ABSTRACT
The resistance against pullout failure of the soil nails in the passive zone is provided by the friction between soil nails and the surrounding ground mass. Ultimate pullout resistance is one of the key parameters for design of soil nailed structures. In this chapter, the key factors governing pullout resistance are identified and reviewed, which include the effective normal stress or radial stress acting on the soil nail surface and the apparent coefficient of friction between nail and the surrounding ground. The former is further influenced by various factors, such as soil dilatancy, arching effect, degree of saturation, and the nail installation method, whereas the latter is affected by the soil properties and soil nail characteristics. Given the complication of the soil nail pullout mechanism and the uncertainties involved, different empirical, field testing, and analytical approaches have been developed and proposed for estimating the ultimate pullout resistance. At present, the most common approach to estimate the pullout resistance of soil nails is based on local experience, which includes published bond strength values, established correlations with soil properties, and analytical methods, such as the effective stress method. In practice, the design pullout value is to be verified by field pullout tests during the construction stage. Various types of field pullout tests and their corresponding merits and limitations are also reviewed and discussed in this chapter.
