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。     

用图像分析法研究有纺土工织物单向受拉时孔径的变化

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,变大则不满足保土准则,变小则不满足透水准则及淤堵准则。有纺织物孔径由孔径分布曲线和特征孔径反映,采用数字图像分析法对两种有纺土工织物单向受拉时孔径变化进行精确测定。有纺织物被单向张拉至3%,6%,9%和12%的平面应变,随着拉应变的增加,两种有纺土工织物开孔面积率增大;孔径分布曲线向孔径大的方向移动;3种特征孔径值（O30,O50和O95）增大,其变化率都与拉应变呈近似线性关系,且小孔径部分相对于大孔径部分随拉伸应变的增长而增大较快。     

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。     

Uniaxial strength testing of woven and nonwoven geotextiles

This paper describes the different design approaches using geotextiles and presents two types of uniaxial tensile testing: constant rate of strain and rapid loading creep tests. Tests are conducted using a woven geotextile and two nonwoven geotextiles. The effects of the width to length ratio of the test specimens, test temperature and strain rate are examined. Tests are also conducted with the specimen in air and when confined in-soil. The results illustrate that the load-extension behaviour of the geotextiles tested depends on the test conditions and hence the need to standardise these conditions is established.The relevance of test types and conditions to design and quality control is also discussed.     

不等轴双向拉应变下有纺织物孔径变化试验研究

有纺土工织物的孔径特征是反滤设计的重要指标。工程中有纺织物常处于不等轴双向受拉状态,引起孔径变化,导致织物反滤性能失效。采用数字图像法测试了不等轴双向拉应变下,3种条膜有纺织物的孔径参数变化,包括孔洞长宽比、开孔面积率、等效孔径(O95)等。对比经纬向应变比2∶1,3∶1,4∶1对试验结果的影响,根据孔径特征变化规律,揭示不等轴双向拉伸引起孔径变化的机理。运用图像法试验结果,验证已推导的双向应变下开孔面积率及孔径理论解。试验结果表明:开孔面积率、等效孔径(O95)均随双向拉应变的增大而增大。纬向应变相同时,经纬向应变比越大,孔洞形态(即孔洞长宽比)变化越大,开孔面积率及孔径变化的斜率越大。理论解较好地预测了开孔面积率及孔径的变化率及数值,孔径参数与双向拉应变呈现近似线性关系。但理论解的孔径计算以孔面积为指标,无法考虑应变比造成的孔形态变化对反滤作用的影响。     

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。     

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.     

Prediction of pore size characteristics of woven slit-film geotextiles subjected to unequal biaxial tensile strains

The basic pore unit model is extended to predict the strained pore size characteristics of woven slit-film geotextiles subjected to unequal biaxial tensile strains. The strained per cent open area (POA) and analytical pore size are expressed as functions of the weft strain and the warp strain to weft strain ratio. The influence of the biaxial tensile strain on pore size characteristics is evaluated in three woven slit-film polypropylene geotextile samples using image analysis under the warp strain to weft strain ratios of 1, 2, 3 and 4. It is shown that the experimental POA and O₉₅ increased significantly with increasing strain at different warp strain to weft strain ratios, and the PSD curves moved toward the direction of large open sizes. The analytical models of POA and pore size can accurately predict the increasing trend of POA and O₉₅. Moreover, unequal biaxial tensile strains can significantly change the shape of the pores, which may influence the results of the pore size obtained by indirect methods. A larger warp strain to weft strain ratio can lead to a larger change in the pore shape when the length to width ratios of initial pores are close to 1.     

Improvements in small-scale standardized testing of geotextiles used in silt fence applications

Silt fence have been used as a means for intercepting and treating construction site stormwater runoff prior to offsite discharge for well over 30 years. Standard small-scale testing methodologies for evaluating the filtering component of silt fence installations have failed to mimic realistic flows and sediment loadings commonly seen in field applications. To address these issues, this study evaluated the performance capabilities of two nonwoven and three woven silt fence geotextiles using an innovative testing methodology and a newly developed small-scale testing apparatus. The overall intent for conducting the evaluations was to develop a deeper understanding of effluent flow rates, sediment retention capabilities, and water quality impacts associated with geotextile fabrics. Results suggest that effluent flow rates of nonwoven geotextiles are on average 43% lower than woven materials, which results in extensive upstream retention times of impounded stormwater for nonwoven materials. Sediment retention results indicate that nonwoven geotextiles have an average sediment retention rate of 97% while woven geotextiles average 91%. Finally, water quality analyses suggest that the primary means for turbidity reductions rely on the process of sedimentation during the 30-min test period (i.e., 46% reduction) and filtration during the 90-min dewatering period (i.e., 19% reduction).     

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.     

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.     

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.     

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.     

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.     

结合微孔隙水压力计改良型GR试验系统分析研究(英文)

本研究针对结合微孔隙水压力计改良型GR试验系统与一般GR试验系统进行了一系列的试验分析比较,研究中所使用的试验材料包含4种不同针轧不织布及5种不同比例渥太华砂与风化泥岩混合土壤。试验结果发现,由改良型GR试验系统所得的GR试验值都高于一般GR试验系统所得结果,同时也验证了微孔隙水压力计在GR试验系统中可提供较好的孔隙水压力量测与抗阻塞潜势评估。     

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.     

Micro-scale tensile properties of single geotextile polypropylene filaments at elevated temperatures

Geotextiles are porous and fibrous materials that consist of randomly oriented and isotropically distributed long filaments which vary in terms of spatial distribution, curvature, orientation, size, and mass density. The heterogeneous internal structure of geotextiles constituted from individual/discrete fibers and having different micro-structure and macro-structure properties are prone to exhibit dissimilar tensile stress–strain behavior (i.e. progressive versus reactionary) as well as showing favorable versus adverse response to varied experimental conditions such as temperature and strain rate change when tested at macro scale as opposed to micro-scale level. To this end, in order to evaluate thermo-tensile strength properties as well as to characterize tensile extension behavior of single geotextile filaments at micro-scale level, micro-mechanical tensile tests were performed at different temperatures using a Dynamic Thermo-Mechanical Analyzer (DMA) on single filaments extracted from polypropylene needle punched nonwoven geotextile. Various test temperatures between 21 °C and 50 °C were chosen to represent and simulate the wide range of temperatures encountered in the field for geotechnical applications such as landfill base liners. The paper also presents a statistical analysis of the results of the test program to provide a basis for comparison of inherent filament variability.     

Microstructure characteristics of nonwoven geotextiles using SEM and CT methods

Two digital image methods based on scanning electron microscope (SEM) and computed tomography (CT) were proposed to study the microstructural characteristics of staple fibers and continuous filament geotextiles. Two-dimensional (2D) image analysis was developed for SEM images using a machine-learning-based segmentation algorithm. Three-dimensional (3D) image analysis of the CT images was based on 3D reconstruction and a pore network model. The fiber orientation distribution, porosity, pore size distribution (PSD), and characteristic pore size O₉₅ determined from image analysis were compared with the theoretical equation and bubble point test (BBP) results. It is shown that 2D and 3D image analyses can accurately measure the fiber orientation distribution of the geotextiles. The porosity values obtained using 3D imaging were comparable to theoretical values. The PSD curves obtained in the BBP tests were in good agreement with those obtained using the 3D image method. O₉₅ sizes of continuous filament geotextiles estimated by 2D image analysis compared well with O₉₅ sizes obtained by BBP tests, whereas this was not the case for staple fiber geotextiles. The O₉₅ pore throat sizes of the two nonwoven geotextiles determined by 3D image analysis were comparable to the BBP test-based values and 2D image analysis-based values.     

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.     

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.