Woven Geotextile Research Articles

Testing procedures to assess the viability of dewatering with geotextile tubes

Geotextile tubes are finding increasing market acceptance for dewatering high water content materials. The success of this application depends on the filtration compatibility between the high water content materials and the geotextiles used to make the tubes. In this paper, 26 pressure filtration tests using four woven geotextiles of various materials were conducted to study soil retention and permeability of the sludge/geotextile system and the possible controlling factors. Based on the test results, the filter cake is not only the major contributor to the retention of fine particles, but also causes a decrease in permeability. Controlling the formation of the filter cake on the inside of the geotextiles tube and thus achieving a balance between soil retention and permeability is vital to a successful project. Surprisingly, initial water content may have a significant effect on the dewatering efficiency and dewatering rate. More testing is recommended to gain a deeper understanding into this relationship.

Evaluation of vacuum filtration testing for geotextile tubes

High water content (or low solids content) materials consist of marine sediments, industrial, wastewater, and water treatment sludges, and agricultural waste. Geotextile tubes are emerging as a new technology that can dewater high water content material. The goal of this study was to utilize vacuum filtration testing to evaluate the filtration and retention capacity of woven fabrics used for geotextile tubes and to provide design guidance in selecting appropriate geotextiles to increase solids retention while reducing excessive fines migration. A procedure for analysis of vacuum filtration test results is provided. The results of this study revealed that woven geotextiles provided adequate retention of solids. In addition, empirical equations for retention, clogging, and permeability were assessed for applicability to geotextile tube design.

Behaviour of reinforced clay under monotonic and cyclic loading

The strength improvement due to the provision of sand layers on either side of the reinforcement (sandwich technique) within reinforced clay soils is studied in this paper. The behaviour of reinforced clay was examined in triaxial compression tests under both static and cyclic loading conditions. Effect of the sand layer thickness, moisture content and reinforcement types were studied. Three different types of reinforcements, namely, woven geotextile, non-woven geotextile and micro-grid were used. All the triaxial compression tests were conducted under unconsolidated-undrained (UU) conditions. The results of the tests indicate that a thin layer of high-strength sand provided on both sides of the reinforcement is effective in improving the strength and deformation behaviour of reinforced clay soils under both static and cyclic type loadings.

Filtration Performance of Woven Geotextiles With Wastewater Treatment Sludge

Capping of contaminated soft sediments and sludges for in situ containment provides an efficient remediation alternative. Capping design typically involves the use of geosynthetics for multiple functions, e.g., reinforcement, separation, and filtration. Filtration performance becomes a decisive factor for proper long-term performance of a cap. Because of multiple functions required, woven geotextiles are often the choice geosynthetic in such applications. A research program concerning the filtration behavior of contaminated wastewater treatment sludges was conducted. The laboratory portion of the program included a series of filtration tests with different woven geotextiles. Filtration performance of the sludge-woven geotextile systems was also observed in field test cells. Geotextile samples were exhumed from the cells after exposure and analyzed in the laboratory. The results indicate that the sludges can be filtered using woven geotextiles and the selection of a proper filter can be made on the basis of geotextile pore structure parameters, i.e. percent open area and pore opening size distribution. The standard gradient ratio test did not always reflect the filtration performance and, therefore, other clogging ratios need to be considered. A commonly used geotextile pore opening size-to-soil particle ratio in the existing filter criteria, O95/D85, did not predict the filtration behavior displayed by the sludge; however, another ratio, O50/D 50 , showed general correlation to clogging and retention.

Conversion of Geosynthetic Strain to Load Using Reinforcement Stiffness

Measurements indicative of the internal behavior of full-scale geosynthetic-reinforced soil walls typically consist of reinforcement strains and overall deformations. The focus of this paper is the development of a methodology that can be used to convert measured reinforcement strains to load using properly selected reinforcement stiffness values. The loading of the geosynthetic in the field can be simulated in the laboratory using creep, relaxation, and constant-rate-of-strain tests. It was found that in-isolation creep stiffness data is sufficiently accurate to estimate reinforcement loads from strain measurements, at least for geogrids and most woven geotextiles. The approach is validated using data from carefully instrumented wall case histories in which reinforcement loads were measured directly and compared to loads estimated from measured reinforcement strain data.

Field Evaluation of Construction Alternatives for Roadways over Soft Subgrade

Alternative methods for providing a stable platform over soft subgrades were evaluated using a 1.4-km section along a Wisconsin State highway that incorporated 12 test sections to evaluate 9 different stabilization alternatives. A variety of industrial by-products and geosynthetics were evaluated for stabilization. The industrial by-products included foundry slag, foundry sand, bottom ash, and fly ash as subbase layer materials. The geosynthetics included geocells, a nonwoven geotextile, a woven geotextile, a drainage geocomposite, and a geogrid. The same pavement structure was used for all test sections except for the subbase layer, which varied depending on the properties of the alternative material being used. All test sections were designed to have approximately the same structural number as the conventional pavement structure used for the highway, which included a subbase of granular excavated rock. Observations made during and after construction indicated that all sections provided adequate support for the construction equipment and no distress was evident in any part of the highway. Each of the alternative stabilization methods, except a subbase prepared with foundry sand, appear to provide equivalent or greater stiffness than that provided by control sections constructed with excavated rock. However, the foundry sand subbase is providing adequate support. Analysis of leachate collected from the base of the test sections shows that the by-products discharge contaminants of concern at very low concentrations.

A Method for Tensile Test of Geotextiles with Confining Pressure

Geotextiles are playing an increasingly important role in civil and environment engineering applications. The performance characteristics of woven and nonwoven geotextiles and tensile test methods are reviewed. To better simulate the in-soil tensile behavior of nonwoven geotextiles, it is desirable to test their tensile properties when they are under a lateral confining pressure, and this often requires complex loading fixtures. In this study, a simple test device and a special test method are developed for testing the tensile properties of geotextiles under confining pressure. The confining device consists of two airtight aluminum chambers covered with flexible rubber membranes between which the specimen is placed, pressurized, and tested. By using specially prepared “composite” specimens, the test device can be used as an attachment to any ordinary tensile test setup. Tests are conducted on two types of nonwoven geotextiles, on an Instron tester with the confining pressure device installed. The tensile behavior of the geotextiles with and without confining pressure is evaluated and the results are reported.

Constitutive modeling of geosynthetics

A constitutive model for geosynthetics is presented that incorporates components describing direction-dependent elastic, plastic and time-dependent creep properties. The model is compared to a series of uniaxial tension tests performed on a biaxial geogrid and a woven geotextile. Tension tests to which model predictions are compared include fast and slow monotonic tension, constant load creep tests and two series of cyclic tension. The model is shown to offer reasonable predictions of in-air tensile load–strain properties commonly associated with geosynthetic materials.

Soil-geotextile interface friction by direct shear tests

This paper describes large-size direct shear tests on soil-geotextile interfaces. Medium-grained, uniform sand and three varieties of woven and nonwoven geotextiles manufactured with different techniques are utilized to investigate the soil-geotextile interface friction coefficient (f*). Tests were carried out using an apparatus specifically designed for interface testing, and results were compared with those obtained from the conventional direct shear equipment. The results obtained from this study indicated that the determination of peak interface behaviour was not a trivial matter, as the results were significantly affected by the boundary and testing conditions of the testing apparatus. The residual interface behaviour was investigated by multiple reversal direct shear tests. Since the use of multiple reversal direct shear tests on the proposed apparatus can impose a high degree of shear displacement and stress uniformity on the soil-geotextile interface, a more reliable definition of the residual interface friction can be obtained. The results indicate that woven-nonwoven geotextile interfaces exhibit a significant postpeak strength loss after a number of shear cycles. In the case of woven geotextiles, this is attributed to the opening up of the filaments associated with the physical damage caused during shear, whereas for nonwoven geotextiles it is due to the pulling out or tearing of filaments.Key words: geotextile, direct shear test, interface friction coefficient, peak shear strength, residual shear strength.

Assessment of Falling Weight Deflectometer Data for Stabilized Flexible Pavements

Backcalculation of pavement moduli through the utilization of the falling weight deflectometer (FWD) is used for pavement monitoring and evaluation. The performance and structural condition of nine flexible pavement test sections built in Bedford County, Virginia, have been monitored over the past 5 years using FWD. The nine sections include three groups with aggregate base layer thicknesses of 100, 150, and 200 mm, respectively. Sections 1, 4, and 7 are control, whereas Sections 2, 5, 8 and 3, 6, 9 are stabilized with geotextiles and geogrids, respectively. The FWD testing used five double-load drops ranging from 26.5 to 58.9 kN. The deflection basins obtained from the testing have been analyzed using the ELMOD backcalculation program to find the pavement structural capacity and to detect changes in the aggregate resilient modulus. The analysis shows a reduction in the backcalculated resilient modulus of the 100-mmthick base layer. The reduction was 33 percent over 5 years for the nonstabilized section compared with the geosynthetically stabilized section. The reduction in base layer resilient modulus may have resulted from subgrade fine migration into this layer as confirmed by excavation. The study confirms the effectiveness of using woven geotextile as a separator in a pavement system built over weak subgrade. This supports the continuous rutting measurements and ground truth excavation conducted in late 1997.

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.

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.

Modeling the In-Plane Permeability of Woven Geotextiles1

The in-plane permeability or transmissivity of a geotextile becomes an important property when it is used in applications involving cohesive soils (clays). Because cohesive soils are relatively impermeable, the geotextile is mainly responsible for drain ing the water from the soil structure, thus releasing the pore water pressures. When developing a woven geotextile for reinforcing cohesive soil structures, there is a need to predict transmissivity in addition to tensile properties. Existing models for predicting flow through porous media are not sufficiently accurate to predict a relatively small flow through woven fabrics. This paper presents a modeling approach, taking into consideration the intra- and interyarn geometry for any weave.

Enhancements in surface quality of concrete through use of controlled permeability formwork liners

This report presents results of a study to compare the performance of concrete wall surfaces cast against controlled permeability formwork (CPF) liners with that of concrete surfaces cast against conventional impermeable plywood formwork Two formwork liners were used, namely 'Zemdrain', a proprietary spun-bonded formwork liner manufactured by Dupont, and 'Lotrak FL', a woven geotextile manufactured by Don & Low. A variety of test methods were used to assess performance, including surface hardness, initial surface adsorption, sorptivity, depth of carbonation, chloride penetration and freeze–thaw resistance. In addition, the quality of the surface finish was assessed visually. Two concrete mixes and two different curing regimes were tested. The variation in surface quality of concrete with depth from the top of the pour was also examined. Results demonstrate that surface qualities of concrete can be markedly improved by use of CPF liners. The two liners produced identical enhancements in surface quality. They differed in one aspect of performance only, as cement particles were able to travel through the Lotrak fabric and to bond to the backing plywood, necessitating cleaning of the plywood after each cast. This problem did not arise with Zemdrain. Effectiveness of CPF liners was slightly greater for the lower grade mix and slightly lower close to the top of a pour. It is also observed that measured enhancements in performance may be strongly influenced by test duration.

Constitutive modelling of a reinforced soil using hierarchical model

Drained triaxial tests are conducted on natural and reinforced sand under various stress paths. Direct shear tests and pull-out tests are conducted on soil–reinforcement interface and on reinforcement, respectively. The effects of two types of reinforcement, viz, woven and non-woven geotextile and number of layers of reinforcement are investigated. Hierarchical single surface model is used to depict the behaviour of natural and reinforced soil by treating the soil as a single composite material and by considering soil, reinforcement and interface as independent elements. It is shown that the material parameters are very much affected by the type and the number of layers of reinforcement. The hierarchical model provides satisfactory prediction for both natural and reinforced soil. Copyright © 1999 John Wiley & Sons, Ltd.

Interaction between Reinforcing Geosynthetics and Soil-Tire Chip Mixtures

The objective of the present study was to evaluate the mechanical properties of the tire chips and soil-tire chip mixtures relevant to geosynthetic-reinforced earthworks. Tests were conducted to evaluate shear strength and pull out capacity with a woven geotextile and two geogrids. Soil-tire chip mixtures made with clean sand and sandy silt were tested. These properties were then used to assess the potential advantages of using soil-tire chip backfills for geosynthetic-reinforced retaining walls and embankments. The test results show that the geosynthetic pull-out force in tire chip and soil-tire chip backfills increases with displacement—i.e., no peak pull-out force is generally obtained, at least for displacements ≤100 mm. Pull-out interaction coefficients for tire chip backfills are typically greater than 1, whereas for soil-tire chip backfills they typically range between 0.2 and 0.7, even though the pull-out capacity for soil-tire chip backfills is generally similar to or greater than the pull-out capacity in a soil backfill. The higher strength, lower unit weight and good backfill-geosynthetic interaction obtained with soil-tire chip backfills can result in walls requiring less geosynthetic reinforcement than walls backfilled with soil. In addition, embankments can potentially be constructed with steeper slopes and a smaller volume of material when soil-tire chip fill is used, while providing greater resistance against lateral sliding and foundation settlement.

The Effect of In-Plane Tensile Loads on the Retention Characteristics of Geotextiles

AbstractThe results of hydrodynamic sieving tests in which pretensioned geotextile specimens were tested using glass beads as the suspended particles are reported. Biaxial as well as uniaxial tensile loads were used. Two types of geotextile were tested, a woven slit-film polypropylene geotextile and a nonwoven needle-punched polyester geotextile. In all but one of the tests reported, the effect of a tensile load was to reduce the filtration opening size. The effect was most pronounced with the woven geotextile, where an equal biaxial load of only 8% of the minimum tensile strength of the geotextile resulted in a 28% decrease in the filtration opening size. Since all the tests resulted in a decrease in the filtration opening size, it appears unlikely that inplane tensile loads will exacerbate problems of loss of particles through a geotextile. However, it is suggested that increased problems associated with geotextile clogging and blinding can be expected. Preliminary tests in a modified permeameter on uniaxially loaded geotextile specimens in contact with a fine sand confirmed this hypothesis.

The Abrasion Test for Geotextiles Used as Filter-Sheet

In practical construction works, installed geotextiles used as filter-sheets are often kept uncovered for several months to a year. Since the friction between geotextiles and rocks due to wave or wind action is severe, the abrasion resistance is an important factor for selecting geotextiles. In this paper, the results of the abrasion resistance test (JIS D 4604) for eight different geotextiles including three non-woven geotextiles, four woven geotextiles, and a multi-layered woven geotextile are presented. The test results are shown in terms of the percent strength retained. Among the test results, 1) the usual woven geotextiles showed a low percent strength retained (about 40%), 2) the coated woven geotextiles with synthetic resin and the multi-layered woven geotextiles showed a good percent strength retained (more than 90%), 3) the non-woven geotextiles showed a moderate percent strength retained (about 65%). Further, weft strands of the usual woven geotextiles shifted laterally and which did not occur with resin coated geotextiles.

Interaction Between Tire Shreds, Rubber-Sand and Geosynthetics

Waste tires can be shredded (tire shreds) and re-used as fill material. The fill material may be comprised solely of tire shreds or mixed with sand (rubber-sand). If geosynthetics are to be used with fills containing tire shreds, it is necessary to understand the physical interaction between tire shreds, or rubber-sand, and the geosynthetic of interest. A laboratory testing program consisting of direct shear tests, interface direct shear tests, and geosynthetic pullout tests was conducted to determine the interaction properties of tire shreds and rubber-sand fills with three different flexible geogrids and a woven geotextile. Direct shear and interface direct shear tests were conducted using a large direct shear box with dimensions of 300 mm by 300 mm and a total depth of 230 mm. Pullout tests were carried out in a large pullout box with dimensions of 1.2 m in length by 0.9 m in width and a total depth of 0.5 m. The details of the testing program, the test results, and conclusions based on the test results are presented in this paper.

Results of direct shear tests on geotextile reinforced cohesive soil

The results of direct shear tests on near-saturated silty clay samples reinforced with woven and nonwoven geotextiles are presented and analyzed in terms of the strength increase, shear and volumetric deformation of reinforced soil, and soil/reinforcement interface bond development. The analyses—which are based on total stresses—indicate that the inclusion of nonwoven geotextiles resulted in a significant strength increase of the wet cohesive soil. The inclusion of woven geotextiles, however, did not offer any strength increase. This differentiation of behaviour was attributed to the nil water transmissivity of the woven geotextile. By further analyzing the test results it was found that the magnitude of the interface bond increased with the transmissivity of the geotextile and varied with the normal interfacial stress. By utilizing a simple soil-reinforcement interaction model, values of interface friction angles were computed for different assumed values of adhesion efficiency between cohesive soil and geotextile.