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 small-scale hammer was developed to install open-ended monopiles with 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. (i) 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 3 times compared with the 1g installation.For large amplitude of displacement, the lateral capacity increased by 1.3 times. (ii) 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.
An experimental campaign is conducted on 100g centrifuged monopile model, impact driven, into saturated dense sand, down to three embedding depths, corresponding to three slenderness ratios of 5, 4 and 3. These models are instrumented with optical fibres to measure the bending moment profile along the monopile. A new method is developed to determine the experimental soil reaction curves by considering the distributed moment part from the measured bending moment. This distributed moment is assessed by the one-dimensional finite-element model of the PISA method. The key features of this study are: (i) The monopile behaves from pure rotation to combined rotation-flexure as the slenderness ratio enhanced from 3 to 5, inducing a less pronounced linear rotation-deflection response at ground-level. (ii) Although the distributed moment assessed in the PISA project is very low, the developed method is useful to explore the experimental local behaviour of laterally loaded monopiles. (iii) The 1D FE PISA model captures reasonably well the overall behaviour of laterally loaded centrifuged driven monopiles, even if it is less accurate for the local behaviour.
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