Experimental Investigation of Scour Prediction Methods for Offshore Tripod and Hexapod Foundations

Leiping Xue,Xuan Ni

doi:10.3390/jmse8110856

Abstract

Scour prediction is essential for the design of offshore foundations. Several methods have been proposed to predict the equilibrium scour depth for monopiles. By introducing an effective diameter, such methods could also be applied to predicting scour depth for pile groups. Yet, there are still difficulties in estimating the equilibrium scour depth of foundations in complex shapes, such as the tripod foundation. This study investigates the clear-water scour around the tripod and hexapod foundations through laboratory experiments, with uniform bed sediment and steady current. Here, the authors propose an approach to calculate the effective diameter for the tripod and hexapod models, which is similarly as for the pile groups. Three widely-used methods in predicting equilibrium scour depth have been evaluated, and the best method is recommended.

Highlights

The pile-supported foundation is one of the commonly used foundations in the offshore environment, such as bridges, breakwaters, offshore wind turbines, and so forth
Raudkivi and Ettema [3] pointed out that the equilibrium scour depth around a vertical cylinder under clear-water condition is related to the following parameters: mean particle size of the bed sediment, distribution of particle size, and water depth relative to the pier diameter, and so forth
We study the clear-water scour around pile groups and complex foundations, including triangular arrays of circular cylinders (TACC), hexagonal arrays of circular cylinders (HACC), tripod model and hexapod model

Summary

Introduction

The pile-supported foundation is one of the commonly used foundations in the offshore environment, such as bridges, breakwaters, offshore wind turbines, and so forth. These foundation structures change the flow pattern in their vicinity, which may increase the local sediment mobility and result in scour around the structures. Monopile is the most common supported foundation, and many studies have been done on scour around a single vertical cylinder. Raudkivi and Ettema [3] pointed out that the equilibrium scour depth around a vertical cylinder under clear-water condition is related to the following parameters: mean particle size of the bed sediment, distribution of particle size, and water depth relative to the pier diameter, and so forth. More studies to understand the scour around a circular cylinder are given by References [5,6,7,8,9]

Methods

Results

Conclusion