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Wonsook Ha Robert S. Mansell Dilip Shinde Nam-Ho Kim Husein A. Ajwa Craig D. Stanley 《Transport in Porous Media》2009,78(1):77-99
Pre-plant application of toxic fumigants to soil beds covered by plastic film is commonly used in agriculture to control soil-borne
pathogens. Plastic mulch covers tend to physically suppress the emissive loss of gaseous fumigant to the atmosphere. When
liquid fumigant metham sodium (MS) is applied in irrigation water to field soil, it is rapidly transformed to the gaseous
methyl isothiocyanate (MITC). The gaseous MITC is a potential atmospheric contaminant, and any untransformed MS is a potential
contaminant of underlying groundwater due to the high water solubility of MS. A finite element numerical model was developed
to investigate two-dimensional MITC fate/transport under non-isothermal soil conditions. Directional solar heating on soil
beds, coupled heat and water flow in the soil, and non-isothermal chemical transport were included in the model. Field soil
data for MITC distribution, soil water content, meteorological data, and laboratory data were used to verify the model for
soil beds covered with plastic mulch. Four possible scenarios were considered: low and high drip-irrigation rates and low
and high water contents. The movement of the center of MITC mass in the soil profile was effectively simulated. The lower
drip-irrigation rate of MS yielded more extensive coverage of MITC in the plastic-covered soil bed. The lower soil air contents
due to higher soil water contents for the higher irrigation rate resulted in high concentrations of soil MITC. NRMSE (normalized
root mean square error) calculations further verified that the model predicted fumigant fate/transport well under these non-isothermal
field conditions. 相似文献
2.
建筑物内火灾烟羽流和顶蓬射流诱发的空气运动盐水模拟实验研究 总被引:3,自引:0,他引:3
盐水在清水中的扩散与火灾烟气在空气中的蔓延相似,因而可用盐水的扩散来模拟火灾烟气的蔓延;同样地,由于盐水的扩散而导致的环境清水的运动也可用来模拟烟气蔓延诱发的空气运动。基于这一原理,本文用实验的方法,研究了建筑物内初起火灾产生的烟羽流和顶蓬射流所诱发的空气运动,并对走廊空气层生长规律和运动特性进行了初步的测量和分析。所得结果基本合理,对建筑物通风排烟及疏散通道设计有帮助,从而为建筑火灾环境空气的运动的实验研究开辟了新的思路,也为火灾区域模拟提供了实验依据 相似文献
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Problems of flow through porous media in which irrigation and drainage are simultaneously taken into account are very often
encountered in connection with reclamation projects in arid zones. This article investigates the percolating flow in a soil
of finite thickness under conditions of seepage and horizontal closed drainage. The soil is drained by a system of horizontal
parallel equidistant circular pipes buried at the same depth. It is assumed that the drains are completely full of water;
the pressure head in the soil along the line of contact with the drain is equal to the elevation of its upper point, at which
there is no excess pressure. At the surface of the soil the moisture content is constant. This may be the result of a nonuniform
irrigation rate distribution. If the irrigation is uniform, the surface layer of soil is nonuniformly moistened: maximum saturation,
often supersaturation, occurs midway between the drains, while over the drains the soil is practically dry. The corresponding
problem of steady state percolating flow reduces to a boundary-value problem of the theory of analytic functions, by solving
which it is possible to determine the irrigation rate distribution needed to ensure uniform humidity of the soil surface.
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 66–71, November–December, 1986. 相似文献
4.
特定模数硅酸钾溶液(PS)已广泛的用于我国西北干旱地区土遗址加固保护工程中,并且取得了显著的效果。但是PS对潮湿地区遗址土加固效果,目前尚缺乏成熟的理论和实验验证。本文从室内试验的资料出发,研究PS对潮湿地区土遗址非饱和土的增强效应。本次研究土样取自位于潮湿环境中的浙江杭州良渚土遗址(3000 B C.),在实验室内对高含水量(13% ~25%)的重塑土样进行了PS渗透加固。通过研究对比加固前后重塑土样的固结特性和抗剪强度,发现 PS对潮湿地区遗址土也有一定的加固效果。加固效果随初始饱和度的不同而不同,但初始含水量达25%的土在PS作用下仍可能得到增强。经PS渗透的土样不仅提高了初始固结性能和抗剪强度,而且加固土样而且呈现出一定的弹脆性特征,呈现出塑脆性转化,表明PS渗透可能产生对土初始结构的稳固作用。这一探索研究将为扩大PS在土遗址加固保护工程的应用提供一定的理论支持。 相似文献
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Hot water flooding is a thermal nonaqueous phase liquid (NAPL) recovery technology originally developed in the petroleum industry
that has recently been proposed for enhanced recovery of NAPLs in the contaminated subsurface. This technology, however, has
received relatively little laboratory or numerical modeling investigation in the contaminant hydrology community. In this
study the utility of flooding NAPL contaminated source zones at elevated water temperatures was investigated. Simulations
were conducted using 16 different geostatistical representations of an actual field site. Two NAPLs were selected for this
study—a light NAPL with hydraulic properties that have moderate temperature dependencies and a dense NAPL with significant
viscosity temperature dependency. For these two NAPLs, flooding the source zone with water at elevated temperatures resulted
in enhanced NAPL recovery. However, injection of hot water also resulted in accelerated downward movement of coal tar DNAPL
due to the reduced viscosity at elevated temperatures. NAPL recovery was also dependent on the source zone architecture with
greater NAPL mass recovery when the NAPL was localized in a small volume at high saturations. These results suggest that hot
water flooding can significantly speed up the recovery of viscous NAPLs and, as such, is a powerful technique for the remediation
of viscous NAPLs. 相似文献
6.
盐渍土工程与力学性质研究进展 总被引:3,自引:0,他引:3
介绍我国西部地区大开发高等级公路、铁路网建设中盐渍土病害的力学相关问题. 综述了对盐胀、溶陷和腐蚀3大工程危害的机理研究以及对盐渍土的工程及力学特性的研究进展, 回顾了盐渍土水、盐、热的数学运移模型的发展, 盐渍土水、盐、热、力4场耦合模型的数值与实验探索, 对盐渍土研究领域中亟待进一步研究的问题进行了展望. 相似文献
7.
The removal of salt from porous building materials under the influence of an applied voltage gradient normally results in high pH gradients due to the formation of protons and hydroxyl ions at the electrodes. The formed acidic and alkaline regions not only lead to disintegration of the porous material, but also affect the salt transport. In this work we use ion exchange membranes between the electrodes and the porous material to prevent the protons and hydroxyl ions from intruding into the material. The porous material used in this study is fired clay brick, which has been saturated with a 4?mol/l sodium chloride solution prior to the desalination treatment. In order to experimentally determine the salt removal, we monitored the sodium ion concentration profiles across the material with nuclear magnetic resonance (NMR). In addition, we present theoretical predictions for the salt removal according to a model based on the Poisson?CNernst?CPlanck theory for ion transport. From the work reported here, we can conclude that the use of ion exchange membranes to desalinate porous building materials is not useful since it reduces the salt removal rate to such an extent that desalination with poultices, which is driven by diffusion only, is more efficient. The reason behind this is twofold. First, the ion exchange membranes provide a penalty for the ions to leave the material. Second, in the absence of acidic and alkaline regions, the salt concentration at the edges of the porous material will reduce to almost zero, which leads to a locally increased electrical resistance, and thus a reduction of the electrical field in the bulk of the material. Due to this reduction the effect of the applied voltage gradient across the material vanishes, and the salt removal is limited by diffusion. 相似文献
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膨胀土胀缩性评价中有关问题的研究 总被引:3,自引:0,他引:3
膨胀土吸水膨胀、失水收缩,产生地表变形,进而导致建筑物破坏。本文就现行膨胀土胀缩性指标试验及地基变形量评价计算中有关问题进行了研究,认为以天然含水量为起始含水量测定土样胀缩率是不合适的,建议以缩限为起点进行膨胀试验,以胀限为起点进行收缩试验,采用加荷膨胀量(而非卸荷膨胀量)参加有荷载下的膨胀率计算。膨胀土地基勘察必须结合场地条件分析可能影响土体含水量变化的因素,对同一工程采用几种方法评价,互相对比、参照。 相似文献
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A computer based numerical method is presented for the analysis of water and solute movement in unsaturated heterogeneous porous materials. Such a method is necessary since, for those field studies where solute movement is of concern, the soil profiles under consideration are invariably heterogeneous. The numerical analysis is based on a general one-dimensional finite difference soil water flow model which includes a numerical technique combining the concepts of scale heterogeneity with an interpolative soil water hysteresis model. An explicit finite difference solute movement subroutine is incorporated into the unsaturated flow model to describe the transport of nonreactive solutes. A velocity dependent longitudinal dispersion coefficient is used in the solution of the hydrodynamic dispersion equation. The resulting hysteretic scale heterogeneous solute movement model permits the study of solute dynamics during infiltrating and redistribution in realistically complex spatially varying soil profiles. Results are presented for the leaching of both coarse grading to fine and fine grading to coarse sand profiles. Both vertical and horizontal profiles are studied using either a constant flux or a constant concentration input boundary condition. The four cases studied demonstrate the versatility of the numerical method and emphasise the substantial differences in transport behavior that can arise between heterogeneous and homogeneous profiles.Now with BHP Petroleum Pty. Ltd., GPO Box 1911R, Melbourne, Vic. 3001, Australia. 相似文献
11.
Oswald Sascha E. Scheidegger Markus B. Kinzelbach Wolfgang 《Transport in Porous Media》2002,47(2):169-193
Solute transport in saturated artificial porous media was observed in a series of laboratory experiments using magnetic resonance imaging. The objective was to study a situation of density-dependent flow in three dimensions both qualitatively and quantitatively. The time-dependent measurements visualised inflow from below of dense salt water into a freshwater reservoir, internal density-driven flow and the behaviour of a salt water layer below freshwater flow including plume development by dispersion. The main feature of the flow experiment was the strong tendency for the salt water to remain stagnant and to resist being swept out by the freshwater. Additional measurements were performed to gain information about reproducibility, flow field and breakthrough curves. 相似文献
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利用真空预压法处理吹填土时,孔隙水压力变化常常反映土体固结程度的好坏。通过6个模型箱试验,监测不同排水系统下孔隙水压力变化,确定有效排水体间距。研究发现0.4m间距的土内孔压下降效果比0.8m间距的土内孔压下降效果好; 排水体内的孔隙水压力与排水体类型有关,且距离排水体10cm处土体内的孔隙水压力仅为排水体内孔隙水压力的1/2弱; 滤膜排水系统中的吹填土孔隙水压力下降幅度最快,B型排水板系统次之,而砂井系统最慢。另外,对于吹填土而言,排水体有效间距介于0.4m与0.8m之间,其中滤膜的有效间距最大,B型排水板次之,砂井远小于前两者。 相似文献
14.
Internal erosion has long been a major problem associated with earthen structures, and its field investigation has been limited because of its complexity. Laboratory experiments provide a potential insight into the induced processes. Soils suitable to suffusion involve an easy movement of fine particles between the coarse ones. In this study, suffusion experiments were performed on a laboratory column packed with different sand–fines mixtures and subjected to controlled flow conditions. The mixtures are made of Fontainebleau sand (NE34) and fines (kaolinite or illite or silt). The initiation and the progression of soil suffusion were investigated for soil mixtures, and the hydraulic conductivity variation was derived from pressure measurements. Attempts are made to assess the influence of the type and content of fine particles on mixtures suffusion. The results show that among the tested fine particles, illite exhibits a great resistance against suffusion. Fine content increase involves less suitability to suffusion till a threshold value. Recorded pressures indicate that detachment of fines may be followed by clogging in the soil matrix, leading to a decrease of hydraulic conductivity. Furthermore, analytical solutions of simplified mathematical model based on the mass conservation of eroded particles (Govindaraju et al., J Hydrol 172:331–350, 1995) were used to simulate the recorded soil suffusion curves, and the model performance was evaluated. Comparisons between numerical and experimental results indicated a quite good agreement, and allowed the estimation of the model parameters. 相似文献
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To improve the quality of parameter optimization, estimability analysis has been proposed as the first step before inverse modeling. When using field data of irrigation experiments for the determination of soil hydraulic parameters, wetting and drying processes may complicate optimization. The objectives of this study were to compare estimability analysis and inverse optimization of the soil hydraulic parameters in the models with and without considering hysteresis of the soil water retention function. Soil water pressure head data of a field irrigation experiment were used. The one-dimensional vertical water movement in variably saturated soil was described with the Richards equation using the HYDRUS-1D code. Estimability of the unimodal van Genuchten–Mualem hydraulic model parameters as well as of the hysteretic parameter model of Parker and Lenhard was classified according to a sensitivity coefficient matrix. The matrix was obtained by sequentially calculating effects of initial parameter variations on changes in the simulated pressure head values. Optimization was carried out by means of the Levenberg-Marquardt method implemented in the HYDRUS-1D code. The parameters \(\alpha , K_{s}, \theta _{s}\) , and \(n\) in the nonhysteretic model were found sensitive and parameter \(\theta _{s}\) strongly correlated with parameter \(n\) . When assuming hysteresis, the estimability was decreased with soil depth for \(K_{s}\) and \(\alpha ^{d}\) , and increased for \(\theta _{s}\) and n. Among the shape parameters, \(\alpha ^{w}\) was the most estimable. The hysteretic model could approximate the pressure heads in the soil by considering parameters from wetting and drying periods separately as initial estimates. The inverse optimization could be carried out more efficiently with most estimable parameters. Despite the remaining weaknesses of the local optimization algorithm and the inflexibility of the unimodal van Genuchten model, the results suggested that estimability analysis could be considered as a guidance to better define the optimization scenarios and then improved the determination of soil hydraulic parameters. 相似文献
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为了研究动力排水固结法加固吹填土地基的效果,研发了大比例尺的室内模拟试验装置并开展了试验。重点对夯沉量、土体内孔隙水压力的瞬时和长期变化进行了监测和分析,得到如下结论:夯击产生的能量以波的形式向土体内部传播,由于波的作用造成土体拉伸形成裂隙,这些裂隙成为初期的排水通道; 孔隙水压力的动态变化具有明显的脉动特性,夯击瞬间出现负增长,然后再累积增长; 不同深度土体的孔隙水压力增幅不一样; 土体表面铺设的砂垫层不仅可以用做排水,还可以作为静力荷载,有助于土体的排水固结。 相似文献
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