Needle-punched Nonwoven Geotextiles Research Articles

Filtration compatibility of clay-nonwoven geotextiles under normal stress

Nonwoven geotextiles are commonly utilized as filter materials in drainage and filtration engineering. This study focuses on the clogging phenomenon of the nonwoven geotextile filter wrapping the blind drain in the active anti-floating technology of underground structures. In this paper, the filtration compatibility of clay-nonwoven geotextiles was evaluated using a newly developed gradient ratio test device that can apply normal stress. Two fabrication technics and four specifications of nonwoven geotextiles were used to filter clay, and the geotextiles’ clogging degree was assessed after the test. The influences of normal stresses, hydraulic gradients, and fabrication technics on nonwoven geotextile filtration performance were discussed based on results from a series of gradient ratio tests. Relevant assessment parameters (clogging coefficient, soil retention, and equivalent porosity) were also presented to quantify the clogging degree of nonwoven geotextiles after the test. Furthermore, the clogging process of nonwoven geotextiles filtering clay was initially explored, and the filtration effect of the needle-punched and heat-bonded nonwoven geotextiles was evaluated. The results showed that normal stress had a significant effect on nonwoven geotextile filtration, with needle-punched nonwoven geotextiles having better soil filtration and water permeability. Discussions on nonwoven geotextile applications in specific environments or conditions are also presented.

Tensile behavior of needle-punched nonwoven geotextiles based on in-situ X-ray computed tomography and numerical simulation

There are situations where geotextiles are subjected to uniaxial tensile strain, which may result in noticeable variations in their filtration performance. This study accordingly investigated the behaviors of needle-punched nonwoven geotextiles during tensile testing using in-situ X-ray computed tomography. Furthermore, a numerical analysis of the variation in pore size characteristics was performed by establishing a geotextile model based on the web formation and bonding manufacturing process. The pore size and fiber orientation distributions were subsequently investigated and a model for the changes in the pore characteristics was established and validated. With increasing tension strain in the machine direction, the pore throat size distribution curve exhibited an overall shift towards larger sizes, and the characteristic pore sizes ranging from 10% to 98% either initially decreased, then increased or consistently increased. Furthermore, the fiber distribution was predominantly within the geotextile plane along the machine direction, and as the strain increased, the fibers stretched and aligned along the direction of the tensile load along the machine direction. Finally, the experimental findings of this study and relevant test results from the literature were thoroughly interpreted. The numerical model align well with the actual changes in pore size characteristics observed under tensile strain.

Permeability of needle-punched nonwoven geotextiles subjected to uniaxial tensile strains

During service life, needle-punched nonwoven geotextiles are frequently subjected to uniaxial tensile strains, which may impact their permeability behavior. The basic model of the permeability coefficient in nonwoven geotextiles is extended to the uniaxial tensile strain condition. The influence of the fiber orientation distribution was considered. The model is expressed as the functions of the tortuosity fractal dimension, pore size characteristics, fiber orientation, physical parameters, and tensile strain. To address the errors in the results of traditional permeability tests attributed to the inhomogeneity and multiple layers of specimens, in-situ X-ray computed tomography (CT) was employed to acquire three-dimensional images of the geotextile during stretching. The three-dimensional imaging technique was employed to extract the microstructure, facilitating fluid flow simulations for determining the permeability of two nonwoven geotextiles, thereby validating the theoretical method. It is shown that the simulated permeability coefficient decreases slightly and then increases with increasing uniaxial tensile strain and necking ratio. The permeability theoretical model exhibits a decreasing trend and then increases around 0.3% strain. The theoretical model can accurately predict the permeability values and rate of change of geotextiles subjected to specific uniaxial tensile strains, thereby offering valuable insights and tools for their effective utilization in various engineering applications.

Permeability Prediction in Nonwoven Geotextiles Using Mathematical Modeling and Numerical Simulation

The vertical permeability coefficient is a pivotal hydraulic index of needle-punched nonwoven geotextiles. The accurate determination of the permeability coefficient is important for assessing engineering properties. This study employed mathematical modeling, numerical simulations, and physical experimentation to investigate the permeability behavior of nonwoven geotextiles. Mathematical modeling relies on the fiber and pore size characteristics of the geotextiles extracted through two-dimensional image analysis. The numerical simulation method was based on a pore network model acquired through three-dimensional image analysis. The results of the physical experiments served as benchmarks for evaluating the precision of the two methods. These findings underscore the efficacy of mathematical modeling and numerical simulation in predicting the permeability characteristics of nonwoven geotextiles.

An Experimental on Filtration and Clogging of Geotextile Filters around Drain Pipes in Fine Tailings

Needle-punched nonwoven geotextiles have been used as filters for decades in mine drainage systems. But the physical clogging of geotextiles by fine particles has continued to receive increasing attention. In this study, the permeation characteristics of a drain pipe wrapped with geotextiles were investigated based on a new radial flow experiment apparatus, and particle size distribution (PSD), pore water pressure (PWP), and scanning electron microscopy (SEM) analyses were employed to identify the geotextile clogging mechanism. The geotextile cleaning methods after clogging were also discussed. The results showed that an exponential decay of hydraulic conductivity (K) with time under different flow conditions. Particles less than 30 μm migrated to the drainage pipe under the action of seepage forces, and a dense and thick cake layer was formed upstream of the geotextile filter. According to microscopic analysis, the clogging process of geotextiles was divided into three stages: pore blockage and cake formation, filter cake dynamic growth and cake layer filtration. Backwash cleaning is a good way to remove a filter cake layer on the surface of geotextiles, which can recover 60% of the hydraulic conductivity (K0).

Filtration behaviour of staple fibre geotextiles under unequal biaxial tensile strains

Gradient ratio tests were conducted to investigate the filtration behaviour of staple fibre needle-punched nonwoven geotextiles subjected to unequal biaxial tensile strains. Three groups of biaxial tensile strains were designed, with the ratios of the strain in the machine direction to that in the cross-machine direction set to 1, 2, and 4, respectively. The strains in the machine direction in the three groups were the same, ranging from 10% to 30%. The tested filtration properties included the gradient ratio (GR), permeability of the soil-geotextile system, mass of soil loss, and permittivity of the pure geotextiles. Comparisons were made between the filtration properties of staple fibre (SN) geotextiles and continuous filament (CN) geotextiles. It is shown that for a certain strain ratio, the GR value at the time of test termination increases with increasing strain, and the permeability of the soil-geotextile system, soil loss, and permittivity of the pure geotextiles decrease with increasing strain. The soil loss and permittivity under equal biaxial tensile strains tend to be higher than those under unequal biaxial tensile strains. The CN geotextiles have better retention capability and more clogging potential for the tested soils than the SN geotextiles for a similar mass per unit area.

Numerical investigation of the tensile behaviors of needle-punched nonwoven geotextiles

A numerical modeling method to reproduce the structures of needle-punched nonwoven geotextile based on the actual manufacturing process (web formation and web bonding) was developed. The geotextile model was built based on the statistical characteristics of the computed tomography (CT) observations, physical and mechanical properties of fibers, and physical parameters of the geotextile. A combination of the finite element model and pore network model method was proposed to obtain the pore size characteristics. The appearance and pore size characteristics before and under uniaxial tensile strains were investigated. It is shown that the method can simulate the geotextile manufacturing process satisfactorily. The pore size distribution (PSD) curves obtained from the model show good agreement with the CT-based results. Moreover, the method can reasonably simulate the tensile behaviors of geotextile under uniaxial tensile strain. The specimen necking phenomenon during the uniaxial tensile test was well reproduced. The PSD curves moved towards the direction of larger pore size with increasing uniaxial strain, and characteristic pore sizes (O98, O95, O50, O30, O10) all show a relatively steady increasing trend.

Laboratory evaluation of the filtration behavior of three filters wrapped around drain pipes in fine tailings based on a radial flow test

Installing drain pipes is an effective way to control the height of the saturation line to improve the stability of tailings dams in mine projects. The filtration and clogging behaviors of filters wrapped around drain pipes have a great impact on their drainage capacity. This article presents results from radial filtration tests with drain pipes wrapped by filtration materials in fine-grained tailings. In the tests, three fibrous filters with different production technologies were used under different hydraulic conditions. The test results were interpreted based on the drainage characteristics of the system, the clogging characteristics and mechanism of each filter after testing, and the particle gradation passing through each filter. The results showed that the needle-punched nonwoven geotextiles had good soil retention properties and poor drainage properties, and one denser cake layer was formed upstream as the experiment progressed. For the heat-bonded nonwoven geotextiles with larger apertures and thinner thicknesses, there was a slight degree of clogging and acceptable drainage capacity. Steel wire mesh with a thinner thickness and homogeneous mesh structure seemed to offer the best anti-clogging and drainage performance by retaining coarse particles and washing out fine particles. Thus, it is inferred that drain pipes wrapped with steel wire mesh are a good choice for alleviating the physical clogging problem.

Long-term permeability tests on clogging and permeability of nonwoven geotextile filtering silty clay

Geotextile filters have gained extensive applications in geotechnical and geoenvironmental drainage systems. Despite of the abundant research about geotextiles filtering coarse-grained soils, there is little experimental study on the performance of geotextiles filtering fine-grained soils. Since clogging and blinding of geotextiles are more likely to occur in clayey soils, a complex filtration performance of the filters is expected, posing great challenges to the long-term durability of the filtration system. In this research, long-term permeability tests were conducted on silty clay filtrated by three types of nonwoven needle-punched geotextiles. Comprehensive results regarding the permeability evolution, soil retention and clogging behavior were obtained. Interior clogging behavior of the geotextile was checked after the tests by means of scanning electron microscopy. Significant reduction around two orders of magnitude from 10−8 m/s to 10−10 m/s was observed in the permeability coefficient of the silty clay-geotextile system after 90 days of seepage flow. The influence of filtration opening size of the geotextile was obviously noticed in the initial permeation process, while the thickness played an increasingly important role at the later stage. Geotextile with the larger thickness and smaller filtration opening size had more soil retention and poorer filtration performance. In addition, a theoretical equation relating permeability coefficient and filtration opening size of nonwoven geotextile under clogged condition was proposed.

Forecasting the moisture dynamics of a landfill capping system comprising different geosynthetics: A NARX neural network approach

Engineered landfill capping systems consist of geosynthetics and soil layers, which often experience inconsistent and extreme weather events throughout their service life. Complex moisture dynamics in the capping layers can be created by these weather events in combination with other field conditions and can be detrimental to the system's integrity. The limited data on the hydraulic performance of landfill capping systems is a major challenge that hinders the development, validation, and calibration of models that can be used for realistic forecasting of these dynamics. Using the field-level data collected at the Bletchley landfill site, UK, this study develops a data-driven forecasting approach employing a non-linear autoregressive neural network with exogenous inputs (NARX). The data includes precipitation and volumetric water content (VWC) of the capping soil overlaying different geosynthetic layers recorded from Nov 2011 to July 2012. The NARX network was trained using the VWC data as inputs and precipitation data as the exogenous input. Also, the accuracy of NARX predictions was compared against that of a state-space statistical model. NARX-predicted VWC values for a period of 21-days ahead are distributed with a mean error of 0.05 and a standard deviation of 0.2. In the majority of prediction windows, NARX approach outperforms the state-space model. For all NARX prediction periods, RMSEr has been less than 10% for the cuspated core geocomposite. Comparatively, RMSEr values increased to approximately 15% and 19% for the non-woven needle-punched geotextile and the non-woven needle-punched geotextile with band drains, respectively.

Clayey sand–nonwoven geotextile interface characterisation through gradient ratio test

Nonwoven geotextiles have been widely used as a substitute for mineral materials to provide filtration functions in civil engineering. However, in filter systems, geotextiles are the first to be in contact with soft, saturated, and fine soils. For that reason, the selection of a geotextile filter depends on the characteristics of the geosynthetics and the base soil (e.g. grain size distribution, internal stability, permeability) and on the design and boundary conditions such as continuity of the soil–geotextile filter contact interface. The geotextile filter must be properly designed to avoid clogging. The most commonly method used for measuring filtration compatibility of soil–geotextile systems is the gradient ratio test. This paper presents the gradient ratio test program for needle-punched nonwoven geotextile used as a filter layer and internally unstable soil. Laboratory tests were conducted in a modified gradient ratio test apparatus. Test results show that gradient ratio increases with time due to clogging. Also the need for a measurement of water heads very close to the geotextile to measurement of water heads very close to the geotextile to provide additional information on the soil–geotextile system behaviour were presented.

The heavy metal adsorption and plant cultivation performance of grafting modified plant medium made with recycled fibers

This paper proposes an environmental friendly nonwoven geotextile with good heavy metal adsorption properties and beneficial promotion of plant cultivation to potentially replace the riverbank soil or cover on the shoreline surface to rebuild up a healthy ecosystem. In this paper, waste fibers were adopted and carded into even fiber web, followed by needle-punching technology with several layers of fiber web to strengthen the plant medium with satisfying mechanical properties. Then, the grafting modification was conducted on the needle-punched nonwoven geotextiles and the optimum combination of grafting factors were obtained via orthogonal experiments. The tensile, heavy metal adsorption and plant cultivation performances of modified and untreated plant medium were systematically compared and analyzed by infrared absorption spectrum, SEM, XRD, TG, ICP-OES, universal material testing machine, and contact angle tester. The results showed that β-cyclodextrin was well grafted on the substrate. The orthogonal experiments results showed that the best combination of Pb2+ and Cu2+ adsorption was 4% sodium hydroxide (NaOH), 2% β-cyclodextrin, 170 °C heating temperature, and 50 min heating. The adsorption effects of Pb2+ and Cu2+ were 14.32 mg/g and 38.99 mg/g, respectively. The grafted fabric was hydrophilic and a more suitable culture medium for plants. These results provide not only a novel solution for reuse of recycled fibers but also a feasible strategy to construct a new water ecosystem.

Classification of geotextiles and analysis on tests for their tensile properties

Geotextiles are classified into various types which are Synthetic staple fibers needle-punched nonwoven geotextiles, Synthetic filament spunbond and needle-punched nonwoven geotextiles, Synthetic filament woven geotextiles, Slit and splitfilm yarn woven geotextiles, Plastic woven film yarn geotextile based on different weaving methods and property parameters. The applicability of wide-width strip method and narrow strip method for testing the tensile properties is compared and analyzed.

Improvement in CBR value of soil reinforced with nonwoven geotextile sheets

Geosynthetics are human made material used to reinforce soils to improve the bearing capacity and permeability of the soil, reducing soil settlement. Geosynthetics application plays a vital role in the highways constructions with no additive layers, such as cement concrete, asphalt concrete, or in a subgrade layer that affects the bearing capacity of unbounded layers. This paper presents the geosynthetics as a tensional material that has been used for reinforcement of clayey soil. Laboratory California bearing ratio (CBR) test samples were prepared with clayey soils. Clayey soil containing unreinforced soil and reinforced soil. The sample comprised thermally bonded nonwoven geotextiles (NW) and superior needle-punched nonwoven geotextiles (SNW) with different characteristics (NW 8, 10, 21, 30 and SNW 14, 25, 62, 75) with three-layered, based on the sample materials to perform defined tests. These tests show that, bearing ratio of reinforced soils with thermally bonded nonwoven geotextiles increases.

Effect of unequal biaxial tensile strains on the filtration behaviour of continuous filament needle-punched nonwoven geotextiles

The effect of unequal biaxial tensile strains on the filtration behaviour of continuous filament needle-punched nonwoven geotextiles was investigated via gradient ratio tests. The filtration behaviour of four groups of unequal biaxial tensile strains were examined, including the gradient ratio (GR), permeability of the soil-geotextile system, mass of soil loss, and permittivity of pure geotextiles. The strains in the machine direction of a geotextile in the four groups were the same, ranging from 10% to 30%, with the ratios of the strain in the machine direction to that in the cross-machine direction set to 1, 2, 3, and 4, respectively. It is shown that for the same strain ratio, the GR value at the time of test termination (GRt) increases with increasing strain, and the permeability of the soil-geotextile system, permittivity of pure geotextiles, and the soil loss decrease with increasing strain. For the same strain in the machine direction, there are general decreasing trends for the GRt value and soil loss with increasing strain ratio, and the permeability of the soil-geotextile system and permittivity of pure geotextiles under equal biaxial tensile strains are higher than those under unequal biaxial tensile strains.

Thermal conductivity of nonwoven needle-punched geotextiles: effect of stress and moisture

This paper explores the use of geotextiles as insulation material for energy geostructures made of compacted soil. This work is based on measurements of the thermal conductivity of four nonwoven needle-punched geotextiles of varying thicknesses made from virgin or recycled fibres. These values were measured using the hot-plate method. Then, to assess the use of these geotextiles under a covering soil layer, compression tests were performed. For each sample, the relation between thickness and vertical stress was thus established. The thermal conductivities varied from 0.04 to 0.06 W/m/K depending on the geotextile type and the compression stress applied. Subsequent measurements focused on the thermal conductivity of a bilayer compacted soil plus geotextile. Results revealed a water migration towards the geotextile and therefore a larger thermal conductivity. These results highlighted the main importance of compression load and moisture environment in the use of geotextiles as insulation products.

Spunbonded needle-punched nonwoven geotextiles for filtration and drainage applications: Manufacturing and structural design

Recently, geotextiles have gained widespread popularity as porous materials in the fields of geotechnical and geoenvironmental engineering. Spunbonded needle-punched nonwoven geotextiles are an important part of the nonwoven geotextile family. In these geotextiles, filaments are mechanically entangled to form a complex three-dimensional structure, which provides the geotextile a bulky nature. Additionally, this unique fabrication process ensures provision of a variety of widely distributed pores which are essential for the targeted functions of filtration and drainage. This review summarizes manufacturing process of spunbonded needle-punched nonwoven geotextiles and highlights the relationship among process parameters, fabric structure and hydraulic properties. At last, the paper reviews the failure mechanism and design principle of the filtration and drainage performance of geotextile.

The mechanical and ultraviolet aging properties of needle-punched nonwoven geotextiles made with recycled fibers

There are more and more waste textiles in modern times while the recycling efficiency is relatively low. In order to increase the recycling of waste textiles, this paper proposes a kind of low-cost, environmental protection, good permeability, tough and anti-aging substrate geotextile which can replace the riparian soil to support normal growth of plants. First of all, the fiber web was formed by waste fibers (polyester 78 wt%, cotton 20 wt%, others 2 wt%) after carding and reinforcing with different needling parameters. The comprehensive properties of designed nonwoven geotextiles were estimated via a series of tests such as tensile, bursting, air permeability, morphology, thermal stability and porosity. Moreover, the ultraviolet-aging tests were also conducted with both an accelerating aging box and natural aging methods to assess the possibility of outdoor-usage as plant blanket. The comprehensive assessment of results has shown that the optimum processing parameter was the needle depth of 12 mm combined with the needling frequency of 700 times/min. The ultraviolet-aging results have revealed that manufactured geotextiles have comparatively good anti-aging performance, which is suitable for long-term exposure outside. This result of this research provides a feasible and convenient application field for recycled textiles.

Determination of geomembrane – protective geotextile friction angle: An insight into the shear rate effect

This study investigates how the shear rate can affect the geomembrane – protective geotextile friction angle. Four types of geomembranes (GMB) were considered (EPDM, HPDE, PP, and PVC) and a single nonwoven needle-punched geotextile (GTXnw) was used to make the interfaces with the geomembrane. Three shear devices were used: a large-scale inclined plane (IP), a shear box (SB), and a small-scale shear device (ssSD). The ssSD allows two shear modes to be compared: one mode involves incrementally increasing the shear stress, and the other involves imposing a constant tangential velocity at the interface. Only the PP GMB- GTXnw was tested with the SB and the ssSD. Inclined plane standardised tests show that for the three interfaces that undergoes gradual sliding (EPDM, PP and PVC GMB- GTXnw), it is shown that a step-by-step experimental procedure gives significantly lower interface friction angle than that given by the procedure from the current international standard, which is explained by the increase of interface shear stress with sliding speed. These observations are confirmed by shear box tests. One major practical result is that, following the nature of geosynthetics, the shear rate applied in large-scale shear box tests should be adapted to assess a safety value of a geosynthetic - geosynthetic interface friction angle.

Comparison between tensile and damage analysis of hybrid jute/polypropylene needlepunched nonwoven geotextiles produced from untreated and alkali treated jute fibers

The tensile properties of virgin and mechanically damaged samples are investigated for hybrid needlepunched nonwoven geotextiles consisting of untreated Jute/Polypropylene (PP) and alkali treated Jute/PP fibers in defined weight proportions. The damages in nonwovens were induced by two types of mechanical damages (circular hole and horizontal cut) in the center of hybrid nonwovens tested in the cross-machine direction. It was found that the horizontal cut was more detrimental than circular hole in nonwoven geotextiles consisting of jute (both untreated and alkali treated) and polypropylene fibers, specifically when the nonwovens were tested in the cross-machine (preferential) direction. Furthermore, Jute/PP hybrid nonwoven geotextiles were found to be notch-sensitive in nature. The ratio of damaged area of untreated and alkali treated Jute/PP nonwovens at the maximum level of tensile strain to that of the area of corresponding Jute/PP nonwoven determined in the beginning was found to be higher in untreated Jute/PP nonwovens. Similarly, Poisson’s ratio of untreated Jute/PP nonwovens was also found to be higher in comparison to alkali treated Jute/PP nonwoven geotextiles. The initial region of non-linearity of stress–strain curves matched well with that of volumetric deformation for both damaged nonwoven geotextiles. Accordingly, the initial region of stress–strain curves of damaged needlepunched nonwoven can be modeled as a linear region with constant volume deformation.