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.     

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。     

Nonwoven geotextiles from nettle and poly(lactic acid) fibers for slope stabilization using bioengineering approach

This article deals with needle-punched nonwoven geotextiles prepared from nettle and poly(lactic acid) fibers in different weight proportions for potential slope stabilization application using bioengineering approach. The geotextiles were tested for tensile strength, biodegradability, and enhancement of soil fertility. The tensile strength of the geotextiles was found to decrease with addition of stronger nettle fibers. This apparently surprising behavior was explained in the light of theoretical tensile mechanics of nonwovens. Further, the nettle fibers displayed higher biodegradability than the poly(lactic acid) fibers, and when buried under soil, all the geotextiles exhibited a loss in tensile strength. Interestingly, the fertility of the soil was remarkably improved after biodegradation of poly(lactic acid) fibers. Overall, the nonwoven geotextiles prepared in this work were found to be promising for slope stabilization application.     

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.     

Durability studies of surface-modified coir geotextiles

Coir (Cocos nucifera) is a natural fibre known to retain its strength and resist biodegradation far better than other industrial natural fibres. However, systematic studies in this discipline are scarce. Geotextiles are usually exposed to diverse pH, salinity, moisture, and microbial association conditions. In the present work, specific surface modifications of coir geotextiles using a natural agent (cashew nut shell liquid) have been carried out to enhance their long-term performance depending on the end applications. The modified and unmodified geotextiles were subjected to acidic, alkaline, and neutral pH conditions, saline conditions, alternate wetting and drying cycles, and thermal cycles for the assessment of their durability, measured in terms of tensile strength. In situ soil burial studies in a tropical climate were conducted in specially prepared soil to follow the biodegradation behaviour of geotextiles at various depths. The surface-modified geotextiles were found to resist adverse chemical, physical, and biological conditions much better than the unmodified geotextiles. Alkaline conditions marginally accelerated the degradation rates when compared to acidic environments. The saline conditions, as well as alternate wetting and drying conditions, resulted in marginal loss of tensile strength (<7%). The surface-modified geotextiles buried within lower depths of soil under field conditions retained 70–80% of their initial tensile strength after 12 months, whereas the unmodified geotextiles lost 88% strength in four months. The positive impact of surface modification on durability is confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results indicate the excellent potential of suitably surface-modified coir geotextiles for long-term use in adverse conditions.     

Filtration performance of non- woven geotextiles with internally-stable and -unstable soils under dynamic loading

In many applications, geotextiles are subjected to dynamic loading conditions, for example, below roads and railways, for which a Gradient Ratio (GR) test is often used to assess filtration compatibility of soil-geotextile systems. This paper presents results from GR filtration tests with internally-stable and -unstable soils under dynamic loading conditions. In the tests, four non-woven geotextiles were used with varying types of soils under a hydraulic gradient of 5. Test results were interpreted in terms of GR values, permeability values, and mass and gradation characteristics of the soil before/after testing as well as the particles passing through the geotextiles. The test results show that the dynamic loading resulted in an increase of soil migration within the soil as well as an increase in the quantity of soil passing through the geotextiles. The available criteria for evaluating the internal stability of soils are evaluated based on the experimental data. Based on the test results, improvements to filter retention design criteria are suggested which take into account the internal stability of soils under dynamic loading.     

Geotextiles in coastal engineering—25 years experience

During the use of geotextiles in coastal engineering for over 25 years many construction methods have been improved or have been made more economical. Sometimes completely new solutions for coastal engineering problems can be recommended. This paper gives information about the long-term behaviour of geotextiles in coastal engineering and the minimum requirements for their application. Some case studies show the necessity of careful geotextile selection, considering the special requirements of the application, the harsh coastal engineering environment and the rough building practice found in all fields of hydraulic engineering.     

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.     

Drainage performance of geotextiles

It should be noted that the drainage conditions and mechanisms are somewhat different when geotextiles are used as back fill material behind retaining walls. One of the major differences is that the soil installed by the geotextile may not necessaroly be saturated. Generally, the drainage performance of geotextiles can be evaluated by examining combined behavior of geotextiles, soil particles and water. However, in addition to the above materials, in investigating the drainage performance of geotextiles as back fill material behind retaining walls, the effect of air should be taken into account. Therefore, this study has concentrated on investigating the effect of drainage performance of an initially dry geotextile. A further long-term test was carried out primarily to examine the mechanism and development of self-induced filters, which is believed to determine the drainage performance of the geotextile.     

Bioengineering of river earth embankment using natural fibre-based composite-structured geotextiles

A Jute-HDPE composite structured geotextile was developed to improve the performance of earthen structure of river embankment. The optimized geotextiles (430 g/m²) containing 86% natural component (on weight) having better physical, mechanical (tensile strength, 10 kN/m (machine direction) and 18 kN/m (cross direction), index puncture (163 kN) and CBR (1.5 kN)), hydraulic (AOS 178 μ) and endurance properties than 100% HDPE geotextiles. A coconut fibre geotextile net was placed over jute-polyolefin geotextiles to resist washing-off of loose cover soil until the establishment of vegetation. Placing of continuous seamless geotextile tube (weight 196.2 kg/m) filled with moist river sand at the anchor trench-cum-toe guard assisted in safeguarding from eddies. It was observed that initially closed structure of the geotextile assisted in efficient filtration leading to soil stabilization through compactness of soil layer (14 cm thick). The uniqueness of work lies in conversion of closed structure of geotextiles to open-mesh of HDPE slit film on degradation of jute, remained beneath the cover-soil, through which grass root penetrated the geotextiles sheet and riveted both the layers of soil, the cover and the compacted back layers. The remnant synthetic part thus acts as durable reinforcing element and its increased porosity provides breathability for growth of soil flora and fauna. Bermuda grass turf provided very high nailing strength (658.8 kN/m²) with the soil through intertwining of grass roots with durable synthetic network.     

Laboratory tests on geosynthetic-encapsulated sand columns

Granular columns have been introduced into engineering practice to improve the bearing capacity and reduce settlement of sand column in a weak or soft soil. The improvement can be enhanced by encapsulating the column with tensile resistant material. The improvement depends on the confinement offered by the surrounding soil, the reinforcing material and the granular column material. In this study, the extent of improvement for a sand column subjected to constant confining pressures is studied through laboratory experiments. A series of triaxial compression tests were carried out in laboratory to investigate the response of sand columns encapsulated by geotextiles. The tests consisted of triaxial compression tests on sand columns with two different densities and encapsulated by sleeves fabricated from three different geotextiles. The increase in deviatoric stress, the reductions in volumetric and radial strains, and the increase in confining pressure generated by the encapsulating reinforcement were measured and analyzed. The mobilized pseudo-cohesion and friction angle corresponding to various axial strains are analyzed to interpret the reinforcing effect. The experimental results are compared with data obtained from analytical method reported in the literature.     

Puncture resistance of polyester (PET) and polypropylene (PP) needle-punched nonwoven geotextiles

It is common practice to use needle-punched nonwoven geotextiles as puncture protection for geomembranes against sharp objects like gravel or stones in either the soil above or the underlying soil/rock below. There are several design and experimental methods available for geotextile selection in this regard. None, however, directly address the type of resin or fiber from which the geotextile is made. This paper does exactly that insofar as a direct comparison of similar mass per unit area polyester (PET) versus polypropylene (PP) geotextiles are concerned. Furthermore, two types of PP geotextiles are evaluated; one made from continuous filaments and the other from staple fibers. Three different size and shaped puncture probes are used in the testing program. All three are ASTM Standards, i.e., D4833, D5495 and D6241.The test results clearly indicate that geotextiles made from PP fibers outperform those made from PET fibers at all masses evaluated. Clearly, the present trend of using PP resin for heavy nonwoven protection geotextiles seems justified on the basis of these test results. In addition, the continuous filament PP and staple fiber PP geotextiles performed equivalently over all mass ranges for the three different types of puncture tests.     

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.     

单向拉伸对土工织物反滤性能影响的试验研究

为研究单向拉伸对土工织物反滤性能的影响，选取两种条膜机织有纺织物和两种短纤针刺无纺织物，将不同拉应变下的织物与非连续级配土组成反滤系统，利用梯度比渗透仪测试系统反滤参数随拉应变的变化。根据反滤设计的透水、保土和防淤堵3个准则，分析拉应变对透水率、漏土量、梯度比等各参数的影响。试验结果表明：随着拉应变增加，有纺织物透水及防淤堵性能增强，保土性能减弱；无纺织物则相反，透水及防淤堵性能减弱，保土性能增强；同种土工织物厚度越大，拉应变对其反滤性能影响越大。     

深圳河反滤土工布试验研究

对深圳河治理工程边坡防护反滤运行期的土工布进行了综合试验研究 ,分析了土工布长期运行过程中的渗透性、保土性和淤堵性能 ,从强度损失角度分析了土工布长期运行的强度衰减情况 ,并对土工布的耐久性进行了试验分析。由试验知 ,土工布渗透系数降低约 10 0倍左右 ,而土工布强度降低了 5 0 %左右 ,强度衰减速率小于 0 .2 6% /月。试验表明 ,土工布已进入稳定渗透期和强度的稳定衰减期 ,土工布满足防护反滤的要求     

Zum Sicherheitspotential des geotextilbewehrten Gründungspolsters gegenüber Setzungen

Regarding the safety margin of cushion foundation armed with geotextiles in order to reduce settlements. For construction of foundationes in areas with possible local weak zones or cavities often cushion layers armed with geotextiles are applied and considerationes of possible settlements in their safety margin are claimed. In practical experience a simple soil mechanical model with derived calculation was helpful. In the following the soil mechanical model of an idealized conical and cylindrical loosening zone within the cushion layer will be presented and their safety margin will be discussed. Subsequently the possiblility of reducing further settlements by arming the cushion layer with tensile geotextiles is described and calculated by an an approximate method provided by Rafael [2]. A calculation done as example shows a close correlation to observed in‐situ settlements. It has to be taken into consideration that the loosened cushion soil and settlement trough elaborated above will suffer additional settlements where being exposed to static and particularely dynamic loads. For estimating such settlements common calculation methods can be used.     

Application of innovative meandrically arranged geotextiles for the protection of drainage ditches in the clay ground

The geotextiles produced from meandrically arranged Kemafil ropes were prepared. The ropes were produced from textile waste materials: woollen nonwoven and nonwoven from the blend of recycled fibres. The ropes were arranged into segments which were used for the protection of the bank of the deep drainage ditch and reinforcement of shallow roadside ditch in the clay ground. The geotextiles were installed in the ground and their behaviour during one vegetation season was observed. It was stated that during heavy rains the meandrically arranged ropes form a system of micro-dams which slow down the stream of water flowing down on the surface of the ditch bank as well as the stream flowing along the ditch. The geotextiles installed on the ditch banks eliminate the formation of erosive channels and protect the banks against sliding. The geotextiles absorb water what ensures retention of water flowing along the ditch. Due to enhanced soil and water holding capacity geotextiles protect grass seeds from being washed out and facilitate the development of protective vegetation. Materials used for the production of the ropes reveal sufficient resistance to biological degradation. Slow biodegradation of the materials enable keeping the protective potential of geotextiles for at least one vegetation season.     

Interface shear strength between geosynthetic clay liner and covering soil on the embankment of an irrigation pond and stability evaluation of its widened sections

Geosynthetic clay liners (GCLs) are typically used for widening sections of an embankment. They are also used as low permeability liners to minimize water leakage from reservoirs such as irrigation ponds. However, few investigations have been carried out on the specific properties of GCLs, such as granulated bentonite sandwiched between geotextiles, their internal shear strength, and the shear strength at the interface between a GCL and an embankment body. In this study, a series of direct box shear tests were performed to determine the shear strength properties of bentonite and compacted soils as well as at the interface between a GCL and bentonite or compacted soil. In addition, a series of field-loading tests were conducted to investigate the failure behaviour of an embankment body containing a GCL when changes in the water content of the bentonite of the GCL in a real embankment occur. Furthermore, the stability of widened embankment bodies that incorporated GCLs were evaluated. The main conclusions of this study are as follows: (1) The shear strength of the interface between the covering soil and geotextiles varied according to the soil type, geotextile type, and the submergence period, (2) the maximum safety factor was observed at the interface between decomposed granite soil and the geotextiles, while the minimum safety factor was observed at the interface between the bentonite and the geotextiles, and (3) the influence of GCLs on the instability of a widened embankment was extremely small.     

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.     

Experimental studies of the geosynthetic anchorage – Effect of geometric parameters and efficiency of anchorages

The soil reinforcement by geosynthetic is widely used in civil engineering structures: embankments on compressible soil, slope on stable foundations, embankments on cavities and retaining structures. The stability of these structures specially depends on the efficiency of the anchors holding the geosynthetic sheets. Simple run-out and wrap around anchorages are two most commonly used approaches. In order to improve the available knowledge of the anchorage system behaviour, experimental studies were carried out. This paper focuses on a three-dimensional physical modelling of the geosynthetics behaviour for two types of anchors (simple run-out and wrap around). The pull-out tests were performed with an anchorage bench under laboratory controlled conditions with three types of geosynthetic (two geotextiles and one geogrid) and in the presence of two types of soil (gravel and sand).The results show that there is an optimum length for the upper part of the geosynthetic for the wrap around anchorage.