Monopiles - Riffgat Offshore Wind Park, Germany

21-06-2012

In the summer of 2012, CAPE Holland used their in house developed Super Quad Kong to install 30 monopiles for the Riffgat Offshore Wind Farm in the Northe Sea. The piles weighed between 500 and 750 tons, with a diameter a the pile top of 4.7m and at the bottom up to to 6.2m and a length between 51 and 72 meters. The piles were driven to target penetration (last8 to 10 m) by impact Hammer according to project specifications. During the project CAPE developed its Inclino System to be able to measure verticality during driving, saving valuable installation time by not having to stop working for manual verticality checks every few meters. It also makes adjusting verticality during driving much easier. For the vibro driving , no Noise Mitigation System was required to stay below the German Regulations stipulated levels of 160dB at 750m. For the impact hammer installation , a Noise Mitigation System was used. 

Reason for equipment choice 

  • Fast installation
  • No noise mitigation required
  • Stable pile before Impact Hammer was placed
  • Option to extract if out of tolerance

 

Strict environmental regulations

APE Holland is pleased that the contractor Seaway Heavy Lifting choose the option of using a vibratory hammer.
“By choosing this innovative way of vibrating, CAPE Holland can comply to the strict environmental rules which apply in Germany,” explains a spokesman CAPE 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 it causes major damage to marine life. “There are various solutions to reduce the noise, but it does imply that the piles have to be vibrated first.” 
From the wish to have such piles driven without the use of impact hammers, CAPE Holland developed modular vibration techniques. “The noise of our hammer is much lower than a traditional hammer and the vibration process is faster than piling”.

Innovative

The Super Quad Kong is specially developed for this offshore wind farm Riffgat in the North Sea, where Seaway Heavy Lifting is using their newest state of the art 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. 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.
CAPE: “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.” 

Heavyweights

The monopiles which are used for the Riffgat wind farm project weighing between the 480 en 720 ton each. The length of the piles are between 53 and 70 meters with a diameter of 4,7 m on the top of the pile and a diameter of 5,7 up to 6,5 m at the pile tip.
APE Holland got this contract awarded thanks to a nice reference project in China. For the construction of two artificial islands in the fixed link between Hong Kong and Macau, the APE OctaKong was used. This enormous vibrator was built up out of 8 linked vibrators which vibrated 130 steel monopiles with a length of 40 m. about 25m into the seabed. The piles with a diameter of 22 m had a weight between 500 and 650 tons each. The insertion of each pile take less than 10 minutes.

Drive-ability studies

CAPE Holland cooperated on this project with Allnamics (www.allnamics.eu), who carried out the drive-ability studies for the monopiles. The long and extensive experience in Geotechnical Engineering of Allnamics was of great value for the Octakong project and showed the value on the Riffgat project again, for getting the convidence of the feasibility of the project.

 

 

 

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