Geotextiles in India

Applications of geotextiles in civil engineering have been successfully developed and offer benefits in terms of economics, durability and p performance. Geotextiles play an important role in geotechnical engineering works, especially highways and railroads, reinforced soil, stabilisation of soil or rock slopes, drainage control, embankments and dams, tunnel constructions, reservoirs, coastal engineering and canals. This paper mainly gives information about the development and use of geotextiles in India.     

Extrusion fillet welding of geomembranes

This paper focuses on some of the basic principles that underly the fillet extrusion welding process. It explains why mixing tips in the melt enhance heat transfer and why peel test results of extrusion fillet welds are not directly comparable with results obtained by other welding methods.     

复合土工膜的试验技术和作用机理

综合分析了复合土工膜的特点和研究现状，对复合土工膜的材料特性提出了分解试验与整体试验综合进行的新颖研究方法，通过大量的分解与组合试验研究工作，得到了复合土工膜整体的力学、防渗特性与各种组合材料之间的关系，以及复合程度对整体特性的影响，研究了复合土工膜试验技术，提出了合理的试样宽度，解决了以往试验技术中一些模糊问题，分析了复合土工膜的受力和防渗作用机理。     

Geotextiles in landfill closures

There are numerous areas of geotextile application in landfill covers, each with a somewhat unique set of requirements and considerations for the proper selection and evaluation of the most appropriate material. This paper provides an overview of geotextile requirements and specific references to available design literature for each of these application areas.     

Geotextiles: Their rationale and future

Over the last decade there has been much interest shown in the use of textiles in civil engineering construction, particularly in geotechnical engineering where geotextiles are associated with soil. Is this a fad, or something more profound and durable? In attempting to rationalize this dramatic development it is concluded that geotextiles do offer many technical and economic advantages. However, at present geotextiles are commonly used as a replacement for traditional building materials using traditional construction methods rather than more innovative techniques that could only be employed using geotextiles. It is concluded that the development of these techniques is the real future of geotextiles and that this future can only be secured by the close cooperation of both textile and civil engineers.     

Coextruded HDPE/VLDPE multilayer geomembranes

High density polyethylene (HDPE) geomembranes have been used extensively during the last decade and very low density (VLDPE) geomembranes have been introduced during the last few years. Both materials have properties that are desirable for particular applications. HDPE has excellent chemical resistance, UV resistance and high modulus. VLDPE is very flexible and is capable of much more elongation in field applications than HDPE.

A geomembrane made by the coextrusion of HDPE and VLDPE has several advantages over geomembranes made from either HDPE or VLDPE alone for many applications. These advantages are realized due to synergistic effects that occur between the two polymers, resulting in a product that incorporates desirable properties of the two materials and eliminates some of the less desirable ones. The Coextruded Multilayer Sheet (CEMS) addressed in this paper has better tensile strength, tear resistance, seam strength, chemical resistance, permeability and UV resistance than VLDPE and better puncture resistance, elongation and stress crack resistance than HDPE. Coextruded, multilayer geomembranes make available more options for the design engineer attempting to find the best product for a given application.     

Hot wedge fusion welding of HDPE geomembranes

Double track fusion welding offers more control, produces more consistent welds and is easier to nondestructively test than other types of welding system. However, as with other types of welding, there are a number of parameters which need to be understood and controlled in order to make consistently good welds. Heat, pressure and speed must be properly set, taking into consideration the resin being welded, the thickness of the sheet and environmental conditions.

Speed, heat and pressure must be controlled and their effect on weld quality understood. The ‘welding window’ for these variables has distinct boundaries. A test weld which exhibits melting, ‘squeeze-out’ and peels without breaking the liner may not need more pressure or heat. Tests show that for some bonds which peel apart, reducing the heat and/or pressure may be the correct action in order to obtain a film tearing bond (FTB).     

Controlling leakage through installed geomembranes using electrical leak location

Installed geomembranes typically contain holes, which can be located for repair in most cases using electrical leak location (ELL) technologies. It is of special interest to quantify the likelihood that a geomembrane has holes, the impact of such holes with respect to a facility's expected performance, and subsequent remedial actions. In addition to providing a summary of research to date on these topics, the aim of this paper is to answer these questions with modern case studies, contextual hole frequency statistics and a recapitulation and reexamination of leakage data from double-lined landfills. Finally, the physics of electrical leak location technology is explained in order to illustrate the capabilities and limitations of the methods as well as to provide guidelines for maximizing the effectiveness of the technologies.     

垃圾填埋场边坡上土工膜的受力分析

在垃圾填埋场中,土工膜可以隔离垃圾体与周围环境,避免地下水受到污染。在土工膜上填埋垃圾和土层,沿其长度方向将有剪应力作用,使得土工膜发生变形,内部产生拉力,为保证土工膜的安全使用,需要对土工膜的拉力进行分析。将土工膜与黏土界面的剪应力–位移关系曲线分为弹性、软化和残余强度3阶段,采用三阶段弹塑性模型来描述土工膜与黏土界面的剪切变形特性,推导出了界面处于弹性、软化和残余强度3阶段时土工膜位移–拉力的微分控制方程,由于3个阶段分界点的位置是未知的,利用迭代法求解土工膜的拉力,分析了填埋高度和坡度的变化对土工膜拉力的影响。     

Long-term performance and binder chemical structure evolution of elastomeric bituminous geomembranes

This paper presents the results of uniaxial tensile tests, flow-rate measurements, and size-exclusion chromatography (SEC), which are used to evaluate the ageing of elastomeric bituminous geomembranes (BGMs) that were installed 6, 10, 15, 20, and 30 years ago in ponds at two different sites in France. SEC was used to detect oxidation and the absence of polymer in the bitumen at the surface of the 20- and 30-year-old BGMs. The results indicate that, for BGMs exposed less than 20 years, there was no oxidation or degradation of the polymer at the core. However, the elastomeric polymer was altered at the core of the 30-year-old BGM, resulting in an embrittlement of the bitumen, but this did not affect the mechanical properties of the glass veil and nonwoven polyester geotextile in the BGM core. Lastly, the flow rates through the BGM measured according to EN 14150 are still below 10^?6 m³ m^?2 d^?1, which indicates that the elastomeric bituminous GM is still watertight after 30 years of exposure.     

Technical note on hot air seaming of high-density polyethylene geomembranes

Hot air fusion welding is widely used as a secondary seaming method for welding high-density polyethylene (HDPE) geomembranes, although seldom as a primary seaming method. This method is based on a very simple principle and can withstand comparison with the other main seaming methods. However, the strength and long-term durability of seams made with this method are still poorly known, and should be explored, as compared to the other welding methods.