Physical modelling of helical pile anchors

Abstract

Helical piles design is based usually on empirical correlations between the uplift capacity and the torque resistance of the pile during installation. A simplified theoretical relationship to predict the uplift capacity of deep helical piles in sand from the installation torque was reported. The purpose of the present study was to verify a component of this relationship, related to the contribution of helical plates to the uplift capacity, using centrifuge modelling. A servo-controlled equipment was adapted to carry out the pile installation and pull-out tests in-flight. Twelve different model piles were tested in two sand samples with different relative densities. The results demonstrate strong influence of sand relative density on installation torque and uplift capacity of helical piles. Also, in almost all tests performed the increase in pile sizes and number of helices causes increases in the uplift capacities and installation torques. Generally, in the pull-out tests, the ratio of the measured displacement at failure to the helix diameter was larger in dense sand models, and was not affected by the number of helices. The magnitude of the relationship between uplift capacity and installation torque found in this investigation was in agreement to that observed in true scale helical piles. Direct shear interface tests were conducted to complement this research. The theoretical results compare favorably with the experimental data. This shows that the presented expression is applicable to different pile dimensions, number of helices, and sand relative density.