Project

Dredging and backfilling works for the installation of 10 km sewage pipeline across Dublin Bay,

Location : Ireland – Dublin Bay
Client : Dublin Corporation / MC O'Sullivan & C Ltd
Contractor :
Pierse – Mc Alpine – Tideway* Consortium
Period : March 2001 – January 2002
Value : USD/Euro 36 mio

* Tideway is a 100 % subsidiary of Dredging .International

Scope of work

Dredging
Backfilling
Reclamation
Rock protection works

General Information

A pipeline right across Dublin Bay should put an end to the wastewater problems in the Irish capital.

Description of the works

Overall the pipeline will be 10.5 kms long, 7.5 kms of which will have to be positioned in a trench, tracing a wide arch under water. The pipeline crosses the Dublin Port shipping channel at a depth of – 20 mtrs below Mean Sea Level. To avoid disruption of shipping traffic the shipping channel had to be widened first before actual trench dredging could commence. Part of the out coming material was used for Port reclamation works.

Trench dredging tolerances were minimal due to minimum gradient requirements directed by the Client

The pipe with a diameter of 1.8 mtr has been pulled from the stringing yard in one continuous bottom pull. The pulling process only temporarily ceased when a new string of 400 mtrs had to be welded on.

Apart from the widening of the shipping channel, reclamation works and trench dredging Tideway was responsible for all marine and intertidal land survey works.

In total, over 2.6 million m³ has been shifted including 600.000 m³ of sand backfill and 50 to 70.000 tonnes of rock for the shipping channel back filling.

During the course of the works a 15th century ship’s wreck was discovered in the middle of the proposed pipeline trench Separate measure had to be taken to accommodate the Irish Heritage.

The shallow intertidal areas and the position of the pipeline underneath the shipping channel requested a variety of equipment and techniques on a relatively small surface.
On a narrow strip, less than 10 kms long some ten metres wide, we were working with two hoppers, a cutter, a backhoe dredger, two split barges, a self-made spreader pontoon, a crane pontoon, rock barges and a number of assistant tugs, multicats and auxiliaries.

Main Equipment

Trailing suction hopper dredgers : KRANKELOON and PANTAGRUELE,

Cutter suction dredger BRABO,

Backhoe dredger BIG BOSS,

Split barges DI 68, DI 69,

Crane pontoon BEVER

Rockbarges