Renewable Energy - Research & Development
Increasing the Lateral Load Capacity of Monopile Foundations for Offshore Windfarms

Introduction

The cost of offshore wind energy is still greater than that of more conventional sources electricity, one of the main reasons for this is the high capital cost of installing the turbines in an offshore environment. A significant proportion of that cost is the turbine foundation, therefore any reduction in foundation cost could have a considerable effect on the overall cost.

Currently the preferred foundation option is the monopile. Environmental forces such as wind and waves exert large lateral loads upon the foundations, because of these forces monopiles are often significantly longer than required for vertical load capacity. The aim of this programme is to demonstrate that the addition of fins to the top of a monopile will result in an increase in lateral capacity and will allow a reduction in pile length.

The cost of the monopile foundations is governed by steel weight and the addition of fins may allow the pile length to be substantially reduced meaning a considerable cost saving. Also the reduced pile length may mean savings in the piling operations, as the required driving depth has decreased.

Development Programme

SEtech have been working jointly with Newcastle University conducting a phased development programme into improving the lateral capacity of monopile foundations. The initial investigations are concentrating on the monatomic loading of piles.

Phase One

The aim of Phase 1 was to use computer modeling to show that the addition of fins to a monopile would give an increase in lateral capacity. Software designed for the analysing laterally loaded piles was used and the fins were modeled as an increase in pile volume and stiffness. The results of the modeling showed that the fins had a noticeable effect in increasing the lateral capacity of the piles.

Phase Two

Following the success of the computer modeling, Phase 2 commenced in March 2003 and constituted the small-scale model testing of finned piles. The testing was carried out in the Soil Mechanics Laboratory at Newcastle University using 1/100th scale models with various fin configurations. During the tests an increasing load was applied to the piles and the resulting displacement was measured as well as the load. Plotting the results show the piles fins give an increase in lateral capacity that the size of the fin has a significant effect.

Phase Three

The aim of Phase 3 is the installation and testing of large-scale model piles in the artificial seabed at the Euro-Seas Engineering Solutions & Testing (EEST) facility in Blyth, Northumberland. The 8 piles are approximately 1/16th scale. The lateral load testing of the piles will shortly be underway and the initial results will be available soon.