Rehabilitation of a Dry Dock

The French company DCNS, which is active in ship construction around the world, recently repaired one of its dry docks in its yard in Lorient, Brittany.

Dry dock No. 3 was originally built between 1912 and 1920 and is principally used for the repair and maintenance of ships. The basin is 206m long, 36m wide and 14.70m deep. As the lock gate of the dry dock no longer complied with modern requirements, DCNS decided to build a new gate.

First, the contractor SEMEN TP had to seal all the joints, creases and gaps around the old lock gate so that the gate would be able to resist the exterior water pressure. On the horizontal side of the joint, the sill had to be waterproofed and the weathered concrete had to be rehabilitated. Consequently, the cavities under the sill were grouted in several steps.

Construction work was carried out on dry ground, protected by the old gate that served as a cofferdam.After dismantling the old reinforced concrete sill, a new cross bar was concreted on the floor parallel to the old gate. For reinforcing the bar, boreholes were drilled in the dry dock at distances of one meter between holes. DSI supplied a total of 32 75mm Ø DYWIDAG Bar Anchors that were installed at distances of 1m in a row, anchored at a depth of 8m into the slate bed underneath the sill and the concrete was subsequently grouted.

Stress monitoring devices were installed on the permanent anchors, and the data provided by these devices was continuously read and evaluated. Additional empty sleeves for possible future anchorages were included in the horizontal bar – these would have been used if the stress monitoring had shown a need for action. After the installation and tensioning of the DYWIDAG Bar Anchors, the anchor heads were permanently concreted into the new cross bar.

At the same time, the side walls of the dry dock were reinforced in the area in which the new lock gate was to be installed. The old inner lining of the dry dock had to be removed in this area before reinforced concrete bracket connections were installed on both sides of the gate. Afterwards, core holes were drilled into the outer walls. Subsequently, a total of 33 double corrosion protected 40mm Ø DYWIDAG Bar Anchors that were preassembled and supplied by DSI were used to connect the bracket connections to the anchor wall. Finally, the side walls were reinforced using 6 40mm Ø DYWIDAG Bar Anchors.

DSI not only supplied the required anchor systems for this project, but also supported the contractor just in time by comprehensive calculations and by supplying all of the measuring instrumentation. Thanks to the excellent co-operation of all partners involved, this exceptional project was completed within the tight schedule to the full satisfaction of the owner.

Supplytechnical assistancepost-tensioning workrental of equipment

DCNS, Lorient, France

SEMEN TP, France