SCALE EFFECT ON THE SHEAR STRENGTH OF TWO-LAYER SOIL REINFORCED BY GEOGRID

Geosynthetics are used to reinforce soils and improve their mechanical characteristics, especially when soft low-bearing capacity soils are encountered in civil engineering projects. Particularly, in roads, geosynthetics are placed between the interface of granular materials and soft-soil sub grade to improve composite layers’ bearing capacity. This paper presents the results of the finite element analysis of the two-layer soil(granular base-clayey sub grade) reinforced by geogrid and discusses the effect of the reinforcement on the shear strength. As the primary aim of the study, the numerical model was calibrated in comparison with the experimental results of large scale direct shear tests. The results showed that the shear strength improved in the two-layer soil which had been reinforced by geogrid. The predictions made by the developed model were found to be in line with the experimental data obtained from large scale direct shear tests. As another aim of the study, different dimensions of shear box were used for modelling in order to investigate the scale effect on the shear strength of double-layered soil (clay-sand). The results showed that the increase in the dimensions of the reinforced shear box leads to the enhancement of peak shear strength. Moreover, several analyses were conducted on geogrid in shear box with different dimensions in fixed and unfixed states. The results demonstrated that the shear strength of treated geogrid was higher than the shear strength of those in which untreated geogrid was utilized.