Le plus grand réservoir d’eau du monde

The goal

Construction of five mega drinking water reservoirs, including infrastructure
The project is intended to increase drinking water reserves. A large quantity of formwork was needed to build the reservoirs with a total capacity of 17 million m³, as well as the new pumping stations and 145 km of adductors. Special requirements also had to be met, in particular to ensure the safety of the work and guarantee the quality of the water.

The project

Summary :
The water tanks were able to be made according to the demanding requirements of the client by using ingenious formwork solutions. MEVA systems perfectly mastered the many difficulties of this major project.

Challenge :
Faced with a project of this magnitude, with a number of specific requirements, innovative solutions had to be mobilized. For example, the formwork had to have fewer rod passages to reduce the number of holes to be filled. This meant that the formwork, to withstand the pressure of the fresh concrete, in turn had to be stabilized with additional props. The hot desert climate, which affects the concrete setting time and the pressure developed by the fresh concrete on the formwork, also had to be taken into consideration.

The facings of the various sails had to be perfectly smooth, with no cracks, edges or openings, in order to resist the strong pressure of the water and not deteriorate over time. Many sails had to be canted on one or two sides, which resulted in complex geometry at the corners. In addition, the foundations had to be watertight and the reservoirs perfectly sealed to prevent the desert sand from being blown into the drinking water.

Solution

1. Tailor-made design solutions
    
   a) Innovative stabilization props
   The walls were 12 to 12.6 m high, with only four strut rods allowed over the full height of the formwork. Because of this reduced number of anchors, it was necessary to develop an unconventional method to stabilize the large panel assemblies, which were going to be subjected to high pressures. The assembly, handling, reinforcement, pouring, as well as other work to be carried out at the level of the various sections of sails, had to be carried out simultaneously and without overlapping. All these requirements and constraints had to be taken into account when choosing the formwork and the layout of the different formwork rotations.

   On the upper end of the formwork sets, the spacer rods were placed outside the veil. To reinforce the stabilization of the imposing formwork trains, a system of U200 vertical anchoring rails, which extend over the entire height of the formwork, and four rows of horizontal steel stiffeners was placed on the panels. Thanks to the robust Mammut formwork panels and the alkus polypropylene skin, it was possible to design 15 m long formwork trains, which made it possible to control the large dimensions of the tank and withstand the high pressures to obtain the expected result.

   b) Ingenious solutions for assembly without a crane
   Moving the formwork trains with tower cranes was not possible, due in particular to the scale of the project, the weight of 15 tonnes and the interference between the jibs of the cranes. Gantry cranes on rails were thus implemented for the parallel walls, whose formwork trains were pulled from one rotation to another using a winch.
    
   c) Technical know-how for oblique “high pressure” shoring
   For the inclined walls, it was necessary to resort to additional stiffeners. On the inside of the structure, oblique props for heavy loads have been installed. To prevent the inclined walls from being displaced by the pressure of the concrete, the vertical anchor walers were reinforced at the bottom using alignment rails. These rails were attached to the foundation slab using DW 15 rods and anchor screws, which could be reused up to 50 times. This saved material and left no degradable parts in the foundation slab.

   d) Custom angles for sloping sails
   The four corners of the exterior walls of the various tanks were cast with 8.80 m long formwork trains. Their installation, including stabilization, alignment, resistance to thrust and oblique shoring, was carried out in the same way as that of the parallel sails. But as the interior sides of the corners were inclined, it was necessary to use special steel panels for the realization of the interior corners. These corner panels have been designed so that they can be connected to Mammut panels with Mammut locks .

   The sets of formwork used to connect the sails intended to direct the flow of water to the outer wall at an angle were designed in the same way as the corner solutions. With one difference: they are 6.70 m long and the special trapezium-shaped panels implemented at the inclined walls are made of steel, but could still be connected to standard formwork with the Mammut formwork lock . The formwork sections of the angled outer walls were moved with tower cranes, as it was impossible to lay rails for the gantry cranes there.

   e) Special formwork tables: quick and easy laying of slabs
   The reservoirs had to be completely closed, in particular to prevent the desert sand from being blown into the drinking water. To make them hermetic, it was necessary to make a slab resting on eight circular posts. These slabs had to be cast in place. This work was carried out with three different formwork tables and MEP shoring towers , which made it possible to cast the slabs at approximately 12 m in height.

   The shoring towers were easily and safely assembled on the ground, then lifted and put into place using a crane. The same was true for the formwork tables and the H20 beams. The wooden boxes intended for the construction of the arches were put in place last, then the H20 beams and the wooden boxes were covered with alkus skins. As soon as a portion of the slab had been poured, and the concrete was strong enough, the slab formwork, consisting of MEP shoring towers and formwork tables, was moved in its entirety to the next rotation using MEP traverse beams. It was therefore not necessary to disassemble and reassemble the formwork floors, which resulted in considerable savings in time and labour.

2. Good technical knowledge
   During the casting of the large walls, it was necessary to be particularly attentive to the pressure of the fresh concrete, because of the reduced number of crossing rods and the fact that it was necessary to stabilize from the outside. The desert climate affected the hardening time of the concrete. This duration was therefore measured with samples of the concrete used, on site, in real time at the supplier’s, using the SolidCheck durometer. By knowing the hardening time, the height of the wall and the resistance of the formwork to the pressure of the fresh concrete, it was possible to define the right pouring speed for the concrete. For this site, it was between 1.70 and 2 m per hour. The dynamometric boxes placed on the formwork made it possible to constantly monitor the pressure of the fresh concrete. Thanks to that,
    
3. Des formes spéciales pour nombre de réemplois
    
   a) Coulage simple et rapide des extrémités de voiles arrondies
   Pour éviter que les angles et arêtes ne soient endommagés, les voiles destinés à diriger l’écoulement de l’eau – à l’endroit où l’eau arrive – ont des extrémités arrondies. Les demi-coquilles du coffrage de poteaux circulaires Circo ont été utilisées pour couler facilement et rapidement ces arrondis. Comme leur hauteur correspondait à celle des panneaux Mammut, les demi-coquilles ont simplement pu être mises en place avec des serrures de coffrage Mammut. Grâce à cette technique d’assemblage, il n’a pas été nécessaire de recourir à des compensations ou à des coffrages spéciaux tout aussi chronophages, ce qui a permis d’accélérer les travaux.

   b) 548 poteaux circulaires supportent le toit
   Pour être à l’abri du sable, les réservoirs ont été exécutés de manière à être complètement hermétiques, et avec une dalle de couverture. 548 poteaux circulaires, de 60 cm de diamètre et de 12 à 15 m de haut, ont ainsi été coulés par bassin pour soutenir la dalle de couverture. Les poteaux sont pourvus d’un chapiteau en partie supérieure. Des coffrages avec une résistance de 90 kN à la pression du béton frais ont été fabriqués sur place, d’après les prescriptions de MEVA, pour procéder au coulage de ces poteaux. Les panneaux standard mesuraient 4 m de haut, les rehausses 3 m de haut. 36 kits ont été mis en œuvre pour les poteaux de 12 m de haut, 20 kits pour les rehausses. Chaque coffrage de poteaux a été étayé à l’aide d’un échafaudage K-Lock de MEVA, fixé à l’aide de vis et de clavettes.

Le résultat

The completion of this large-scale project required more than 13,000 m² of Alkus skins, 20,000 m² of Mammut wall formwork , 73,000 ml of MevaFlex , 16,000 MEP shoring towers , more than 1,100 t of concrete reinforcement and 52 gates. Thanks to the formwork solutions that MEVA developed especially for the project and to an intelligent and efficient handling of all the technical difficulties on the part of the construction company, the realization of the project went according to plan.

Featured Products

• Mammut 350 Wall formwork 
•  MevaFlex Slab formwork 
• Circo Column formwork 
• MEP Shoring Tower 
• Special formwork

Entreprise de construction:
Consolidated Contractors Company, Athènes, Grèce et Égypte

Donneur d’ordre:
Qatar General Electricity & Water Corporation (KAHRAMAA)

Projet:
Réservoir d’eau potable et réseau d’adduction

Lieu du chantier:
Umm Birka and Al Thumama, Qatar

Planification du coffrage:
MEVA Schalungs-Systeme GmbH, Haiterbach, Allemagne