Project: Drinking water reservoirs at five locations to increase Qatar’s strategic drinking water reserve. Work includes building pumping stations and pipelines.
Owner: Qatar General Electricity & Water Corporation (KAHRAMAA)
Contractor: CCC Consolidated Contractors Company, Athens, Greece (Umm Birka and Al Thumama sites)
MEVA wall systems and material: Ultrasonic measuring device SolidCheck, Over 215,000 ft² Mammut wall formwork, Circo circular column formwork for round baffle wall ends, 52 gantry cranes on 3.1 mile rails, Over 1,100 tons of steel for rails, special parts, connectors etc.
MEVA circular column system and material: Tailor-made circular column formwork, 36 sets for height 39 ft, 20 sets for height 49’ n MEVA K-lock systems for bracing and pouring
Engineering and support: MEVA Formwork Systems, Haiterbach, Germany, Stefan Kappler
As Qatar’s population and economy keep growing and water demand is increasing, the Qatar General Electricity & Water Corporation (KAHRAMAA) has launched an ambitious water project to provide increased water storage capacities and extend the supply reserve of drinking water from two to seven days. This first phase will cover the expected water demand by 2026 with five mega reservoir sites. The second phase will provide the 10 days of water storage for the daily demand expected in 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 4.5 billion gallons. The reservoirs are built along with pumping stations and 90 miles of pipelines that provide the reservoirs with water from three desalination plants and distribute it from the reservoirs to any place 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 – pours the reservoirs with MEVA formwork. MEVA delivered the material for both sites and all-plastic alkus facing for a third site at Umm Slal where it is used for the slab tables. MEVA material shipments include approximately 140,000 ft² alkus facing and about 215,000 ft² Mammut wall formwork, more than 16,000 MEP props and nearly 240,000 linear feet of MevaFlex, over 1,100 tons of steel and 52 gantry cranes that MEVA constructed and had built for this project.
... and special requirements to be met by the contractor
The base slabs must be waterproof and also be joint-free. 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 41 ft 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 stabilize the large panel gangs that are exposed to high fresh concrete pressure. Assembly, transport, rebar, pouring and other work must be carried out simultaneously at large and high wall sections without one job interfering with another. These are the requirements and restrictions that 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 500’ wide and 1000’ long, requiring 13 parallel walls in longitudinal direction to be poured: two external walls, two dividing walls and nine baffle walls. An external wall in cross direction at an angle of 90° degrees closes the reservoir at either end. All walls are from 39’ to 41’ high. In addition, tower cranes would not be capable of lifting the 15-ton panel gangs that are used to pour the walls. Using tower cranes to transport and position the panel gangs would have required a countless number of cranes whose arms might interfere with each other when in operation. Therefore, rail-guided gantry cranes are installed to carry and move the panel gangs. The rail guided gantry cranes are moved from cycle to cycle with power pushers or winches.
Special requirements for hydraulic structures to be considered
The external walls are inclined on the inside and the dividing walls on both sides while the 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 the water pressure might eventually damage to the extent that water can flow out of the reservoirs. This means that
Equipped with all-plastic alkus facing, and capable of handling fresh concrete pressures up to 2,025 psf, the Mammut wall formwork fully meets these requirements and is used to pour all walls with panel gangs up to 49’ long.
Only four tie levels per wall height
The number of ties is reduced to an absolute minimum for waterproofing reasons. The tie holes are made waterproof by using D20 water barriers and by closing the openings with plugs.
Anchoring rails and steel walers to brace and stabilize the panel gangs
Dry ties are used at the top of the panel gangs, which makes a total of five tie levels per height. In order to further brace and stabilize the large gangs and withstand the 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 braces made of steel 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 the hydrostatic uplift; especially at the inclined walls. Both the heavy-duty braces and vertical anchoring rails are attached to the base slab with DW 15 ties and reusable anchor screws. This not only saves material and money but also makes sure that no parts that may corrode remain in the base slab.
Round wall ends poured easily and fast with Circo half shells
To prevent the water from damaging any edges, the baffle walls have rounded ends on the side of the reservoir where the water flows in. The rounded ends are are poured fast and easily with half shells of the Circo circular column formwork. The half shells are connected to the panels with Mammut assembly locks. No fillers or other time-consuming solutions built on site are required.
Corners and T-wall connections
The four corners between the longitudinal and cross external walls are poured using 28.9’ long panel gangs. Their setup: including alignment, bracing, and support against uplift matches the setup of the aforementioned wall formwork units, but 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 external wall in cross direction are poured using 22’ long panel gangs. Their setup is identical with the corner solution, but these units use special trapezoidal parts rather than special inside corners. The trapezoidal parts are also connected with Mammut assembly locks to the adjacent Mammut panels. Both the corner and T-wall units are moved with tower cranes as no rails for gantry cranes are possible along the cross external wall.
Fresh concrete pressure and rate of pouring 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 the actual concrete setting time with 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 5.6 to 6.6’ per hour. Pressure gauges attached to the panels constantly monitor the fresh concrete pressure, allowing the formwork’s capacity to be fully utilized without exceeding it.
High-quality concrete surface with alkus facing and external vibrators
The all-plastic alkus facing is standard in all MEVA formwork systems and delivers the even, high-quality concrete surface that is required for the walls of the reservoirs. The all- plastic facing is not affected by the humidity and high ambient temperatures that may damage plywood facing. Another benefit is that any facing damages can be repaired on site. What is also very important on these large sites is that frequent re-uses do not affect the facing quality, keeping the quality of the concrete surface consistent, no matter how many times it is poured on.
Apart from the correct facing, careful and thorough concrete compacting is another must to achieve a smooth, pore-free, high-quality concrete surface. There are different compacting methods and they may be combined for optimum results, but they 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, ensuring that air bubbles can rise to the surface. This procedure is a must as it is the only way to avoid pores on the concrete surface.
548 circular columns for the slabs The reservoirs must be completely closed to prevent dessert sand from blowing 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 39’ to 49’ high, their diameter is 23.6”. They are equipped with mushroom column heads measuring 13.8” in diameter. The columns are poured with a special column formwork that handles fresh concrete pressures up to 1,880 psf and was locally produced according to MEVA specifications. The 39’ high columns are poured with 36 sets consisting of 13’ high panels while 20 extension sets with 9.8’ high panels cater for columns higher than 39’. The column formwork is supported by and attached to MEVA K-lock system towers with 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 in approximately 39’ height. The shoring towers have nine legs and an integrated ladder access. They are assembled safely 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. This saves a lot of work and time.
Excavation work on the sites started in 2013 and was followed by concrete work starting in 2016. There is still much work to be done yet, and all work is progressing as scheduled thanks to the formwork solutions developed for these sites and the conctractor’s smart and efficient handling of all challenges.
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