Geosynthetic materials are used in a wide variety of applications within civil engineering. Some are used to retain earthen embankments allowing vegetation time to grow and stabilise the structure hence avoiding erosion. Most are involved with providing strength to unstable surfaces. An extreme example of a Geotextile application is debris capture from demolition projects.
Geotextiles and geosynthetics are essentially composite sheets made up of a mixture of traditional fabrics and both oil and bio based plastics. As in all composites each material will contribute its own advantages to the whole system. When trying to prevent coastal erosion it maybe more suitable to use a fabric inter woven with compostable plastics to stabilise a dune, as once the vegetation starts to grow and stabilise the dune the retaining material will be consumed by the plants.
ISO 10319 describes a test method for determining tensile properties of geosynthetic materials using 200 mm wide strips. Instron can supply side acting and capstan style grips for gripping the geotextiles. The method can be applied to geotextiles, nonwoven geotextiles, geocomposites, knitted geotextiles and felts, geogrids and open structure geotextiles.
Due to the variety of materials, colors and properties of geosynthetics selecting appropriate extensometry has always been difficult. In fact it has presented such an issue that many companies testing these materials simply rely on crosshead displacement. Relying solely on displacement readings from the crosshead can result in erroneous and inconsistent results. The standard itself stipulates that ‘an extensometer capable of measuring the distance between two reference points on the specimen without damage to the specimen or slippage.’ The extensometer should have a measuring accuracy of ±2% of the indicated reading.
Instron has a non-contacting solution that customers can use. The standard for advanced video extensometers (SVE and AVE) measure elongation by tracking marks on the specimen. This avoids any mechanical influence on strain data which can be an issue when using contacting extensometry. The videos also posses the ability to work with a whole range of colors by adjusting a polarising lens.