Gigantic water reservoir project in the Qatari desert
Reservoirs with a total capacity of 17 million cubic metres are being built to increase drinking water reserves
Data & Facts
- Drinking water reservoirs at five locations to increase Qatar’s strategic drinking water reserves. Work includes building pumping stations and pipelines.
- Qatar General Electricity & Water Corporation (KAHRAMAA)
- Consolidated Contractors Company, Athens, Greece and Egypt (Umm Birka and Al Thumama sites)
- MEVA wall systems and material
- SolidCheck ultrasonic measuring device
- Over 20,000 m² of Mammut wall formwork
- Circo circular column formwork for round baffle wall ends
- 52 gantry cranes on 5 km of rails
- Over 1,100 tonnes of steel for rails, special parts, connectors, etc.
- MEVA circular column system and material
- Custom-made steel circular column formwork: 36 sets for 12 m height, 20 sets for 15 m height
- MEVA K-lock systems for bracing and pouring
- MEVA slab systems and material
- 73,600 linear meters of H20 girders
- 13,700 m² alkus all-plastic facing
- 16,500 MEP props plus extensions and accessories
- 3,000 m of boxes for concrete haunches
- Engineering andsupport
- MEVA Formwork Systems, Haiterbach, Germany
Special requirements for hydraulic structures
As Qatar’s population and economy continue to grow and water demand is increasing, the Qatar General Electricity & Water Corporation (KAHRAMAA) has launched an ambitious water project to provide increased water storage capacity and expand drinking water reserves from the present two days to seven days. This first phase will cover the water demand expected by 2026 through the construction of five mega reservoirs. The second phase will provide the ten days of water storage required for the daily demand expected by 2036 by adding additional reservoirs within the five mega reservoir complexes.
Each complex will have up to nine reservoirs, with the water storage capacity totalling 17 million cubic metres. The reservoirs are being built along with pumping stations and 145 km of pipelines that provide the reservoirs with water from three desalination plants and distribute it from the reservoirs to any location in Qatar.
Enormous quantities of MEVA formwork shipped to three sites ...
The contractor in charge of the Umm Birka and Al Thumama complexes – the Athens-based Consolidated Contractors Company – is pouring the reservoirs with MEVA formwork. MEVA delivered the material for both sites and alkus all-plastic facings for a third site at Umm Slal where it is used for the slab tables. MEVA material shipments include more than 13,000 m² of alkus facing and 20,000 m² of Mammut wall formwork, more than 16,000 MEP props and 73,000 linear metres of MevaFlex, over 1,100 tonnes of steel and 52 gantry cranes that MEVA constructed and built for this project.
... and special requirements to be met by the contractor
The base slabs must be waterproof and no joints are permitted. The outside and dividing walls must also be waterproof and the number of tie levels has been reduced to four for the total wall height of up to 12.60 m so that waterproofing the tie holes can be kept to a minimum. With the number of ties reduced, an unconventional method had to be developed to brace and stabilise the large panel gangs that are exposed to high fresh-concrete pressure. What’s more, assembly, transport, rebarring, pouring and other work must be carried out concurrently on large and high 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.
52 gantry cranes with panel gangs to pour 13 parallel walls
Each reservoir is approximately 152 m wide and 305 m long, requiring 13 parallel walls to be poured in the longitudinal direction: two external walls, two dividing walls and nine baffle walls. A lateral external wall at an angle of 90° degrees closes the reservoir at either end. All walls are between 12 m and 12.60 m high. 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 are installed to carry and move the panel gangs. These are moved from cycle to cycle using power pushers or winches.
Special requirements for hydraulic structures
External walls are inclined on the inside, dividing walls are inclined on both sides, and baffle walls have round ends. The concrete surface of all walls must be smooth and the walls must have no cracks, edges or openings that water pressure could damage over time, or through which water could escape from the reservoirs. This means:
-the wall formwork must be robust enough to allow the use of large panel gangs, even with minimal tie levels, and
-the formwork’s facing must deliver a consistently high-quality concrete surface from the first to the last pour, even when used many times.
Equipped with the alkus all-plastic facing and capable of handling fresh-concrete pressures up to 97 kN/m², the Mammut wall formwork meets all these requirements and is used to pour all walls with panel gangs up to 15 m (2 x 7.50 m) in length.
Only four tie levels permitted per wall height
The number of ties is reduced to an absolute minimum for waterproofing reasons. The tie holes are rendered waterproof using D20 water barriers and by sealing the openings with plugs.
Anchoring rails and steel walers to brace and stabilise the panel gangs
Dry ties are used at the top of the panel gangs, which makes a total of five (4 + 1) tie levels across the full height. To further brace and stabilise the large gangs subject to high concrete pressure, vertical U200 anchoring rails extending over the entire formwork height and four rows of horizontal steel walers made of steel profiles are attached to the panels.
Oblique bracing and hydrostatic-uplift compensation
Specially designed heavy-duty steel braces are used on the inside of the structure to take up the pour pressure while special cross stiffeners connect the vertical anchoring rails at their base to compensate for the hydrostatic uplift, especially on the inclined walls. Both the heavy-duty braces and the vertical anchoring rails are attached to the base slab with DW 15 ties and anchor screws which can be used up to 50 times. This not only saves material and money, it also makes sure that no parts that may corrode remain in the base slab.
Round wall ends poured easily and quickly with Circo half shells
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 are poured easily and quickly with half shells of the Circo circular column formwork. Their heights match those of the Mammut panels and the shells are connected to the panels with the Mammut assembly lock. No fillers or other time-consuming job-specific solutions are necessary.
Corners and T-wall connections
The four corners between the longitudinal and lateral external walls are poured using 8.80 m long panel gangs. Their setup including alignment, bracing and support against uplift matches the setup of the wall formwork units described above, except that special steel inside corners are used to cater for the inclined inside walls. The design and construction of the corner units allows 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 are poured using 6.70 m long panel gangs. Their setup is identical to the corner solution except that these units use special trapezoidal parts rather than special inside corners. The trapezoidal parts are also connected to the adjacent Mammut panels using Mammut assembly locks. Both the corner and T-wall units are moved using tower cranes, as no rails for gantry cranes are possible along the lateral external wall.
Fresh-concrete pressure and pour rate require special attention
When pouring large and high wall sections, special attention must be paid to the fresh-concrete pressure, especially when the number of ties is kept to a minimum and ties are replaced by unconventional bracing, as is the case on this site. In addition, the hot climate reduces the concrete setting time, which is why the local concrete supplier measures current concrete setting time in real time using MEVA’s ultrasonic measuring device, SolidCheck. Once the concrete setting time is known, the pouring rate can be calculated based on the wall height and the formwork’s pressure capacity. The pouring rate ranges from 1.70 to 2.00 metres per hour. Pressure gauges attached to the panels constantly monitor the fresh-concrete pressure, allowing the formwork’s capacity to be fully utilised without exceeding it.
High-quality concrete surface with alkus facing and external vibrators
The alkus all-plastic facing is standard in all MEVA formwork and delivers the even high-quality concrete surface that is required for the reservoir walls. The all-plastic facing is not affected by the humidity and high ambient temperatures which can affect plywood facing. Another benefit of alkus is that any facing damage caused by drill holes or rough handling can be repaired directly on site. Also very important on these large sites is that frequent reuse does not affect the facing quality and thus does not negatively influence the concrete surface quality. The alkus facing delivers a consistently high concrete surface quality from the first to the last pour, no matter how often it is reused. Aside from the right facing, careful and thorough concrete compacting is also required to achieve a smooth, pore-free, and high-quality concrete surface. There are various compacting methods that can be combined for optimal results in different circumstances, although these are not interchangeable. The inclined walls require outside compacting, which is done with vibrators attached to the outside of the panels. They compact the poured concrete layer by layer, thus ensuring that air bubbles are pressed away from the outside to the inside of the concrete and rise to the surface. This is vital, as it is the only way to avoid pores on the concrete surface. Please refer to FormworkPress issue XII/2013 if you would like to learn more about effective compacting. It contains a detailed report on the subject and can be ordered free of charge from firstname.lastname@example.org.
548 circular columns to support the slabs
The reservoirs must be completely closed to prevent desert sand being blown into the drinking water. 548 circular columns are poured for each reservoir to support its slab. The columns are located between the parallel walls and are 12 to 15 m high with a diameter of 60 cm. They are fitted with mushroom column heads measuring 35 cm in diameter. The columns are poured with a special column formwork that handles fresh-concrete pressures up to 90 kN and was produced locally according to MEVA specifications. The 12 m high columns are poured with 36 sets consisting of 4 m high panels while 20 extension sets with 3 m high panels cater for columns higher than 12 m. The column formwork is supported by Cuplock towers, attached using screws and wedges.
Slab tables equipped with wooden boxes for haunches
Three different slab tables on MEP shoring towers are used to pour the slabs at a height of approximately 12 m. The shoring towers have nine legs and integrated ladder access. They are assembled safely while flat on the ground, then erected and positioned with tower cranes. The slab tables are also assembled on the ground using H20 girders and then lifted onto the erected MEP shoring towers. Then the wooden boxes for the concrete haunches are installed and alkus facing is placed onto the H20 girders and wooden boxes. After a slab cycle has been poured and the concrete has achieved the required minimum strength, the entire slab unit consisting of MEP shoring towers and slab tables is wheeled on MEP transport walers to the next cycle. No disassembly and reassembly of the slab units is required, saving substantial work and time.
Excavation work on the sites started in 2013 and was followed by concrete work starting in 2016. There is still much to be done, yet all work is progressing as scheduled thanks to the formwork solutions developed for these sites and the contractor’s clever and efficient management of all challenges.