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1.
Successful design of soil liner and covers for landfills and waste impoundments involves selection of liner material and assessment of chemical compatibility of the liner material. In this work locally available materials with different mineralogy have been evaluated from the viewpoint of liner application. Many local soils may not meet the requirements of liner material; often it is necessary to amend these soils with commercially available processed bentonite. Clay liners may be attacked by chemical waste or leachate, concentrated organic chemicals can attack compacted clay effectively destroying the characteristics of liner material. Thus the main aim of this work has been to assess the suitability of different types of locally available materials for their potential use as liners for waste containment facilities. The materials studied are kaolinitic red earth, illite and fly ash. Based on literature survey and experimental work in this laboratory, 20% by weight of bentonite has been chosen for amending selected materials. Addition of 20% bentonite to selected liner material improved the hydraulic conductivity and adsorption capacity of the amended mixture but, reduced the volume stability. To improve the volume stability of the amended material and to have better resistance towards chemicals attack, stabilizing the amended mixture with 1% by weight of lime has been considered. The relative advantages and disadvantages of four materials namely; red earth with 20% bentonite, illite with 20% bentonite, fly ash with 20% bentonite and illite alone, stabilized with 1% by weight of lime were brought out. The chemical compatibility of the materials to electrolyte solution (0.5 N NaCl), alkaline solution (0.5 N NaOH), acid (0.5 N HCl) and organic fluid (CCl4) has been studied. The relative efficiency of the selected materials with selected pore fluids was compared.  相似文献   

2.
This paper details technical aspects associated with electrical conductivity measurements within saturated clays and presents experimental work to show the direct application of electrical techniques to track ionic movement through clay under chemically induced flow. The study confined itself to kaolin using both naturally sedimented samples and consolidated samples. Regarding the latter, a Rowe cell was adapted to allow electrical measurements to be taken both normal and parallel to the direction of loading. Bulk conductivity measurements and measurements on the conductivity of the interstitial pore fluid were used to quantify the pore tortuosity and effective diffusion coefficient of saturated clay. In addition, predicted concentration time curves agreed well with those estimated from conductivity measurements.  相似文献   

3.
Shear Strength Behavior of Two Landfill Clay Liners   总被引：1，自引：0，他引：1  
Direct shear tests were conducted to obtain both the shear strength of compacted clay liners (CCLs) specimens and the interface shear strength between compacted clay liner and base soil. These experiments were conducted under the conditions of five different water contents. The experimental results show that shear strength of both CCLs and CCLs/base interface decreases with the increase in the water content of CCLs and base soil. In addition, the considerate concentration of NaCl in leachate has no deteriorating effect on the shear strength of liners. Triaxial shear tests were also conducted on clay liner specimens to obtain total and effective shear strength under a fast compression. The shear strength c‘=100 kPa for sand-bentonite, respectively. These results indicate that the compacted clay-bentonite shows normal consolidation, but that the compacted sand-bentonite exhibits over-consolidation.  相似文献   

4.
膨润土改性黄土衬里防渗性能室内测试与预测   总被引：2，自引：0，他引：2  
试验测定了膨润土改性黄土试样的渗透系数,研究膨润土改性黄土用作废弃物填埋场衬里的可行性,为天然黏土匮乏地区防渗材料本土化提供依据。选取两种代表性黄土,即黏性较大的兰州黄土(LH)和砂性较大的榆林黄土(YH),分别向其中添加不同比例的两种膨润土后击实成样,利用柔性壁渗透仪测定改性黄土的渗透系数,分析了改性黄土渗透系数随膨润土添加率增大的变化规律,确定了满足衬里防渗要求的膨润土添加率。利用扫描电镜照片统计了改性黄土的孔隙特征参数,发现添加膨润土后黄土中原有的大孔隙被充填或分隔成更多的中、小孔隙,有效阻滞了渗流液体通过,从微观结构的角度揭示了改性黄土渗透性降低的实质。依据实测数据建立了膨润土改性黄土的渗透回归模型,据此可以预测不同添加量的膨润土改性黄土的渗透系数。  相似文献   

5.
首先对斑脱土衬里(粘土-斑脱土、砂-斑脱土) 进行变水头实验, 得粘土-斑脱土的渗透系数为6.0×10-9~3.0×10-8cm/s, 砂-斑脱土的渗透系数为1.0×10-9~3.0×10-9cm/s.从防渗角度分析, 2种斑脱土混合物均适合作垃圾填埋场的底层衬里.然后对斑脱土衬里进行持水与水迁移实验, 评价斑脱土衬里水的迁移特性.以水迁移实验为基础, 模拟斑脱土衬里与地基5种不同含水量的条件, 对斑脱土衬里进行直接剪切实验, 测定斑脱土衬里的剪切强度及斑脱土衬里与地基接触面的剪切强度.再对斑脱土衬里进行三轴固结不排水实验, 测定其总剪切强度与有效剪切强度.实验结果表明: 地下水具有很大的潜力从地基流向斑脱土衬里, 从而大大提高斑脱土衬里的含水量; 随着含水量的增加, 粘土-斑脱土、砂-斑脱土衬里的抗剪强度逐渐减小.根据实验所获得的抗剪强度参数, 选择日本山谷型垃圾填埋场典型剖面, 对山谷型垃圾填埋场进行稳定性评价.结果表明: 对于角度小于20°的缓倾角山谷型垃圾填埋场, 使用粘土-斑脱土、砂-斑脱土作为底层衬里是稳定的.因此, 2种斑脱土混合物适合作山谷型垃圾填埋场的底层衬里.   相似文献   

6.
Pollution of the environment due to leakage from waste repositories is a well-known and wide spread problem. Emphasis has therefore been put on design of liners for such repositories, focusing on hydraulic conductivity and its variation with time, liner composition, water content, compaction etc. The paper addresses the hydraulic conductivity of sand/bentonite mixtures, especially the variation of the hydraulic conductivity as a function of bentonite content, compaction and degree of saturation. In order to better understand the variation of the hydraulic conductivity of a sand–bentonite mixture a new parameter k 1 has been proposed. The parameter reflects the amount of bentonite per pore volume and can easily be calculated based on the amount of bentonite and the dry density of the soil mixture. Thereby, the hydraulic conductivity can be predicted as a function of different degres of compaction. This method can be used for engineering purposes to predict the hydraulic conductivity at an early stage of a design to get an idea of the required design and hence, cost.  相似文献   

7.
 The design of environmentally sound liquid waste containment structures has become a crucial task in engineering applications due to ever increasing groundwater contamination from such sites. Construction of such structures usually requires a bottom liner of low hydraulic conductivity as part of the design. In order to reduce the hazards associated with liquid wastes including landfill leachate, bentonite-amended natural zeolite is proposed as an alternative to conventional earthen liners. Among many contaminants associated with liquid wastes, heavy metals are the most dangerous ones. This paper deals with determining the ability of natural zeolite to remove heavy metals from aqueous waste. For this purpose, crushed natural zeolite (clinoptinolite) is amended with commercial powdered bentonite to yield a soil mixture low in permeability and high in ion-exchange capacity. Leachate from a conventional landfill is used as the percolation fluid. Concentrations of certain heavy metals in the effluent fluid percolated through the bentonite-zeolite mixture are compared with that of initial leachate. The conclusion is reached that certain metals are efficiently removed from the influent solution by the soil matrix whereas some ions do not show significant reduction in concentration. This is attributed to high hydraulic conductivity of the bentonite-zeolite mixture.  相似文献   

8.
An analytical solution for one-dimensional contaminant diffusion through multi-layered media is derived regarding the change of the concentration of contaminants at the top boundary with time. The model accounts for the arbitrary initial conditions and the conditions of zero concentration and zero mass flux on the bottom boundary. The average degree of diffusion of the layered system is introduced on the basis of the solution. The results obtained by the presented analytical solutions agree well with those obtained by the numerical methods presented in the literature papers. The application of the analytical solution to the problem of landfill liner design is illustrated by considering a composite liner consisting of geomembrane and compacted clay liner. The results show that the 100-year mass flux of benzene at the bottom of the composite liner is 45 times higher than that of acetone for the same composite liner. The half-life of the contaminant has a great influence on the solute flux of benzene diffused into the underlying aquifer. Results also indicates that an additional 2.9–5.0 m of the conventional (untreated) compacted clay liner under the geomembrane is required to achieve the same level of protection as provided by 0.60 m of the Hexadecyltrimethylammonium (HDTMA)-treated compacted clay liners in conjunction with the geomembrane. Applications of the solution are also presented in the context of a contaminated two-layered media to demonstrate that different boundary and initial conditions can greatly affect the decontamination rate of the problem. The method is relatively simple to apply and can be used for performing equivalency analysis of landfill liners, preliminary design of groundwater remediation system, evaluating experimental results, and verifying more complex numerical models.  相似文献   

9.
For materials of very low hydraulic conductivity used in the landfill liner systems, e.g., natural clay liners, soil-cement liners, etc., diffusion characteristics should be evaluated, as the transport mechanism of contaminant through them is diffusion controlled. Studies on the diffusion characteristics of the hardened liner materials, such as the soil cement, are relatively few compared with those of clayey soils. In this paper, diffusive characteristics of hardened liner materials (HLMs) applied to the liner system of Sudokwon Metropolitan Landfill in Korea, were studied. Laboratory pure diffusion column tests in the pure- and the advection-diffusion status were performed for the chemicals, NaCl, KCl, and CaCl2. To evaluate the diffusion coefficient of a HLMs system, a one-dimensional numerical transport program was developed for use in a multi-layered HLMs system. The range of dispersion coefficients of advection diffusion column tests was a little narrower than that of diffusion coefficients of pure diffusion tests, although the two coefficients were quite close. The effective diffusion coefficients of chloride ions of a HLMs were about a half of those in clayey soil due to the high density by compaction and curing. Diffusion coefficients of chloride ions in this study were correlated closely with hydraulic conductivities of the materials tested and were consistent with work in the literature.  相似文献   

10.
Compacted soil–bentonite mixtures are finding wide application as buffer material for waste repositories for their favorable self-sealing qualities. The swelling properties of such materials which serve as a measure of their self-sealing capabilities and, thus, the efficiency of the repository in sealing off their contents from the environment are closely related to the chemistry of the leachate that emanate from the wastes. For this reason, the swelling parameters (namely swelling potential and pressure) of compacted lateritic soil–bentonite mixtures under consideration for use as barrier in municipal waste landfill were evaluated. Series of swelling potential and pressure tests were performed using variable content (0–10 %) of bentonite at predetermined optimum moisture content. Soil mixtures were compacted with British Standard Heavy compactive effort and saturated with processed tap water as well as three leachate solutions of varying ionic strength that were generated in active open dump landfills. Experimental results showed that swelling potential based on the free swell together with the maximum swell pressures of compacted soil mixtures measured at equilibrium increased approximately linearly with increase in the amount of bentonite when inundated with processed tap water and the three leachate solutions. On the other hand, these swelling parameters decreased as the ionic strength of the leachate solutions measured by their electrical conductivity increased for the various soil mixtures. These results provide an insight into the swelling behavior and the possible degradation in the efficiency of the proposed lateritic soil–bentonite mixtures in relation to their use as buffer material in waste landfills.  相似文献   

11.
Hydraulic conductivity is a dominant parameter in the design of engineered waste disposal facilities such as landfill liners and covers, lagoon liners and slurry walls. It is of interest to a geotechnical or geo-environmental engineer to develop a predictive method of determining the hydraulic conductivity of fine-grained soils, in order to assess its suitability as a liner material. To predict the hydraulic conductivity of soils, researchers and geotechnical engineers have attempted to correlate it with index properties of the soils, such as the liquid limit, void ratio and specific surface. Based on the present study a predictive method has been developed in this paper to predict the hydraulic conductivity in terms of void ratio and shrinkage index (Liquid limit – shrinkage limit) for remoulded fine-grained soils. Though the initial conditions for the soil will affect the hydraulic conductivity behaviour to some extent, both the void ratio and soil characteristics are primary factors in affecting the hydraulic conductivity. Therefore for predictive purpose, the study of hydraulic conductivity behaviour of remoulded fine-grained soils as presented in this paper can be found to be useful for compacted soils also.  相似文献   

12.
Clay liners or compacted earthen barriers are important barrier materials used for preventing contaminant transport through soils. A low hydraulic conductivity (k) is a significant parameter that governs the design and construction of clay liners. Compacted expansive clays, which are montmorillonite clays, also have a very low hydraulic conductivity (k). When expansive clays are blended with fly ash, an industrial waste, the hydraulic conductivity (k) further reduces as the ash-clay blends result in increased dry densities at increased fly ash contents. Hence, fly ash-stabilised expansive clay can also be proposed as a unique clay liner material. As expansive clays undergo heave when they come into contact with water, it is necessary to study the heave behaviour of fly ash-stabilised expansive clay liners. This paper presents heave studies on fly ash-stabilised expansive clay liners. Fly ash in different contents by dry weight of the expansive clay was added to the clay, and the ash-clay blend was compacted as a liner overlying a natural field soil layer. Compacted lateritic clay was used for simulating the natural field soil into which contaminants migrate. Calcium chloride (CaCl2) solution of varying concentration (5, 10, 20, 50, 100 and 500 mM) was used as the permeating fluid in the heave studies. The rate of heave and the amount of heave of the fly ash-stabilised expansive clay liners were monitored. Deionised water (DIW) was also used as inundating fluid for comparative study. Heave (mm) decreased with increase in solute concentration for all fly ash contents. For a given solute concentration, heave decreased up to a fly ash content of 20 % and thereafter it increased when the fly ash content was increased to 30 %. Heave of the fly ash-stabilised expansive clay liners was correlated with their permeability, liquid limit (LL) and free swell index (FSI) pertaining to the respective fly ash content and CaCl2 concentration.  相似文献   

13.
Compacted soil–bentonite liners, consisting of a sandy soil mixed with bentonite as backfill, are used extensively as engineered barriers for contaminant containment. This paper studies the valorization of local materials containing calcareous sand, tuff obtained from Laghouat region (in the South Algeria), to associate with bentonite in order to improve their hydraulic characteristics for use as landfill liner material. Firstly, a geotechnical characterization of mixtures chooses from a fixed percentage to 10% bentonite and different percentages of calcareous sand and tuff so that they are complementary to 90% by not 10%. Thereafter, the determination of saturated hydraulic conductivity at falling-head permeability (Kv) and oedometer (Kid, indirect Measure) tests of all compacted mixtures at Optimum Normal Proctor have been carried out using both permeates by tap water and a landfill leachate in order to simulate long-term conditions. The results showed that the saturated hydraulic conductivity of tap water is relatively lower than the one saturated by leachate in the falling-head test, unlike the oedometer test. The B10CS20T70 mixture has satisfied the hydraulic conductivity criterion of bottom barriers (i.e. water permeated: kv20° = 1.97 × 10?9 and kid from 7 × 10?9 to 1.83 × 10?10 < 10?9m/s; leachate permeated: kv20° = 2.91 × 10?9 and kid from 7 × 10?9 at 1.44 × 10?10 < 10?9 m/s). Finally, a comparison between direct measurements of the saturated hydraulic conductivity by triaxial (Kd) test and oedometer test (Kid) in the range of effective stress applied 100–800 kPa led to propose equations of correlations between these two methods. In conclusion, adopted formulation B10CS20T70 perfectly meets the regulatory requirements in force and constitutes an economic product based on available local materials for engineers barriers.  相似文献   

14.
徐江伟  余闯  蔡晓庆  杨萌 《岩土力学》2015,36(Z1):109-114
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   

15.
Clay-bearing Upper Pliocene red clastics and Quaternary alluvial deposits occupy the Ankara basin. The clayey levels of the Upper Pliocene deposits, referred to as Ankara clay, is considered as a source for compacted clay liners due to their low coefficients of permeability and widespread distributions throughout Ankara. This study investigates the geological, geotechnical and mineralogical properties of the founding clayey soils at two sites of the Ankara region. The geotechnical index properties along with the hydraulic conductivities of the clayey soil samples collected from these sites were determined. A mathematical relation between the clay mineralogical content and hydraulic conductivity was established. The results of this investigation show that, from a geotechnical point of view, Ankara clay may be regarded as a highly suitable material for a compacted clay landfill liner given that its mineralogical compatibility with leachate is confirmed.  相似文献   

16.
The degree of saturation of compacted bentonite buffer in deep geological repositories is subject to alterations from infiltration of groundwater and heat emanated from the waste canisters. The matric suction (ψ)–degree of saturation (S r ) relations of unsaturated clays is represented by soil–water characteristics curves (SWCC) that are influenced by soil structure, initial compaction condition and stress history. Infiltration of groundwater besides increasing the degree of saturation can also alter the pore water chemistry; the associated changes in cation hydration and diffuse double layer thickness could impact the micro-structure and matric suction values. This study examines the influence of infiltrating sodium chloride solutions (1,000–5,000 mg/L) on the transient ψ–S r relations of compacted bentonite–sand specimens. Analysis of the ψ–S r plots, and X-ray diffraction measurements indicated that infiltration of sodium chloride solutions has progressively less influence on the micro-structure and SWCC relations of bentonite–sand specimens compacted to increasingly higher dry densities. The micro-structure and SWCC relations of specimens compacted to 1.5 Mg/m3 were most affected, specimens compacted to 1.75 Mg/m3 were less affected, while specimens compacted to 2 Mg/m3 remained unaffected upon infiltration with sodium chloride solutions.  相似文献   

17.
扩散系数和渗透系数是设计与评价垃圾填埋场衬垫等环境工程研究时需要确定的重要参数。通过分析粘土衬垫材料中渗透系数和扩散系数的物理意义和确定方法,在土多孔介质微观结构分析的基础上得到渗透系数和扩散系数的关系表达式,并基于蒙脱石层间Poiseuille定律得到膨润土有效扩散系数的计算公式。验证表明,在一定精度范围内文中表达式是有效的。得出的渗透系数和扩散系数的关系表达式,对于根据已有渗透系数的研究成果来预测和分析扩散系数是有意义的。   相似文献   

18.
The effects of post-compaction residual lateral stress and salt concentration in the hydrating fluid on swelling pressures of compacted MX80 bentonite is brought out in this paper. In order to release the residual lateral stresses, following the static compaction process during preparation of specimens, compacted bentonite specimens were extruded from the specimen rings and then inserted back prior to testing them for swelling pressures in isochoric condition. The swelling pressure tests were carried out at several dry densities of the bentonite with distilled water and solutions of NaCl (0.1 and 1.0 M) as the hydrating fluids. With water, the test results showed that specimens that underwent extrusion and insertion processes exhibited about 10–15 % greater swelling pressures as compared to the specimens those that were compacted and tested. The influence of saline solutions was found to reduce the swelling pressure of the bentonite, but their impact was less significant at high compaction dry densities.  相似文献   

19.
In this study, an investigation was performed to determine if lime-stabilized sand–bentonite mixtures are appropriate for the construction of sanitary landfills liners. For this aim, the hydraulic conductivity tests were conducted in the laboratory on sand–bentonite mixtures and lime-stabilized sand–bentonite mixtures to evaluate the effect of wetting–drying cycles. The hydraulic conductivity tests were performed to see if their hydraulic conductivities are affected by wetting–drying cycles. First series of specimens have been prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in proportions of 20, 30, 40, and 50 %. In the second series of the specimens, lime in proportions of 1, 2 and 3 % by weight was added to the mixtures of sand–bentonite in proportions of 20, 30, 40, and 50 %. From the results of the tests, it was observed that while optimum water content increased, maximum dry density decreased with addition of lime to the sand–bentonite mixtures. Generally, the hydraulic conductivity increased with the addition of lime to the mixtures but at low percentages of lime (1–2 %), however, slight decreases in k were recorded. It was also observed that the wetting–drying cycles on the permeability test indicate cure effect on specimens with addition of lime which resulted in decreased the hydraulic conductivity.  相似文献   

20.
In current geoenvironmental practice, design engineers usually require that soil liners in waste landfills be compacted within a specified range of water content and dry unit weight. This specification is based primarily on the need to achieve a minimum dry unit weight for factors controlling the performance of compacted soil liners most especially the hydraulic conductivity, k. In this study, lateritic soil treated with up to 10% bentonite, prepared at various compaction states (dry of optimum, optimum and wet of optimum moisture content) was compacted with four compactive efforts (i.e., the reduced British Standard Light, British Standard Light, West African Standard, and British Standard Heavy) to simulate the range of compaction energies expected in the field. Prepared soil mixtures were permeated with water and specimens that yielded the permissible limit of k????1?×?10?9?m/s were enclosed in an envelope (known as the acceptable zone) on the water content?Cdry unit weight curve. It was observed that compaction conditions resulting in moisture content slightly wet of optimum led to the lowest values of k and that the shapes and boundaries of the acceptable zones gradually increased in extent, shifting to wet side of optimum moisture content as the bentonite content increased to 10%. This approach provides good control over the quality of compacted soils and has great potential for field application.  相似文献   

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