Simplified Analysis Method for Micropile Pullout Behavior

Micropiles are being applied in foundation rehabilitation projects to enhance the pullout capacity of the existing foundation system and minimize the vertical deflection of the structures. Consequently, the pullout load-displacement behavior is important for the design of micropiles used for the rehabilitation of foundations subjected to pullout. In this paper, we present and evaluate analytical relationships for micropile pullout load-displacement behavior, which explicitly considers the micropile–soil interaction. The analytical relationships are kept simple and accessible to designers by assuming the micropile–soil interface to be elastoplastic. The model parameters are combined into scaling factors and a normalization factor that are found to significantly influence micropile load-displacement behavior. The closed-form analytical relationships are used to study the effect of model parameters on the predicted micropile yield behavior. The micropile load transfer behavior calculated by the model is discussed. The model is shown to replicate the field measured load-displacement curves for two cases. A variety of cases are analyzed to study the effect of grout pressure on micropile–soil interface parameters.