Dec 12, 2008
Global economic slowdown not a concern for Gautrain projectBack
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Van der Merwe explains that the contract for the public-private partnership (PPP), which is a joint venture between the Gauteng provincial government and Bombela Concession Company, which consists of Bombardier Transportation, Bouygues Travaux Public, Murray & Roberts and the Strategic Partners Group as shareholders, is based on a fixed price, scope and time contract, securing the project against fluctuations in the economy. He notes, however that other factors could increase the price tag of the project.
He says that when there is a variation order, for instance, if the project is extended or a deviation on the project is required, the project price will increase. Also, if the consumer price index is higher than initially predicted and the inflation cost is higher than the amount predicted, the province will have to pay the difference. Van der Merwe says that any claims from contractors will also increase the project price; however, no claims have been reported to date.
Another aspect that has to be accounted for, is the exchange rate. All the Gautrain certificates are paid in rands, pounds and euros. Van der Merwe assures that all foreign currencies have been hedged, and consequently, the volatility of the market does not hold any real danger. The project works on a year-to-year basis, which means what is spent in excess one year, can be balanced with the expenditure of the following year. He says the budget is a challenge that every construction site in South Africa faces.
As part of the socioeconomic development component of the project 20 of the Gautrain train sets are being assembled at Union Carriage Works in Nigel, in an effort to create jobs and develop local skills.
Van der Merwe says that four complete train sets were manufactured and assembled in London. The remaining train sets were built in segments, and transported to South Africa by sea freight. In total, 24 train sets will be in use on the Gautrain project.
One train set is four carriages long. A static test is carried out on each carriage; the carriage is then linked into a train set, followed by another static test and lastly, a dynamic test, where the train set will run on the tracks at the depot.
Van der Merwe says that dynamic tests will be conducted in February next year. "By February 2009, the trains will be running on the test track. The test track will run from the depot site to the Midrand station, covering a 7-km stretch of track," he says.
All the tracks in the depot have been laid and contractors are now laying the tracks on the main lines. Van der Merwe says that to date, the production on site has mainly concentrated on the civils side of the project, however, significant progress is now being seen on the mechanical and electrical side of the project.
The assembly of the train sets will be completed around the last two quarters of 2009.
Van der Merwe reports that 9 km, out of the 15 km of tunnelling necessary for the Gautrain project, has already been completed. The tunnels are constructed by means of drilling-and-blasting, cutting-and-covering and by boring through underground sections using the tunnel-boring machine (TBM).
The bulk of the tunnelling is done through drilling-and-blasting. Van der Merwe explains that with the drill-and-blast method a section is primed and filled with dynamite. With every blast, a 5-m segment of the tunnel is created. It takes about 12 hours to repeat the process, and currently, the production rate of the tunnelling stands at about 10 m/d, says Van der Merwe.
He notes that about 12 km of tunnelling has to be completed by drilling-and-blasting. Bombela opened as many faces to the tunnels as possible to achieve this objective quicker and more efficiently
The longest continuous tunnel is the 6-km section between the Marlboro station and the Sandton station, which is why an extra face was opened at Mushroom Farm park. In September this year the connection between the Marlboro portal and Mushroom Farm park was opened, forming a continuous tunnel of just over 4,2 km long.
In instances where the tunnel is shallow the cut-and-cover method is used. This method involves the excavation of a large open cavern in the ground, which is covered up again after the completion of the structure. The Gautrain project uses the cut-and-cover method at its underground stations at Park station, the Rosebank station and the Sandton station, as well as for structures at the Marlboro portal.
Van der Merwe says the cut-and-cover process firstly involves the excavation of a shallow trench. Drilling-and-blasting is used to excavate rock. While the rock underneath the highway is being excavated, lateral supporting pillars are put in place to stabilise the highway and prevent the trench from collapsing.
Traffic flow continues undisturbed on the temporary deviations, while excavation continues. Once the underpass structure has been completed, the surface is reinstated or roofed over. This process is a significant engineering challenge that has been achieved through careful design and construction techniques.
Cut-and-cover tunnels at shallow depth have been used worldwide for centuries. New technology now allows the use of cut-and-cover methods at increasing depths and very close to, or even under, existing tall buildings.
Meanwhile, a 3-km portion of the tunnel between the Park station and the Rosebank station is being excavated using the high-technology TBM.
The R300-million TBM was designed and custom-built by Herrenknecht, in Germany, to cope with the complex underground geological conditions south of Rosebank. Geology in this area features a high-water table, as well as varying degrees of hard rock, sand, and soft, waterlogged soil.
At the front of the TBM machine is a rotating cutting wheel, which excavates the ground. Behind this wheel is a chamber where the excavated material accumulates, before being extracted by a pressure relief discharge system called a screw conveyor.
Excavated soil is then transported by means of a conveyor belt up to the Rosebank shaft opening, and weighed. The front cutter head of the machine advances at roughly 220 m a month. A concrete tunnel lining is built ring-by-ring in the rear.
A computerised guidance monitoring system provides information to the TBM pilot on a continuous basis.
It also allows the pilot to steer the machine, and to continuously monitor the actual position of the TBM in relation to the theoretical centre line of the tunnel at any given location along its route.
Van der Merwe notes that some sinkholes at Oxford road were formed while tunnelling with the TBM machine. However, he points out that this was not a significant engineering challenge, and that the integrity of the tunnel was never in question.
The Gautrain project requires the construction of 80 bridges and a number of very large culverts, equates to about 11 km of bridges.
Civil engineers constructing the close to 100 piers that will support the viaducts, or elevated railways, have had to develop a technique to overcome the problematic dolomitic ground in the Centurion and Pretoria area.
Between Centurion and Pretoria, the Gautrain alignment traverses through about 16 km of dolomitic ground, of which 5,8 km will be on viaducts, with the remaining portion constructed at surface level. To manage the risk associated with the dolomite rock, the construction of the viaducts includes the sinking and concreting of shafts down to the dolomitic rock, on which the foundations for viaduct piers are laid.
Van der Merwe says that one of the key performance indicators of the Gautrain project, where R3-million is spent every hour for 54 months, is the land use around the Gautrain system.
The Gautrain project has affected 1 142 property stands. Van der Merwe reports that the last four property stands have now been handed over to the Bombela concession, giving the consortium access to the entire site.
Van der Merwe points out that when the system was designed, an average of 50% of land within a 2-km radius of the anticipated project was undeveloped, as was 75% within a 5-km radius. "When building a system like the Gautrain, an initial uncertainty develops, with property values falling."
As densification around the system develops, property values begin to increase again. "We expected this would happen in South Africa, but could not predict the pace at which this property explosion would occur," says Van der Merwe.
He reports that investment group Old Mutual will develop 250 000 m2 of mixed land next to the station in Midrand. This development has a value of around R20-billion and will be almost three times larger than the Menlyn shopping centre in Pretoria.
Van der Merwe concludes that the success of the Gautrain system lies in developing a train system that is constantly running on a planned schedule and not just during peak times.
Edited by: Laura Tyrer© Reuse this
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