Impacts of Tensile Strength and Spacing of Geogrids on the Compressive Strength and Deformation of Reinforced Sand in Triaxial Compression

Behaviours of reinforced soil are affected by the ultimate tensile strength (T_ult) of geogrid and the vertical spacing (S_v) of geogrid arrangement. Basically, the concept inferred from the current design approach of a reinforced-soil retaining wall shows that, if the T_ult-to-S_v (or TVR) ratio is kept the same, the outcoming performance is also the same. In this research, a series of triaxial compression tests was performed with sand either unreinforced or reinforced with polypropylene geogrids having four different T_ult values. Number of geogrid layers and S_v were adjusted, therefore, three different TVRs were obtained. The effects of varying T_ult and TVR values were studied by comparing the compressive strength (R_max) and Poisson’s ratio (n_sec) among different geogrid-reinforced sand samples. The followings are found from the results of this study. For the same TVR, the R_max decreases, while the n_sec increases or the lateral deformation increases, with increasing T_ult. This implies that the performance of reinforcing with the geogrids having lower T_ult but are closely spaced is better than that of reinforcing with the geogrids having higher T_ult but are coarsely spaced. On the other hand, when comparing at the same T_ult, the R_max increases with increasing TVR but n_sec decreases with increasing TVR, because of the increasing of reinforcing density. The influences of T_ult and TVR on the R_max and n_sec can be explained by the development of deterministic zone resulted from no connection between the geogrid and facing at the end. This deterministic zone negatively affects the transferring of the tensile force mobilised in the geogrid to additional confining pressure to sand.