Evaluation of the Pullout Resistance of Soil Nails in Tehran Alluvium by Considering the Overburden Pressure Effect

The present study evaluates the pullout and bond resistance of soil nails by considering the overburden pressure effect in Tehran alluvium consisted of four units depending on the deposition age. In order to investigate the pullout resistance, a series of 42 in situ pullout tests are performed in unit A, B and C contained coarse grained soils and clayey soils chosen from unit D of Tehran alluvium. Moreover, a one-way analysis of variance has been conducted to evaluate the proportion of soil and overburden pressure effect on the pullout resistance. The obtained results were compared with a conventional code (FHWA-NHI-14-007) criterion and it was concluded that the SPT base pullout resistance is more conservative method for evaluating soil nail pullout resistance. The results indicate that the bond resistance of soil nails increases as the overburden pressure increases in coarse grained soil, but the overburden pressure does not have a significant effect on the bond resistance in clayey soil. It seems that the overburden pressure effect is mobilized by inter granular stress transmission. Furthermore, it was found that the soil nail bond resistance is depended on the construction quality. As the quality of construction reduces, the bond strength decreases. The construction quality is highly affected the soil nails nearby the excavation ground surface where the overburden pressure does not have a significant influence on the pullout capacity.