Rock installation and ballasting

The Group operates DP2 Fall Pipe Vessels, of which two are the largest in the world and able of installing 32,000 ton of rock in water depths up to 2,000 m. The vessels are able to install rocks very precisely, within a tolerance of only a few centimeters. With the positioning of the vessels, one remaining in the western hemisphere and the other one in the eastern hemisphere, Jan De Nul Group can offer considerable savings on mobilization costs to its clients.

The Group also disposes of DP vessels able to install rocks using an inclined fall pipe, making it possible to reach areas beneath the structures.

 

Germany, Global Tech One

Global Tech I is one of the first offshore wind farms developed in the German North Sea. The Global Tech I wind farm’s array consists of 80 wind turbines each...

Global Tech I is one of the first offshore wind farms developed in the German North Sea. The Global Tech I wind farm’s array consists of 80 wind turbines each with a capacity of 5 MW adding up to a total installed capacity of 400 MW.

 

Jan De Nul Group was contracted to install scour protection around the foundations of the offshore substation. The works were performed by the DP2 Fall Pipe Vessel Simon Stevin with its large rock carrying capacity of 32,000ton. In order to enable installation of scour protection under the center of the platform, the vessel had to approach the substation up to a minimum distance of 10 m and the inclined fall pipe had to be redesigned to fit over and in between the cross-beams of the substation.

Key figures
Country

Germany

Client's name

Global Tech I Offshore Wind GmbH

Contractor's role

Main Contractor

Technical specs
Equipment

FPV Simon Stevin

Scope

Remediation of initial scouring to original seabed by installation of a 2-layer scour protection around/under Offshore SubStation

Volume

Filter layer (initial scouring + scouring protection): 18,000 tonnes
Armour layer (scouring protection top layer): 8,000 tonnes

Water depth

40 m

Australia, Wheatstone Project

Installation of rock blanket, solid ballasting and scour protection

Installation of rock blanket, solid ballasting and scour protection

Key figures
Country

Australia

Contractor's role

Subcontractor to Heerema Marine Contractors Australia Pty Ltd (Part JDN: 50%)

Technical specs
Equipment

FPV Joseph Plateau

Scope

Installation rock blanket for SGS: 30,000 tonnes of rock, accurate levelling tool, with tolerance max (+/-) 50 mm
Solid ballasting: 110,000 tonnes of iron ore, pumped into SGS using pumping and mixing plant
Scour protection along SGS: 8,000 tonnes of rock installed with inclined fall-pipe and installation of 79 concrete mattresses / steel mattresses and geotextile mattresses

Volume

38,000 tonnes of rock
110,000 tonnes of iron ore
79 scour protection mattresses

Water depth

70 m

United Kingdom, Gunfleet Sands OWF Contract for Rock Installation

The offshore wind farm Gunfleet Sands in the UK has a total capacity of 172 MW. Jan De Nul Group was in charge of the scour remediation around 27 foundations,...

The offshore wind farm Gunfleet Sands in the UK has a total capacity of 172 MW. Jan De Nul Group was in charge of the scour remediation around 27 foundations, export cables, and the substation. The works were executed using the vessel Tiger, equipped with an inclined fall pipe. Over 50,000 ton of rock was needed for the job.

Key figures
Country

United Kingdom

Client's name

Dong Energy Power (UK) Ltd

Contractor's role

Main Contractor

Period
March 30, 2015
Technical specs
Equipment

Inclined Fall Pipe Vessel Tiger

Volume

50,000 tonnes of 1-8" rock

Water depth

0 m to 15 m LAT

Germany, Butendiek Wind Farm

In early 2014 the construction of the German offshore wind farm Butendiek, located in...

In early 2014 the construction of the German offshore wind farm Butendiek, located in the North Sea west of Sylt, started. Butendiek comprises 80 turbines with each 3.6 MW, resulting in a total capacity of 288 MW. Jan De Nul Group was in charge of the installation of scour protection for the 80 monopiles. The rock was purchased at a Norwegian quarry. The filter rock, approximately 71,000 ton, was loaded at the quarry and installed by the Fall Pipe Vessel Simon Stevin. The armour rock, approximately 123,000 ton, was installed by the vessel Tiger. This vessel used to be a Split Hopper Barge but has been equipped with an inclined fall pipe to execute the rock installation works closely to the offshore structures.

Key figures
Country

Germany

Client's name

OWP Butendiek GmbH & Co. KG

Contractor's role

Subcontractor to Ballast Nedam NV

Period
March 30, 2015
Technical specs
Equipment

FPV Tiger

Scope

Installation of filter rock (1-3”) prior to installation of monopiles by using the vessels fall pipe.
Installation of large armour rock (40-200 kg) after installation of mono-piles by using large diameter inclined fall pipe

Volume

90,000 tonnes

Depth

20 m

Italy, Adriatic LNG - Solid Ballast and Scour Protection Installation

The natural gas supply to Italy had to be increased by the installation of an offshore LNG terminal. After the GBS had been towed to the location 16 km...

The natural gas supply to Italy had to be increased by the installation of an offshore LNG terminal. After the GBS had been towed to the location 16 km northeast of Porto Levante and placed on the seabed, solid ballast was pumped into it to gain necessary permanent on-bottom weight. At the same time, scour protection in the form of rock was installed around the perimeter of the GBS and around the base of the two mooring dolphins. The solid ballast and scour rock installation were awarded to Jan De Nul Group. To install the scour protection, the vessel La Boudeuse was modified to work as an inclined fall pipe vessel with dynamic position and/or dynamic tracking, allowing the vessel to reach areas between the mooring dolphins and the GBS. 

 

Key figures
Country

Italy

Client's name

Terminale GNL Adriatico (JV 45% Exxon Mobil, 45% Qatar Petroleum and 10% Edison)

Contractor's role

Subcontractor to Aker Kvaerner Contracting Italy AS assigned to Aker Kvaerner Contracting AS

Period
September 20, 2008 to November 11, 2008
Technical specs
Equipment

Solid ballast installation barge DN143, La Boudeuse with inclined fallpipe

Scope

Ballasting and rock installation

Soil

270,000 tonnes of natural sand and partly crushed sand with D50 = 2 mm

Rock Installation

15,000 m³ with D50 0.2 m

Sweden, Karehamn Wind Park

For the Karehamn offshore wind farm in the Swedish part of the Baltic Sea, 16 foundations were required for the 3 MW turbines. Jan De Nul Group was awarded the...

For the Karehamn offshore wind farm in the Swedish part of the Baltic Sea, 16 foundations were required for the 3 MW turbines. Jan De Nul Group was awarded the design, construction and installation of these foundations.

All foundations were constructed on top of two large barges in the port of Zeebrugge (Belgium) in over a period of only 5 months. Because of the varying water depths in the Baltic Sea, the height of the cylindrical part had to be uniquely designed. The height of the elements ranges from 15 to 25 m with the heaviest element weighing approximately 1,940 tons.

The seabed had been prepared before installation of the foundations.
The first half a meter of the seabed was removed.  In order to provide an even cushion layer for the foundations, a gravel layer was installed. To level the cushion layer, a levelling system has been developed by means of a levelling beam installed on the Cutter Suction Dredger Vesalius. This allowed for gravel bed foundation to be levelled within the design tolerances of 45 mm.

With the gravel bed installed and levelled, the Heavy Lift Vessel Rambiz lifted the foundations off the barges and installed the foundation to within 30 cm of the theoretical position.

After installation, they were ballasted so they could withstand the forces of waves and currents and carry the actual wind turbine. 

The shaft of the foundation was filled with magnadense crushed iron ore. The other compartments were filled with crushed iron ore, and finally a layer of heavy quarry stone was placed as a top capping layer in order to provide scour protection.

Stones of up to 130 kg were placed in the ballast caissons by means of the inclined fall pipe of the vessel Simon Stevin positioned in DP2 mode. To prevent the gravel bedding layer from being washed away, an anti-scour quarry stone layer was installed around the external edge of each foundation.

Key figures
Country

Sweden

Client's name

E.ON Vind Sverige AB

Contractor's role

EPC Contractor

Period
September 7, 2011 to April 21, 2013
Technical specs
Scope

Engineering, procurement, construction and offshore installation of 16 concrete gravity based foundations for Vestas V112 wind turbinegenerators. The foundations were poured on barges after which they were installed. The seabed had been excavated and a gravel bed been installed. Subsequently these foundations are protected from seabed erosion by means of scour protection. Heavy fill ballast such as iron ore is installed in the shaft and ballast bins. Appurtenances (J-tubes, ladders, handrails, etc) were included in the design.

Soil

Clay and sand overlaying bedrock

Volume

10,000 m³ of reinforced concrete
2,000 ton weight of GBF
5,000 m³ of seabed excavation works and gravel bed
7,000 m³ of scour protection outside GBF
50,000 ton heavy ballast fill, includes 25,000 ton iron ore based fill

Dredging depth

8 m – 21 m

Equipment

Multipurpose spudpontoon DN109, Levelling vessel Vesalius, HLV Rambiz, Transport barge DN143 (DWT 24,000 tonnes), Transport barge DN120 (DWT 10,000 tonnes),
4 Towercranes (Civil Works), 2 Mobile cranes (Civil Works)
Truck mixers & concrete pumps (Civil Works)