Impact driving of monopiles in centrifuge: effect on the lateral response in sand

Abstract

This study examines the influence of impact-driven installation on the subsequent horizontal monotonic response of small-scale monopiles by using a large-beam geotechnical centrifuge at 100g. A special device including a small-scale hammer was developed to install open-ended monopiles 50 mm in diameter to an embedment depth of 250 mm in flight, and then to apply lateral loading on the monopile head without stopping the centrifuge. The horizontal global and local responses of the monopiles were investigated for two methods of installation: impact driven at 100g, and monotonically jacked at 1g into saturated dense sand. The results highlighted two main features. (a) The effect of impact driving was pronounced for small amplitudes of horizontal loading. With regard to the conditions of serviceability, the in-flight installation increased the secant stiffness by about three times compared with the 1g installation. For a large amplitude of displacement, the lateral capacity increased by 1.3 times. (b) The experimental p–y curves obtained from the in-flight impact-driven installation remained smoother than those predicted by using offshore standards, but were similar to them.