Pullout of geosynthetic reinforcement with in-plane drainage capacity in cohesive soil

Freely draining soils have been used as backfill materials because they have higher shear strength and hydraulic conductivity than cohesive soils. While there are significant economic reasons for relaxing the current strict specifications for backfill materials, most reported failures in reinforced geotechnical structures have been related to backfill soils which have inadequate drainage conditions and low shear strength. However, cohesive soils can be used as backfill materials if geosynthetic inclusions provide both reinforcement and lateral drainage. Even though the advantage of dual-function (reinforcement + drainage) geosynthetics is conceptually enticing, the transmissivity requirements for such applications have not been properly quantified. This thesis presents the results of geogrid pullout tests performed using cohesive soils. Two types of geosynthetics were used for the tests: a conventional geogrid and a geogrid with in-plane drainage layers. Both geogrids were manufactured using the same material and have the same tensile strength. All tests were performed using the same soil preparation conditions with constant normal pressures. The pullout force, internal displacement of the geogrids and pore pressures were monitored during the tests. The results indicate that geogrids with in-plane drainage layers have a higher pullout resistance than conventional geogrids at the same normal pressure due to dissipating the excess pore pressure more effectively. As expected, a higher pullout strength was obtained for higher normal pressures for both geogrids. The findings of this study are expected to promote the use of poorly draining soils as backfill material