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Calais - Rehabilitation works of Perré Risban

As part of the rehabilitation works of the "Perré Risban" forming the access channel to the outer harbour west of the port of Calais, Ghent Dredging has been assigned the bank protection works, whilst our partner Spie Batignolles has executed the civil engineering works.

With a length of 460m, the existing "perré Risban" consisted of an anchored sheet pile wall, supporting a layer of sandy marl protected by a reinforced concrete slab. The "Perré Risban" in its present design dated from the 70's. The sheet pile construction has been heavily corroded, causing many disorders (fissuring of the slab, flow of fine materials).

The adapted solution is a new combi-wall (combination of sheet piles with H-profiles) standing autonomously in front of the existing sheet piles, and the infill of the space between the sheet pile walls. This way, the existing sheet piles no longer play a role in supporting the embankment.

The new construction is protected wave-attacks by a layer of quarry stones 1/3T.

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Our work consisted of:

  • Dredging of a slot at the base of the existing wall to allow for the piling of the new combi-wall
  • Filling in the intermediate space with a layer of sand
  • Demolition of the old concrete slab and excavation to allow for the infill of the rock fill
  • Placement of a geotextile associated with a granular filter
  • Installation of a first layer of quarry stones (60/300kg)
  • Installation of a second layer of quarry stones (1/3T)
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To realize our scope of the contract, two sets of equipment have been deployed:

  • A floating set: Consisting of a pontoon mounted excavator (85T) and two barges with tug
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  • A land-based set: consisting of two crawler excavators (45T) and two dump trucks operating from the crest of the embankment
 
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A total quantity of 16.000m³ quarry stone, 8.000m² geotextile and 10.000m³ backfill has been incorporated.

 
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