Doha metro, a tunnelling challenge
01 October 2012
PHASE One of Doha Metro, believed to be one of the world’s largest infrastructure projects in the planning stage, is expected to involve up to 55 km of underground track, incorporating between 26 and 35 stations.
This entails an extensive volume of tunnelling in a country with no experience in railway or metro construction. This is compounded by the fact that as hosts to the 2022 Fifa World Cup, Qatar is looking at completing the $12.9-billion Phase One within seven years, according to the Germany-based Tunnel magazine.
The 354-km-long metro project is part of the integrated railway system for which the Qatari government has enlisted Deutsche Bahn, a subsidiary of DB International, as a major strategic partner. The project will include four rail lines – Red Coast Line, Golden Historic Line, Green Education Line and Blue City Line – and 98 stations and will link stadiums for the 2022 tournament. Up to 30 per cent of the network is expected to run underground.
With tunnel boring work for the metro earmarked to start early next year extensive efforts are under way to select the most suitable system and technique.
Besides the training and qualification of the Qatari staff, DB International is taking over the ongoing engineering services, as well as the technical consulting under a contract signed in late 2011.
According to the magazine, geological exploratory drilling and lab tests were initiated to get an exact picture of the soil in the project area. Given the lack of experience in the field, an extensive study was required to determine the geological values pertaining to tunnelling and special foundation engineering. The soil in the project area mainly comprises fill material, Simsima Limestone, Midra Shale and the so-called Rus Formation, which is characterised by the presence of various extensive layers of saline residues, mainly of gypsum and anydrites that present challenges for tunnelling.
In terms of hydrology, the conditions lead to a situation where no European norm can be applied for the aggressive ground water and in turn additional investigations must be carried out in the field of concrete technology, says the report in Tunnel.
DB International has embarked on planning of the underground structures and the essential conditions for establishing the tunnel cross-sections – which were determined to be roughly 6 m in internal diameter – have been laid down. A risk assessment and comparison of the double-track bore (as applied for the Dubai Metro) or two single-track bores (as according to TSI guideline) was initiated. Towards this end, a cross-section of a double-track bore was devised. Following evaluation of the study, the client Qatar Railway Company has decided on a tunnel system with two single-track bores, says the report.
In view of the project schedules, reducing the depth at which individual stations are built would help the construction process but cannot be implemented as other projects are running in parallel. Also, while additional tunnel boring machines (TBMs) would help speed up work, this is made impossible by the location of the site in the city centre.
The project is expected to involve four tunnelling contracts, with the initial packages including the Msheireb station – which is expected to be the busiest on the network – and Education City station.
