Clay Reinforcement Using Geogrid Embedded In Thin Layers of Sand

Large size direct shear tests (i.e.300 x 300mm) were conducted to investigate the interaction between clayreinforced with geogrids embedded in thin layers of sand. Test results for the clay, sand, clay-sand, clay-geogrid, sandgeogridand clay-sand-geogrid are discussed. Thin layers of sand including 4, 6, 8, 10, 12 and 14mm were used toincrease the interaction between the clay and the geogrids. Effects of sand layer thickness, normal pressure andtransverse geogrid members were studied. All tests were conducted on saturated clay under unconsolidated-undrained(UU) conditions. Test results indicate that provision of thin layers of high strength sand on both sides of the geogridis very effective in improving the strength and deformation behaviour of reinforced clay under UU loading conditions.Using geogrids embedded in thin layers of sand not only can improve performance of clay backfills but also it canprovide drainage paths preventing pore water pressure generations. For the soil, geogrid and the normal pressuresused, an optimum sand layer thickness of 10mm was determined which proved to be independent of the magnitude ofthe normal pressure used. Effect of sand layers combined with the geogrid reinforcement increased with increase innormal pressures. The improvement was more pronounced at higher normal pressures. Total shear resistance providedby the geogrids with transverse members removed was approximately 10% lower than shear resistance of geogridswith transverse members.