一维均质与非均质土柱中溶质迁移的分数微分对流-弥散模拟

分数微分对流-弥散方程(FADE)是模拟溶质迁移问题的新理论,但应用FADE来模拟溶质迁移时能否克服弥散的尺度效应尚待验证。利用长土柱实验资料结合FADE的解析解拟合推求FADE的弥散系数,并分析其与尺度之间的相关关系。研究结果表明,FADE的弥散系数具有随尺度增大而增大的现象,且均质土柱中FADE的弥散系数尺度效应小于非均质土柱中弥散系数尺度效应。在均质土柱中,弥散系数与尺度之间成指数相关关系,在非均质土柱中,弥散系数与尺度之间成幂相关关系。考虑了弥散系数分别与迁移时间和迁移距离呈线性递增两种相关关系,进而分别构建了3种考虑弥散尺度效应的FADE模型,并提出了求解的差分方法。利用上述3种考虑弥散尺度效应的FADE来模拟和预测不同空间位置处的溶质迁移过程。结果表明,对均质土柱中的溶质迁移可得到较好的模拟结果;对于非均质土柱,其模拟结果与实测结果仍然存在一定的差异。     

地下水溶质迁移模拟研究进展

在地下水的相关研究中,农药和石油等地下水污染、土地盐碱化、海水入侵等诸多实际问题主要的研究方法都涉及地下水溶质迁移模拟. 相比地下水水流模拟的相对完善,对溶质迁移的模拟比较薄弱且迁移过程本身复杂性较高,目前地下水溶质迁移的研究工作还处在全面发展的阶段. 文中阐述了反映地下水溶质迁移机理和过程的数学模型,综述了溶质迁移模拟在地下水污染物防治、土地盐碱化、海水入侵、石油和放射性废物扩散等问题的诸多应用,归类了目前溶质迁移模拟所使用的对流迁移、对流-弥散模拟等主要数值方法,并对这些方法的优缺点和应用实例做了总结. 最后,分析了目前溶质迁移模拟中存在的不足,展望了未来在参数确定、裂隙介质运移机理和多相介质条件下运移模拟可能取得的突破.     

多孔介质中非均匀流动特性的染色示踪试验研究

通过土壤染色剂进行的4组试验,对不同介质结构条件下的水流和溶质非均匀运动规律,非均匀流动变异信息分布特征关系以及全局性非均匀流动示踪方法进行了研究。结果表明,即使在相对比较均匀的介质条件下,流动也表现出明显的非均匀特性;对数正态分布能够较好的反映水流的运动分布模式,相比水流运动,溶质的运动和分布规律明显不同,表现出更多的不确定性和变异性。     

地浸过程中铀迁移特征研究

通过室内溶质迁移试验，对地浸过程中铀迁移的规律进行了研究。结果表明：地浸过程中溶质铀主要以铀酰、硫酸铀酰为主要存在形式；铀迁移经历了溶解迁移、沉淀、再溶解迁移的多次旋回；浸出铀浓度最大值和浸出速度与浸出距离和浸出时间密切相关。     

地浸过程中溶质(铀)迁移特征研究

本通过室内溶质迁移试验，运用化学热力学计算，对地浸过程中的溶质迁移规律进行了研究。溶质（铀）迁移研究表明：随着水地球化学条件的改变，溶质（铀）经历了溶解迁移、水解沉淀、再溶解迁移的多次旋回，章还根据铀浓度和水地球化学指标，在整个渗透途径中划分出不同特征的浸出带。     

连续时间随机游动理论模拟多孔介质中溶质运移的研究进展

近年来,基于连续时间随机游动(Continuous Time Random Walk, CTRW)理论所建立的模拟非均质多孔介质中溶质运移的方法已在大量的数值实验、室内实验、野外实验中得到了广泛的验证,为非均质多孔介质中的溶质运移行为提供了一种有效的模拟方法。简述了提出和发展CTRW的研究背景、基础理论以及与经典的对流-弥散方程等其他模拟方法的关系,综述了该理论在模拟溶质运移中的发展和应用,分析了实际应用中的关键问题,并展望了将其进一步发展应用于模拟反应性溶质运移的前景。     

砂岩型铀矿地浸过程中的溶质迁移机理

讨论了“溶质迁移、溶质迁移面和特征性溶质迁移面”的概念，以及研究溶质迁移的方法和实例。在对381砂岩型铀矿床进行地浸模拟试验的基础上，应用以上概念和方法，对地浸过程中的溶质迁移过程进行了讨论，探讨了地浸过程的机理和发生的水文地球化学作用，总结了溶浸试验过程中的溶质迁移分带。在以上溶质迁移机理研究的基础上．论证了地浸地质工艺参数。地浸过程中分带的研究清楚地显示了浸铀的发展过程及其在各个时期各个地段铀浸出作用的进展程度。     

水溶液中溶质的扩散同位素分馏研究

稳定同位素分析是判定水溶液中溶质的组成、来源、迁移和转化过程与规律的重要工具,在自由扩散等物理化学作用下,对溶质的同位素分馏研究是稳定同位素技术应用的重要基础.本研究介绍了溶质的扩散过程与其同位素分馏效应之间的联系,论述了研究溶质扩散过程中引入的稳定同位素分馏现象的意义,描述了水溶液中溶质扩散的不同模拟实验方法及相关研...     

PHREEQC在研究地浸溶质迁移过程中的应用

应用地球化学模式PHREEQC，揭示地浸过程中溶质迁移的存在形式及各种形式之间的转化关系。通过计算饱和指数，确定溶质水解沉淀的水文地球化学条件临界值。     

基于层序地层模拟的湖岸线迁移对层序定量识别的指示:以鄂尔多斯盆地山2段为例

湖岸线是水陆沉积的分界线,为探讨其迁移规律与层序间的关系,利用SEDPAK二维层序模拟软件,以鄂尔多斯盆地山2段作为地质原型,对湖岸线迁移进行了定量模拟,进而提出了其可以有效指示层序及内部体系域识别的新认识.对湖岸线迁移规律在水平方向与垂直方向重新进行了划分、定义.在水平方向上,向物源区方向的迁移定义为“正向”,对应于...     

A general polynomial solution to convection–dispersion equation using boundary layer theory

A number of models have been established to simulate the behaviour of solute transport due to chemical pollution, both in croplands and groundwater systems. An approximate polynomial solution to convection–dispersion equation (CDE) based on boundary layer theory has been verified for the use to describe solute transport in semi-infinite systems such as soil column. However, previous studies have only proposed low order polynomial solutions such as parabolic and cubic polynomials. This paper presents a general polynomial boundary layer solution to CDE. Comparison with exact solution suggests the prediction accuracy of the boundary layer solution varies with the order of polynomial expression and soil transport parameters. The results show that prediction accuracy increases with increasing order up to parabolic or cubic polynomial function and with no distinct relationship between accuracy and order for higher order polynomials (\(n\geqslant 3\)). Comparison of two critical solute transport parameters (i.e., dispersion coefficient and retardation factor), estimated by the boundary layer solution and obtained by CXTFIT curve-fitting, shows a good agreement. The study shows that the general solution can determine the appropriate orders of polynomials for approximate CDE solutions that best describe solute concentration profiles and optimal solute transport parameters. Furthermore, the general polynomial solution to CDE provides a simple approach to solute transport problems, a criterion for choosing the right orders of polynomials for soils with different transport parameters. It is also a potential approach for estimating solute transport parameters of soils in the field.     

Boundary element analysis of Biot consolidation in layered elastic soils

Biot's linear consolidation analysis of three-dimensional fluid saturated layered soils is investigated. The time marching method, uncoupled boundary element method, and successive stiffness method are applied for the numerical modelling of this study. Settlement induced by surface loading and land subsidence due to pumping is studied. The results show that settlement induced by surface loading is mainly influenced by the properties of the soil layer, and that the settlement is larger for soil layers with smaller stiffness and greater thicknesses. The land subsidence induced by pumping is influenced by the properties of the soil layer as well as by the permeability of the pumped layer and the conditions at the top and bottom boundaries. The land subsidence is larger for soil layers with a smaller stiffness, lower permeability of the pumped layer, deeper pumping depth, larger pumping rate and an impervious top surface.     

基于分层假设的Green-Ampt模型改进

传统Green-Ampt入渗模型由于假设过于简化而限制了计算精度,针对这一问题,在分层假设的基础上对模型进行了改进:将均质入渗土壤分为饱和层、过渡层和干土层,采用Richards模型分析了不同入渗条件下各层的厚度以及各层内含水率和导水率的变化规律,结果表明,入渗条件一定时,过渡层占湿润层(包括饱和层和过渡层)比例会随湿润层厚度的增加线性减小,积水深度和土壤初始含水率分别会影响这一线性关系的纵轴截距和斜率,而土壤饱和导水率则对其没有明显影响;过渡层内土壤含水率分布为椭圆形曲线,而导水率随深度增加线性减小。在此基础上,通过引入湿润层的等效导水率并相应给出锋面吸力的计算方法,对传统Green-Ampt模型进行了改进。结果显示,改进后模型计算精度显著提高。     

冻结-冻融过程中水分运移机理

为研究冻结-冻融过程中水分运移机理,在天山北麓平原通过人为控制潜水不同埋深条件下的模拟试验和田间土壤水分运移观测试验,分析了土壤水势分布和土壤含水量分布特征,发现冻结过程不同潜水埋深条件下的土壤水分运移机理、土壤水与潜水之间的相互转化关系有明显差异.在冻结过程中,潜水浅埋条件下,冻结层下界面与潜水面之间土壤水分运移状态呈上渗型,土壤水向冻结层下界面处运移、积累,同时引起潜水蒸发损耗使潜水位下降,表现出地下水向土壤水转化的基本特征.潜水深埋区,土壤水分运移状态呈上渗-入渗型,同样土壤水向冻结层下界面处运移、积累,同时潜水得到一定的入渗补给并使潜水位上升,表现为土壤水向地下水转化的特征.冻融过程中对于不同潜水埋深,由原来各自的土壤水分运移状态均逐渐转变为入渗型,形成潜水入渗补给,表现为土壤水向地下水转化的特征.冻融期是土壤水资源、地下水资源形成的重要时期,对于干旱少雨的西北地区而言,冻融水的形成、运移和入渗补给地下水具有重要的生态环境意义.     

榆神矿区基岩顶面土层缺失机理分析及其防治水意义

为研究榆神矿区局部基岩顶面中新世-中更新世土层缺失的机理及其与矿井涌水灾害的关系,采用地质钻探、野外观测、数理统计的方法分析了基岩顶面标高与残留土层厚度的关系,运用"将今论古"的方法分析了土层成因及剥蚀机理。结果表明:榆神矿区土层剥蚀是降水、风和线状流水地质营力共同作用的结果,线状流水是土层颗粒冲蚀以及土层纵向剥蚀直至缺失的主要因素。榆神矿区基岩顶面标高与残留土层厚度呈正相关线性耦合关系,土层缺失可以作为古河流发育的直接标志,据此恢复了与基岩顶面连通的古河流形态、分布范围及古分水岭。基岩顶面古河床充填的含水层是煤矿涌水的主要充水来源,将对煤矿安全生产构成威胁。      

Analysis of a rigid footing lying on three-layered soil using the finite difference method

A numerical procedure is described for the analysis of the vertical deformation and the stress distribution of the strip footings on layered soil media. Three layers of soil with different stiffness are considered with the middle soil layer the thinnest and most stiff layer. The soil media is discretized and using the theory of elasticity, the governing differential equations are obtained in terms of vertical and horizontal displacements. These equations along with appropriate boundary and continuity conditions are solved by using the finite difference method. The vertical and horizontal displacements, strains and stresses are found at various nodes in the soil media. Parametric studies are carried out to study the effect of the placement depth of the middle soil layer, the relative ratios of the moduli of deformation of the soil layers on the vertical displacement of the footing and the vertical stress distribution. These studies reveal that the middle thin but very stiff layer acts like a plate and redistributes the stresses on the lower soft soil layer uniformly. The displacement on the top and bottom of the middle soil layer is almost the same showing that the compression of the middle layer is negligible as it is very stiff.     

Analytical layer‐element method for non‐axisymmetric consolidation of multilayered soils

A numerically efficient and stable method is developed to analyze Biot's consolidation of multilayered soils subjected to non‐axisymmetric loading in arbitrary depth. By the application of a Laplace–Hankel transform and a Fourier expansion, the governing equations are solved analytically. Then, the analytical layer‐element (i.e. a symmetric stiffness matrix) describing the relationship between generalized displacements and stresses of a layer is exactly derived in the transformed domain. Considering the continuity conditions between adjacent layers, the global stiffness matrix of multilayered soils is obtained by assembling the inter‐related layer‐elements. Once the solution in the Laplace–Hankel transformed domain that satisfies the boundary conditions has been obtained, the actual solution can be derived by the inversion of the Laplace–Hankel transform. Finally, numerical examples are presented to verify the theory and to study the influence of the layered soil properties and time history on the consolidation behavior. Copyright © 2011 John Wiley & Sons, Ltd.     

煤层地下开采地表沉陷预测的边值方法

采空区上覆岩、土体对地表沉陷的耦合行为可归结为弹性理论的边值问题,由不同性状松散表土层确定的应力边界和岩、土体之间形成的位移边界构成了相应边值问题的定解条件。在已有研究成果的基础上,提出了地表下沉预测研究的边值提法,以探讨地下开采引起的地表沉陷规律。给出了采空区上覆表土层内任一点的位移和地表下沉的计算公式,确定了地表沉陷的范围,并以神东矿区大柳塔1203工作面开采引发的地表沉陷为例给出了工程实例。研究结果表明,采空区上覆岩体对地表及表土层内任一点下沉的影响取决于上部岩层破断后的结构形态;采空区上覆土体对地表下沉量的作用与土体性质及表土层厚度有关,土体对表土层下沉的影响由下而上增大,呈非线性变化,至地表达最大值;地表沉陷区域随表土层厚度的增加而增大,其影响范围远大于采空区。     

A general approach to the modelling of contaminant transport through composite landfill liners with intact or leaking geomembranes

Finite‐element models of contaminant transport through composite landfill liners require highly refined meshes around the interface between the geomembrane and the clay layer, especially if leakage through holes in the geomembrane is considered. In addition, no general formulation for transport through leaking geomembranes can be found in the literature. The paper develops a general approach to time‐dependent contaminant migration through composite liners with intact or leaking geomembranes. Equations are derived for various combinations of system conditions including Dirichlet and Neumann boundary conditions in the waste, constant mass of contaminants in the waste, steady state or transient transport in the geomembrane, and steady state or transient seepage velocities in the mineral liner. The effect of the geomembrane on transport in the soil is converted into an equivalent boundary condition applicable at the top of the clay layer. Hence, only the media underlying the top geomembrane are explicitly represented in the numerical model, yielding a computationally efficient algorithm. The new formulation is validated in conjunction with finite‐layer, finite‐element and boundary‐element methods, by comparing its predictions to those of more conventional approaches which represent the geomembrane explicitly. The scope of the method is illustrated by modelling a landfill liner with a geomembrane leaking in five locations. Copyright © 2007 John Wiley & Sons, Ltd.     

贵州喀斯特区域土壤水分时空分布特征

基于贵州喀斯特区域2011-2015年53个自动土壤水分观测站0~100 cm的逐日土壤水分、降水、气温资料,分析了不同农业气候区土壤水分时空分布特征、变异系数以及土层之间的相关关系。得出以下主要结论:（1）各区土壤水分的范围总体相差较小,据 0~100 cm层土壤水分相对小值区的分布形态,可分为持续性土壤干旱区、季节性土壤干旱区、土壤湿润区。（2）依据各区土壤水分的变异系数相对大值区的时空分布形态类似可分为变异一致区、季节变异区及持续变异区。（3）通过10~50 cm对其下层土壤水分的关系研究发现,温暖湿润区、温和湿润区、高寒区研究土层（10~50 cm）与其下层（20~90 cm）土壤水分相关系数均>0.60,其余各区土层只与其下20~40 cm土层相关系数较大,而对其下更深土层相关系数较小;从滑动日数来看,各区10~50 cm土层与其下10~20 cm、30~50 cm、60~100 cm层最大相关系数的滑动日数随深度的增加而增加,分别为3~10日、10~20日、20~30日。（4）通过对比各区土壤水分与其变异系数分布特征发现,土壤水分的低值区发生的层次及时间与变异系数大值区基本相对应,土壤水分的变化除与降水、气温直接关系外,还可能与土质及环境等其他要素有关。