Font Size

- Aa +

Sat 13 Nov 2010 12:00 AM

Font Size

- Aa +

Think tank

Qatar continues to spend hundreds of millions on water production, distribution and storage every year. CW visits two major reservoir projects in Doha. By Carlin Gerbich

Think tank
Alwaha has used Doka’s Staxo 100 tableform to create the water tank roof.

Qatar
made headlines earlier this year when the government signed off $722 million
worth of infrastructure projects that would see six major water supply, storage
and distribution contracts carried out around the city.

It may have seemed a considerable sum, but it was just the
latest round of funding for the country’s major water projects by the Qatar
General Electricity and Water Corporation (Kahramaa) and part of an ongoing
programme of works designed to improve the state’s water supply throughout the
city.

In fact, since 2006, Qatar has continued to pour
millions of riyals into major water projects around the capital annually.
Earlier this year it was announced that construction of the largest power and
water plant in Doha , the QR14 billion 2,730MW Ras Industrial
City plant, complete with
10 desalination units, had finished its first phase of construction.

Once fully operational, the plant will boost Qatar’s daily
desalination capacity 320 million gallons per day, keeping pace with demand
from its ever growing population.

However, producing Qatar’s water supply and
distributing it to public are two separate matters – which is where two
large-scale reservoir projects, secured by local firm Alwaha Contracting, come
in.

The company secured the $104 million contract to build two
12 million gallon reservoirs in south Doha,
to store and distribute water to the surrounding areas.

The firm had already secured a contract to build another,
far larger reservoir project to feed households in both north and south Doha, and work had
already started on that when the second contract win
was announced.

The two projects were designed by KEO Consultants to store
and supply each of their respective areas with potable water.

American contractors
DYK, a company well versed in massive bulk storage tank construction, was
brought in ensure the reservoirs were earthquake resistant. The company
also  oversaw the pouring of the floors
and constructed the exterior walls, while Alwaha created the support columns
and roof.

Construction of the tanks is a relatively straight-forward
process. After the ground works have been prepared, the highly reinforced
concrete floor is laid in a minimum number of pours. The tank slopes slightly
upwards towards the middle (around 1.5 degrees) to help provide strength and to
avoid sagging in the centre. Each floor joint incorporates a waterstop, and
only galvanised or epoxy coated bars are allowed to span the joint.

The tank walls are cast in situ, using a shuttering system,
and are supported by a continuous layer of neoprene and closed cell neoprene
sponge rubber pads, to help give the tank its earthquake resistant properties.
The pads allow the walls to give slightly, while the walls themselves are also
attached to the wall-footing with seismic cables, which are encased in closed
cell sponge rubber. The tank is sealed at the base, between the wall and the
wall footing, with a PVC waterstop.

The roof follows the slight upward slope of the floor and is
supported by a series of columns – both of which fall under Alwaha’s remit.

Basel Maher, project engineer on the Muaither project where
two enormous 21.6 million gallon tanks are being constructed and are designated
to serve both North and South Doha, says the
roofs of both tanks on his project were split in to 17 separate pours each,
which were still being phased during CW’s visit to the site in September.

Once the columns and bases have been prepared, Alwaha erects
its tableform using three different configurations to prepare the roof.

“We purchased Doka’s 
Staxo 100 system in order to build our reservoirs. It consists basically
of tower assemblies that carry table forms which, put together, make-up for the
roof element, whereas the other parts of the reservoir, like the walls and the
columns, are made up by different means, not using Doka,” he said.

“We use the system to create three elements for the roof:
the column tower assemblies, which carry the capitals on top of the columns;
the roof slab tower assemblies which directly carry the roof slab, and the
construction joint tower assemblies. The reason we used construction joint tower
assemblies is simply because we can’t do the full roof at once,” he said.

It’s a fairly
repetitive task, and Maher says the Staxo system means that there is very
little set up time between the pours.

“There are micro adjustments you can make, but it’s minimal
because it stays quite well intact, especially when you move it by crane, or
during repetitive movement caused by high winds, or loadings coming from. It
just stays together, so you don’t have to do a lot of maintenance when you’re
moving it,” he said.

The roof will also sit on neoprene cushions which are
designed to allow a degree of movement should an earthquake strike the area.
Once concrete work is complete, the reservoir will have stressing cable wrapped
around them to, as Maher says, “basically hold it together like a belt”.

Seismic activity in Qatar is rare, but Maher says
building in earthquake resistant measures were a safeguard against the
possibility of anything happening, should a quake hit the region.

“Actually, in 2008 we had a small earthquake here. It wasn’t
felt in all parts. It didn’t even make some of the local news, but you don’t
need a very big earthquake to cause major problems with a structure such as
this.”

“The smallest crack caused by a fairly small earthquake in
such a large reservoir might cause a lot of loss; money wise and
environmentally,” he said.

Once finished, the tank will then be sealed, sterilised and
filled, to test for leaks, before it is rubber stamped for operation. At the same time, work on the project’s main
pumping station and the associated piping, electrical works, instrumentation,
boundary walls, landscaping, drainage, asphalting and around 6 km of 900 mm
diameter water mains work.

Ghassan Abbas is managing the design, supply, and
construction of the South Doha reservoirs and
associated pipelines for the two 12 million gallon reservoirs, plus all the
work for the supporting water
pumping station.

Abbas’s crew is using an older Doka tableform system on the
two reservoirs, but has opted to try the company’s new Framax Xlife formwork
for the pumping station.  The system
bolts together quickly and is designed to make work swift, economical (the facing
sheet is plastic-coated for easy cleaning and refurbishing, while the steel
frames are hot-dip galvanised for long life) and easy to plan.

“We have a lot of work to do yet. As you can see, we’re just
setting out the pumping station now – so there is still a way to go on this
project,” Abbas said.

Abbas says his project is due finish in August 2011, while
Maher says construction will finish on his project in April.

While testing will take some time, to make sure the
reservoirs are water-tight and working smoothly, but both men believe their
projects will be operational by December next year.

For all the latest construction news from the UAE and Gulf countries, follow us on Twitter and Linkedin, like us on Facebook and subscribe to our YouTube page, which is updated daily.