After Seaway Heavy Lifting chose to use a vibratory hammer to install monopile foundations at the Riffsgat offshore wind farm, APE Holland informed that vibrating 30 steel monopiles started mid-June.
The piles will be driven with the Super Quad Kong (SQK), a modular vibratory driver/extractor consisting of four APE vibros, which are connected to four powerpacks, providing a total eccentric moment of 920 kgm. Using the SQK vibratory hammer enables driving the monopiles in a single run in the correct position at the bottom of the sea, in an environmentally friendly way.
“By choosing this innovative way of vibrating, APE Holland can comply to the strict environmental rules which apply in Germany”, said Martijn Kleine , Sales Manager at APE Holland. “The damage to the environment by noise and vibrations remains within acceptable limits”.
By using the traditional piling techniques with the conventional hydraulic hammers, the noise is at a level that causes major damage to marine life, APE Holland states. “There are various solutions to reduce the noise, but it does imply that the piles have to be vibrated first”, Kleine said. “The noise of our hammer is much lower than a traditional hammer and the vibration process is faster than piling”.
The Super Quad Kong is specially developed for the Riffgat offshore wind farm in the North Sea, where Seaway Heavy Lifting is using their crane vessel Oleg Strashnov.
“After driving the first monopiles it was clear that our modular built vibratory hammer supplies sufficient power to show impressive results. For the first piles, we only used 50% of the total power of these hammers. With our SQK vibro we are able to drive these monopoles to a penetration of 31 meters in one run” , said Martijn Kleine . “The reason that the last 10m of the piles on the Riffgat field still had to be driven with an impact hammer has a reason. The owner of the field required a so called ‘blowcount’, which indicates the bearing capacity of the pile. This can only be done with an impact hammer until now.”
After the vibratory hammer was taken off the pile, a Noise Mitigation System (NMS) was put around the pile, after which the IHC S-1800 hydrohammer was put on the pile.
“Where the pile was moving in only a few seconds after the SKQ was switched on, driving the first 10 meters with the hydrohammer started labored. For the first 25cm 100 blows of 1200 kJ were required to get the pile moving again. After that, the blowcount went back to 25 blows on the 25 cm”, Kleine said.