Vibro piling: an idea whose time has come? 

The concept of ‘vibro piling’ to drive monopile foundations into the seabed has been understood for many years. It has been used in the offshore oil and gas industry and on 1-2 projects in the offshore wind industry. It is technically proven; its use can reduce the cost of diving piles and it is more environmentally friendly than conventional pile driving.

Uncharacteristically for an industry in which innovation and cost reduction are bywords, the offshore wind industry has been slow to take it up, but innogy’s Kaskasi offshore windfarm could mark a breakthrough in the more widespread use of the technology.

After years of development and successful tests that proved its advantages, the 343-MW Kaskasi project, for which innogy took a final investment decision in April 2020, will be the first offshore wind project in which the monopiles will be driven into the seabed to full penetration depth using a vibro hammer alone.

Back in 2012, Seaway 7 – which will install the monopiles for the Kaskasi project – first used vibro equipment provided by Dutch company CAPE Holland to drive the monopiles for the Riffgat offshore windfarm, although on this project the equipment was not used to drive the piles to their full depth. Since then, the vessel owner/operator has also used vibro equipment on oil and gas projects and on an offshore wind project in Taiwan.

In 2014, a research project led by the Carbon Trust saw three piles vibrated into the ground at Cuxhaven in Germany using vibro piling equipment from Dieseko, a project that by all accounts was a great success. The project found that, in suitable soil conditions, vibro piling was up to 10 times faster than conventional piling.

Another well-known contractor, Heerema, installed a monopile on Eneco’s Prinses Amalia windfarm using equipment supplied by CAPE Holland, a project that was carried out with the installation vessel in dynamic positioning (DP) mode with the monopile free-hanging from the hook of the vessel’s crane without using a motion-compensation frame.

Now, with the award of the Kaskasi project, CAPE Holland believes vibro piling’s time has finally arrived, as the company’s business development and marketing manager Dick van Wijngaarden tells OWJ.

“It is odd the offshore wind industry has not adopted vibro piling much sooner and on a larger scale,” Mr van Wijngaarden says. “It is not really a conservative industry like oil and gas. With vibro piling you avoid the cost of using a noise mitigation system, which is one reason it is less expensive than conventional piling, when you hammer the pile into the seabed.

“Another reason it is less expensive is that you can do it from a floating vessel on DP rather than from a jack-up. That saves a huge amount of time that would otherwise be spent jacking the vessel up and down. Vibro piling is less well-suited to use in stiff clays and dense soil types but is ideal for sandy substrates of the type found on most offshore windfarms in Europe.”

Other benefits claimed by proponents of vibro piling include reduced pile fatigue life because it imparts much less energy to the monopile than hammering it into the seabed. It has also been suggested that because of this monopiles with thinner wall thickness could be used, leading to significant material savings and handling costs. A further advantage is it provides a high level of control over the piling process.

The equipment for the Kaskasi project combines the capabilities of an offshore lifting tool with the ability to upend and drive the piles. The vibro lifting tool CAPE Holland will supply will have multiple vibro hammers linked together to provide a total force of 1,920 kg, which makes it the most powerful vibro pile driver in the world. The tool is able to pick up a stored pile, upend into a vertical position, lift it to the correct position and drive it down, monitoring verticality while driving, in a single operation without needing a gripper or seabed installation frame.

“It has been a long time since the Riffgat project, when vibro piling was used to drive the monopiles part-way into the seabed, until they reached stable depth. It was used there because of the need to mitigate noise levels. The project went really well, and we are confident the Kaskasi project will prove the advantages of vibro piling once and for all,” Mr van Wijngaarden concludes.