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.     

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。     

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.     

A study on biological clogging of nonwoven geotextiles under leachate flow

This paper presents results of long-term permittivity tests using leachate to evaluate biological clogging of nonwoven geotextiles. Three types of geotextiles with varying masses per unit area were used in the tests. The identification and quantification of microorganisms in the geotextile were carried out as well as microscopic investigations. The accuracies of semi-empirical models to evaluate the kinetics of bacteria growth and to correlate hydraulic properties and microbiological parameters were examined. Permittivity tests under increasing water heads were also performed on the geotextile samples already subjected to long-term leachate flow in order to evaluate the values of water heads required to wash the biofilms out of the geotextile pores. The results of the tests showed the marked reduction of geotextile permeability due to biological clogging and that the results of the predictions by semi-empirical methods were consistent with the biological mechanisms observed.     

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。     

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.     

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。     

Improved design criteria for nonwoven geotextile filters with internally stable and unstable soils

In geotextile filtration, the soil fines are either accumulated near the interface, clogged, or washed out, which primarily depends on the grain size distribution (GSD) of soil and the constriction size distribution (CSD) of geotextile. Also, the movement of fines significantly affects the flow capacity of geotextile. Currently, the retention requirement is satisfied based on representative grain and opening sizes, whereas the hydraulic conductivity and clogging requirements are satisfied considering the properties of virgin geotextile. This paper presents a probabilistic retention criterion considering the grain and constriction sizes as random variables. The influence of geotextile thickness is incorporated into the criterion by considering the number of geotextile constrictions in a filtration path. A theoretical approach to predict CSD is presented if the measured data is unavailable. For hydraulic conductivity and clogging requirements, a criterion is presented considering the expected partial clogging of geotextile, which is predicted based on the semi-analytical approach. The limit states for the developed criteria are evaluated based on the wide range of experimental data from the current study and published literature. The developed design criteria are applicable to internally stable and unstable soils, which offers an improvement in design compared to the existing criteria in practice.     

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.     

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.     

Effect of coating optimization on performances of glass fiber geogrid for semi-rigid base asphalt pavement

Glass fiber geogrid (GFG) is one of the most commonly used materials to mitigate reflective cracks in semi-rigid base asphalt pavement, but there are still some defects in the application of GFG at present. Therefore, GFG was optimized from the perspective of coating treatment. In this paper, the coating materials were firstly optimized from a variety of compounded emulsions (CE) composed of polymer and emulsified asphalt (EA). Then, the properties of the CE and the effect of CE on performances of GFG were studied. The results show that the weighted average particle size, contact angle, viscosity and coating uniformity of polyacrylate compound emulsion (PA-CE) are smaller, higher, higher and better than those of styrene-butadiene compound emulsion (SB-CE), respectively. The GFG impregnated by PA-CE (PA-GFG) has better strength, folding resistance and durability than the GFG impregnated by SB-CE (SB-GFG) and GFG impregnated by EA (EA-GFG). The interlaminar bonding performances and resistance to reflective cracks from flexural-tensile loading of PA-GFG and SB-GFG are not significantly different, while the resistance to reflective cracks from shear loading of PA-GFG is higher than that of SB-GFG.     

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。     

Effect of antistripping additives on environmental damage of bituminous mixtures

The main objective of this study was to investigate the effect of environmental damage (stripping) on the hot mix asphalt (HMA) creep behavior. To achieve this objective, 24 different HMA combinations using different mix parameters were evaluated for their resistance to static creep deformations. The mix parameters include: two types of asphalt cement, three types of aggregate gradation, and two types of antistripping additives (limestone dust and calcium stearate hydroxide). Marshall specimens were prepared at optimum asphalt contents and tested for static creep. Part of the prepared specimens were exposed to freezing–thawing conditioning according to AASHTO T283.     

Centrifuge model tests on the use of geosynthetic layer as an internal drain in levees

The objective of the paper is to examine the use of a geosynthetic layer as an internal drain in a levee subjected to flooding through centrifuge model tests. Three levee sections, having an upstream slope of 1V:1H and downstream slope of 1.5V:1H, were modelled at 30 gravities in a 4.5?m radius large beam centrifuge available at IIT Bombay. Out of the three levee sections modelled, one levee section was without any drainage layer (or clogged drain), while the other two had different types of horizontal drainage layers, namely, sand and nonwoven geotextile layer. The flood was induced with the help of a custom developed and calibrated in-flight flood simulator. At the onset of flood and subsequent seepage, pore water pressures within levee section, and surface settlements were measured using pore water transducers (PPTs) and linear variable differential transformer (LVDTs) respectively. Digital image analysis was employed to trace surface settlements, and downstream slope face movements at the onset of flooding during centrifuge tests. Levee section without any horizontal drain or clogged drain experienced a catastrophic failure. In comparison, the levee sections with an internal drain (sand/geotextile) remained stable at the onset of flooding. In the case of a levee with a sand drainage layer, the phreatic surface was observed to confine within the levee section itself, whereas it was found to migrate towards toe gradually in the levee section with a nonwoven geotextile layer. It is attributed to either due to suppression of drainage capacity of nonwoven geotextile layer or due to washing of fine particles into pores of nonwoven geotextile layer. Further, seepage and stability analyses were carried out numerically and compared with centrifuge test results. In order to address blocking of pores of nonwoven geotextile layer, a concept of sandwiching nonwoven geotextile layer with sand was explored. By sandwiching nonwoven geotextile layer with sand on either side, the thickness of drainage layer can be of the order of 0.05H.     

Impacts of impregnation with Imersol-Aqua on the compression strength of some solid wood materials

The aim of this study was to investigate the effects of impregnation with Imersol-Aqua on the compression strength of some solid wood materials. For this aim, Oriental beech (Fagus orientalis Lipsky), European oak (Quercus petrea Liebl.), Scotch pine (Pinus sylvestris Lipsky), Uludag fir (Abies Bornmülleriana Mattf.), Oriental spruce (Picea orientalis Lipsky) and Lombardy poplar (Populus nigra Lipsky) wood samples were prepared according to TS 2595 and impregnated with Imersol-Aqua, commonly being used in construction wood materials by the method of short, medium and long-term of dipping according to ASTM D 1413 and producers’ definition. After the impregnation process, compression strength was measured according to TS 2595. Consequently, among the non-impregnated wood materials, the highest compression strength was obtained in beech and pine samples. Compression strength at this situation from the highest to lowest can be enumerated beech, pine, oak, spruce, fir and poplar. With regard to the impregnation period, the sequence form the highest to lowest was as long-term, medium-term and short-term dipping. In the interaction of wood material and impregnation period, the highest compression strength values were obtained in Scotch pine (71.220 N mm⁻²) impregnated with long-term dipping method whereas the lowest in Lombardy poplar (35.710 N mm⁻²) impregnated with short-term dipping method.

In consequence, in the massive constructions and furniture elements that the compression strength after the impregnation is of great concern, long-term impregnation of solid wood material could be recommended.     

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.     

城市旧混凝土路面加铺沥青罩面层改造工艺的探讨

简要介绍了旧混凝土路面加铺沥青层的防治重点和减少反射裂缝的防治措施，通过理论分析说明加铺层厚度和土工布对加铺层底部应力的影响，并以工程实践为例说明采用该改造工艺的有效性。     

沥青路面低温抗裂性能研究

介绍了沥青路面低温开裂的类型,并对影响沥青路面低温开裂的因素进行了分析,提出了提高沥青路面抗裂性能的措施,以提高沥青混合料的低温抗裂性能,达到减少温缩裂缝的目的,从而改善沥青路面的路用性能。