Wide-width Tensile Tests Research Articles

Application of the digital image correlation technique in wide width tensile test of geogrids

This paper aims to explore the DIC technique for use in wide width tensile testing of geogrids, from specimen preparation to selection of DIC parameters required for analysis to provide a guide for a proper use. A series of monotonically loaded wide width tensile tests were conducted on a PET geogrid to investigate the effects of specimen surface preparation methods and the user-defined DIC parameters. An additional set of tests under cyclic loading was conducted to investigate the effect of the image sampling rate. The results indicate that the speckle pattern (image texture) has a significant effect on the DIC results such that the larger is the speckle size, the greater is the uncertainty level, eventually leading to increased nonuniformity in the calculated strains. Also, it was revealed that a subset size smaller than optimal, typically 20–30 pixels, results in highly localized strain distribution. A similar trend was observed in step size. In addition, the image sampling rate was found to have a significant effect on the DIC-calculated cyclic strains, such that the lower is the image sampling rate, the lower is the calculated cyclic strain.

Interaction Between a Lateritic Soil and a Non-woven Geotextile in Different Moisture Conditions

This work evaluates the increase in stiffness provided by the variation of moisture content (matrix suction) and the grain size structure at the interface between a cohesive tropical soil (lateritic clay) and a nonwoven geotextile. For this purpose, monotonic pullout tests with soil suction monitoring were performed on small-sized equipment under three scenarios (O Optimum, D Dry and DP Dry Post-Compaction) and two vertical pressures (14 and 28 kPa). The Dry Post-Compaction tests were conducted with the same matrix suction of the Dry tests. The monotonic pullout tests evaluated the soil-geosynthetic interaction under constant displacement to calculate the apparent confined stiffness of the geosynthetic (Jc). The Wide Width Tensile tests were conducted to assess the unconfined stiffness of the nonwoven geotextile (Jn). The Dry scenario, compacted with higher compaction energy than the others and, consequently, altering its grain size structure, presented the best performance. This indicates that other parameters besides the suction may be influencing the interaction between the soil and the non-woven geotextile. Even under small vertical pressures, the apparent confined stiffness improves considerably compared to the unconfined stiffness. This indicates that the use of the unconfined stiffness obtained by index tests may be a conservative measure in paving projects.

Use of Particle Image Velocimetry (PIV) technique to measure strains in geogrids

Geosynthetics are widely used in Geotechnical Engineering to reinforce soil/gravel in pavements, retaining wall backfills, and embankments. It is important to measure strains in geogrids in the determination of their strength parameters such as tensile strength and secant stiffness, and in evaluating their performances in geogrid-reinforced structures. Strain gauges are commonly used in measuring strains in geogrids. However, it is important to verify the strains measured by strain gauges as these strains are affected by the data logging device, gauge factors, quality of bonding between grain gauge and geogrid, and temperature. Therefore, this study was conducted to verify the performance of strain gauges attached to Geogrids and also to investigate the possibility of using PIV technique and GeoPIV-RG software to measure the local strains developed in a geogrid specimen under tensile testing in the laboratory. In the experimental program of this study, six composite geogrid specimens were tested for tensile strength (wide-width tensile tests) while measuring/calculating its tensile strain by using strain gauges attached to the specimens, Geo-PIV-RG analysis and crosshead movements of Instron apparatus. Good agreement between the strains obtained from strain gauges and geoPIV-RG analysis was observed for all the tests conducted. These results suggest that the PIV technique along with geoPIV-RG program can effectively be used to measure the local strain of geogrids in the laboratory tests. It was also able to verify that properly installed strain gauges are able to measure strain in the geogrids which are used in the field applications.

Damage Induced by Recycled Aggregates on the Short-Term Tensile Behaviour of a High-Strength Geotextile

This paper presents the mechanical, chemical and environmental degradation induced by recycled Construction and Demolition Wastes (C&DW) on the short-term tensile behaviour of a nonwoven polypropylene (PP) geotextile reinforced with polyester (PET) yarns. In order to study the chemical and environmental degradation a damage trial embankment (2m x 3m in plant) was constructed using recycled C&DW as filling material. The damage caused by the mechanical actions during installation was also simulated by installation damage laboratory tests. Wide width tensile tests were performed on geotextile samples exhumed from the trial embankment after 12 months, on laboratory damaged samples and on intact (as-received) samples. Their short-term tensile behaviour is compared. Scanning electron microscope (SEM) images of intact and exhumed specimens are also presented.

Damage induced by recycled Construction and Demolition Wastes on the short-term tensile behaviour of two geosynthetics

Geosynthetics have been used as a reinforcement material in roadways and railways construction. Notwithstanding, one of the main questions of using is their durability. The damage caused by the mechanical actions during installation and the chemical and biological degradation are important issues to consider in the physical, mechanical and hydraulic behaviour of geosynthetics. The change in their properties induced by these degradation processes can compromise the performance of these materials. In order to study the chemical and environmental degradation induced by a recycled Construction and Demolition Waste (C&DW) on the short-term tensile behaviour of two geosynthetics (a uniaxial HDPE geogrid and a nonwoven PP geotextile reinforced with PET yarns) used commonly as reinforcement material, a damage trial embankment (2 m × 3 m in plan) was constructed. This paper presents and discusses the effects produced by the recycled C&DW on geosynthetic samples exhumed after 6 months of the embankment construction. The constituents and the leaching behaviour of the recycled C&DW are presented. Wide width tensile tests were performed on exhumed and intact (as-received) geosynthetics and their tensile behaviour is compared. Scanning electron microscope (SEM) images of intact and exhumed specimens are also presented. As expected the degradation induced by the recycled C&DW after 6 months of exposure is not very expressive. On the HDPE geogrid the recycled C&DW induced a small decrease on the tensile strength and the reduction of the tensile stiffness modulus. The geocomposite experienced some reduction on the tensile strength (16% on average) but the effects on tensile stiffness and shape of the load–strain curves were not significant.

Effect of Soil Grain Size Distribution on the Mechanical Damage of Nonwoven Geotextiles Under Repeated Loading

Installation processes (which induce mechanical damage) may cause undesirable changes on the properties of geosynthetics, affecting their performance. This work evaluates the effect of mechanical damage on the short-term tensile behaviour of two nonwoven geotextiles (with different masses per unit area). The geotextiles were damaged in laboratory using a standardised procedure and an artificial aggregate (corundum) and eight other soils. The damage induced was characterized using wide-width tensile tests. Results showed reductions of the tensile strength of both geotextiles, which depended on the grain size distribution and uniformity of the soils and on the mass per unit area of the geotextiles. The reduction in tensile strength provoked by corundum was higher than the decreases caused by most of the other soils. The mechanical damage tests also led to a reduction of elongation at maximum load and an increase of stiffness.

A comparison of wide-width tensile strength to its axi-symmetric tensile strength of hybrid needlepunched nonwoven geotextiles

Geotextiles are placed between the subbase and subgrade in order to enhance the bearing capacity of soft subgrades. The concentrated forces perpendicular to the plane of geotextile as a result of subgrade surface irregularities can impart axi-symmetric loading to the geotextile. In this study, a simple model of axi-symmetric tensile strength for anisotropic hybrid needlepunched nonwoven geotextiles has been proposed by relating to its in-plane tensile properties obtained from wide-width tensile tests in the weaker direction. A range of hybrid geotextiles has been produced from a blend of polypropylene/viscose fibers in defined weight proportions to validate the model of axi-symmetric tensile strength. In general, a good correlation has been observed between the theoretical and experimental results of axi-symmetric tensile strength of hybrid needlepunched nonwoven geotextiles.

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.

Tensile Test Method Effect on the Tensile Strength of Flexible PET Geogrids

For single rib tensile tests using GRI-GG1, the ultimate and 5 % strain tensile strengths obtained from tests with an extension rate of 50 mm/min are greater than those obtained using a 10 mm/min extension rate. However, the elongation at the break occurs in reverse order. For wide-width tensile tests using ASTM D4595, the unit tensile strengths and elongations at break decrease as the number of specimen ribs increases. The repeatability of the test results decreases as the number of ribs increases. The tensile strengths obtained from wide-width tensile tests are 1–8 % less than those obtained using GRI-GG1. The elongation at the break is about 92–99 % of that obtained using GRI-GG1. Rib breakage at peak load is randomly distributed for different specimens and samples.

Large-scale drainage behaviour of composite geotextile and geogrid in residual soil

The reinforcing capability of high strength geotextile and geogrid in residual soil has been studied recently, using pullout tests and wide width tensile tests. However, the drainage behaviour of these geosynthetics products in reinforcement applications has not been well addressed so far. This paper presents experimental evaluation of the drainage performance of a high strength composite permeable geotextile and a HDPE geogrid in a poorly draining Singapore residual soil. The drainage behaviour of these geosynthetics products embedded in poorly draining Singapore residual soil was evaluated with large-scale drainage behaviour tests. Pore pressure transducers were installed at strategic locations in the soil mass to evaluate the development and dissipation of excess pore pressure. The test results showed that with the placement of permeable geosynthetics materials, the rate of pore pressure dissipation was faster than without any geosynthetics product or with a non-permeable geosynthetics product.

Installation Survivability of Flexible Geogrids in Various Pavement Subgrade Materials

An on-site installation survivability study of polyvinyl chloride-coated polyester flexible geogrids from a single manufacturer, placed in three types of commonly used pavement subgrade material, was performed to evaluate the amount and degree of installation damage. A series of singlerib strength tests, in-isolation junction strength tests, and wide-width tensile tests was performed to evaluate the strength of reduction due to the installation procedure. The results of the study indicated that installation damage to a flexible geogrid is a function of grain size distribution and angularity of backfill materials, and lift thickness. The test results showed that the tensile strength retained for flexible geogrids placed within clayey gravel, poorly graded silty gravel, and well-graded crushed stone gravel is 84 percent to 95 percent, 66 percent to 88 percent, and 57 percent to 88 percent. The reduction factor for tensile strength due to installation damage is related significantly to soil type and varies from 1.05 to 1.74. The retained strength of junction for flexible geogrid ranges from 71 percent to 100 percent for various types of subgrade material. The reduction factor for junction strength due to installation damage varies from 1.00 to 1.40 for different types of soil. Additionally, 2 percent of the maximum load is recommended as the preload for single-rib tensile strength test. Comparison of the test results shows that wide-width tensile strength of the test geogrids is about 10 percent to 20 percent lower than that obtained from single-rib tensile strength tests.

Puncture resistance of pre-strained geotextiles and its relation to uniaxial tensile strain at failure

The principal focus of this study is the puncture resistance of geotextiles under uniform radial pre-strain. A test frame which can apply preset radial strain and measure puncture resistance of geotextiles has been developed. A number of commercially available woven and nonwoven geotextile materials have been evaluated for puncture resistance while held under a preset radial strain. The test results show lower failure strain in puncture if the test sample is pre-strained. The failure strain measured in wide width tensile tests are much higher than calculated strains in puncture.