钠基膨润土防水毯防渗效果有限元分析研究

根据石家庄市滹沱河防洪综合整治工程的实际情况和钠基膨润土防水毯的渗透系数,在河道中选取典型的断面,对铺设的钠基膨润土防水毯进行有限元渗流模拟,主要计算典型断面处的水力特性参数。模拟结果表明:钠基膨润土防水毯作为一种新型环保防渗材料,其防渗效果显著。随着水头的逐渐增加,单宽渗流量和各断面的最大水力梯度值均逐渐增大。模拟结果可为钠基膨润土防水毯在水利工程中防渗应用提供理论和技术支撑。     

膨润土防水毯在水利工程中的应用

介绍了钠基膨润土防水毯的优点,通过水利工程中底部防渗处理对钠基膨润土防水毯应用的工程总结,提出了对水利工程中钠基膨润土防水毯施工的几点建议。     

膨润土防水毯在地下室防水工程中的应用

膨润土防水毯(以下简称防水毯)是一种新型的环保型防水材料?它是由经级配过的天然钠基膨润土颗粒和相应的外加剂混合均匀后，经特殊的工艺及设备将其均匀、牢固地固定在两层土工布之间制成的防水毯。该材料具有优异的防水防渗性能，施工中可根据工程的需要单独使用或与其他防水材料共同使用，是一种较好的地下防水防渗材料。     

一种新型膨润土防水卷材的研制及其性能

以湖北某地的钙基膨润土为原料,经过人工改性处理,添加海藻酸钠作为粘结剂,并在多种化学药剂和工业用水的参与下充分搅拌均匀,在高温高压密闭的环境中充分反应,将反应后的物料通过真空挤出机制成致密薄片状产品,覆膜打卷最终制成新型膨润土防水卷材.对新型膨润土防水卷材的生产过程进行了叙述;并对其防水防渗性能进行测试,主要包括相同水利坡度下的渗透系数、耐静水压、模拟不同浸出液试验,新型膨润土防水卷材的应用领域可拓展到海水、油类和渗透液复杂情况下的防水防渗,而且其性能明显优于普通膨润土防水毯.     

世博主题馆地下民防工程防渗施工工艺

介绍了世博主题馆地下民防工程采用膨润土防水毯进行防渗的施工工艺,重点对大面积铺设膨润土防水毯的施工工艺及细部防水处理进行了详细阐述。     

膨润土防水毯的施工与质量控制

膨润土防水毯(以下简称防水毯)是一种新型的土工合成环保型防水材料.它由经级配过的天然钠基膨润土颗粒和相应的外加剂混合均匀后,经特殊的工艺及设备,依靠成千上万纤维的强度把高膨胀性的钠基膨润土层均匀、牢固地固定在两层土工布之间.如此制成防水毯,既具有土工材料的全部特性,又具有优异的防水防渗性能,施工中可根据工程的需要单独使用防水毯防水,也可与其他土工材料或防水材料共同使用,是现代土工工程中无可替代的地下防水防渗材料.……     

膨润土防水毯的研制及其在垃圾填埋场中的应用

在简单介绍膨润土材料的性能特点、防水机理和作为防水材料的发展历史的基础上，着重介绍膨润土防水毯(GCL)的研制过程及其主要技术指标，并对生产和使用中需要关注的问题进行讨论。结合垃圾填埋场对防渗材料要求的分析，介绍膨润土防水毯在垃圾填埋场中的应用方法。     

膨润土防水毯在垃圾填埋场中的应用

简要介绍了国内外膨润土防水毯在垃圾填埋场中的应用情况,分析了膨润土防水毯作为垃圾填埋场防渗层的防水机理,阐述了其主要技术性能指标、优缺点和施工技术。     

关于膨润土防水毯防渗性能及稳定性的影响因素分析

总结了钠基膨润土防水毯（GCL）的防渗机理,从膨润土质量特性、渗透液水质、干湿循环、冻融循环等方面对GCL防渗性能及服务期稳定性的影响因素进行了论述,希望对改善防水毯性能研究提供参考。     

常州北站人工湖防渗工程施工技术

介绍了常州北站北侧公园人工湖防渗工程中主要采用Bentomat膨润土防水毯的施工应用技术,重点阐述了人工湖防渗工程的基面处理、材料准备、细部节点处理、铺设工艺等环节,指出只要认真把握每一个影响工程质量的关键环节,Bentomat膨润土防水毯在人工湖防渗工程中应用就可以获得良好的效果.     

膨润土中饱和渗透系数的计算

 当土工合成黏土衬垫用作垃圾填埋场衬垫时，渗滤液可能对其渗透性能产生重要的影响。为克服渗透试验可重复性差和试验时间长等缺点，从微观角度对土工合成黏土衬垫的饱和渗透系数进行研究。首先，以现有的膨润土微观结构的研究成果为基础，结合SEM方法对膨润土微观结构的分析结果，得出粒内孔隙比随CaCl2溶液浓度的变化规律。然后，将膨润土看作双重孔隙介质，推导出粒间孔隙内凝胶态蒙脱石矿物层间距离的计算公式。最后，根据Poiseuille定律，得到能够考虑CaCl2溶液浓度和孔隙比变化的膨润土饱和渗透系数的改进计算方法，并通过计算渗透系数与实测值的比较验证了这种渗透系数计算方法的有效性。结果表明，膨润土饱和渗透系数的变化是由表观孔隙率和凝胶体蒙脱石层间距离的共同作用引起的。     

氨氮在土工合成黏土衬垫中的扩散行为研究

氨氮是垃圾渗滤液中最具代表性的污染物之一,但其在土工合成黏土衬垫(GCL)中的扩散行为至今尚未得到重视。开展批式吸附试验和扩散试样浸提试验测定氨氮在GCL中的吸附分配系数;进行扩散试验测定氨氮在GCL中的扩散系数;基于试验得到的吸附分配系数和扩散系数,使用数值软件POLLUTE v7.0对氨氮在GCL中的运移行为进行模拟。试验结果表明,氨氮在膨润土上的吸附分配系数为0.017L/g,在GCL中的扩散系数约为9.0×10^-11m²/s。POLLUTE v7.0的模拟结果显示,当考虑扩散存在时,氨氮将提前30 a击穿GCL。     

Shear strength of geosynthetic composite systems for design of landfill liner and cover slopes

Torsional ring shear tests were performed on composite specimens that simulate the field alignment of municipal solid waste (MSW) landfill liner and cover system components. Simultaneous shearing was provided to each test specimen without forcing failure to occur through a pre-determined plane. Composite liner specimens consisted of a textured geomembrane (GM) underlain by a needle-punched geosynthetic clay liner (GCL) which in turn underlain by a compacted silty clay. Hydrated specimens were sheared at eleven different normal stress levels. Test results revealed that shear strength of the composite liner system can be controlled by different failure modes depending on the magnitude of normal stress and the comparative values of the GCL interface and internal shear strength. Failure following these modes may result in a bilinear or trilinear peak strength envelope and a corresponding stepped residual strength envelope. Composite cover specimens that comprised textured GM placed on unreinforced smooth GM-backed GCL resting on compacted sand were sheared at five different GCL hydration conditions and a normal stress that is usually imposed on MSW landfill cover geosynthetic components. Test results showed that increasing the GCL hydration moves the shearing plane from the GCL smooth GM backing/sand interface to that of the textured GM/hydrated bentonite. Effects of these interactive shear strength behaviors of composite liner and cover system components on the possibility of developing progressive failure in landfill slopes were discussed. Recommendations for designing landfill geosynthetic-lined slopes were subsequently given. Three-dimensional stability analysis of well-documented case history of failed composite system slope was presented to support the introduced results and recommendations.     

粘土环境岩土工程特性对填埋场衬垫防渗标准的影响

采用溶质运移的一维迁移模型,研究了粘土环境岩土工程特性对填埋场衬垫防渗标准的影响,对目前采用的填埋场粘土类衬垫防渗设计标准及其有效性进行了多参数组合的计算分析;此外,还比较了粘土衬垫与复合衬垫对污染物离子的防渗阻隔性能,对土工膜在衬垫中的作用进行分析;研究表明,应针对不同地区的情况(干旱少雨或多雨等)考虑衬垫的形式。与其他因素相比,粘土的渗透系数对衬垫层渗漏影响最大,以水力渗透系数作为填埋场粘土衬垫的设计标准是可行的,但离子扩散系数的影响也不可忽略;而增强粘土的活性,提高粘土吸附离子的性能,则可延长离子通过衬垫的击穿时间;与单纯的粘土衬垫相比,复合衬垫对离子具有更好的阻隔性能,故在南方多雨地区宜采用复合衬垫;而用污染物的渗漏总量作为填埋场衬垫的设计标准比击穿时间更合理。     

Evaluation of interface shear strength of composite liner system and stability analysis for a landfill lining system in Thailand

The paper presents the case history of laboratory evaluation of the interface shear strength properties of various interfaces encountered in a modern day landfill with emphasis on proper simulation of field conditions and subsequent use of these results in the stability analyses of liner system. Over 70 large direct shear tests were systematically conducted to evaluate the interface shear strength properties of composite liner system using project specific materials under site specific conditions, being used at non-hazardous and hazardous landfills project situated in Sa Kaeo Province, Thailand. The critical interfaces were located between the geotextiles and the smooth geomembrane (GM), the smooth GM and the geosynthetic clay liner (GCL), and the smooth GM liner and the compacted clay liner (CCL) with the interface friction angles ranging from 6.5° to 10.5° for dry conditions and 6.5° to 9.5° in wet conditions. The residual shear stress for these interfaces was attained at a displacement less than 4 mm. Three methods, namely, limit equilibrium method (LEM), limit method (LM), and the simple composite column (SCC) approach were used to evaluate the tensile loads induced in the geosynthetic components. The SCC approach proposed by Liu, C.N. [2001. Tension of geosynthetics material regarding soils on landfill liner slopes. Proceedings, National Science Council ROC(A), 25(4), 211–218] that takes into account the force equilibrium as well as displacement compatibility yielded satisfactory results. The factor of safety for geosynthetic components in the liner was found to be greater than 3.0 for both types of landfill.     

我国四类衬垫系统防污性能的比较分析

对我国填埋场采用的四类衬垫进行了防污性能的比较分析。评价参数包括渗漏率、污染物击穿时间及衬垫系统底部浓度值。除了2m压实黏土衬垫(CCL)外,其余3种均为包含土工膜(GM)的复合衬垫。分析模型采用了污染物通过有缺陷膜复合衬垫的一维运移解析解。以镉离子(Cd2+)为渗滤液中重金属离子的代表;以苯为其中挥发性有机污染物的代表。研究表明土工复合膨润土垫(GCL)复合衬垫的渗漏率最小,2m黏土最大,两者的差别可在3～5个数量级。GCL复合衬垫对重金属离子具有较好的防污性能,尤其是在高水头及复合衬垫接触较差的情形。厚度较大的2m黏土对挥发性有机污染物的防污性能较好,其击穿时间要比GCL复合衬垫大2～3个数量级。随着水头的增大,CCL复合衬垫的防污性能逐渐地优于2m黏土。在10m水头作用下,CCL复合衬垫底部的100年浓度可比2m黏土小近一个量级。单层膜衬垫的防污性能较差,不适合作为填埋场的衬垫系统。控制填埋场复合衬垫的施工质量和渗滤液水头尤为重要。     

Landfill side slope lining system performance: A comparison of field measurements and numerical modelling analyses

Low permeability engineered landfill barriers often consist of a combination of geosynthetics and mineral layers. Even though numerical modelling software is applied during the landfill design process, a lack of data about mechanical performance of landfill barriers is available to validate and calibrate those models. Instrumentation has been installed on a landfill site to monitor multilayer landfill lining system physical performance. The lining system comprises of a compacted clay layer overlaid by high density polyethylene geomembrane, geotextile and sand. Data recorded on the site includes: geosynthetic displacements (extensometers), strains (fibre optics, Demec strain gauges, extensometers) and stresses imposed on the liner (pressure cells). In addition, temperature readings were collected by a logger installed at the surface of the geomembrane, at the clay surface using pressure cell thermistors and air temperature using a thermometer. This paper presents readings collected throughout a period of three years and compares this measured performance with the corresponding numerical modelling of the lining system for stages during construction. Numerical modelling predictions of lining system behaviour during construction are comparable with the measurements when the geosynthetics are covered soon after placement, however, where the geosynthetics are left exposed to the sun for an extended period of time, in situ behaviour of the geosynthetics cannot be replicated by the numerical analysis. This study highlights the significant influence of the effect of temperature on geosynthetics displacements. A simple thermal analysis of the exposed geosynthetics is used to support the explanation for observed behaviour.     

Prefabricated bentonite clay liners

The development and use of prefabricated bentonite clay liners is a relatively recent development, even for a technology as young as geosynthetics. There are four currently available commercial products, each of which consists of essentially dry bentonite clay agglomerates (with or without a dry, but water soluble, adhesive) placed on a geotextile or geomembrane carrier layer. Often a covering geotextile is used above the clay, and for two of the products, the entire ‘sandwich’ is needled throughout.

For landfill liner systems, the major use of these materials appears to be as the lower component of a composite primary liner. This use is particularly interesting in the light of response action plans (RAPs) which are being required by many regulating agencies. For landfill closure systems, these materials can readily form the lower component of a composite cap system. Of interest here is their possible capacity to follow subsidence of the landfill and their ability to deform in an out-of-plane manner.

With the newness and potential of prefabricated bentonite clay liners, however, comes a number of questions. This paper attempts to present these questions and the currently available answers regarding the various products. In concludes by giving a number of suggestions and cautions for field placement based on the authors' experiences to date.     

Controlling strain in geosynthetic liner systems used in vertically expanded landfills

According to relevant new regulations in China,a composite liner system involving geosynthetic materials must be installed at the bottom of an expanded landfill.The deformation and integrity of the composite liner under a variety of factors are important issue to be considered in the design of a landfill expansion.In this paper,we investigate the strain distribution in geosynthetic materials within the composite liner system of expanded landfills,including strains in geosynthetic materials resulting from overall settlement and lateral movement of landfills,localized subsidence in landfills,and differential settlement around gas venting wells.The allowable strains of geosynthetic materials are discussed based on the results of tensile tests,and the corresponding design criteria for composite liner systems are proposed.Meanwhile,practical measures allowing strain control in geosynthetic materials used in landfill engineering are proposed.