Needle-punched Nonwoven Geotextiles Research Articles

Conventional and accelerated creep tests on nonwoven needle-punched geotextiles

Nonwoven needle-punched geotextiles are prone to creep deformations when subjected to sustained tensile loads. Creep characterization of these materials is particularly relevant in countries such as Brazil, where nonwoven geotextiles are often used in soil reinforcement applications. However, creep testing is time consuming and requires rigorous quality control. Consequently, a research effort was conducted to develop reliable test methods suitable for expeditious determination of creep curves. Creep tests at elevated temperatures are a promising alternative in polymer engineering to accelerate creep deformations. However, only limited information is currently available on the suitability of temperature-accelerated methods for nonwoven needle-punched geotextiles. In particular, this paper presents the results of a creep study on polyester and polypropylene nonwoven needle-punched geotextiles conducted using the stepped isothermal method (SIM) to accelerate the creep process. Not only axial strains, but also lateral strains (necking) were monitored using photographic techniques. The results obtained using temperature-accelerated methods were compared with those obtained using conventional creep tests. The experimental results indicate that the accelerated creep tests can accurately characterize both axial and lateral creep phenomena in nonwoven needle-punched geotextiles.

Effect of wetting on gas transmissivity of non-woven geotextiles

A laboratory study was undertaken to assess the gas transmissivity of two needle-punched non-woven geotextiles subjected to partial wetting. Each geotextile was subjected to 10 and 20kPa effective stress, respectively. For the geotextiles and conditions examined, it was found that the gas transmissivity decreased as the effective stresses and moisture content increased. More importantly, it was observed that the thicker geotextile achieved a higher transmissivity than the lighter geotextile. This is most likely due to the lower porosity and the large number of needle holes present in the thicker geotextile. The loss in transmissivity was found to be more pronounced at moisture content lower than a threshold value (w≈160%), the variation of the transmissivity loss beyond the threshold value was found to be insignificant. The present investigation has shown that there is a need to include a wettability factor if the geotextile is to be used as a gas drain. Reductions factors are proposed to account for the wettability parameter.

Comparison of the oxidative resistance of various polyolefin geotextiles

Data are reported from oven aging in circulating air and water immersion tests at 80°C on various polyolefin (polyethylene (PE) and polypropylene (PP)) needle-punched nonwoven geotextiles (GTnws) and the results of these long-term tests are compared with the oxidative resistance of high-density PE geomembranes (HDPE GMs) described in a preceding paper (Polym. Degr. Stability 79(1) (2003) 161). Polyolefin fibers used in geotextiles are typically less stabilized, have a very high surface-to-volume ratio and an oriented morphology compared with HDPE GMs. Therefore, significant differences in the oxidation behavior of these products are expected which may affect their durability. Two general results can be obtained from our measurements: Firstly, while the lifetime of the HDPE GM is essentially determined by the slow loss of stabilizers, for all GTnws a rapid reduction in the oxidative induction time (OIT) and, as we conclude, in the amount of stabilizer was observed during water immersion and air aging. Secondly, the mechanical property degradation of the GTnws depended strongly on the oxidation conditions: the induction period prior to the degradation was much longer for immersion in water than for oven aging in circulating air. After antioxidant depletion, an induction time of the oxidation reaction, which depends on the draw ratio of the stretched fibers and the oxygen supply, might substantially contribute to the induction period of the mechanical property degradation of GTnws. For one PP GTnw product, a sudden reduction in the mechanical strength occurred after onset of degradation which continued rapidly until complete deterioration. For other PP samples as well as for all PE GTnws the reduction in mechanical strength proceeded slowly. Best fits were obtained by modeling the degradation process of the PE GTnws by a second-order kinetic. Using an activation energy of 60 kJ/mol (Geotextiles, Geomembranes and Related Products, Balkema, Rotterdam, 1990; Conference Proceedings of the Sixth International Conference on Geosynthetics, Industrial Fabrics Association International (IFAI), Atlanta, USA, 1998, pp. 683–690; Clay Geosynthetic Barriers, Balkema, Lisse, The Netherlands, 2002, pp. 87–96), lower limits of the half-live of the degradation at worst case field conditions were obtained in the range 30–83 years. Some decades have to be added for the overall induction time. However, under field conditions with limited oxygen supply, the expected service lifetime might be at least half an order of magnitude longer.

Clogging Phenomena of the Residual Soil-Geotextile Filter System

Abstract Clogging tests on residual soil-geotextile filter systems were performed, and the permeability reduction due to clogging was evaluated. An extensive experimental program was performed using two typical weathered granite residual soils that were sampled at Shinnae-dong and Poi-dong areas in Seoul. Weathered granite residual soils, which are found in much of the Korean peninsula, pose unique challenges in terms of internal stability and filtration. Two separate simulation tests with weathered residual soils were performed: the cross-plane permittivity test (filtration) and the in-plane transmissivity test (drainage). Needle-punched non-woven geotextiles are selected since they are often used as drainage material in the field. The compatibility of residual soil-geotextile filter systems was investigated with emphasis on the clogging phenomenon. It was found that filter clogging was more significant in filtration than in drainage. The permeability reduction in the coarser Shinnae-dong soil-filter system was more serious than in the finer Poi-dong soil-filter system.

Interaction of nonwoven needle-punched geotextiles under axisymmetric loading conditions

Geotextiles have been successfully used for reinforcement of unpaved roads on soft subgrade to improve the performance of a reinforced fill layer placed on soft ground. The tension–strain behavior of a nonwoven needle-punched geotextile under axisymmetric loading condition as well as the mechanism and effects of the different grades of geotextile on the increase in bearing capacity of reinforced unpaved roads over weak subgrade under traffic load were considered. The strain energy capacity concept is proposed to describe the tension–strain of geotextile under an axisymmetric loading condition. Modified CBR tests on soft and weathered clay overlain by compacted sand as well as on soft and weathered clay overlain by compacted sand reinforced with fix- or free-end nonwoven needle punched geotextile were carried out. Finite element method (FEM) using the PLAXIS software was utilized to back-analyze the results of the modified CBR tests. No significant difference between in-air and in-soil stiffness has been found for geotextile reinforcement of unpaved road. The calculated results indicate an additional load capacity due to the presence of the geotextile using an axisymmetric stiffness which demonstrated a significant contribution of membrane action by the different types of geotextile on the increase in bearing capacity of soil–geotextile system. The effects of the different types of geotextile obtained in this study can be used to preliminary select the appropriate grades of nonwoven needle-punched geotextile corresponding to the allowable rut depth in the design of the reinforced unpaved roads under traffic load.

Comparison of the Durability of Geotextiles in an Alkaline Mine Tailings Environment

This is the last of a three-part study (Grubb et al. 1999, 2000) that explores the issues related to the use and durability of geotextiles in Andean mining environments. Additional outdoor exposure tests were completed on a woven multi-filament polyester (PET) geotextile, and on two nonwoven needle-punched polypropylene (PP) geotextiles with carbon black in Vijus, Peru, and Atlanta, Georgia, USA. The average retained strengths of each geotextile in both locations did not exceed 60%. Five geotextile samples (those previously mentioned and two additional nonwoven needle-punched PET geotextiles) were also embedded in freshly deposited alkaline tailings with a pH of 11.3 and 178 mg/L total cyanide. The retained strengths of the lighter PET geotextile varied from approximately 43 to 338%. The average retained strengths of the four nonwoven geotextiles ranged from approximately 84 to 92%. Two geotextiles placed directly on the surface of the tailings demonstrated that chemical-induced erosion processes could be mitigated. Batch immersion experiments were performed on the PET geotextiles in two alkaline sodium hydroxide solutions (one containing cyanide) to quantify whether the cyanide ion produced any degradation in addition to that measured for the hydroxyl ion at the same pH. The retained strength data indicated that the alkaline solution containing cyanide best matched the alkaline mine tailings environment.

Geomembrane–geotextile interface shear properties as determined by inclined board and direct shear box tests

Geomembrane–geotextile interface shear strength parameters were measured using inclined board (tilting table), standard size (60 mm×60 mm) and large-scale (300 mm×300 mm) direct shear box tests. Smooth and rough HDPE, PVC geomembranes and nonwoven needle-punched geotextiles were used in the experiments. Inclined board tests were conducted under a normal stress range of about 5–50 kPa on variable size interface areas. In direct shear tests the applied normal stresses were about 25–300 kPa and 110–400 kPa in the small and large size tests, respectively. The interface friction angle and adhesion intercept values obtained by fitting a straight line through the plots of interface shear strength versus the normal stress were compared for different tests. It has been found that inclined board test results produce envelopes with relatively small adhesion values for both smooth and rough HDPE geomembrane–geotextile interfaces. The size of the interface does not appear to be a significant factor. For smooth geomembranes direct shear and inclined board tests give comparable interface friction angle and adhesion values. For rough geomembranes, however, the direct shear adhesion values are markedly higher and friction angle values are a few degrees higher when compared to the inclined board test results.

Selection of geotextiles to filter broadly graded cohesionless soils

The retention of soils with a coefficient of uniformity greater than 8 by geotextile filters is not properly addressed in existing filter criteria. For these soils, the rearrangement of the particles in a restricted zone adjacent to the filter interface is complex and results in variations of local hydraulic conductivity. These changes have been related to the ratio between the opening size of the filter and the indicative size of the base soil. A test program was performed to evaluate the compatibility of seven nonwoven needlepunched geotextiles and ten broadly graded cohesionless soils. Variations in hydraulic conductivity with time and in the mass of washed out particles disclosed the occurrence of piping, bridging and blinding of the base soil. After a description of these phenomena, a new retention criterion based on the test results is proposed in the form of a flow chart, for the selection of geotextile filters.

Transmissivity Behavior of Layered Needlepunched Nonwoven Geotextiles

Needlepunched nonwoven geotextiles contain considerable void space that is available for liquid transmission. Compressing a geotextile reduces its in-plane and cross-plane liquid flow because it alters the fabric's pore structure. In this study, we investigate single-fiber and layered needlepunched nonwoven geotextiles as a function of various needlepunching parameters and fiber linear density. We also evaluate the transmissivity parameter β, which describes the transmissivity property of needlepunched nonwoven geotextiles. Experimental results indicate that these transmissivities decrease to a constant value with increasing normal stress. The transmissivity behavior of needlepunched non woven geotextiles depends on raw material characteristics, needlepunching parameters, and normal stress. This study also proposes relationships to predict the transmissivity behavior of two needlepunched nonwoven geotextiles in parallel.

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 m 2/s over the normal stress range examined (5–200 kN/m 2). 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.

Design Methodology for a Gas Pressure Relief Layer Below a Geomembrane Landfill Cover to Improve Slope Stability

Pore pressures generated by landfill gas underneath a final cover system that incorporates a geomembrane can significantly reduce the effective normal stress on the lower geomembrane interface to the point of creating cover veneer instability. To the author's knowledge, no design methodology has previously been published to address this issue. Recently, however, large-scale slope failures have been attributed to landfill gas pore pressures. Therefore, a need for a design methodology exists. An estimation of gas flux from a landfill surface can allow a gas-relief layer to be designed using Darcy's law for gas flow through a porous medium. The methodology incorporates knowledge of the gas transmissivity of a chosen medium to design a spacing for highly permeable strip drains. The strip drains in turn can discharge the gas either to vents or an active gas collection system. The gas-relief layer typically consists of sand or a geonet composite. Limited testing of nonwoven, needle-punched (NWNP) geotextiles indicates that these materials may also be acceptable for gas relief in some designs. However, more testing is recommended before using NWNP geotextiles alone in this application. The greatest assumption in the proposed methodology concerns the estimation of gas flux. More research is required in this regard; however, the basic concept of providing a gas-relief layer with intermittent highly permeable strip drains is recommended as a prudent engineering measure for landfill final cover systems incorporating geomembrane barriers.

Performance of Protective Cover Systems for Landfill Geomembrane Liners Under Long-Term MSW Loading

This paper presents the results of large-scale laboratory simulation tests conducted to evaluate the relative performance of different cover systems, consisting of a granular soil layer (i.e. a drainage layer) both with and without the presence of a needle-punched nonwoven geotextile, to protect a 1.5 mm thick smooth HDPE geomembrane liner under long-term municipal solid waste (MSW) loading conditions. Five different granular soils that range from a coarse gravel to a medium sand were used in the testing program. The protective cover system and the geomembrane liner were subjected to incremental loading to a maximum pressure of 1.4 MPa. The effect of long-term loading on the characteristics of the cover soils was assessed by performing particle size analyses, and the physical damage that occurred to the geomembrane liner was visually assessed in addition to performing multi-axial tension, wide strip tension, and water vapor transmission tests. The test results revealed that the degree of geomembrane liner protection decreases as the soil mean particle size increases and as the soil particle sphericity decreases. This study demonstrates that a 300 mm thick granular soil layer consisting of particles with a mean size less than 30 mm and a sphericity greater than 0.8, combined with a 270 g/m2 nonwoven geotextile provides adequate protection for a 1.5 mm thick HDPE geomembrane liner from MSW loading.

Stress-Confinement Effect of Nonwoven Geotextile on Design of Reinforced Soil Retaining Wall

The design implication of stress-confinement effect of nonwoven geotextile is addressed. The unconfined and confined strengths of a selected needle-punched nonwoven geotextile are used to conduct a comparative design of a granular soil retaining wall based on a limit equilibrium approach. A higher wall may be allowed when considering the confined strength as compared to the unconfined strength. For a selected wall height, confined strength allows for fewer geotextile layers when compared to that designed using unconfined strength. It is recommended that stress-confinement test procedure should be standardized so that confinement effect of some nonwoven geotextiles may be incorporated into an individual wall design procedure.

Puncture Protection of Geomembranes Part II: Experimental

Geomembrane protection materials should be considered in design if geomembranes are to properly serve the role of barrier materials. The type, thickness and properties of the required protection material are in significant need of a rational design method. This series of three papers provides a design method for the inclusion of geomembrane protection materials, geotextiles in particular. Part I focuses on theory, this paper, Part II, focuses on experiments, and Part III focuses on design examples. In this paper, truncated cone and stone puncture test results for both short and long term durations are presented. A 1.5 mm thick high density polyethylene (HDPE) geomembrane, and various nonwoven needle punched geotextiles with varying masses per unit area made from virgin polyester and polypropylene continuous and staple fibers were tested. Using the results of this testing program, a design methodology was developed for calculating the required mass per unit area of a puncture protection material for a given factor of safety. Conversely, the design can be used to determine the unknown factor of safety for a given type of protection material.

Puncture Protection of Geomembranes Part III: Examples

Geomembrane protection materials should be considered in design if geomembranes are to properly serve the role of barrier materials. The type, thickness and properties of the required protection material are in significant need of a rational design method. This series of three papers provides a design method for the inclusion of geomembrane protection materials, geotextiles in particular. Part I focuses on theory, Part II focuses on experiments, and this paper, Part III, focuses on design examples and presents a comparison of results presented in Parts I and II. The design developed in Part II is used in this paper to provide several numerical examples that highlight the different strategies used in Germany and in the USA for the selection of protection geotextiles. This paper also includes a number of design charts for a wide variety of practical situations. Finally, puncture resistance results for a geomembrane with different types of protection materials (other than virgin polymer nonwoven needle punched geotextiles) are presented in the Appendix. The design procedures presented result in a site specific and material specific factor of safety.

Compressional behaviour of layered needle-punched nonwoven geotextile. Technical note : Kothari, V K; Das A Geotext GeomemV12, N2, 1993, P179–191

Compressional behaviour of layered needle-punched nonwoven geotextile. Technical note : Kothari, V K; Das A Geotext GeomemV12, N2, 1993, P179–191

Thickness equation for nonwoven needle-punched geotextiles under normal loading. Technical note : Weggel, J R; Gontar, W A Geotech Test JV15, N4, Dec 1992, P404–408

Thickness equation for nonwoven needle-punched geotextiles under normal loading. Technical note : Weggel, J R; Gontar, W A Geotech Test JV15, N4, Dec 1992, P404–408

Compressional behaviour of layered needle-punched nonwoven geotextiles

Compressional behaviour of nonwoven fabrics depends on various raw material characteristics. Experiments to see the effect of fibre denier on the compressional behaviour of needle-punched nonwoven fabrics of different mass per unit area have been carried out. The effect of percentage of finer fibre content in different layers on the compressional behaviour of layered needle-punched nonwoven fabrics of polyester and polypropylene fibres has been reported. Relationships have been proposed to predict the compressional behaviour of two needle-punched nonwoven fabrics in series.