Abstract
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.
Highlights
Nailing is a stabilisation system in excavations and slope surfaces
Bond strength is rarely measured in the laboratory and no standard for laboratory tests can be used to evaluate the bond strength (Su, 2006; Yin and Su, 2006), so only a pull-out test in the field can provide a credible estimation of bond strength
Zhou et al (2010) found that, by increasing the injection pressure from 250 to 350 kPa, the bond strength would increase about 80%.Yin and Zhou (2009) concluded that the effect of injection pressure on the shear strength in pressures
Summary
Nailing is a stabilisation system in excavations and slope surfaces. The main reasons for using this system are: (a) short constructing period, (b) it does not require a lot of equipment and (c) cost-effective implementation (Chu and Yin, 2005; Schlosser, 1982). Nailing was used for the first time in 1980 in Hong Kong to stabilise trenches and slope surfaces Using this method increases the general shear strength of soil, which leads to limited displacements in the excavation walls and slopes. Su et al (2008) preformed a series of laboratory pull-out tests on samples of completely decomposed granite (CDG) in order to evaluate the effect of overburden. These researchers found that increasing the stresses caused by overburden did not affect the pull-out resistance of gravity-injected soil–nail. Friction angle, modulus of elasticity, moisture content and percentage of coarse- and fine-grained soils were determined in the laboratory, and the effect of these parameters on the bond strength is examined
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