区域饱和-非饱和多孔介质的溶质运移简化模型

在迭代求解区域饱和非饱和拟三维渗流模型的基础上,建立区域溶质运移简化模型。该模型将溶质运动在非饱和带简化为一维垂直运动,饱和带简化为二维剖面运动,在非饱和带与饱和带分别形成对流_弥散方程,并通过维持近饱和带溶质质量守恒组成统一的系统,采用有限单元法数值处理技巧,在同一个矩阵方程中求解饱和与非饱和含水层的浓度变化。该模型无需迭代计算,大大减少工作量,为求解区域溶质运移问题提供了新方法。算例验证表明,区域溶质运移简化模型技术可行,结果可信。     

特大型变坡土壤槽纵向垂向弥散系数试验研究

本文借助于特大型变坡土壤槽物理模型装置，试验研究了污染物在饱和土壤中水平运移规律，得到了连续输污条件下，饱和土壤中污染物浓度二维时空变化的过程，在分析实测资料的基础上，运用数学模型解 优化技术率定模型参数，得到了具有重要应用价值的纵向、垂向弥散系数。     

污染物及土壤水动力迁移的数值模拟

本文在分析水分及污染物在土壤中迁移物转化规律的基础上，建立了水分及污染物迁移的耦合数学模型。采用有限差分法离散水分方程和污染浓度方程，得到了数值计算模型。运用分散平均方法估算水力传导率，并用中心差分和隐式差分格式并存的系数矩阵求解方法，加快计算的收敛性。利用该数值计算模型，模拟计算了具有应用背景的水分及污染物在非饱和土壤中的迁移规律，数值计算成果得到了试验资料的验证，两者吻合良好，为研究和解决地下水污染问题提供了有效的手段     

包气带垂向渗透系数的原位试验研究

野外试验测定包气带渗透系数对于研究非饱和带水分运移过程、植物根系吸水特征及产汇流规律具有重要意义。本文采用Inverse Auger法在毛乌素沙地开展了原位包气带垂向渗透系数测定实验。通过实验数据分析表明:①为获得较可靠的垂向渗透系数,野外实验时,需要重复注水过程,使包气带应尽可能湿润,消除水平吸渗对垂向入渗的影响;②采用Porchet推导的计算公式计算包气带垂向渗透系数时,应对获取的数据进行统计分析,放弃不符合实验物理背景的数据。在上述分析基础上,计算得到实验介质平均垂向渗透系数为2.23 cm/h。上述原位实验数据的分析方法和实验结果对相关实验研究具有一定的借鉴意义。     

Effect of immobile water content on contaminant transport in unsaturated zone

The effect of immobile water content on contaminant advection and dispersion in unsaturated porous media has been studied using a formulation which assumes that even in the immobile liquid zone, there occurs minor liquid flow. An approach is proposed for computing this liquid velocity. One dimensional numerical simulation is carried out to study the effect of immobile water content on the time of appearance of contaminant at the bottom of an unsaturated column. The numerical model developed is verified using analytical solutions for simple advective-dispersive cases. From the simulations, it was observed that increase in the immobile water content leads to quicker appearance of contaminant.     

A NEW NUMERICAL METHOD FOR GROUNDWATER FlOW AND SOLUTE TRANSPORT USING VELOCITY FIELD

A new numerical method for groundwater flow analysis was introduced to estimate simultaneously velocity vectors and water pressure head. The method could be employed to handle the vertical flow under variably saturated conditions and for horizontal flow as well. The method allows for better estimation of velocities at the element nodes which can be used as direct input to transport models. The advection-dispersion process was treated by the Eulerian-Lagrangian approach with particle tracking technique using the velocities at FEM nodes. The method was verified with the classical one dimensional model and applied to simulate contaminant transport process through a slurry wall as a barrier to prevent leachate pollution from a sanitary landfill.     

A NEW NUMERICAL METHOD FOR GROUNDWATER FIOW AND SOLUTE TRANSPORT USING VELOCITY FIELD

A new numerical method for groundwater flow analysis was introduced to estimate simultaneously velocity vectors and water pressure head. The method could be employed to handle the vertical flow under variably saturated conditions and for horizontal flow as well. The method allows for better estimation of velocities at the element nodes which can be used as direct input to transport models. The advection-dispersion process was treated by the Eulerian-Lagrangian approach with particle tracking technique using the velocities at FEM nodes. The method was verified with the classical one dimensional model and applied to simulate contaminant transport process through a slurry wall as a barrier to prevent leachate pollution from a sanitary landfill.     

Method of coupling 1-D unsaturated flow with 3-D saturated flow on large scale

A coupled unsaturated-saturated water flow numerical model was developed. The water flow in the unsaturated zone is considered the one-dimensional vertical flow, which changes in the horizontal direction according to the groundwater table and the atmospheric boundary conditions. The groundwater flow is treated as the three-dimensional water flow. The recharge flux to groundwater from soil water is considered the bottom flux for the numerical simulation in the unsaturated zone, and the upper flux for the groundwater simulation. It connects and unites the two separated water flow systems. The soil water equation is solved based on the assumed groundwater table and the subsequent predicted recharge flux. Then, the groundwater equation is solved with the predicted recharge flux as the upper boundary condition. Iteration continues until the discrepancy between the assumed and calculated groundwater nodal heads have a certain accuracy. Illustrative examples with different water flow scenarios regarding the Dirichlet boundary condition, the Neumann boundary condition, the atmospheric boundary condition, and the source or sink term were calculated by the coupled model. The results are compared with those of other models, including Hydrus-1D, SWMS-2D, and FEFLOW, which demonstrate that the coupled model is effective and accurate and can significantly reduce the computational time for the large number of nodes in saturated-unsaturated water flow simulation.     

填海工程背景下半岛地下水流场及污染物运移的数值模拟分析

以古雷半岛为例,基于GMS地下水数值模型探索海砂填海(情景一)、海砂+黏土填海(情景二)、黏土填海(情景三)这三种填海情景对研究区地下水流场及污染物运移的影响。结果表明:(1)研究区在填海背景下地下水水位整体抬升,水位上升幅度由小到大依次为情景一、情景二、情景三,最高升幅达4.78m。(2)不同填海情景下的地下水流场差异在填海区的黏土区域最为明显,情景二、情景三与情景一的地下水水位差最大值分别为4.44 m和8.20m。(3)在仅考虑物理作用的情况下,三种填海情景下污染物运移均呈现以水平运移为主、垂向运移为辅的特点。(4)相较于污染物运移基本相同的情景一与情景二,预测时间30a时,水平方向上情景三污染物迁移面积、迁移速率分别下降23.07%、18.89%;垂向上污染物主要积聚于第一层含水层,情景三观测井在第一层含水层的污染物浓度为情景一(或情景二)的5.87倍。说明采用低渗透性黏土填海对于污染物运移具有一定的阻滞作用。     

降水补给地下水过程中包气带变化对入渗的影响

采用野外试验和室内试验方法,通过对不同降水量的入渗过程中岩土含水率和水势变化规律分析,发现入渗水流在包气带内下渗过程的岩土吸水、过水(即水分通量不变、且不等于零)和脱水的不同阶段,当岩土水势的梯度分别大于、等于和小于1cmH2O/cm(厘米水柱/厘米)时,岩土含水率分别表现为增加、稳定和减少。对包气带不同埋深的岩土含水率和水势变化特征分析表明,随着地下水位不断下降,包气带增厚对降水入渗补给地下水的影响程度和方式都发生改变。当包气带厚度小于潜水蒸发极限深度时,包气带的增厚使得岩土水分亏缺累积量增大,导致入渗速率和地下水获取的总入渗补给量减小;当包气带厚度大于潜水蒸发极限深度时,随着包气带厚度增大,入渗速率趋于稳定,无限时间内地下水获取的总入渗补给量不因包气带增厚而变化,但是有限时间内地下水获取的入渗补给量趋小。这是因为入渗途径的延长导致入渗所需时间增加,以至在有限时间内包气带内过剩的入渗水分尚未充分排出补给地下水。     

基于多单元均衡法的地下水流与水质联合数值研究

针对地下渗流与污染物迁移数值模拟中计算程序复杂、效率偏低等不足,开展了地下水流与水质联合数值研究。首先基于多单元均衡法,建立了渗流与污染物迁移的联合模型,采用Matlab语言编制了联合程序,使之能够求解单一地下水渗流、初始流场稳定的地下水污染和初始流场不稳定的地下水污染等多种情况。然后计算了一维对流弥散问题,并与多种计算方法进行对比分析。最后对某地地下水污染物的扩散分布进行了模拟。结果表明:通过控制自定义特征数,实现了对不同水文地质特征问题的求解;采用上游加权法解决大Peclet数污染物迁移问题时,并无明显数值弥散现象,又能抑制数值解的振动;本程序具有较高的计算效率,并能够显著提高后处理的可视化程度。     

NUMERICAL SIMULATION FOR CONTAMINANTS AND WATER TRANSPORT IN SOILS

ＮＵＭＥＲＩＣＡＬ　ＳＩＭＵＬＡＴＩＯＮ　ＦＯＲ　ＣＯＮＴＡＭＩＮＡＮＴＳ　ＡＮＤ　ＷＡＴＥＲ　ＴＲＡＮＳＰＯＲＴ　ＩＮ　ＳＯＩＬＳＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＦＯＲＣＯＮＴＡＭＩＮＡＮＴＳＡＮＤＷＡＴＥＲＴＲＡＮＳＰＯＲＴＩＮＳＯＩＬＳ￥Ｗａ...     

污染物击穿防污屏障与地下水土污染防控研究进展

鉴于防污屏障是控制固废填埋场地下水土污染的重要结构,为评价防污屏障的服役寿命,分别针对重金属和有机污染物,总结了污染物在黏土屏障和复合屏障中的一维运移解析解,包括非线性吸附条件下污染物在黏土屏障中的一维扩散解、污染物在有缺陷膜复合屏障中的一维运移解和温度场作用下污染物在黏土屏障中的耦合运移解析解等。评价了污染物击穿防污屏障长历时过程超重力离心模型试验的可靠性。对运行了17 a的安徽某填埋场进行现场调查,发现氯离子运移最大深度达9 m,钠离子和COD的运移深度在3~4 m。总结和评价了地下水土污染控制的竖向屏障技术,认为土-膨润土系竖向隔离墙技术在我国具有广阔的应用前景,并对今后的研究进行展望。     

饱水格栅加筋土挡墙结构特性数值分析*

格栅加筋土挡墙由面板、格栅和土体组成。本文根据加筋土挡墙筋土相互作用的特点，将格栅与其上下表面一定厚度的土层视为具有应变相容条件的筋土复合材料。引入饱和多孔介质模型来模拟土体和筋土复合材料，由此建立了饱水格栅加筋土挡墙结构特性数值分析的数学模型。采用Galerkin加权残值法推导出有限元平衡方程，求解该方程，得到饱水格栅加筋土挡墙的动力响应。算例分析表明，格栅加筋土挡墙在饱水状态下的变形和塑性区分布有明显增大，且呈现外倾变形特征，挡墙的承载力也有较大幅度的降低。     

河套平原次生盐渍化地区地下水动态调控模拟研究

在盐荒地野外水盐运移试验的基础上,建立了基于饱和-非饱和带的土壤水盐运移模型,以地下水埋深为调控关键因子,利用HYDRUS软件模拟了河套灌区荒地不同时段的不同控制地下水埋深条件下包气带水盐变化规律。通过模型反算,定量确定了不同时段防治盐渍化的地下水埋深临界值。模拟结果:在年内2~3次灌溉淋滤的条件下,3月-6月份(春融返盐期)控制地下水埋深大于2.4~2.7 m,7月初-9月初,控制地下水埋深大于1.8~2.1 m,9月中旬-11月中旬(秋浇积盐期),控制地下水埋深大于1.5~1.8 m,11月下旬-3月上旬(冬封期)控制地下水埋深大于2.0~2.3 m可使0~50 cm土层的全盐量基本小于0.2%,处于非盐渍化状态。研究结果可为河套平原次生盐渍化区水盐运移调控和盐渍化改良提供借鉴和依据,具有重要理论和应用意义。     

地下水污染试验研究进展

本文在总结国内外众多学者有关污染物在含水层中的运移规律研究成果的基础上，介绍了地下水污染试验研究的最新进展；并据此认为，三维弥散，各向异性含水层介质中污染物的迁移，非饱和土层中的污染物多相迁移和吸力的关系等将成为今后地下水污染传播研究的主要问题。     

Transport characteristics of surface-modified nanoscale zero-valent iron in porous media.

Highly efficient, versatile, adsorbent, nanoscale zero-valent iron (NZVI) was synthesised and encapsulated by an anionic polymer to make it a mobile delivery vehicle (DV-NZVI) for in-situ groundwater and soil remediation. NZVI was found to be highly dispersed with surfactant within a size of 1-100 nm. Laboratory column experiments were conducted by employing glass beads as a porous medium to delineate the characteristics of DV-NZVI transport as a reactive material in saturated zones under a number of conditions. It was observed that there was an optimum concentration of polymer, i.e. 6 g/L, for maximum transport of DV-NZVI, at which point, as the flow rate increases, the transport of DV-NZVI increases. Similarly, at the optimum concentration we observed that as the depth of porous media increased, the breakthrough of DV-NZVI was retarded. These results confirmed that DV-NZVI has significant potential for use as a colloidal reactive barrier material in deep groundwater systems in lieu of pump and treat approaches and conventional permeable reactive barriers (PRB).     

A comparison of various uncertainty models: An example of subsurface contaminant transport

Groundwater resources are under increasing threat of contamination and wasteful use in many parts of the world. Groundwater flow and integrated contaminant transport models are commonly used to predict the fate of contaminants in the subsurface environment. However, the lack of reliable data and complexity of the natural environmental systems, the predictions are subjected to large uncertainties. For reliable decision-making, these contaminant transport models are required to explicitly consider associated uncertainties in their parameters. This paper aims to compare the results of four common uncertainty models using an example of contaminant transport in groundwater. The research employed an advection–dispersion equation (ADE) to describe the transport of a contaminant in groundwater. For simplicity, two parameters – dispersion coefficient and velocity – were considered in the uncertainty analysis. Fuzzy set theory, one- and two-dimensional (1-D and 2-D) Monte Carlo simulations, and Probability Box (P-Box) methods were investigated. The cumulative distribution functions generated from these analyses were compared to evaluate the capabilities of these methods. The comparison showed that P-Box method provides a more comprehensive analysis with lesser assumptions as compared to other methods, and also found to be more pragmatic way to describe and propagate uncertainties in complex environmental systems. Furthermore, execution time required to perform uncertainty analysis using P-Box method is comparatively much less than 2-D Monte Carlo simulations.     

对栾城地区降雨蒸发条件下的土壤水分运动模拟研究

数值模拟方法是评价地下水资源量、模拟自然界一些水文地质过程发生和发展的主要方法和手段之一。 HYDRUS－1D 是用于模拟变量饱和孔隙介质中水流和溶质运移的模型软件。本文应用 HY－DRUS－1D 软件,模拟了河北省栾城县实验地在降雨蒸发条件下的土壤水分运动情况。通过对模型的校正与识别,得出了栾城地区的水分运动形式。     

The impact of contamination from a municipal solid waste landfill (zagreb,croatia) on underlying soil

The present study was conducted on the main landfill of the city of zagreb which contains about 5 million tons of waste disposed of directly onto highly permeable alluvial sediments. The investigations were aimed at assessing the impact of contamination from the landfill on underlying soil and comprised the determination of a broad spectrum of inorganic and organic constituents in the samples (size fractions <2 mm) of solid waste, soil and aquifer sediments. Both the total content of various contaminants as well as their part which is readily leachable with water were determined in the examined samples. Compound classes identified in the landfill can be classified into the two main categories: (I) markers of biological waste and of its microbial transformation (ammonia, dissolved organic carbon, short-chain aliphatic acids, phenols, derivatives of abietic acid) and (2) markers of anthropogenic waste (toxic metals, hydrocarbons, chlorinated hydrocarbons, surfactant-derived compounds, phthalates, pharmaceutical chemicals). The complex assemblages of contaminants were shown to change dramatically during the transport from the solid waste through unsaturated zone of the soil to aquifer sediments. It was shown that, in addition to the vertical infiltration of leachate from the solid waste, the hydrological regime of groundwater has also a strong impact on the contaminant distribution in soils below the landfill.