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.     

Measuring hydraulic properties of geotextiles after installation damage

Since geotextiles have been progressively incorporated into coastal protection structures, the influence of installation damage on them has been the primary concern. During installation/construction, geotextiles are repeatedly subjected to high mechanical stresses which often exceed service stress. It is therefore vital to evaluate the mechanical and hydraulic damage and determine the consequences of these damages to better develop criteria for selection of suitable products. As these damages could reduce the material's mechanical strength and hydraulic efficiency, or in the severest form of damage, puncturing, would end the separation function. The properties investigated in this paper include the permittivity and apparent opening size (AOS) of geotextiles. Generally, the greater the drop energy of armour units applied to geotextiles, the greater the potential for damage. Findings show that the residual permittivity could increase significantly, 45% during installation. The preliminary design of coastal structures will be optimised as engineers and designers can better estimate the amount of damage on geotextiles upon installation.     

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.     

Long-term performance of nonwoven geotextile filters in five coastal and bank protection projects

This paper evaluates the long-term performance of needle punched nonwoven geotextiles used as filters in coastal and river bank applications. Filtration and mechanical properties of nonwoven geotextiles exhumed from five separate projects in Europe and the Far East sites are reviewed. Hydraulic conditions varied from wave action to stream flow, and the filtered soils ranged from sands to marine clays. Performance was based on the condition of the site and the hydraulic and mechanical condition of the exhumed geotextiles as well as a comparison of the geotextiles used with respect to current filter design criteria.     

土工布在工程实践中的应用

介绍了我国土工布的发展及应用现状,分析了土工布的工程特性,通过工程实践体现了其广阔的应用领域,最后提出其施工要点,从而推广土工布的应用使土工布充分发挥工程价值。     

Stabilisation of soil using hybrid needlepunched nonwoven geotextiles

In the past, natural and synthetic fibre based geotextiles have been used for short- and long-term applications of soil erosion. It is well known that these geotextiles complement each other in terms of various physical and mechanical properties. In this study, an attempt has been made to study various properties of hybrid geotextiles. These hybrid geotextiles have been produced from the blend of polypropylene/viscose and polyester/viscose fibres in defined weight proportions (0%, 20%, 40%, 60%, 80% and 100%). Subsequently, a comparison has been made between various physical and mechanical properties of needlepunched nonwoven geotextiles. In this research work, it was found that hybrid geotextiles made of viscose (up to 40 wt.%) can replace 100% polypropylene or polyester based geotextiles.     

Geosynthetics reinforcement application for tsunami reconstruction: Evaluation of interface parameters with silty sand and weathered clay

Great attention is directed to rebuild livelihoods and rehabilitate coastal communities affected by the Tsunami in the Indian Ocean in South Asia. It takes years of effort of different engineering disciplines to recover from recent devastations caused by the Tsunami. Geosynthetics can play important and vital roles in the protection, mitigation and rehabilitation efforts in affected coastal areas. Geosynthetics can be applied for reinforcement, filtration, drainage, protection, lining, and containment. Particularly, geotextiles can be used effectively for erosion protection and for reinforcement of earth embankments to resist failure during the occurrence of earthquakes associated with tsunami. Presented in this paper is the interaction behavior at pullout interfaces of high strength geotextile confined in weathered clay and silty sand. The interface parameters which are needed for both finite element and conventional analyses of geotextile-reinforced earth structures such as the local shear stress/shear displacement, the interface interaction coefficient and the in-soil stress/strain of the reinforcement have been successfully interpreted by the newly proposed method considering the softening behavior and non-uniform distribution of shear stress along the extensible reinforcement. Results from this study indicate that the interpretation of pullout tests using conventional methods underestimated both the shear stiffness and the peak shear strength at the pullout interface of extensible reinforcement.     

The application and manufacture of woven geotextiles

Some criteria for geotextile selection are considered and the specifications of various geotextiles are related to various case histories cited. Consideration is given to the special filtration capacity of fabrics and the possibility of adapting manufacture to optimise the geotextile to specific circumstances. The possibilities of reinforcement offered by fabrics are also illustrated by examples and it is shown that in extreme cases the application of geotextiles allows safe technical solutions coupled with economy. The manufacture of woven geotextiles is characterised by the various procedures in weaving preparation where technical and economic requirements have to be met. The influence of various factors on economy is explained and their effects shown.     

土工织物直剪摩擦试验研究

土与织物界面相互作用的机理十分复杂 ,80年代我国各大单位进行了不少这方面的试验和研究。本文主要介绍土工织物与土的直剪摩擦试验方面的研究     

Geotextile filtration opening size under tension and confinement

Nonwoven geotextiles have been used as filters in geotechnical and geoenvironmental works for half a century. They are easy to install and can be specified to meet the requirements for proper filter performance. There are situations where a geotextile filter may be subjected to tensile loads, which may alter relevant filter properties, such as its filtration opening size. Examples of such situations are silty fence applications, geotextile separators, geotextile tubes and geotextiles under embankments on soft soils. This paper investigates the effects of tensile strains on geotextile pore dimensions. A special equipment and testing technique allowed tests to be carried out on geotextile specimens subjected to tension and confinement. The results obtained showed that the variation in filtration opening size depends on the type of strain state the geotextile is subjected, under which the geotextile pore diameter may remain rather constant or increase significantly. However, confinement reduces the geotextile filtration opening size independent on the strain mobilised. An upper bound for the filtration opening size of strained nonwoven geotextiles is introduced and was satisfactory for the geotextile products tested.     

Pore size distribution of hybrid nonwoven geotextiles

Pore size distribution has become a prerequisite in determining the performance of geotextiles for various functions including filtration, separation and reinforcement. The pore structure and morphology in a nonwoven geotextile are known to be complex and it becomes further complicated in hybrid nonwoven geotextiles consisting of two types of fibers. In this study, a modified model of pore size distribution of hybrid nonwoven geotextiles has been proposed based on sieving-percolation pore network theory. A comparison has been made between theoretical and experimental pore size distributions of hybrid needlepunched nonwoven geotextiles consisting of predefined weight proportions of viscose and polyester fibers. The weight proportions of the constituent fibers have been theoretically analysed for obtaining the desired pore size distributions of hybrid nonwoven geotextiles.     

Long-term performance assessed from compatibility tests

The long-term filter performance of 15 geotextiles differing in permittivity, thickness, mass per unit area and type of polymer was studied experimentally in large filtrameters subjected with three different soils. Geotextile samples of 500 mm diameter were submitted to steady-state seepage under different hydraulic gradients for up to 600 days. In the first two performance tests, the water flow was in the direction of gravity. A third test series simulated the case of upward water flow. Although the geotextiles differed in their parameters, their filter performance exhibited very similar characteristics and satisfied the requirements for stable filter performance. A detailed microscopic investigation into the soil structure directly above the geotextiles confirmed that the geotextiles formed an internal soil filter with a bridging network.     

Reclamation of abandoned open mines with innovative meandrically arranged geotextiles

For over fifty years, geosynthetics have been used for land reclamation of degraded areas. Several years ago for this purpose innovative geotextiles formed from meandrically arranged thick ropes were invented. The geotextiles were used for reclamation of abandoned lignite open-mine in Germany and disused gravel pit in Poland. The geotextiles were installed in abandoned mines. In next years positive influence of geotextiles on slopes behaviour and vegetation was observed. It was stated that the geotextiles provide stabilization of steep unstable slopes and significantly accelerate vegetation development. The innovative geotextiles perform functions unobtainable for other traditional products. The products are useful in an effective reclamation of open mines and constitute a valuable extension of the geosynthetic assortment applicable in land reclamation.     

South West Water's 'Clean Sweep' Programme: Some Engineering and Environmental Aspects

The requirements of environmental legislation demand a massive clean-up of coastal discharges for Devon, Cornwall and West Dorset. South West Water Services Limited have developed a marine improvement programme which (a) is the largest of its type in Europe and (b) seeks to address the requirements of legislation incorporating town planning policies together with the increasing public awareness of environmental issues. The pressures around the region's coastline within the foregoing framework set the challenge of achieving the required understanding of coastal processes, together with the implementation of engineering solutions to meet with society's expectations. These have to be achieved at least cost and provide the most innovative and effective engineering solutions for the efficient implementation and management of such a programme.     

Tailings-nonwoven geotextile filter compatibility in mining applications

Nonwoven geotextiles have been commonly used in filtration and drainage of geotechnical engineering works. This paper presents a study on the use of such materials in drainage and filtration systems of tailings dams. Different combinations of tailings and geotextiles were submitted to gradient ratio (GR) tests under confinement in the laboratory with varying values of stress levels and hydraulic gradients. The results of GR tests under confining stresses up to 2000 kPa are presented and discussed. The dimensions of the tailings particles entrapped in the geotextile specimens and those that piped through the geotextile were also assessed. Geotextile specimens from the drainage system of a tailings dam were exhumed for analyses, as part of the research programme. The results obtained showed that stress levels and the hydraulic gradients used in the tests influenced the behaviour of the system. Physical and microscopic analyses of the specimens tested showed greater geotextile impregnation by tailings particles in the field than in the laboratory. The overall performance of the geotextiles tested under laboratory conditions was satisfactory. However, in the field segregation of tailings particles and transport of fines in suspension can subject the filter to more complex and severe clogging mechanisms, not properly simulated in current standard testing procedures.     

On the hydraulic behavior of unsaturated nonwoven geotextiles

Geotextiles have been widely used in soil structures for separation, filtration, reinforcing, and drainage. They are often used to provide reinforcement and drainage for retaining walls and embankments. It has been reported, however, that geotextiles may not drain water as effectively as was initially expected. In this study, published data on the hydraulic properties of unsaturated geotextiles are compiled and analyzed in order to highlight the hydraulic characteristics of unsaturated geotextiles.

The application of the van Genuchten equations originally developed for the water characteristic curve and the hydraulic conductivity curve of unsaturated soil to unsaturated geotextiles is then examined and discussed. Finally, the drainage from a one-dimensional sand column having a horizontal geotextile layer was analyzed using the finite element method and the van Genuchten equations to assess the utility of this procedure for further study of unsaturated/saturated water flow within the soil–geotextile system.     

The ecological potential of geotextiles in hydraulic engineering

Geotextile materials find increasing use in coastal protection as an alternative material to natural stone, slag, and concrete. In this environment geotextiles, like all surfaces of technical objects immersed in seawater, are subject to accumulation of organisms on their surfaces, a process usually called biofouling. In a 2-year experiment we investigated the colonization of benthic organisms on two different geotextile materials (woven fabric and non-woven fabric) in the Elbe estuary, Germany, and compared it with the colonization on unglazed ceramic tiles as reference representing the nearest compromise to natural hard substrates. Then, non-woven fabric was colonized by significantly less species, fewer individuals, and lower biomass values than the woven fabric and the ceramic tiles (one-factor ANOVA, p < 0.05); no such significant differences were noted between woven fabric and ceramic tiles. Over time, the numbers of species and numbers of individuals did not show significant increases between the first and the second year (Student’s t-test, p ≥ 0.05), while the biomass was still increasing significantly on all materials (t-test, p < 0.05). However, biomass was almost two orders of magnitude lower on non-woven geotextiles than on woven material. Exposure to seawater and fouling organisms had no adverse effect upon the stability of the geotextiles (wide-width tensile test results; t-test p ≥ 0.05). Geotextile materials therefore offer a unique choice in coastal and hydraulic engineering: depending on the application, engineers can choose between a material that is easily colonized by benthic species, or one that minimizes such colonization where it is undesired.     

Changes in filtration opening size of woven geotextiles subjected to tensile loads

A modified hydrodynamic sieving technique in which the geotextile is subjected to a tensile load is described. This load may be either uni-axial or bi-axial. To date tests have been conducted on two different woven slit-film polypropylene geotextiles and the results illustrate a marked change in the filtration opening size of the geotextiles as the tensile load is increased. The opening size of the thicker geotextile decreased with increasing biaxial load, whereas the opposite occurred for the thinner of the two geotextiles. The geotextiles were loaded up to only about 10% of their minimum ultimate tensile strength and the filtration opening size changed by up to 28%. It is suggested that this effect cannot be ignored in applications where there are in-plane tensile stresses.     

Reexamination of traditional testing techniques for determining WRCs of woven geotextiles in full suction range

Woven geotextiles have been widely used in soil infrastructures for the reinforcement purpose. The hydraulic properties of a woven geotextile are not major reinforcement design parameters and the water retention capability of a woven geotextile is often ignored. The traditional testing techniques were designed for soils or nonwoven geotextiles, but not for woven geotextiles. Nowadays, a new type of woven geotextile with wicking fibers was developed which could be used for both drainage and reinforcement purposes. However, there are no proper testing techniques to determine the full-range water retention curve (WRC) for a woven geotextile, let alone for the wicking geotextile.This paper aimed at proposing a proper testing technique to determining the full-range WRC for the wicking geotextile and to compare the water retention capability of wicking and non-wicking geotextiles. Firstly, the traditional testing techniques were re-examined to check the suitability for characterizing the WRCs of woven geotextiles whose pore size distributions were anisotropic. Secondly, a proper testing technique was proposed and the WRCs of different types of woven geotextiles were determined. Thirdly, the WRCs of wicking and non-wicking geotextiles were compared to demonstrate the advantages of the wicking geotextile to hold and transport water under unsaturated conditions. Finally, the effect of wicking fiber on the water retention capability of the wicking geotextile was quantified.     

无纺织物单向受拉时孔径变化研究

现有反滤设计中保土准则使用土工织物未受拉时的等效孔径,但平面单向拉伸会导致该值变化,影响土工织物反滤性能。采用动力水筛法对三种无纺土工织物单向受拉时等效孔径变化进行测定。无纺织物被单向张拉至3%、5%和10%的平面应变,随着拉应变的增加,三种针刺无纺土工织物等效孔径减小。推求了无纺织物单向张拉时的等效孔径计算公式,对于较厚无纺织物,公式计算值和测试值较吻合,但对于较薄无纺织物,二值有一定差异。