Effect of soil type on nail pull-out resistance

Nowadays, soil nailing is widely used to stabilize slopes and excavations. The bond strength is integrated shear strength along the interface area between grout and soil. Choosing a value for bond resistance is one of the effective parameters in nailed wall design, which is generally determined by the values proposed by FHWA guidelines. A designer uses a high safety factor that makes the design safe but sometimes it is not economical. Therefore, in this study, an attempt is made to investigate the effects of overburden, injection pressure and soil strength parameters on the bond strength of nails in field. For this research, five different sites in Tehran were considered with a total number of 20 soil–nail pull-out test. Values such as cohesion, friction angle, modulus of elasticity, moisture content, percentage of coarse- and fine-grained soil were determined in the laboratory, and the effect of these parameters on the bond strength was examined. The results of the tests showed that by increasing injection pressure and overburden height, bond strength increases, and that the effect of injection pressure is much more than that of overburden height. Finally, a relationship was suggested to estimate the bond strength in terms of soil specifications and overburden height.