸力段内的土水特征曲线,并且根据测试结果分析土体中由于范德华力与毛细凝聚作用产生的不同吸力的变化特征;同时进一步利用蒸汽吸附法测试了含NaCl地仗层土水特征曲线并探讨水汽吸附过程中渗透吸力特征;此外利用热重分析方法测试地仗层土体中在范德华力与毛细凝聚作用下所吸附水分的特征。结果表明:地仗层水汽吸附过程中土体内大部分基质吸力来自于毛细凝聚作用,土颗粒分子间范德华力仅在含水率极低的情况下为土体提供比较明显的吸力,湿度影响下地仗层水汽吸附过程中土体内渗透吸力仅在外界环境湿度大于地仗层中盐分的潮解临界湿度时才比较明显;地仗层土体所吸附的水分大部分以弱结合水形式存在,并且地仗层中澄板土含量越高,弱结合水临界含水率越大。结论可以为湿度影响下的壁画病害机理以及地仗层中水汽运移等问题的研究提供理论基础。 相似文献
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采用等温条件下饱和盐渍土的固结蠕变试验研究了其蠕变特性。在元件模型的基础上,通过引入Abel阻尼器和渗透吸力后,建立了饱和盐渍土的分数阶蠕变模型,从表观现象学方面展开了含盐量与饱和盐渍土蠕变特性的相关性讨论。结合试验结果和分数阶模型,拟合分析了渗透吸力同次固结系数与压缩指数的比值 和初始剪切模量以及初始剪切应变的相互作用关系。在蠕变试验的基础上,通过不同应力水平、含盐量的试验结果对分数阶模型进行了拟合分析,并结合给出的黏度系数公式对模型的有效性进行了验证。分析结果表明：次固结系数与压缩指数的比值 随着渗透吸力的增大而增大且呈指数关系,初始剪切模量随着渗透吸力的增大而减小,初始剪切应变与渗透吸力呈现出线性关系。相比与整数阶元件模型,所提出的分数阶蠕变模型更适合于饱和盐渍土蠕变行为的预测。结合试验和模型分析结果,发现含盐量的增大促进了盐渍土的蠕变行为。 相似文献
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土-水特征曲线（SWCC）在非饱和土力学中扮有重要的角色,是非饱和土力学研究的核心问题。以西北地区黄土中含有的典型硫酸钠盐为变化因素,采用滤纸法测得了兰州黄土及不同含盐量黄土状硫酸钠盐渍土的基质吸力并绘制土-水特征曲线,通过试验测试和理论分析来解释硫酸钠盐分对黄土状硫酸钠盐渍土基质吸力的影响规律,以期为工程实践提供一定的理论依据。结果表明：相同含水率下硫酸钠盐渍土的含盐量越高,基质吸力越大。以非饱和土力学理论和表面物理化学理论为基础,考虑了土中的盐分对基质吸力的毛细部分及吸附部分的影响,得到了土中含盐量与基质吸力关系的半经验公式。利用该公式计算得到不同含盐量硫酸钠盐渍土的土-水特征曲线,计算曲线与试验曲线吻合程度较高,表明该公式可以很好地描述盐渍土中不同含盐量与基质吸力的关系。 相似文献
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以非饱和土张力计原理为基础,制作了一种新型的基质吸力量测装置,并通过实测过程的不断总结与改进,得到了一种成本低廉、制作简单、操作便利、试验快速和结果可靠的非饱和土基质吸力量测装置,以此装置测定了不同体积含水率、不同压实度和干湿循环后粉土的基质吸力变化规律,得到了不同压实度粉土的土-水特征曲线,并通过Origin软件中的Boltzmann模型进行拟合对比分析,得到了与压实度相关的土-水特征曲线,比较了不同压实度粉土的含水率变化对基质吸力的不同影响特点。试验结果表明,干湿循环对粉土的基质吸力和强度有很大影响。 相似文献
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Soil salinisation determines the distribution pattern of crop processes in irrigation districts. The research presented here was conducted in the Luohui Canal Irrigation District, which is located in the loess area of Shaanxi Province, China. A back-propagation artificial neural network (BPANN) for the soil water-salt state was established to predict soil salinity and alkalinity. The degree of influence of numerous factors on the dynamics was quantitatively determined using the default factor testing method and verified with grey relational analysis. The results show that the BPANN prediction accuracy is very high, and it can efficiently depict the comprehensive relationships between the influential factors and dynamic states. The influence of soil moisture, evaporation, groundwater salt and groundwater depth on the dynamics is significant in the region. The current irrigation method, used for many years, cannot meet the water necessities for the vegetation, causing the groundwater levels to decline and a lowering of the soil moisture zone, leading to the occurrence of serious soil salinisation. Under the action of evaporation, more salt accumulates in the upper part of the soil, resulting in extensive soil salinisation. The higher the groundwater salt content, the more salt is carried by rising capillary water, and the more the soil is salinised. If groundwater depth was to exceed the critical water table, then groundwater and salt would move to the soil surface by moisture evaporation, and salt would build up on the soil surface in this irrigation district. The interactions between each factor forms a complex coupling relationship state. 相似文献
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针对盐碱化土壤地表蒸发速率研究的不足,以表层土壤为研究对象,采用土壤蒸发试验和数学模型相结合的方法分析了溶质势对地表蒸发速率的影响。结果表明:当土壤中盐分没有沉淀结晶时,溶质势是盐分引起地表蒸发速率降低的主要原因;溶质势越低,蒸发速率下降比例越大,该下降比例与溶质势有近似线性关系,但同时还受到空气温度与相对湿度、土壤温度以及土壤基质势等因素的影响;当表层土壤存在水盐补给时,地表蒸发速率总是变化趋向于水分补给速率,但含盐土壤蒸发速率变化较慢,而且若补给水分中含盐,那么其稳定蒸发速率会低于水分补给速率。 相似文献
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This paper presents a study on osmotic suction of compacted highly plastic clays. Two different types of bentonite (i.e. Calcigel
and a bentonite from India called herein as Indian bentonite) were used. Squeezing technique was utilized to obtain soil pore-water
of the specimen. Using relationship between electric conductivity and osmotic pressure of salt solution, osmotic suction of
soil pore-water was obtained. Additional tests (i.e. total and matric suction using filter paper method and swelling pressure
using constant volume swelling pressure test) were performed. The results show that osmotic pressure of soil pore-water obtained
decreases by increasing squeezing pressure. Based on experimental result, osmotic suction of the specimen is osmotic pressure
of the first drop of extracted soil pore-water. An empirical method was suggested to determine the squeezing pressure in squeezing
technique. In addition, roles of osmotic suction in thermo-hydro-mechanical behavior of highly plastic clays were presented
and discussed in the paper. 相似文献
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Dr. Jiftah Ben-Asher 《GeoJournal》1987,15(3):267-272
The potential of the saline water for irrigation against the background of the world's food shortage is reviewed. It is shown that irrigation has improved food situation wherever it has been used. However, irrigation is always associated with salinity problems. Leaching techniques and drip irrigation suggest a partial solution for the problem. The objective of this paper is to review and examine additional solutions in order to increase the use of saline water for irrigation. A quantitative approach to further research on the use of saline water for irrigation is suggested. An analytical solution to the mass-balance equation of nutrients and salt in the soil, which includes a sink term for absorption by a plant, revealed some valuable derivatives, both for planning further research in irrigation with saline water and making decisions about fertilization and soil leaching throughout the growth period of a crop. Preliminary attempts to meaningfully increase the fertilization level of crops irrigated with saline water support the approach that was developed from one of the model's derivatives. 相似文献
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Irrigated agriculture is a clear source of non-point pollution by salts and nitrogen species. The impact of such pollution should be quantified according to specific cases. The case of the Malfarás creek basin, a sprinkler irrigation district located in the semiarid Ebro valley in northeast Spain, has been evaluated. The main crops in the district were corn, barley and alfalfa, occupying 93 % of the irrigated area. The fate of water, salts and nutrients was evaluated by a daily water balance developed at a field scale for the natural year 2010. The yearly data of the whole set of 101 irrigated fields plus the non-irrigated area compared to the measured drainage produced a basin water balance with a low degree of error. The basin consumed 90 % of the total water input of which 68 % was used for crop evapotranspiration and the rest was lost due to non-productive uses. 16 % of the incoming water left the irrigation area as drainage water. The irrigated area was responsible for 87 % of the drainage. The average volume of drained water was 152 mm year?1 for the whole basin area. The irrigated area drained 183 mm year?1. The basin exported 473 kg of salt per hectare during 2010. This value was the lowest of the sprinkler irrigation areas in the Ebro valley, mainly due to the lower soil salinity. All the crops except barley received a nitrogen surplus of 10–50 % above their needs. The extra nitrogen entered the water cycle increasing the nitrate concentration in the aquifer water (150 mg L?1) and drainage water (98 mg L?1). In 2010 the mass of nitrogen exported by drainage was 49 kg per irrigated hectare. This value is too high for this type of irrigation system and implies that 17 % of nitrogen applied as a fertilizer was lost to drainage water. The key to decreasing the nitrogen leaching and pollution that it causes could be appropriate time-controlled fertigation along with better irrigation scheduling. 相似文献
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孔隙溶液浓度及组份改变会影响膨胀土颗粒间作用力,改变微观孔隙结构,从而影响土体的物理力学特性。为此,以宁明膨胀土为研究对象,采用不同浓度NaCl溶液制备泥浆预固结重塑样开展一维压缩试验和压汞试验,研究化学作用对重塑天然膨胀土的压缩性和微观孔隙结构的影响规律。结果表明：随着渗透吸力增加,颗粒间水化能力降低,物理化学力使土颗粒由分散状态转变为集聚体状态,形成了集聚体内孔和集聚体间孔,土体表现出双峰孔隙分布特征。预固结样（压力为20 kPa）的初始孔隙比随渗透吸力增加而减小,进而导致固结屈服应力增加;但是渗透吸力对压缩性影响不大,压缩指数和回弹指数基本不变。此外,利用固结系数计算了土体的渗透系数,随着竖向压力增加渗透系数降低;当竖向压力小于200 kPa时,随着渗透吸力增加,渗透系数先增加后减小,但是竖向压力超过200 kPa后,渗透系数变化不大。分析发现,渗透吸力增加导致大孔隙增加,渗透系数增加,但同时密实度增加会导致渗透系数降低,低竖向压力下渗透性受密实度和微观孔隙结构变化耦合作用控制。 相似文献
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采用蒸馏水以及浓度不同的NaCl溶液作为浸泡溶液,对商用膨润土进行了膨胀变形试验。结果表明在相同的荷载作用下,膨胀变形随浸泡溶液浓度的增加而减小。这是因为浸泡溶液的浓度越大,溶液的渗透吸力也越大,渗透吸力的增加将引起施加在黏土颗粒上有效应力的增加,使得在外部施加荷载相同时膨润土的膨胀变形随溶液浓度的增加而减小。当压实膨润土在盐溶液中膨胀时,其有效应力pe可分为两部分,即施加荷载部分p和渗透吸力部分p。对于浸泡于蒸馏水和NaCl溶液中的膨润土试样,其膨胀后的蒙脱石孔隙比em与有效应力pe之间的关系可采用同一关系曲线表示,此时施加于黏土颗粒上的有效应力的渗透吸力部分p=(p/)0.66。 相似文献
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季节冻土区特殊的温湿环境造成盐渍土累积变形是导致众多工程问题的主要原因,但其变形破坏机理尚不十分明确。通过配制不同含盐量的粉土开展冻融循环试验,研究试验过程中温度、未冻水含量、孔隙水压力、基质吸力和位移的变化规律。结果表明：孔隙水压力和基质吸力对土体温度敏感,对土体变形有重要影响。类比于非饱和土有效应力原理,给出了冻结盐渍土的有效应力方程,将土体变形分为温度应变、盐胀、冻胀、溶陷、融沉和残余应变,很好地解释了冻结盐渍土的变形机理。研究了含盐量对土体变形的影响程度,发现低含盐量时土体应变以冻胀和融沉为主;随着含盐量的增加,盐胀和溶陷的贡献越来越大;而含盐量为1%时土体变形最小,表明适当控制含盐量可有效抑制土体变形。 相似文献
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为了解环渤海低平原微咸水灌溉的土壤容盐能力问题,对大量野外监测和采样测试数据进行了研究。结果表明,该平原的土壤盐分剖面分布特征具有表聚型、中聚型和底聚型3种类型,其与蒸发、降水或灌溉入渗影响和潜水位埋深变化相关。不同聚型剖面形成的水动力特征各不相同：表聚型土壤盐分剖面的水势梯度指向地表,其绝对值远大于1.0 cmH2O/cm;中聚型土壤盐分剖面上部的水势梯度指向地下水面,剖面下部的水势梯度指向地表;底聚型土壤盐分剖面的水势梯度指向地下水面,水势梯度大于1.0 cmH2O/cm。表聚型土壤盐分剖面不利于微咸水灌溉农田和作物生长。 相似文献
18.
以河套灌区永联试验区的六队六八斗渠控制区域为研究区域,采用荷兰Wageningen农业大学开发的SWAP(Soil Water Atmosphere Plant)模型,模拟分析了引水减少条件下的田间水均衡要素变化规律。结果显示蒸散发量占总耗水量的比例在90%以上,验证了河套灌区的耗水类型是以垂向的蒸散发为主。随着引水量减少,模拟的相对产量也显著降低。可见,当灌区年平均引水量从52亿m3减少到40亿m3时,现有种植结构下的作物产量将会受影响。因此,引水减少后的种植结构和灌溉制度需适度调整。 相似文献
19.
The soil fabric plays an important role in complex hydromechanical behaviour of the expansive soils. This article addresses the influence of the wetting and drying paths on the soil fabric of compacted bentonite and silt mixtures at two different initial dry densities corresponding to loose and dense states. To obtain the hydric response of the soil, two suction imposition techniques were used: osmotic technique for the suction range less than 8.5 MPa and the vapour equilibrium or the salt solution technique for the suction range between 8.5 and 287.9 MPa. Additionally, the soil fabric analysis was performed using mercury intrusion porosimetry (MIP) and nitrogen gas adsorption (BET) techniques. The dense samples produced cumulative swelling strains during the suction cycles, while shrinkage was observed for the loose samples. The suction cycles induced an equilibrium state indicative of the elastic behaviour of the samples. The soil fabric analysis showed that regardless of the soil's initial state (loose or dense), the samples obtained the same soil fabric at the equilibrium state. The experimental results illustrated also the existence of an elastic void ratio (e0el) where the compacted soils at this state present an elastic hydric behaviour during the successive suction cycles. 相似文献
20.
Soil suction is the most relevant soil parameter for characterization of the swell behavior. An attempt was made to predict swell pressures from soil suction measurements. In this study, Na-bentonite was mixed with kaolinite in the ratios of 5, 10, 15, 20 and 25% of dry kaolinite weight to obtain soils in a wide range of plasticity indices (i.e. 30, 50, 68, 84 and 97%). Suction measurements using thermocouple psychrometer technique were made on statically compacted specimens. The dependence of soil suction on water content, dry density and bentonite content was examined. Soil suction was correlated to the soil properties, namely, water content, plasticity index, dry density, cation exchange capacity and specific surface area using multiple regression analyses. The correlations revealed a simple regression equation for a quick prediction of soil suctions from easily determined soil properties. In order to investigate soil suction versus swell pressure behavior, the results of standard constant volume swell tests (ASTM, 1990) performed on statically compacted samples of these clay mixtures were used. A linear relationship was established between the logarithm soil suction and the swell pressure. It was also found that an experimental relationship which would directly relate the initial soil suction to the swell pressure can be established. 相似文献