When the Kembs lock on the Grand Canal of Alsace needed servicing, Nantes-based company Sogecofa (part of the Mediaco Group) used three heavy Terex all terrain cranes for the project. Planned months in advanced, the whole operation was a logistical masterpiece and included rerouting of boats through the lock's eastern chamber.
The hydroelectric power station of Kembs, operated by Electricité de France (EDF), is the first and largest of eight power plants along the Grand Canal of Alsace. Located on French soil, the Canal originates close to the Swiss border and follows the course of the Rhine for fifty kilometers. It allows for continuous commercial river shipping all the way from the North Sea to the Port of Basel. Each of the power station's plants has its own dual-chamber lock to allow boats to pass the falls which drive the power turbines. The Kembs lock, commissioned in 1932, currently averages 15,000 boats transiting through it annually.
When planning to service the lock and replace the gate, engineers had to deal with a gate that was 26 meters wide, 18 meters tall and weighed 500 tons. The lack of space and the antiquated construction of the chamber made things even more challenging.
In order to allow the boat transporting the gate segments to unload them as close to the worksite as possible, the western chamber (which was the place where the job was carried out) had to be temporarily filled once again with 60,000 m³ of water.
For the lifting operation, Sogecofa used three Terex all terrain cranes: an AC 350, an AC 500-2 and an AC 700.
Before any actual lift started, four of the gate's sections were laid down along the western wall of the lock. Due to the lack of space, a fifth section had to be pre-positioned at the bottom of the “wet” lock with the assistance of divers. The other sections were placed and joined together. The entire assembly operation was to take ten days.
“Sogecofa is one of our longstanding partners,” said Rémy Verdaine, supervisor of the assembly team. “Here in the Alsace region they are a well-established firm and have done previous jobs for EDF. Sogecofa worked out a very efficient method of lifting and assembly that helped expedite the whole process.”
“This was not just a simple lifting operation,” noted Serge Dietrich, who is responsible for the sales department at Sogecofa. “We had to deliver results, so we put together a very experienced team. Each one knew the complexity involved in this operation, each being aware of the tasks they had at each step of the way. The Terex all terrain cranes were perfect for the job because of their compact dimensions. We even had to place a 500 ton crane INSIDE the lock. As this job was in such a tight deadline, Terex also sent us a technician who knew cranes inside and out.”
As the gate lock was surrounded by water and it was impossible to position the cranes for a coordinated tandem lift, the Sogecofa team decided that the only way they could lift the gate pieces was with a crane inside the lock. For this, they used the Terex AC 700 crane to lift, or more appropriate, lower, and position the Terex AC 500-2 crane inside the lock. Later fitted with 160 t of counterweight, the AC 500-2 crane was ready to start the maneuvers.
First of all, there was the question of how to position the AC 500 crane. This all terrain crane was designated to perform the most delicate job: lifting the gate sections onto their rails, with hardly more than 20 cm of maneuvering room, because the lock's command post projected out over the gates. To facilitate this maneuver, the technicians decided to conduct it from the floor of the chamber.
The lifting of each section depended on all three machines. Due to space constraints, each section of the gate was lifted by the three cranes, brought to a closer radius of the AC 500-2, and from there on the AC 500-2 could bear the full weight of the section and place it on its rails.
The operators of the two cranes on the lock wall (AC 700 & AC 350) had no direct view of the load and received instructions from Yann Exel, Head of Maneuvers for Sogecofa, who was assisted by an observer. This part of the operation entailed turning the section on its edge prior to swiveling it around for placement on the rails. Once swiveled and brought to a close radius, the load was hoisted by the AC 500-2 crane alone, which was equipped with two 80 t slings fitted with a 9.50 m spreader bar. The load was then righted and the upper slings released.
The length of each load exceeded the width of the chamber, so rotational movements required great precision to avoid any impact which could have halted the entire operation. “The most difficult thing was to synchronize the three cranes,” noted Exel. “As I was involved in the planning of the lift operations, I followed strictly all the planned phases of the operation. I maintained constant contact with the crane operators, but I was the one who had to make the final decisions.” In the final rotation, skimming the walls of the chamber, it was finally possible to wedge the section into its projected resting place.
“One must stay very concentrated, follow every single instruction and maneuver carefully. But none of this really worries me, its demanding, but we're used to working together as a team,” mentioned one of the crane operators.
The same operation was repeated four times. On the last crane maneuver, there was just a 20 centimeter margin remaining between the load and the control building of the lock.