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The paper describes the development of a method, based on the direct measurement of extension or contraction over a 100mm gauge length, for measuring the in-situ strain in geogrids. The direct method of strain monitoring is carried out by a device consisting of an L VDT protected within a sliding guide tube. This type of strain monitoring system was developed because of its robustness during installation and, unlike electrical resistance gauges, the strain readings are unaffected by disconnections, which is an important requirement in field studies. The system has a high degree of resolution and is capable of measuring strains up to 20%. The system has been applied successfully in large-scale laboratory tests and also in full-scale field trials. The strain monitoring system is shown by the results presented from laboratory tests, to be a reliable, safe and cost effective method of measuring strain in buried geogrids·.