共查询到20条相似文献，搜索用时 199 毫秒
1.
土工膜和下伏压实黏土组成的复合衬层已被广泛用作填埋场的防渗屏障系统。有机污染物在复合衬层中迁移时,其主要运移机制是扩散作用。假设有机污染物在土工膜中稳态扩散,并假设在下伏衬层中扩散系数为迁移距离的线性函数,且考虑降解作用的影响,建立了有机污染物在复合衬层中的一维扩散模型,针对零浓度下边界条件,获得了模型解析解。基于该解析解,分析讨论了相关参数的敏感性。结果表明,相关参数对计算结果影响很大,降解半衰期对污染物运移同样存在较大影响。该解析模型仅适用于有机污染物在两层复合衬垫中的迁移问题,可为填埋场的初步设计提供参考 相似文献
2.
This paper gathered available flow and transport solutions and used them for two composite liners, consisting of geomembrane
(GM) overlying either a compacted clay liner (CCL) or a geosynthetic clay liner (GCL). Its aim is to provide a guiding framework
for the possible choices of (a) approaches to bottom liner design, (b) respective analytical solutions to flow and transport
equations, as well as (c) parameters required for each type of solution. On the basis of the obtained results, the following
recommendations are made. When the goal of analysis is to determine material equivalency, leachate flow rate is an adequate
key parameter for GM-CCL composite liners. For GM-GCL composite liners, it is necessary to compute contaminant concentration
or mass flux, considering (a) transport through defects for inorganic contaminants and (b) diffusion and the contribution
of any available attenuation layer for organic contaminants. When the goal of analysis is to assess impact to groundwater,
it is advised to calculate both discharge rate and contaminant mass flux regardless of liner type. The critical parameter
for the transport calculations is the retardation factor of the contaminant, for the case of CCLs, while the results for GCLs
are much less sensitive to this parameter. 相似文献
3.
Abbas El‐Zein 《国际地质力学数值与分析法杂志》2008,32(3):265-287
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. 相似文献
4.
Performance-based design of landfill liners 总被引：6，自引：0，他引：6
Factors affecting chemical transport in geomembrane, clay and composite liners are reviewed, and a simplified performance-based method for evaluating landfill bottom liners is presented. For single geomembrane liners, mass transport of inorganic chemicals is calculated from the leakage rate from holes for an assumed frequency of hole occurrence. Transport of organic chemicals is obtained by accounting for molecular diffusion through the intact geomembrane. Migration of inorganic and organic chemicals in compacted clay liners is calculated using a solution of the 1D advection–dispersion-reaction equation. For composite liners consisting of a geomembrane and a clay liner, 3D flow and transport of inorganic chemicals is approximated using an equivalent 1D model for transport through an effective area of transport. The approximation is based on results from 3D analyses that have been conducted for a variety of cases. Migration of organic chemicals through composite liners is calculated using a 1D diffusion model. Applicability of the method is illustrated by using it to evaluate the relative performance of several different liner systems. 相似文献
5.
The migration of contaminants through a 2.9 m thick compacted clay liner (CCL) for a landfill leachate lagoon is examined 14 years after construction. The clay liner formed the lower portion of the composite liner system but the geomembrane (GM) was found to have defects that had allowed leachate to migrate between the GM and CCL. Chloride, sodium, potassium, calcium and magnesium pore water profiles through the CCL are examined. It is shown that chloride migrated approximately 1.7 m into the CCL during the 14 years of the lagoon operation, sodium approximately 1.2 m, and potassium 0.7 m. Diffusion and sorption data from laboratory diffusion testing are utilized in combination with a finite layer contaminant transport model to predict field contaminant migration profiles through the composite liner system and to establish the time of ‘failure’ of the geomembrane at sometime between 0 and 6 years after installation. Relatively high sorptive uptake of potassium by the CCL soil is observed from batch testing and diffusion testing with field data suggesting an even larger amount of sorption. It is hypothesized that organic sludge matter at the base of the lagoon is responsible for potassium uptake from the leachate. This field case highlights the importance of the compacted clay liner as part of the composite liner system in acting as a diffusion barrier during the lifetime of the lagoon as well as using relatively non-conservative contaminants such as chloride and sodium to estimate geomembrane ‘failure’ times 相似文献
6.
有机污染物在完好复合衬垫中的迁移分析 总被引：1，自引：0，他引：1
在复合衬垫中,有机污染物除了在土工膜缺陷处发生迁移外,在完好土工膜中的迁移也是主要方式。考虑有机污染物在土工膜边界处的浓度跳跃现象,建立了有机污染物在完好复合衬垫中迁移的一维模型,得到了解析解。通过与有限差分解的比较,验证了解答的合理性。应用该解答分析了GCL复合衬垫和CCL复合衬垫防止有机污染物渗漏的效果。结果表明,CCL复合衬垫的效果较好,可以通过黏土改性和增加黏土厚度的方法来提高其有效性。有机污染物类型的选择对GCL复合衬垫的分析结果影响较大,而阻滞系数的变化对分析结果影响较小。 相似文献
7.
CCL吸附特性及孔隙率降低对污染物运移的影响 总被引：1，自引：0，他引：1
假定孔隙均匀地分布于土体的物质空间内和土骨架对污染物的吸附特性服从平衡线性,对基本体积质量关系进行分析,提出了由于土体对污染物的吸附而引起的孔隙率降低的估算公式。在考虑土体孔隙率变化的条件下,建立了污染物一维运移的控制方程,并考虑垃圾生物降解效应、压实黏土衬里（CCL）防渗层、下覆有限厚度含水层等实际情况,确定了初始条件和边界条件。对所建立的初边值问题进行了数值求解,且对某假想填埋场情况进行了变动参数与对比计算,结果表明,由于土颗粒对污染物的吸附所引起的孔隙率降低,显著地降低了污染物对压实黏土衬里的穿透能力。与常孔隙率情况相比,CCL中污染物的峰值浓度降低近10 %,含水层中污染物浓度降低更显著。当考虑土体孔隙率变化时,弥散对污染物运移具有控制作用,分布系数对污染物的运移具有重要影响。 相似文献
8.
In this paper, an extensive parametric sensitivity analysis of coupled consolidation and solute transport in composite landfill liner systems has been undertaken. The analysis incorporates results of more than 3000 simulations for various combinations of barrier thickness, waste loading rate, initial void ratio, compression index, hydraulic conductivity and dispersion coefficient. However, it is noted that to limit the extent of the study a constant coefficient of consolidation is assumed in the analysis presented here, though this assumption is easily relaxed. Results of the parametric sensitivity analysis are succinctly presented using dimensionless plots, which allow the comparison of results for a large number of parameter values, and so the clear identification of the most important determinants on contaminant transport through the liner system. The dimensionless plots demonstrate a pessimum (for which the ‘breakthrough time’ is minimised). Numerical results reveal that in cases of extreme liner compressibility an order of magnitude reduction in contaminant transit time may arise due to coupling between solute transport and consolidation, while for barriers of low compressibility and porosity (such as well-engineered composite compacted clay landfill liners), it is found that the contaminant transit time may still be reduced by more than 30%. The numerical results suggest that the use of coupled consolidation–contaminant transport models are sometimes required for informed and conservative landfill liner design. 相似文献
9.
Consolidation of clayey contaminant barriers such as landfill liners has been postulated as a cause of early breakthrough of contaminants. In this paper we theoretically investigate this proposition. For this purpose a sophisticated one‐dimensional, large‐deformation model of coupled mechanical consolidation and solute transport is employed. This new model is a generalization of existing coupled consolidation and solute transport models described in the literature. It takes into account both non‐linearities in geometry as well as constitutive relations. The latter relate the compressibility, hydraulic conductivity and coefficient of effective diffusivity to the deformation of the soil. The model is applied to a case study of a clay liner and geomembrane system. Results obtained from numerical solution of the model equations are compared with those from various simplified models, including a ‘diffusion only’ (i.e. a rigid soil) model traditionally used in contaminant barrier design. For barriers incorporating low compressibility soils (as for many well compacted clays), there is little difference between contaminant transit (i.e. breakthrough) times predicted by the two models. However, for contaminant barriers incorporating more compressible soils, consolidation is shown to significantly accelerate transport. These results indicate the potential importance of accounting for the effects of soil consolidation and highlight the limitations of existing models when modelling solute transport through composite barriers utilizing soft soils. Based on these limited results, we suggest a possible way of taking into account soil consolidation using simplified models. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
10.
土工合成材料粘土衬垫(GCL)与土工膜(GM)形成的复合衬垫在垃圾填埋场中的应用日益广泛。我国规范中允许在特殊情况下用GCL代替压实粘土(CCL)做垃圾填埋场的衬垫,但是对于“特殊情况”没有明确说明。本文采用数值方法对复合衬垫中无机污染物的对流和扩散进行了计算,从衬垫底部污染物通量和累积量两个角度对GCL复合衬垫和CCL复合衬垫阻滞污染物运移的效果进行了比较,分析两种复合衬垫的等效性,并研究了GCL复合衬垫的适用范围。结果表明,当渗滤液水头较高时,GCL复合衬垫体现出其优势。 相似文献
11.
An analytical model for vapor‐phase volatile organic compound diffusion through landfill composite covers 
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下载免费PDF全文 Haijian Xie Huaxiang Yan Hywel R. Thomas Shijin Feng Qihua Ran Peixiong Chen 《国际地质力学数值与分析法杂志》2016,40(13):1827-1843
One‐dimensional mathematical models for vapor‐phase volatile organic compound (VOC) diffusion through composite cover barriers are presented. An analytical solution to the model was obtained by the method of separation of variables. The results obtained by the proposed solution agree well with those obtained by a numerical analysis. Based on the proposed analytical model, the VOC breakthrough curves of five different composite covers are compared. The effects of degree of saturation of geosynthetic clay liner (GCL) or compacted clay liner (CCL) on VOC migration in the composite covers are then presented. Results show that the composite cover barriers provide much better diffusion barriers for VOC than the single CCL. The top surface steady‐state flux for a composite barrier, consisting of a 1.5 mm geomembrane (GM) and a 20 cm CCL, can be 8.3 times lower than that for a 30 cm CCL. The surface steady‐state flux for the case with (1.5 mm GM + 6 mm GCL) was found to be 2.3 times lower than that for the case with (1.5 mm GM + 20 cm CCL). The degree of saturation Sr of the CCL has a great influence on VOC migration in composite covers when Sr is larger than 0.5. The steady‐state flux at the surface of GM for the case with Sr = 0.7 can be 1.8 times lower than that for the case with Sr = 0.2. The proposed analytical model is relatively simple and can be used for verification of complicated numerical models, analysis of experimental data and performance assessment of composite cover barriers. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
12.
扩散是工程领域中的一种重要现象,尤其是针对填埋场底部的压实黏土垫层。扩散过程受多种因素影响,如离子种类、离子价态和离子浓度等,因此建立准确的扩散模型对填埋场垫层系统设计和评估具有极其重要的意义。引入简化的Guntelberg活度系数表示真实溶液与理想溶液浓度值的偏差,采用化学势和扩散势共同表征多离子扩散的驱动力,并考虑黏土介质特有的半透膜性能对离子扩散规律的影响,建立了复杂机制联合作用下多组分并存时离子在黏土垫层中的扩散模型。采用多物理场仿真软件COMSOL Multiphysics对所建扩散模型进行数值求解,结果表明,黏土半透膜效应、溶液非理想性和扩散势均显著影响多离子扩散行为,考虑黏土半透膜效应及溶液非理想性条件下,多离子扩散进程明显减缓,考虑扩散势时,阳离子扩散速度显著提高。复杂机制联合作用下,多离子扩散规律并非单一影响机制的简单叠加,各机制之间相互制约共同影响多离子扩散行为。 相似文献
13.
以单层压实黏土衬垫为研究对象,在传统对流弥散方程的基础上考虑温度梯度下污染物的热扩散运移,得到简化条件下半无限边界的解析解。研究表明,考虑热扩散效应所得的衬垫底部相对浓度和通量均大于传统对流弥散方程所得结果,ST越大时相对浓度和通量也越大,当ST=0.5 K-1时稳定通量达到ST=0时稳定通量2.5倍。热扩散通量是对流通量的-ASTD/v倍,两者均随时间的增加而增大;分子扩散通量则先增加达到峰值后减小趋于零。同时考虑温度对运移参数的影响和热扩散效应时,温度升高使衬垫底部相对浓度增大,导致击穿时间提前,污染物通量显著增大;当温度从30℃升高至70℃时,击穿时间从8.5 a提前至5.1 a,稳定通量增大约1.7倍。在进行衬垫设计时不考虑温度的影响将使污染风险大幅增加。 相似文献
14.
利用广义积分变换法推导了非等温条件下污染物在压实黏土衬垫中的运移解析解。所提出的解析解考虑了分子扩散、对流、吸附和热扩散的耦合效应,并考虑了压实黏土的渗透系数、分布系数和有效扩散系数3个参数随温度的变化。通过与热扩散试验结果、已有的解析解和基于COMSOL软件的数值模型的对比,验证了所提出的解析解。利用经过验证的解析解,研究了非等温环境以及压实黏土的渗透系数、有效扩散系数和分布系数3个参数随温度的变化对甲苯在压实黏土衬垫系统中迁移的影响。结果表明,非等温环境以及压实黏土的渗透系数、有效扩散系数和分布系数随温度的变化均对甲苯在压实黏土衬垫中迁移有着显著的影响。不考虑非等温环境的影响将极大低估污染物的溢出量和污染物的击穿时间。既有解析解忽略压实黏土的渗透系数和有效扩散系数随温度的变化会极大低估甲苯的流出速率,而忽略压实黏土分布系数随温度的变化会极大高估甲苯击穿衬垫系统的时间和达到稳态的时间。所提出的解析解能够考虑热扩散作用,同时考虑了压实黏土的渗透系数、分布系数和有效扩散系数3个参数随温度的变化,较既有解析解更贴近工程实际,能够为压实黏土衬垫系统的设计和服役性能评价提供指导和借鉴。 相似文献
15.
Saravanan Mariappan Masashi Kamon Faisal Haji Ali Takeshi Katsumi Tomoyuki Akai Toru Inui Masaki Nishimura 《Geotechnical and Geological Engineering》2011,29(5):881-898
This paper addresses the study conducted on the performance of landfill liner interface parameters. Interface shear strength
parameters for various combinations of 9 different lining materials were studied and presented in this paper. This comprehensive
testing program covers the interfaces between: (1) soil and compacted clay liner (CCL), (2) geomembrane (HDPEs or PVC) and
soil, (3) geosynthetic clay liner (GCL)/CCL and soil, (4) geomembrane and geotextile, (5) geotextile and soil, (6) geotextile
and GCL/CCL, and (7) geomembrane and GCL/CCL. The experiments were conducted for both at dry or optimum moisture condition
and at saturated or wet condition. The interface performance under both conditions were compared to access the material performances.
Tabulated summaries of interface test data under dry or optimum moisture condition (OMO) and saturated or wet condition are
presented in the paper. 相似文献
16.
垃圾填埋场复合衬垫剪切特性单剪试验研究 总被引：1，自引：0，他引：1
针对垃圾填埋工程中复合衬垫的界面抗剪特性,利用改进的叠环式单剪仪,对由砂土-无纺型土工布-土工网格-土工膜-夯实粘土组成复合衬垫进行了整体剪切试验研究。重点讨论了复合衬垫整体单剪试验的应力-位移曲线、相同剪切应力下各个界面的位移大小与变化特征和强度特性。研究结果表明：复合衬垫整体单剪试验的应力-位移曲线在低法向应力试验中没有呈现明显的软化特征,在高法向应力试验中有硬化现象;随法向应力增加剪切破坏面会发生转移;目前常用的把复合衬垫拆分为单个界面进行研究来确定最危险界面的方法不能够正确地反映填埋场中的复合衬垫在加载过程中的衬垫单元的实际受压变形情况和在剪切变形过程中最危险破坏面转移的情况;复合衬垫界面的抗剪强度包线呈现双曲线性质。 相似文献
17.
Acta Geotechnica - This paper presents analytical solutions for predicting one-dimensional diffusion of an organic contaminant through a triple-layer composite liner system comprising a geomembrane... 相似文献
18.
针对西北地区特殊的气候条件和砾质土料源丰富的实际情况,提出采用宽级配砾质土代替黏土作为土工合成材料膨润土垫(GCls)的保护层共同构成垃圾填埋场复合防渗系统的构想。文中选取宁夏银川地区冲-洪积作用形成的天然砾质土料,经人工掺和制配成满足规范对GCls防渗垫保护层渗透系数要求的宽级配砾质土样,在实验室对该土样进行了冻融循环作用下的渗透性能试验研究。结果显示,随着冻融次数的逐渐增加,土样的冻胀率逐渐变大,渗透系数也相应增大,经过12次冻融循环后,渗透系数约增大1～2个数量级;冻融循环初期,冻融作用对土样的影响最为剧烈,随着冻融循环次数的增加以及时间的延续,土样性状逐渐趋于稳定。由于宽级配砾质土对冻融循环作用的敏感性小于粉质黏性土,故采用宽级配砾质土作为Cls/GM的保护层共同组成填埋场复合防渗系统是值得期待的。 相似文献
19.
Preventing the penetration of rainwater into a landfill site is the main purpose of the final cover in landfill sites. Conventional designs of landfill covers use geotextiles, such as geomembrane and geosynthetic clay liners, and clay liners to lower the permeability of the final cover of landfill sites. However, differential settlement and climatic effects in landfill sites instigate crack development or structural damage inside the final cover. This study therefore investigates the field applicability of a self-recovering sustainable liner (SRSL) as an alternative to the landfill final cover. The SRSL utilizes the precipitation reaction of two chemical materials to form precipitates that fill the pores and thereby lower the overall permeability of the liner. To examine the field applicability of the SRSL system, uniaxial compression tests and laboratory hydraulic conductivity tests were performed under various climatic effects such as wet/dry and freeze/thaw processes. Furthermore, field-scale hydraulic conductivity tests were performed with intentionally induced cracks to demonstrate the self-recovery performance for practical applications. Extensive laboratory and field test results confirmed the capability of the SRSL final cover system to fulfill the strength and hydraulic conductivity requirements, even in harsh field conditions. 相似文献
20.
Composite landfill liner design with Ankara clay, Turkey 总被引：1，自引：0，他引：1
This study presents an overview of the geotechnical properties of the clayey soils, referred to as Ankara clay, at two sites of the Ankara region in an attempt to design a landfill profile composed of a high density polyethylene (HDPE) geomembrane/clay composite liner through the Hydrologic Evaluation of Landfill Performance (HELP) model and the Water Balance Method. The geotechnical properties of the landfill layers along with the water balance factors (i.e., evapotranspiration, precipitation, temperature, etc.) were assessed to determine the height of the water-saturated zone in the refuse above the composite liner for landfill design. The cumulative expected leakage rates through the composite liner constructed with compacted Ankara clay were related quantitatively to the cumulative average leachate head. The results of this investigation show that the leakage rates through the composite liner are within tolerable limits. 相似文献