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Case Study - Dover Docks, Dunkirk Jetty

Robore were recently engaged to carry out works at Dunkirk Jetty in Dover. Robore’s highly professional team of specialists were required to safely cut and remove over 4,000+ tonnes of reinforced concrete to form a 30m opening through the jetty to allow for temporarily diverted marine traffic as part of the Western Docks Revival – a multi-million-pound initiative to transform Dover’s waterfront with restaurants, cafes, bars and shops.

Requirement:

Dunkirk Jetty measured over 130 meters long. The concrete was reinforced with steel rebar, rail tracks and beams with the piers constructed using concrete within sheet piling. Robore were required to cut and remove six sections of the jetty slab, as well as the four main support columns. Once removed, the concrete would be processed and recycled for use on parts of the Western Docks Revival project.

 

Constraints and Challenges

It was essential not to pollute or damage the surrounding marine environment.

 

Techniques and hardware used

Robore used 4 custom-made frames with diamond wire saw rigs mounted above the cutting wire to cut through the concrete with precision and efficiency. There were two main phases of the project: 1) The removal of the six concrete slabs; and 2) The removal of the four concrete pier columns – (Each pier is over 12 meters in height, 10 meters long, 3meters wide and weighing over 900 tons.)

The sequence of work for removing the concrete slabs was as follows:

Robore diamond drilled the wire feed holes approximately 2m apart.

The saw was fixed to the slab and the wire fed through the feed holes utilising a mewp from a barge where necessary.

The diamond wire was fed around the section being cut and back to the rig and connected and fed back to the saw.

The saw cut the wall progressively from the back.

Steel wedges were inserted to hold the section together until it could safely be removed.

The wire saw was the set up on the vertical cuts and as each section was cut free it was moved clear by crane.

Once the section had been safely lifted away, the process was repeated for the remaining concrete slabs.

The sequence of work for removing the pier columns was as follows:

Robore produced innovative, self-designed cutting frames to mount Tyrolit wire saws. The frames were lowered over each of the four pier columns to the correct cutting height once the slab had been removed the piers measured 10m x 3m and were to be cut into 5 equal weight sections, the first two cuts were above the water and the three lower cuts below the water line. Robore employed divers to assist with the set up and repositioning of the directional wheels for the wire

Four of these frames were manufactured enabling each of the piers to be worked on at the same time.

Once the frame was in place and secured the wiresaw was started, cutting from one end back towards the wiresaw, along the sides of the cutting frame. Directional wheels were fitted to keep the wire clear of the sides of the pier and to keep the wire tight.

As the cutting progressed the wire was released from the directional wheels so the cut could continue.

Steel shims were inserted into the cut to prevent it from dropping and trapping the wire.

Once the cut was completed the rig and frame was then removed by the site crane and the cut section lifted clear.

The frame was then reset for the next cut on land and then lowered over the pier for the next cut.

 

Conclusion:

Robore used 3D pre-visualisation technology along with our expertise in wire sawing techniques to remove the 30m section of the Dunkirk Jetty. Protection and prevention was in place to ensure the surrounding marine environment was not contaminated with slurry and debris.

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