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Compiled by the Government Communication and Information System Date: 10 Jan 2008 Title: Gautrain construction goes underground -------------------- Johannesburg - Construction work on the Gautrain has gone underground, with a 160-metre, 885-ton tunnel-boring machine set to tackle the rock under central Johannesburg. It has been just over a year since groundwork began on the multi-billion rand rapid rail link between South Africa's commercial and administrative centres. Christened "Imbokodo", meaning rock, the Gautrain's tunnel-boring machine (TBM) is to begin underground tunnelling of a three-kilometre section between the suburb of Rosebank and Park Station in central Johannesburg, reports Southafrica.info. At the ceremony to name the machine last month, Gauteng Premier Mbhazima Shilowa said: "Today marks the start of a countdown towards the completion of the construction of the Gautrain rail link." The 80 kilometre rail link will run between central Johannesburg and OR Tambo International Airport, with a separate line linking the system to Pretoria. Work is ongoing at 45 sites across the two cities, and it is expected that the line from the centre of Johannesburg to the airport will be completed in 2010, ahead of the 2010 FIFA World Cup. The line linking to Pretoria will be completed in 2011. So far R7-billion of the project's R25-billion budget has been spent, most of which has been on groundwork along the train route and at the construction sites of future stations. Some underground blasting has also taken place further up the route from Sandton onwards, but the presence of between 300 and 400 metres of granite rock in the three kilometre section between Rosebank and central Johannesburg made it necessary for a TBM to be used. For the most part, the tunnel will be driven through decomposed granite below the water table, according the Gautrain website. "The tunnel will also need to traverse in the soft zones that will often occur be below the water table." Designing and building Gautrain's R300-million Earth Pressure Balance Shield TBM, which is 160 metres long and weighs 885 tons, took about 12 months. After the machine's pre-assembly at the Herrenknecht factory in Swanau, Germany, it was transported by ship to Durban Harbour and overland to Rosebank Station, where it was re-assembled by a team of international and local experts. The Gautrain website says the benefits of using TBMs for tunnelling are recognised worldwide, as the machines are designed to bore tunnels in specific areas and to cope with site-specific ground conditions. "A computerised guidance monitoring system is used to steer the machine accurately underground while the machine and tunnel lining resist the soil pressures during and after the tunnel construction," the Gautrain website states. "This means that [the] TBM is an environmentally sound method of tunnelling, especially in built-up areas." The wheel bores into the earth at 1.5-metres at a time, while the tunnel is lined with concrete rings at the rear of the machine. The TBM will be active for some 14 months, tunnelling 24 hours per day and seven days per week, after which it will be dismantled over a three-month period. It will then be available for use in other projects around the world. Similar Earth Pressure Balance Shield TBMs have been successfully used to construct a 3.6-kilometre underground highway tunnel that crosses the Madrid city centre in Spain, an 8.9-kilometre high-speed railway tunnel from Karlsruhe to Basle in Germany, and in the US to extend the Los Angeles subway network by 10 kilometres. - BuaNews |
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