GDP

Gentle Driving of Piles

Publieke samenvatting / Public summary

Monopiles are the most commonly used foundations of the Offshore Wind Turbines (OWT).  The size of the monopiles grows rapidly together with the size of the offshore wind turbines. A six-megawatt OWT, for example, needs a  monopile of about 80 meters long and 8 meters in diameter which can weigh up to 1300 tonnes. These huge steel piles need to be driven into the ground for a significant part of their length. Organisation and execution of this process are challenging, time-consuming and costly.  Dutch contractors are world-leading in the installation of OWT  foundations and it is in their best interest to make the pile installation process as efficient as possible.

Objective
This project aims to help the contractors achieve the goal of making the pile installation process as efficient as possible by means of testing a  novel pile installation method based on simultaneous application of low-frequency and high-frequency vibrators exciting two different modes of motion of the monopiles. We call the proposed method “Gentle Driving of Piles” (GDP) for its envisaged capability to reduce the driving loads and the emitted installation noise which is harmful to the environment. These goals will be achieved without compromising the pile penetration speed and the soil bearing capacity, which is essential for a  stable OWT operation. During this project, new models will be developed and validated with experimental data collected from a measurement campaign while novel pile installation methods will be tested.

Short description
The project will be executed in two parallel phases: one experimental and one theoretical. The experimental part will provide a first proof of concept that the proposed method of “Gentle Driving of Piles” is advantageous compared to other existing methods, while it does not compromise soil bearing capacity and pile penetration speed. The theoretical part aims to explain the physics governing the novel pile installation technique and optimise the procedure while at the same time it can show that noise generated with GDP is considerably reduced compared to conventional installation methods. In order to enable a speedy, practical implementation of the results, the proposed method will first be validated experimentally such that in a relatively short period after the start of the project, a proposal can be issued for a full-scale verification of the installation method. In parallel, numerical tools will be developed, which will allow an optimization of the installation procedure for new offshore wind farms.

Result
The main result of this project is the development of a novel pile installation technique based on simultaneous application of vibrators acting in several directions.

The desired outcomes are envisaged as follows:

  • Provide a solid “proof of concept” of the proposed installation method  with the aim to show that the pile penetration speed and the soil  bearing capacity stay uncompromised in order to issue a proposal for a full-scale verification of the installation method soon after the start  of the project;
  • Develop models to predict the effects of installation using GDP including noise emission.

Field tests

During a test campaign several field tests with the newly developed pile installation method were executed at the second Maasvlakte in the Netherlands. The field tests are part of the GDP research project that aims to develop a novel pile driving technique that simultaneously improves drivability, reduces noise emission, and ensures that the soil bearing capacity stays intact. In this experimental campaign that is executed from October to December 2019, the newly developed GDP shaker is tested and compared to traditional vibratory and impact hammers. In total eight piles were installed of which four were driven with the GDP shaker, three by impact hammering and one by vibratory driving. At the end of this year the field test finishes and the piles will be removed. 

During the GDP DEMO Day over 100 visitors witnessed a successful test installation and attended the symposium in the afternoon with technical presentations about GDP and other related subjects within the Offshore engineering research group of the TU Delft. Find out more about the project and the DEMO Day or get a short impression of the test installation here: