Vibro-driven pile installation in sand performed in a geotechnical centrifuge

Vibro-installation is being used increasingly for the installation of monopiles for offshore wind turbines due to its efficiency, especially in sandy soils, mitigation against pile run and low acoustic emissions compared to traditional impact-hammer installation. Owing to its intrinsically complex dynamic mechanisms, significant uncertainty still remains regarding the parameters controlling vibro-drivability. Through a series of centrifuge model pile installation tests in silica sand carried out with two mini vibro-drivers designed during this research, this article explores the influence of specific parameters on vibro-installation: dynamic force ratio (which is linked to vibrational frequency), soil relative density and drainage conditions. Results show that penetration rates (in terms of advancement per cycle) do not always increase for increased dynamic force ratios, as is the case for the accelerations and cyclic movements of the pile. As expected, penetration rates increase for sands of lower relative density, although vibro-installation was possible even for dry sand with a relative density of 95%. The paper also highlights the important role of excess pore pressures, which, in the dilatant soil tested here, were shown to increase resistance to vibro-driving. The results expand significantly the publicly available database for vibro-driven cylindrical piles.