Laboratory determination of clay-geotextile interaction

Current design regulations preclude the usage of cohesive backfills in reinforced soil structures regardless of whether the reinforcement is metallic or polymer fabric. The main reasons for this are: firstly, cohesive materials can be expansive; and secondly, the maximum bond strength between the reinforcement and the clay is normally not expected to be more than the undrained strength of the clay, giving no advantage. However, low-plasticity (so-called semi-cohesive) soils are not expansive and could be used in reinforced soil structures provided the reinforcement can give an increase in strength. A large number of shearbox and pull-out tests have been carried out to investigate which are the major factors governing the clay-geotextile interaction in both undrained and drained conditions. Woven and non-woven fabrics and meshes were used in the tests. The results have shown that the shearing strength of clay can be increased by properly selected geotextile reinforcement in both undrained (short-term) and drained (long-term) loading. It has been also shown that the pull-out resistance of the geotextile reinforcement is essentially proportional to the normal stress and for high transmissivity geotextiles or for geogrids it is limited by the tensile strength and relaxation of the material. The low transmissivity however is also a factor obstructing the development of high pull-out resistance in undrained conditions. The results indicate that geotextile reinforced cohesive backfill might be a viable alternative in reinforced soil structures if good-quality granular backfill material is not readily available.