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The world’s biggest water reservoir
Consolidated Contractors Company, Athens, Greece and Egypt
Reservoirs with a total capacity of 17 million cubic metres are built in the Qatari desert with MEVA formwork systems.
To construct five mega drinking water reservoirs, including associated infrastructure
The project will provide increased water storage capacity and expand drinking water reserves. With the new reservoirs totalling 17 million cubic metres, as well as new pumping stations and 145km of pipeline, an enormous quantity of formwork was required. In addition, there were a number of special requirements to be met to ensure structural safety and the quality of the drinking water.
The reservoirs were able to be completed to the owner’s exacting specifications with clever solutions that overcame the many challenges on this megaproject.
The sheer size of the project, as well as the demanding requirements, needed innovative solutions. For example, the formwork needed to have fewer ties to reduce the number of holes that needed waterproofing. However, this meant that the formwork would need additional stabilising to cope with the concrete pour pressures. The hot desert climate also affected the concrete setting time and the pressure exerted on the formwork, and needed to be taken into account.
The surfaces of all walls had to be smooth and free of cracks, edges or openings so that the structure could cope with the high water pressures and not be damaged over time. Similarly, many of the walls needed to be inclined on one or both sides, which created complex geometry in the corners. It also meant that using cranes was much more difficult, and the size of the reservoirs would require an impractical number of cranes to deliver. The reservoirs also had to be completely closed to prevent desert sand being blown into the drinking water.
- Bespoke Design Solutions to Overcome Challenges
a) Innovative stabilising supports for wall panels
The walls were between 12 metres and 12.6 metres high, with only four ties permitted across the wall height. With the number of ties reduced, an unconventional method had to be developed to brace and stabilise the large panel gangs that were exposed to high concrete pressures. In addition, the assembly, transport, rebarring, pouring and other work must be carried out concurrently on the wall sections without one job interfering with another. These requirements and restrictions had to be considered when selecting the formwork and planning their setup, use, and transport from one cycle to the next. Dry ties were used at the top of the panel gangs, to provide a total of five ties across the full height. To further brace and stabilise the large panel gangs subject to high concrete pressure, a bespoke system of vertical U200 anchoring rails extending over the entire formwork height and four rows of horizontal steel walers made of steel profiles were attached to the panels. Together with the large and robust Mammut panels and alkus all-plastic facing, long panel gangs of 15 metres could be created to make the large scale of the reservoir more manageable whilst coping with the high pressures and still achieving the desired finish.
b) Clever solutions for crane-free installation
Using tower cranes to transport and position the panel gangs would have required a countless number of cranes, whose arms could collide when in operation. Further, they would not be able to lift the large formwork units weighing up to 15 tonnes. For this reason, rail-guided gantry cranes were installed to carry and move the panel gangs. These were moved from cycle to cycle using power pushers or winches.
c) Engineering know-how for oblique bracing with high pressures
An additional bracing system was required for the inclined walls. Specially designed heavy-duty steel braces were used on the inside of the structure to take up the pour pressure. At the base, custom-made cross stiffeners connected the vertical anchoring rails to compensate for the hydrostatic uplift, especially on the inclined walls. Both the heavy-duty braces and the vertical anchoring rails were attached to the base slab with DW15 ties and anchor screws which can be used up to 50 times. This not only saved materials and money, it also ensured that no parts that may corrode remained in the base slab.
d) Custom-made corners for inclined walls
The four corners between the longitudinal and lateral external walls were poured using 8.8-metre-long panel gangs. They were set up similarly to the wall formwork units, except that custom-made steel inside corners were used to create the inclined internal walls. The design and construction of the corner units allowed them to be connected with Mammut assembly locks to the adjacent Mammut panels. The T-wall connections of the baffle walls to the lateral external wall were poured using 6.7-metre-long panel gangs. Their setup is identical, except that these units used special trapezoidal parts rather than special inside corners. The trapezoidal parts were also connected to the adjacent Mammut panels using Mammut assembly locks. Both the corner and T-wall units were moved using tower cranes, as no rails for gantry cranes were possible along the lateral external wall.
e) Bespoke slab tables for quick and easy slab placement
The reservoirs had to be completely closed to prevent desert sand being blown into the drinking water, so they required a slab resting on circular columns to seal the reservoirs. Casting slabs of this size and craning into place would have been impractical, so the slabs needed to be placed in-situ. To achieve this, three different slab tables on MEP shoring towers were used to pour the slabs at a height of approximately 12 metres. The shoring towers were assembled safely while flat on the ground, then erected and positioned with tower cranes. The slab tables were also assembled on the ground using H20 girders and then lifted onto the erected MEP shoring towers. Finally, the wooden boxes for the concrete haunches were installed and alkus facing was placed onto the H20 girders and wooden boxes. After a slab cycle was poured and the concrete had achieved the required minimum strength, the entire slab unit (consisting of the MEP shoring towers and slab tables) was wheeled on MEP transport walers to the next cycle. No disassembly and reassembly of the slab units was required, saving substantial work and time.
- Strong Technical Knowledge
When pouring large and high wall sections, special attention must be paid to the fresh-concrete pressure, especially in this situation where the number of ties was minimised and replaced by unconventional bracing. In addition, the hot climate reduces the concrete curing time, which is why the local concrete supplier measured the curing rate in real time using MEVA’s ultrasonic measuring device, SolidCheck.
Once the concrete curing time was known, the pouring rate was then calculated based on the wall height and the formwork’s pressure capacity. The pouring rate ranged from 1.7 metres to 2 metres per hour. Pressure gauges attached to the panels constantly monitored the fresh-concrete pressure, allowing the formwork’s capacity to be fully utilised without exceeding it.
- Special Formwork Shapes for a Range of Applications
a) Round wall ends poured easily and quickly
To prevent the water damaging edges, the baffle walls have rounded ends on the side of the reservoir where the water flows in. The rounded ends were poured easily and quickly with the half shells of the Circo circular column formwork. Their heights matched those of the Mammut panels and the shells were connected to the panels with the Mammut assembly lock. No fillers or other time-consuming job-specific solutions are necessary, making progress swift.
b) 548 circular columns cast with custom-made formwork
To support each reservoir’s top slab, 548 circular columns were poured. The columns were located between the parallel walls and were 12 to 15 metres high, with a diameter of 60 centimetres. They also required mushroom column heads measuring 35 centimetres in diameter.
To create the unique columns, a special column formwork that handles fresh-concrete pressures up to 90 kN was produced locally according to MEVA specifications. The 12-metre-high columns were poured with 36 sets consisting of 4-metre-high panels, while columns higher than 12 metres required 20 extension sets with 3-metre-high panels. The column formwork was supported by Cuplock towers, attached using screws and wedges.
This megaproject required more than 13,000m² of alkus facing, 20,000m² of Mammut wall formwork, 73,000 linear metres of MevaFlex, 16,000 MEP shoring towers, over 1,100 tonnes of steel and 52 gantry cranes that MEVA constructed and built specifically for this project. After the concrete works began in 2016, the work progressed as scheduled thanks to the formwork solutions developed for these sites and the contractor’s clever and efficient management of all the challenges.
- Wall formwork Mammut
- Slab formwork MevaFlex
- Circo circular column formwork
- MEP shoring tower
- Custom-made steel circular column formwork
- SolidCheck concrete measuring device
Consolidated Contractors Company, Athens, Greece and Egypt
Qatar General Electricity & Water Corporation (KAHRAMAA)
Drinking Water Pumping Stations and Pipelines
Umm Birka and Al Thumama, Qatar
Engineering & Support:
MEVA Formwork Systems, Haiterbach, Germany
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