Numerical study on micropile group behavior supporting fixed bottom marine hydrokinetic devices in sandy seabed

Abstract

This study aimed to investigate the behavior of micropile groups supporting fixed bottom marine hydrokinetic (MHK) devices in sandy seabed. A parametric study using PLAXIS 3D was conducted to examine the influence of key design parameters on the lateral load and moment capacity of the micropile group. The parameters considered were micropile diameter, spacing, micropile cap size, number of micropiles, micropile-soil interface properties, and sand packing state. Using the parametric study results, fitting regression techniques were employed to derive equations for predicting the MR (moment resistance in the absence of lateral load) and HR (Lateral resistance in the absence of moment loading), while meeting ultimate limit state (ULS). The equations were formulated based on soil relative density (DR), micropile group polar moment of inertia (J), and an interface reduction factor (Rint). A linear failure envelope is proposed in the Moment-Horizontal (M-H) load space by connecting MR and HR. The proposed framework was then applied to assess the load utilization ratio for various configurations, focusing on a load example of anchoring a 1 MW marine tidal turbine. The results of the study provide insights into the behavior and design of micropile groups supporting fixed bottom MHK devices in sandy seabed.