Seaton Regeneration Project

Client ISG Pearce Value £7m
Location Seaton, Devon Quantity 246,00m3 dredged infill material 15,000m3 bund works to contain 34,000m2 sandfill area 35,000m2 plastic liner placement
Date April 2011

 

Project Information

Approximately 246,000m3 of dredged material was required to raise the level of a 100,000m2 development in the coastal town of Seaton, Devon. Due it’s low lying position, planning conditions for construction dictated that the land must be raised by approximately 2m to mitigate flood risk.

Onto this reclaimed area, a Tesco supermarket, 200 homes and a hotel will be built.

The TSHD Oranje was used to pump ashore the material, dredged offshore from South Wales into the reclamation, along 1.5miles of steel pipeline. The pipeline route included 1 mile of continuous undersea pipeline and 0.5 miles of pipe running from the beach to the site – crossing two busy roads via specially constructed temporary bridges spanning 37m and 40m respectively.

As an environmental protection measure, the mixture of dredged aggregate and sea water was pumped into 1 of 2 specially constructed “pits” measuring 150m x 50m – each lined with an impermeable membrane to prevent the saline seawater leaching into the ground, preventing aquifer contamination. Instead, this water was drained out of the sand, into a separate “settlement lagoon” to allow the fine particles to settle before two large pumps pumped the water to the sea along the same pipeline.

Once a single load of approx. 13,000m3 material was placed in the reclamation pit, another subcontractor excavated and placed it into location on site, to the required compaction,  using dry earth moving equipment, ensuring the pit was empty and ready for the cycle to begin again – 21 times!

Project Highlights:

  •  Preparatory Earthworks

Construction of the pit and lagoons was no easy task. Difficult soil conditions (very wet, clayey ground) made the use of dump trucks very difficult and increased the amount of re-handling required by other machines such as excavators and bulldozers.

The bunds around the edge were constructed using this soft material after careful consideration and design work by our in-house consultants, Hydronamic.

The entire area then had to be lined in plastic which resulted in a winching system to be installed by our sub-contractor Jones Brothers, which removed the need for an excavator to cross the very soft ground.

  •  Sinker Pipeline Construction

In order to create an exceptionally long 1600m sinker pipeline – two smaller pipes had to be joined together. A barge was specially prepared to lift and hold in place the ends of two pipelines on deck while a welded connection was made.

To prepare such a pipeline requires a sheltered position, in this case Southampton Water was chosen – 8 miles upstream of the main port entrance. After joining, this entire mile long pipeline then had to be towed through one of Europe’s busiest shipping areas  toward Seaton where it was sunk onto the seabed.

  •  Bridge Construction

The bridges crossed two roads including the main access road into Seaton. Construction required the transport of 4 large sections, imported from Holland to be welded together to make 2 separate pipe bridges.