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Getting down to it

The challenges for engineers working on infrastructure vital to Qatar’s 2022 World Cup will start underground in Doha’s Dolomitic limestone. Bernadette Ballantyne and Marissa Lynch report.

From the £22bn ($35bn) railway network to nine new stadiums, a £3.4bn seaport and an £7bn airport, Qatar is certainly taking its responsibilities seriously as hosts of the 2022 Fifa World Cup. Much of this infrastructure was already planned, but winning the right to host one of the world’s biggest sporting events has acted as a catalyst to infrastructure investment.

Before any of these huge schemes begin, geotechnical experts have been sizing up the underground space. For geotechnical specialists the challenges for new infrastructure, particularly for roads and rail, lie in the main founding stratum of the region.

Tricky limestone

This stratum contains Simsima limestone, which is a type of Dolomitic limestone that has been known to contain subsurface voids that must be carefully assessed prior to construction undertaken with geophysical studies.

Coupled with this is an incredibly high water table that makes digging holes and building basements tricky and often expensive. “There is quite benign ground here but the main issue is a very high water table,” says Davis Langdon director Neil Hamilton.

This makes building basement car parks challenging as, not only is the water pressure an issue, but more levels have to be dug out owing to the fact that parking space must be provided inside building complexes.

“The planning requirements for car parking spaces per occupant mean that basements have to be two to four levels deep over the entire plot area,” says Hamilton. “Secant wall piles are used and join together to form an impervious layer diaphragm wall. Over time though, the water corrodes the concrete. The pressure is so great, you need to dewater the space as well.”

Expensive dewatering

Keeping water out does not come cheap. “There is a huge cost in dewatering,” Hamilton says. “It will usually be about £10,000 to £20,000 a month. I have a client in the West Bay area with a huge basement who is spending about £50,000 to £60,000 a month and the project has been stalled [further adding to the cost].”

And it’s not just basements that will be affected by the high water table. Around 119km of the new Doha Metro system, as well as the people mover in the financial district of West Bay, will be built underground.

One way of mitigating this is by choosing a tunnel boring machine that will maintain enough external pressure on the excavation to prevent the ingress of water.

Client Qatar Railways Company (QRC) is planning to use TBMs on the project. At July’s London Qatar Infrastructure Conference organised by NCE sister magazine MEED, QRC deputy CEO Geoff Brian Mee outlined plans for the 350km network, including the construction of 119km of underground tunnels.

“No one has ever attempted to run 12 TBMs at the same time in the city so that will be a big challenge”

Geoff Brian Mee, QRC

 

“It takes 18 months to build the TBM and get it into the ground, it then takes about three years of tunnelling,” he said.

“If we split it into big enough pieces to make it attractive to
the market then that means about 12 contracts worth up to £950M going on at the same time in the middle of a highly populated city.”

“No one has ever attempted to run 12 TBMs at the same time in the city so that will be a big challenge. Our plan is all tunnelling will start from the outskirts and move inwards so that we are not removing spoil in the centre of the city. We are also looking at the people mover to see if we can remove spoil straight onto barges.”
In terms of procurement for the project QRC will use design and build contracts and will only prequalify multi-disciplinary consortiums with local involvement. This means a designer, a tunneller, a construction company, and local help.

Local plus international

“There is nobody in Qatar that has ever built a railway, so the logical conclusion is to tie together local specialists
with international specialists,” says Mee.

He also warns that bringing in labour can be difficult due to the immigration rules.

“I would really recommend people form consortiums with local companies. It would be a real shame if people put a lot of effort into bids and didn’t have those vital components.”

2012 start

All primary contracts are due to be let in 2012 with the construction window for phase one running to 2020. This gives two years for commissioning and testing so that, by the time the World Cup kicks off in 2022, Qatar will have an extensive public transport system linking the venues. However, this is not the only reason for the scheme.

“The project is a milestone on the way to providing a public transport network for Qatar, and the World Cup is a milestone in the development of that public transport network, but that isn’t what we are designing it for. It is about building something that is fit for purpose for Qatar as it grows,” says Mee.

Rail projects are not the only Qatari infrastructure requiring tunnelling. Plans for a crossing of the Doha Bay are set to include a 12km tunnel section. The route of the crossing has yet to be finalised but it will run north-south across the bay bypassing the busy city centre and enabling commuters to travel directly from the airport to residential areas north of Doha. This section must be buried underground because it runs close to the airport. However, for the remaining sections of the crossing, design competitions have been held to find an iconic bridge.
Ministry of Municipality and Urban Planning senior transportation engineer Saad Khodr was also presenting at the MEED conference.

Tunnel and bridge

“The concept was originally to have a 12km tunnel, broken up with an island and then some kind of a bridge. We also planned for a link to the Pearl - a residential area created offshore to the north east of Doha,” he says.

“This was presented to his Highness the Emir [Sheik Hamad bin Khalifa Al Thani] but he didn’t like any of this. He wanted something special. He said ‘go and do a competition’.”

This led to the completion of four new concepts created by teams made up of architects and engineers. The plans varied from a number of small bridges to a huge iconic crossing. These were once again presented to the Emir, but he was still unconvinced by the options shown.

“His Highness said unless you bring something special that adds something to the bay then I want it all to be a tunnel,” says Khodr.

New solution

As a result, another consultant has been commissioned to develop another solution, but the plans have not yet been revealed.

In the water sector, Doha is also expected to build its own sewer tunnel project akin to the Strategic Tunnel Enhancement Programme in nearby Abu Dhabi. Details on the Qatari project have yet to emerge.

Across all sectors the engineering challenges are immense, particularly when it comes to working underground. Engineers say attracting the human resources to the country will be an important step in delivering the infrastructure on time and on budget.

Despite the challenges that Qatar may present, Hamilton says the nation is brimming with opportunities and he wouldn’t want to be based anywhere else.

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