Ostsee Anbindungs-Leitung Project

Trench Dredging & Backfilling, Microtunnel Marine Works, Concrete Mattress Installation, Reef Reinstatement

In order to meet the German and European demand for natural gas and to avoid potential gas shortages, Gascade Gastransport GmbH is developing an offshore natural gas transmission system near Lubmin in Mecklenburg-Vorpommern, Germany.

The Ostsee Anbindungs-Leitung (OAL) Project concerns the construction of an offshore natural gas transmission system consisting of a 48” diameter pipeline from the onshore facility near Lubmin (Germany) towards the onshore facility near Mukran (Germany), through the Baltic Sea over a distance of approximately 50km, where a Floating Storage and Regasification Unit (FSRU) will be permanently moored in the Port of Mukran.

In August 2023, Rohde Nielsen A/S was awarded the contract, which includes:

  • Trench dredging of 50km (2M m3)
  • Marine works at two exit pits: one in Lubmin and the other in Mukran. Marine works including:
      • 2 x dredging of exit pit, exposing a 100t tunnel boring machine.
      • 2 x recovery of the tunnel boring machine by use of heavy lift barge.
      • 2 x flooding of 750m microtunnel.
      • 2 x unmounting and recovery of microtunnel bulkhead.
      • 2 x installation of bellmouth and endcap on microtunnel.
      • 2 x wirelay of a 1,500m (129mm) pull-in wire for pipepull.
  • Installation of 700,000m3 intimate fill material around the exposed as built pipeline.
  • Trench backfilling of 50km (~ 1,300,000m3).
  • Installation of 100 concrete mattresses at 3rd party crossings.
  • Reinstatement of subsea reefs (20,000t).
  • All associated turbidity monitoring and environmental management.
  • Bathymetric surveys to support all operations listed above.

The dredging volume was in the region of 2M m3 consisting of sand, pre- and post-glacial clays and peat. Dredging was carried out in water depths ranging from -2.0m (LAT) to – 22.0m (LAT).

The works commenced on site on the 21st of August 2023 and were completed under a fast-track scheme, to a level allowing Gas-In, on the 15th of February 2024.

  • Location: Baltic Sea (GER)
  • Scope: 2,000,000m3
  • Client: Gascade Gastransport GmbH
  • Year: 2023-2024

The fleet that made it possible

  • Njord R
  • Balder R
  • Ask R
  • Embla R
  • Magni R
  • Sif R
  • Tjalfe R
  • Toste R
  • Heimdal R
  • Mjølner R
  • Gungner R
  • Ajax R
  • Gere R/ Freke R
  • Baugi R/ Bjarke R
  • Roar R/ Helge R
  • Hugin R/ Munin R
  • Skjold R
  • Skinfaxe R
  • Rimfaxe R
  • Sleipner R
Hopper capacity
6,000m3
Length overall
111.30m
Breadth
19.40m
Draught loaded
7.00m
Draught unloaded
3.80m
Dredging depth
35.00/75.00m
Hopper capacity
6,000m3
Length overall
111.30m
Breadth
19.40m
Draught loaded
7.00m
Draught unloaded
3.80m
Dredging depth
35.00/65.00m
Hopper capacity
2,700m3
Length overall
85.40m
Breadth
17.40m
Draught loaded
5.40m
Draught unloaded
2.90m
Dredging depth
32.00/52.00m
Hopper capacity
2,700m3
Length overall
85.40m
Breadth
17.40m
Draught loaded
5.40m
Draught unloaded
2.90m
Dredging depth
32.00/52.00m
Hopper capacity
1,570m3
Length overall
75.49m
Breadth
12.80m
Draught loaded
3.80m
Draught unloaded
2.00m
Dredging depth
28.00/40.00m
Hopper capacity
2,173m3
Length overall
80.00m
Breadth
13.80m
Draught loaded
4.87m
Draught unloaded
2.90m
Dredging depth
24.00/46.50m
Hopper capacity
789m3
Length overall
57.50m
Breadth
14.80m
Draught loaded
3.45m
Draught unloaded
1.80m
Dredging depth
up to 100.00m
Hopper capacity
535m3
Length overall
45.70m
Breadth
10.50m
Draught loaded
3.50m
Draught unloaded
2.20m
Dredging depth
up to 100.00m
Hopper capacity
2,100t
Length overall
84.00m
Breadth
18.70m
Draught loaded
5.80m
Draught unloaded
3.80m
Dredging/Installation depth
up to 100.00m
Bucket size
3.5-16m3
Length overall
51.50m
Breadth
17.00m
Draught
1.80m
Depth
3.00m
Dredging/Installation depth
22.00m
Bucket size
5.4-11m3
Length overall
54.88m
Breadth
15.25m
Draught
1.82m
Depth
3.35m
Dredging/Installation depth
20.00m
Bucket size
700 litres
Length overall
51.26m
Breadth
11.75m
Draught
3.12m
Dredging depth
19.00/36.00m

Gere R/ Freke R

Download specifications
Hopper capacity
1,517m3
Length overall
68.40m
Breadth
14.00m
Draught loaded
4.27m
Draught unloaded
2.90m
Type
Split barge

Baugi R/ Bjarke R

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Hopper capacity
1,239m3
Length overall
48.90m
Breadth
14.00m
Draught loaded
4.30m
Draught unloaded
1.10m
Type
Split barge

Roar R/ Helge R

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Hopper capacity
950m3
Length overall
60.30m
Breadth
11.00m
Draught loaded
3.56m
Draught unloaded
1.35m
Type
Split barge

Hugin R/ Munin R

Download specifications
Hopper capacity
778m3
Length overall
59.06m
Breadth
9.50m
Draught loaded
2.90m
Draught unloaded
1.80m
Type
Split barge
Length overall
11.80m
Breadth
3.95m
Draught
1.15m
Speed
33kn
Length overall
27.02m
Breadth
9.74m
Draught
2.63m
Main engine
2×1,230kW
Speed
12.2kn
Length overall
23.35m
Breadth
8.00m
Draught
2.10m
Main engine
2x634kW
Speed
10.5kn
Length overall
15.00m
Breadth
6.00m
Draught
1.70m
Main engine
2x224kW
Speed
7.1kn

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