重金属离子和LNAPLs在非饱和土中的运移规律研究

以重金属和轻非水相流体(LNAPLs)为例,介绍了清华大学开展非饱和土中污染物运移规律研究的部分工作成果。利用土工离心机对污染物的运移过程模拟,取样得到污染物的浓度分布特征。同时采用数值分析手段对污染物的长期运移规律和其影响因素进行分析。研究表明:离心模型试验可以有效模拟污染物的运移过程,离心模型试验和数值分析相结合,是研究污染物在非饱和土中运移规律的有效手段。     

垃圾渗滤液非均质砂箱动态淋溶模拟试验

通过构建二维非均质砂箱试验模拟垃圾渗滤液污染物在土壤-地下水环境中的运移,得出了渗滤液中Cl^-、SO4^2-、总硬度（CaCO3）在地下环境中的迁移和时空分布规律,同时引入一维土柱试验的结果与二维试验结果作了比较,表明二维砂箱中由于所模拟地下水的作用而使两者的污染物运移规律差异较大,这为预测和控制渗滤液污染土壤．地下水提供了一定的理论依据和试验方法。     

非饱和黏土中镉离子迁移规律的数值分析

考虑南昌-莲塘一带镉离子呈高背景或异常,而其迁移转化又是一个十分复杂的物理化学过程。论文在对南昌土质、镉离子分布调研的基础上,采用有限元法对镉离子在非饱和土中的迁移过程进行数值模拟,并与室内土柱试验成果进行对比,探讨了镉离子在非饱和土中迁移的规律,对于污染治理具有一定的参考价值。     

非饱和粉质砂土中铜离子迁移的离心模型试验研究

本文利用土工离心机进行了非饱和土中重金属铜离子迁移的模拟研究,考察在污染物泄漏后的6个月、12个月和24个月时土壤中铜离子的变化和污染物的迁移机理及其对地下水的影响,同时也研究了土性对污染物迁移机理的影响。     

水封石油洞库污染物运移规律研究

水封石油洞库储油可能造成地下水污染。明晰石油污染物在裂隙岩体中的运移规律是库区地下水污染防控的前提。为揭示石油污染物在洞周围岩地下水中的运移规律,基于裂隙-孔隙双重介质模型,采用数值模拟方法研究了石油中的特征污染物——苯的运移扩散过程,并分析了裂隙倾角、裂隙开度、基质渗透率和纵向弥散度对苯运移规律的影响。研究表明:储库正常运行50 a后,苯的迁移被限制在较小的范围内,不会到达水幕系统,也不会进入到地面表层下的水体中。在长期运行条件下,相邻洞周围岩中的污染晕可相互连通,并将引起相邻洞罐中油品污染物之间的交叉污染。苯的竖向污染距离对纵向弥散度和裂隙倾角大小敏感性强,而对裂隙开度和基质渗透率的敏感性较弱。洞室间岩柱中轴线上苯的最大浓度对裂隙倾角最为敏感,且随裂隙倾角和基质渗透率的增大而减小,随纵向弥散度和裂隙开度的增加而增大。     

球形蒸汽源增湿非饱和黄土水热运移规律试验研究

非饱和土中的水-汽-热耦合运移是一个受多因素影响的复杂过程。利用重塑非饱和黄土填筑模型，通入一定压力的高温水蒸气，研究蒸汽压梯度、温度梯度和含水率梯度共同作用下重塑非饱和黄土中的热湿迁移规律，并利用模型试验边界条件，解得球形蒸汽源增湿非饱和黄土时水热运移主控方程的一组特解。结果表明：球形蒸汽源在非饱和黄土中运移时，水分和温度的迁移范围近似于椭球体。水蒸气沿径向运移时，随着蒸汽压逐渐消散，运移速率降低，温度传导速率减小。蒸汽压较大时，增湿速率、增湿范围和增湿程度都将增大；在有效增湿范围内，土体含水率在11%～17%间变化，接近土体的最优含水率，增湿效果较好；高温水蒸气在土体中的传热包括高温蒸汽传热和温度梯度引起的热传导，有效增湿范围内主要以高温蒸汽传热为主，温度迁移速率属于快速迁移阶段。有效增湿范围外以温度梯度引起的热传导为主，属于缓慢迁移阶段；实测值和计算值对比发现，代数显式解析特解能较好地反映试验中土体温度和含水率的变化规律。研究结果可为非饱和黄土中水热迁移和蒸汽增湿技术提供理论参考。     

考虑基质势影响的非饱和土水分运移规律测试系统研制

借助于国内外先进的吸力探头传感器、水分传感器、相应的采集系统、计算机系统和自加工的有机玻璃土样桶等,研制出国内外首台考虑基质势影响的非饱和土水分运移规律测试装置。其结构简单,设计新颖,实用可靠,操作简单方便,能够将不同初始体积含水率的土样的水分运移变化情况,全面的进行数据化的统计、比较,并能够得出可靠的试验数据,能够定量研究不同基质势土样相互接触(水气混合)或不接触(气态水)时非饱和土中不同基质势对水分运移的影响规律;定量研究不同基质势、不同断面和不同时期非饱和土中水分变化和运移情况;直接、实时量测同一断面非饱和土在不同基质势作用下的非饱和土土水特征曲线,解决了非饱和土土水特征曲线无法直接量测或量测不准确的难题;量测范围广,适合多种非饱和土基质势组合时的量测,对基质势影响下的非饱和土水分运移规律做出数据化的展现,能够作为岩土工程、交通工程、水利工程和农业工程相关研究领域的可靠工具。     

全吸力范围非饱和土水力渗透系数的计算

非饱和土水力渗透系数决定了水分在非饱和土体中迁移的速率,因此非饱和土水力渗透系数是研究水分在非饱和土中迁移规律的关键参数.一般情况,渗流数值计算软件将水力渗透系数方程作为输入参数,水力渗透系数方程的准确性直接影响渗流模拟结果的可靠性.常用的非饱和土水力渗透系数方程大多基于毛细水的相关理论,在低吸力区其计算结果与试验数据...     

DNAPLs在低渗透性夹层影响下的迁移和分布特征研究

重非水相流体(DNAPL)在地下介质中的运移分布受多种因素影响,包括DNAPLs的物化性质、泄漏速率、地下水流速、介质非均质性等。本文基于T2VOC程序对DNAPLs在非均质地层(含低渗透性夹层)中的迁移和分布特征进行了数值模拟,分别采用三相毛管压力函数Parker模型和二相毛管压力函数van Genuchten模型,研究了夹层的饱和渗透率、地下水流速对DNAPLs运移和分布的影响。研究表明,地下水流速的增大显著促进了DNAPLs的水平和垂向运移;相同流速情况下,非均质层(低渗透性夹层)饱和渗透率的减小使得DNAPLs污染羽形态及空间路径出现了明显蓄积和绕流。模拟结果可为DNAPLs污染场地识别与修复提供了理论基础与技术支持,便于进一步研究其在地下饱和非均质介质中的运移。     

某油气田污染物的地下运移数值模拟

本文对美国某地一口油气开采井泄漏事故中的污染物在地下运移的过程进行了数值模拟。结果显示在考虑地下水与泄漏污染物的密度效应时,污染物渗透到地下后会污染当地的整个含水层,其滞留时间长达一年之久,对区域生态环境会产生负面影响;在忽略地下水与污染物的密度效应时,污染物主要滞留在地下浅部地区,主要对泄漏区附近的地表生态环境造成污染。因此,泄漏的污染物对当地或区域的生态环境具有长期的负面影响,油气资源的开采需在充分考虑水文地质条件的基础上进行污染防治和环境修复。     

基于高密度电阻率法的水分迁移模型试验研究

在土工模型试验中,常用的应用于水分及溶质迁移过程量测的传感器量测、图像分析及取样分析等方法并不能充分满足三维、无损、实时的量测需求。高密度电阻率成像法为土工模型试验中三维、无损、实时量测需求提供了新的解决思路。基于高密度电阻率成像法发展一套适用于常规物理模型及超重力离心环境中土体电阻率测试设备和分析方法,并通过开展模型试验验证其应用于水分迁移过程量测的适用性及有效性。常规物理模型试验(1g)表明,该设备及方法能够获得模型土体中电阻率的三维时空分布,入渗过程中电阻率与含水率的分布及变化合理反映电阻率与含水率定性关系;在低有效饱和度区间,电阻率法具有很高的灵敏度。离心模型试验结果表明,重力水平的变化可导致水分在模型土柱中的分布发生显著变化;实时量测技术及分析方法可为土工离心环境中渗流及溶质运移过程的分析提供更为准确的依据。高密度电阻率成像法可以成功应用于常规物理模型及超重力离心环境中水分迁移过程量测,并保证一定的精度和灵敏度。     

Experimental Study of LNAPL Migration in the Vicinity of a Steep Groundwater Table

Migration of Light Non-Aqueous Phase Liquids (LNAPLs) in porous soils was studied experimentally, using one-dimensional and two-dimensional laboratory tests. The movement of crude oil under constant pressure was observed in vertical and horizontal transparent columns filled with sand. It was found that in both cases the average oil saturation does not change during the oil propagation. Its value depends on the initial water saturation in sand and the mobility of air in front of the oil front. The hydraulic conductivity to oil was found to be constant along the vertical column, while it decreased exponentially when oil was spreading along the horizontal column. Two-dimensional experiments were carried out in a sand tank with simultaneous water flow and the oil migration. Oil leaked into the sand from a thin feeder above the water table with constant oil level. The experiments were conducted with three types of LNAPL: crude oil, vegetable oil, and engine oil. Evolution of the oil mound was recorded through the transparent front wall of the sand tank, while the water table was monitored using a series of piezometers. Presence of the water table had a major effect on the oil mound shape and size. Downwards movement of the oil front slowed down around the top of the capillary fringe and completely stopped near the water table. The depth of penetration into the capillary fringe depended on the oil viscosity and the pressure at the oil source. Lateral spreading was more pronounced in the direction of the water movement.     

制热工况下地埋管周围土壤的热湿迁移试验研究

基于实际工程建立了地源热泵空调系统运行过程的岩土体原位观测站,实现系统运行状况和换热过程中岩土体温度变化、水分迁移的实时监测,通过冬季工况运行试验,揭示地源热泵运行过程中土体的热湿迁移效应。研究结果表明:冬季工况下该地源热泵空调系统的机组性能系数COP为3.58,具有良好的制热效果;土壤温度场的变化受地埋管热交换和大气环境变化两个因素的影响,但二者的影响范围及程度有所区别;土壤温度场的变化幅度随着与地埋管距离的增加而递减,竖埋管热作用的影响半径约2.0 m左右,水平埋管热作用的影响半径约1.0 m左右;地埋管热交换对土壤湿度场的影响不显著,但大气降雨引起的地表水入渗和地下水位的变迁对土壤湿度场变化有明显影响。     

Use of dyes and proteins as indicators of virus adsorption to soils

Outbreaks of viral diseases have been associated with contamination of ground water sources by viral migration from septic tanks. A better understanding of virus adsorption to soils might help elucidate the possible mechanism of subsurface virus migration and ultimate contamination of ground water sources. The present investigation sought a simple test that could predict virus adsorption to soils. Two dyes, methylene blue (positively charged) and amaranth (negatively charged), and three proteins, ferritin (p¹ 4.5), myoglobin (p¹ 7.3) and cytochrome-c (p¹ 9.3), were evaluated as potential indicators of virus adsorption to 20 different soils. The results indicated that no single indicator could predict the adsorption pattern for the different viruses which were evaluated with the soils tested. However, the viruses could be divided into two groups based on their similarities to adsorption of ferritin and cytochrome-c to soils. The other three indicators, myoglobin, methylene blue and amaranth did not significantly correlate with virus adsorption. Therefore, it is proposed that a two protein indicator system could be used to evaluate soils to predict virus adsorption.     

Modelling water and salt transport in a soil–water–plant system under different groundwater tables

Salinization in a soil–water–plant system is an important environmental issue that has caused public concerns. In this study, field column experiments are conducted to study the transport of water and salt in soils affected by hydrologic circle and plant growth. A soil water and salt transport model (SWSTM) is developed and calibrated for predicting the behaviour of water and salt in a soil–water–plant system. The model takes into account water and solute uptake by crop roots and migration to groundwater. The experiment results demonstrate that the rise of the groundwater table enhances the movement of water and results in the accumulation of salt at a layer of 45 cm depth. With the decline of the groundwater table, the amount of accumulated salt increases correspondingly. The simulation results demonstrate that the SWSTM adequately predicts the water and salt transport in a soil–crop–plant system under different groundwater tables. The use of SWSTM will help to reveal the mechanism of water and salt transport in a soil–water–plant system. The SWSTM can also serve as a useful tool in evaluating the impact of agricultural activities and formulating efficient water management strategies in China.     

CFG桩复合地基施工过程的沉降数值模拟与分析

高速铁路在软弱路基中的施工过程及其工后沉降是影响高速铁路运营安全的重要因素.根据武广高速铁路某段实际工况,选取一典型断面,运用ADINA有限元软件对CFG桩复合地基的施工过程和最终沉降进行数值模拟分析.研究结果表明,CFG桩复合地基能较好地适用于客运专线软土地基加固处理,满足客运专线路基承载力和设计变形值的要求,有效地控制工后沉降,加固效果明显.     

A Simplified Image Analysis Method to Study LNAPL Migration in Porous Media

A novel Simplified Image Analysis Method was developed and tested to assess the saturation distribution values for water and LNAPLs (Light Non-Aqueous Phase Liquids) in granular soils subjected to fluctuating groundwater conditions. This method, based on the Beer-Lambert Law of transmissivity, determines the saturation of water (S_w) and LNAPLs (S_o) by comparing the average optical densities (D_i) for each matrix element of the tested domain to the corresponding average optical densities for three base pictures of the same domain taken with two digital cameras attached to two different band-pass filters (λ=450 nm and 640 nm). Two equations with two unknowns (S_w and S_o) are defined for each mesh element, which enables the saturation distribution to be calculated under dynamic conditions. The three base conditions for the domain are: (i) fully saturated with water (D_i¹⁰), (ii) fully saturated with LNAPL (D_i⁰¹), and (iii) completely dry (D_i⁰⁰). The Simplified Image Analysis Method was then applied to analyze the behavior of two fluctuating groundwater systems, namely, two-phase air-water and three-phase air-water-LNAPL, in a one-dimensional column, 3.5×3.5×50 cm, filled with Toyoura sand. The mass balance of the drainage-imbibition three-phase air-water-LNAPL system showed a difference of just 4.7% in LNAPL, demonstrating that this non-intrusive and non-destructive method is reliable for providing water and LNAPL saturation distributions throughout the domain when studying the effects of porous soil contamination by LNAPLs subjected to dynamic conditions.     

非饱和土水汽迁移与相变：两类“锅盖效应”的试验研究

“锅盖效应”定义为：不透水覆盖层下土体含水率大幅提高甚至饱和。最新的理论研究将“锅盖效应”分为两类,第一类由非饱和土内水气冷凝引起,第二类是冻结条件下由气态水迁移引起。为试验验证两类“锅盖效应”,研究其内在机理,利用新研制的非饱和冻土水汽迁移试验仪,对不同初始含水率的试样开展不同温度条件的水汽迁移试验。试验结果表明：冻结和未冻结两种状态均能使钙质砂试样顶部含水率增加,但冻结状态下的增加幅度显著。冻结状态下,含水率峰值位置与冻结锋面大致相同,且初始含水率越大,试样顶部和冻结锋面处的含水率增加越显著,降温速率越小,气态水迁移越显著;初始含水率增加也能使未冻结状态下的钙质砂试样顶部含水率增加,并且温度梯度对气态水迁移有一定的抑制作用,温度梯度越小,抑制作用越明显。试验结果很好地验证了两类“锅盖效应”的理论。     

Nitrogen leaching in a typical agricultural extensively cropped catchment,China: experiments and modelling

Protecting water resources from nitrogen (N) contamination is an important public-health concern and a major national environmental issue in China. Loss of N in soils due to leaching is not only one of the most important problems in agriculture farming, but is also the main factor causing N pollution in aquatic environments. The study area selected is in a typical agricultural extensively cropped land, Fuxianhu Lake catchment in Yunnan Province, China. Three sets of soil columns laboratory experiments were conducted to investigate the migration dynamics and leaching loss of N under different artificial rainfall intensities. One groundwater observation well in agricultural extensively cropped land was built to investigate the groundwater pollution caused by agriculture N loss. Based on the laboratory experiment and field monitoring results, the migration dynamics of ammonia-nitrogen (NH₄-N) and nitrate-nitrogen (NO₃-N) were analysed in detail. The LEACHMN model was used to test against the laboratory and field data to evaluate the drainage water and N leaching loss from the soil. The results indicate that the LEACHMN model is useful to carry out a numerical simulation of the water and N transport both in a laboratory experiment and in field monitoring. The findings of this paper help to demonstrate the distribution and migration of N in agricultural lands, as well as to explore the mechanism of groundwater contamination resulting from agricultural activities. The work presented in this paper is also believed to be useful in formulating management strategies for an extensively cropped catchment to reduce diffusive pollution from agricultural activities.