INTERACTION BETWEEN COHESIVE-FRICTIONAL SOIL AND VARIOUS GRID REINFORCEMENTS

A total of 52 large-scale laboratory pullout and 24 large-scale direct -shear tests were conducted to investigate the interaction behavior be tween the different reinforcements and cohesive-frictional soil. The r einforcements used were steel grids, bamboo grids, and polymer geogrid s. The backfill material used was locally available weathered Bangkok clay. The test results show that the inextensible reinforcements, such as steel grids, move approximately as a rigid body during the pullout test, and the maximum pullout resistance was reached within a relativ ely small pullout displacement. For extensible reinforcements, such as Tensar geogrids, the degree of resistance mobilization along the rein forcement varies, and the pullout-resistance achieved in the tests was controlled by the stiffness of the reinforcement. For steel grids, th e friction resistance from the longitudinal member contributed only to about 10% of the total pullout resistance of the grids. The pullout o f the bamboo and Tensar geogrids without transverse members yields 80- 90% of the pullout resistance of the corresponding grids with transver se members, attributed to the nodes or ribs on longitudinal members. T he bond coefficient as calculated for steel and bamboo grids demonstra ted that the steel grids yielded a higher bond coefficient than that o f the bamboo grids with the same grid size. However,for a polymer geog rid, the bond coefficient cannot be calculated from a pullout test bec ause of the complicated pullout-resistance-mobilization mechanism alon g the reinforcement. The large-scale direct-shear-test results showed that, for the soil/grid-reinforcement interfaces, shear resistance can exceed the direct-shear resistance of the soil itself owing to the in fluence of the apertures on the grids. Finally, for compacted weathere d clay, the strength parameters obtained from large-scale direct-shear tests were found to be substantially smaller than the results of tria xial UU tests. This may be because the failure plane in the large-scal e direct-shear test was formed progressively, and the peak soil streng th along the predetermined shear plane may not have been mobilized sim ultaneously.