Pullout testing and Particle Image Velocimetry (PIV) analysis of geogrid reinforcement embedded in granular drainage layers

The paper investigates the feasibility of using fine-grained soil as backfill material of geosynthetic-reinforced walls and slopes, through a laboratory study on pullout behavior of geogrids in granular layers. A series of pullout tests was carried out on an HDPE uniaxial geogrid in thin sand and gravel layers that were embedded in clay specimens.Aside from different soil arrangements, the influences of moisture content and overburden pressure on the geogrid pullout behavior is assessed and discussed. The tests were carried out at four different gravimetric water contents (GWC) on the dry and wet sides of the clay optimum moisture content (OMC), and overburden pressure values within the range σ_v = 25–100 kPa. Particle Image Velocimetry (PIV) was used to capture digital images during the tests, which were processed to help with the interpretation and improved understanding of the soil-geogrid interactions at different GWC values. Results show that embedding geogrid reinforcement in layers of sand or gravel can significantly increase the pullout resistance in an otherwise moist clay backfill, and this improved pullout efficiency is greater at higher overburden pressures. The improvement in pullout capacity was observed in clay specimens compacted at both the dry and wet sides of the OMC.