Experimental Studies on Pullout Resistance of Overlapping Geogrids

In the present world, mechanically stabilized earth (MSE) walls are an established technology and have effectively replaced conventional gravity or semi-gravity type concrete retaining walls. The type of wall facia dictates the connection type between geogrid and facia and subsequently the arrangement of geogrid. One arrangement commonly adopted in the field is geogrid overlapped in a trapezoidal shape. In the design of such walls, however, the laboratory pullout is determined typically using ASTM D6706 which uses a single layer of geogrid and subjecting it to axial pullout. In the present study, the actual arrangement (trapezoidal shape) of polyester uniaxial geogrid layers was replicated in the laboratory pullout testing to study the axial pullout resistance of overlapping geogrids. The overlapping of geogrid layers was expressed in terms of the spread area ratio and the effect of spread area ratio on the pullout resistance of the geogrid was discussed. A significant difference in the pullout resistance was observed between single layer of geogrid and the overlapping arrangement of geogrid layers. The pullout resistance of two layers of geogrid was higher than one layer of geogrid. Additionally, the pullout resistance of the geogrids with high spread area ratio exhibited high pullout resistance. The axial pullout resistance factors ranged from 0.69 to 0.85 for one-layered geogrid, while it ranged from 0.98 to 1.74 for two-layered geogrid according to the spread area ratios of the geogrid. The proposed pullout resistance factors can help in realistic design of soil structures reinforced with geogrids overlapped in a trapezoidal shape.