Effect of bituminous impregnation on nonwoven geotextiles tensile and permeability properties

Geosynthetics interlayer systems are effective techniques to control reflective cracking in damaged pavements. It comprises the inclusion of nonwoven geotextiles between the damaged layer and the new overlay of the pavement to reduce the propagation of cracks and to extend pavement life. However, the success of this technique depends directly on the understanding of the geotextile's behavior when impregnated with asphalt. This paper evaluates different nonwoven geotextiles frequently used in anti-reflective cracking systems, focusing on initial stiffness gain and permeability reduction after asphalt impregnation. Fresh and impregnated samples of polyester and polypropylene nonwoven geotextiles were tested. Cationic rapid setting emulsified asphalt was used as asphalt binder. Wide-width tensile tests were carried out based on the specification of ABNT - NBR 12824 (1993). Water vapor transmission tests were conducted according to ASTM E 96M (2005). Results of tensile tests on impregnated geotextiles showed a significant increase on tensile strength values, probably due to the inter contact of the fibers. Results also showed high increase in strength values at strain levels less than 0.05% and decrease on stiffness gains with increase of strains. Water vapor transmission tests demonstrated that cationic asphalt emulsion applied on nonwoven geotextiles allows a drastic reduction in permeability values to turn nonwoven geotextiles into a low permeability barrier.     

A comprehensive method for analyzing the effect of geotextile layers on embankment stability

Commercial software is used widely in slope stability analyses of reinforced embankments. Almost all of these programs consider the tensile strength of geotextiles and soil–geotextile interface friction. However, currently available commercial software generally does not consider the drainage function of nonwoven geotextile reinforcement. In this paper, a reinforced channel embankment reinforced by a nonwoven geotextile is analyzed using two methods. The first method only considers the tensile strength and soil–geotextile interface friction. The second method also considers the drainage function. In both cases, the reinforced embankment is modeled in rapid drawdown condition since this is one of the most important conditions with regard to stability of channel embankments. It is shown that for this type of application, modeling a nonwoven geotextile reinforced embankment using commercial software which neglects the drainage function of the geotextile may be unrealistic.     

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。     

The influence of uniaxial tensile strain on the pore size and filtration characteristics of geotextiles

The influence of uniaxial tensile strain on the pore size distribution and filtration characteristics of geotextiles is studied. An experimental apparatus was designed and used to conduct tests for pore size distribution, flow rate through the geotextiles and the gradient ratio. Four geotextiles made of polypropylene (two heat-bonded nonwoven and two slit film woven) were studied. Throughout the test series, the geotextiles were stretched to maintain 5%, 10% and 20% in-plane uniaxial strains. The strained specimen test results were compared with those from unstrained specimen. The experimental results illustrate the pore size and the mean flow rate through the plain geotextiles increase with the increase in tensile strain. The differences in changed percentages for apparent opening size and flow rate between the two nonwoven geotextiles are much higher than those between the two woven geotextiles. The increase in tensile strain results in reduction in the gradient ratio for the soil–geotextile system. This effect is more pronounced for nonwoven geotextiles. More testing is recommended to gain a deeper understanding into tensile strain effect on various geotextiles.     

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.     

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.     

Biaxial tensile behavior of spunbonded nonwoven geotextiles

Geotextiles can be successfully employed for any geotechnical application when they are able to sustain pre-defined levels of tensile stresses. The biaxial tensile test has an advantage over other tensile test methods in that it does not allow “necking” during deformation which simulates the operational conditions of geotextiles under confined stresses. In this study, the model for uniaxial tensile behavior of nonwovens has been modified to investigate the biaxial tensile behavior of spunbonded geotextiles. The model has included the effect of fiber re-orientation, stress-strain behavior of constituent fibers, and physical characteristics of nonwovens when the geotextile specimen is laterally constrained. A comparison is made between predicted and experimental stress-strain curves obtained from previous work (Bais-Singh and Goswami, 1998). Theoretical findings of biaxial tensile behavior obtained using the layer theory are also critically discussed. In addition, it has been revealed that fiber re-orientation is a key factor in translating the random spunbonded nonwoven geotextiles to anisotropic structures under defined biaxial tensile stresses.     

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.     

Technical note on epoxy bonding of geotextiles

In order to transfer stress between geotextile panels the selvage edges are mechanically seamed by sewing. In light-to-medium-strength geotextiles (geotextiles with wide width tensile strengths of up to 175 kN/m (1000lb/in) it is possible to attain up to 80% efficiency in the final seamed product. Beyond this strength range the sewn seam efficiency is drastically reduced. For applications which require the use of high-strength geotextiles (i.e. soft soil stabilization) a designer is often limited by the seam strength between panels. This paper explores the use of chemical seaming as an alternative joining technique and presents results of a preliminary investigation on the performance of an epoxy resin used to lap seam a high-strength polyester geotextile.     

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。     

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.     

A wave flume experiment for studying erosion mechanism of revetments using geotextiles

Unfavorable erosion to a revetment can affect the stability of the bank and may jeopardize the safety of adjacent structures, thus improvement work is needed to increase the stability of the revetment as well as reducing the possibility of failure. The use of geotextiles as a protection material for banks is not only environmentally friendly, but also stable in the long run. However, improper design of geotextiles may cause considerable loss of soil, which might result in failure. The actual flow behavior in revetments using geotextiles is rather complicated and can be categorized into three zones, namely, the uni-directional flow zone, the cyclic flow zone, and the tangential flow zone. In this study, a wave flume experiment was performed on model revetments using two kinds of geotextiles as the filter material to prevent erosion induced by cyclic flows. Soil migration behaviors were monitored. Furthermore, two kinds of cover blocks, riprap and concrete blocks, were carefully placed on the revetments in order to avoid puncture and abrasion of geotextiles during construction of revetments. The main purpose of this study is to elucidate the erosion control and filtration performance of soil-geotextile filtration systems under wave action. Two nonwoven needle punched geotextiles were tested. The geotextiles both have the same characteristic opening size, but have a different number of constrictions and different structures. One is a thin double-layer nonwoven material consisting of continuous filaments and the other is a thick one-layer nonwoven material consisting of short fibers.     

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.     

Microscale investigation into mechanical behaviors of heat-bonded nonwoven geotextile using DEM

Heat-bonded nonwoven geotextiles (HBNGs) made from synthetic fibers are widely used in engineering practices. One of the challenges on the way is to link the properties of fibers and the fabric's microstructure to the deformation and failure mechanisms of HBNGs. In this study, a random distribution geometry method was developed to reproduce the complex fibrous structure of HBNG. A piecewise linear model was adopted to reproduce the nonlinear stress-strain relationships of single fibers. The present method has been successfully applied in the simulation of uniaxial and biaxial tensile tests and puncture test. The orientation distribution of fibers and the mechanical behaviors (e.g., deformation, strain localization, force-strain relationship) of HBNG specimen were reasonably simulated. Specifically, the hourglass shape during uniaxial tensile test, the axisymmetric deformation pattern during biaxial tensile test and the trumpet shape during puncture test were all well reproduced. The present method provides an applicable tool to study the complicated mechanical behaviors of HBNG and is also helpful to obtain a better understanding of its deformation and failure mechanisms.     

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.     

Manufacturing effects on the hydraulic properties of needlepunched nonwoven geotextiles

Needlepunched nonwoven geotextiles are entangled to form a complex three-dimensional structure by random fibers, accounting for its bulky nature, wide range of pore size distribution, and good drainage. With needlepunched nonwoven geotextiles, water can move in both the vertical and horizontal directions. This paper examines two types of needlepunched nonwovens: one produced from polyester staple fiber and the other made from polyester spunbond continuous filaments. Experimental results indicate that the permittivity of staple needlepunched nonwoven geotextiles varies from 1.77-4.51 s⁻¹; the permeability coefficient varies from 0.63-2.87 × 10⁻² m/s. The permittivity of spunbond needlepunched nonwoven geotextiles varies from 1.13-1.97 s⁻¹; the permeability coefficient varies from 0.48-1.09 × 10⁻² m/s. In addition, the transmissivity of needlepunched nonwoven geotextiles decrease to an essentially constant value as the normal stress is increases. The transmissivity of needlepunched nonwoven geotextiles examined varies from 155-2.75 × 10⁻⁶ m²/s over the normal stress range examined (5-200 kN/m²). The AOS value of 3 denier staple fiber needlepunched nonwovens is less than 0.074 mm, the AOS value of spunbonded 7 denier and, 15 d and 20 d needlepunched nonwovens are 0.21 mm, 0.25 mm and 0.30 mm, respectively.     

Interface shear characteristics of jute/polypropylene hybrid nonwoven geotextiles and sand using large size direct shear test

In this study, large-size direct shear tests were conducted to determine the interfacial shear characteristics of sand–geotextile under three different normal stresses. The geotextiles used in the present study were hybrid needlepunched nonwovens containing defined weight proportions of jute and polypropylene fibers. Subsequently, the interfacial shear characteristics of hybrid and that of a nonwoven geotextile consisting of solely polypropylene fibers with sand were compared and analyzed under different normal stresses. Initial higher shear stiffness of sand-polypropylene geotextiles was observed corresponding to sand-hybrid geotextiles specifically under higher normal stresses. Nevertheless, the contact efficiency of sand-hybrid nonwovens was similar to that of sand-polypropylene geotextiles. The surface morphology of sand particles has been investigated based on the images obtained from scanning electron microscopy (SEM) and quantitatively analyzed by means of Wadell roundness and degree of angularity methods.     

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.     

无纺织物单向拉伸孔径变化试验与理论预测对比分析

无纺织物作为反滤材料,常处于单向受拉工作状态。单向拉伸引起无纺织物孔径变化,易导致反滤工程失效。通过控制织物应变的干筛试验,定量测试了无侧限单向拉应变逐级增大的过程中,两种不同厚度短纤针刺无纺织物的孔径分布曲线变化。采用干筛试验结果,对现有两种体系的单向应变下无纺织物孔径预测理论解进行验证:一类是佘巍等效孔径O95理论解,一类是Rawal孔径分布曲线理论解。通过对比两种理论解对各级拉应变下的O95值预测,归纳二者的预测误差规律,从理论假设出发分析误差原因。同时采用前人图像法测得的热粘无纺织物O95变化验证两类理论解。两种理论解均能较好地预测无侧限单向拉应变下无纺织物O95的变化规律。O95随单向拉应变呈近似线性减小的规律。对于O95变化斜率的预测,佘巍解较准确,Rawal解偏大。对于O95数值预测可结合两类理论解给出变化范围。     

A simple method to assess the wettability of nonwoven geotextiles

This paper presents a simple test method and analysis based on capillary rise in porous media to assess the wettability of nonwoven geotextiles. The apparent opening pore size and porosity of the nonwoven geotextiles and their fibres' surface condition were found to play a significant role in the extent of the water capillary rise in the geotextiles. Prediction of the maximum capillary rise using a theoretical capillary radius compared well with the measured test results. The methodology presented in this paper should help assess wetting of geotextiles in short period of time and less extensive laboratory testing.