Aurecon

The Gautrain Rapid Rail Link is a state-of-the-art dedicated light rail line between Johannesburg, Pretoria and O.R. Tambo International Airport, supporting a fast transit system capable of operating at 160 km/h.

The areas along the Pretoria and Johannesburg route are considered to be a fast growing region within South Africa, with ever increasing pressure on the existing transportation infrastructure. One of ten Spatial Development Initiative (SDI) projects implemented by the Gauteng Department of Public Transport, Roads and Works (Gautrans), the Gautrain, is set to make a major contribution towards the economic functioning of the Gauteng area.

Comprising two links with three anchor stations (Pretoria, Johannesburg and O.R. Tambo International Airport), as well as seven other stations which will be linked by approximately 80 km of rail along the new route. Aurecon was awarded Detail Design Package 6A, which includes the Centurion station. The main distinguishing aspect of this design package is Viaduct V5c. This viaduct is the single longest viaduct on the project, is founded on extremely difficult subsoil dolomite formations and is situated in an urban environment.

“The design challenge that Viaduct V5c presented Aurecon was to address the interaction between the operational requirements, the structural limits and the geological environment in which the structure was constructed,” explains Aurecon project engineer Loest van Eeden. He goes on to say that unique engineering design and innovative solutions enabled Aurecon to overcome construction challenges.

Unique design solutions implemented at V5c:

• The design of Viaduct V5c was influenced by the soil-structure interaction and the rail-structure interaction. Subsoil conditions necessitated the implementation of floating foundations and the installation of a continuous welded rail on top of the structure.
• Floating/raft foundations result in much larger structural movements than piers founded on rock. Predicting the behaviour of the complete system was essential to the overall structural performance of the viaduct.
• All piers and their associated foundations were designed to accommodate possible sinkholes without jeopardising the structural performance of the viaduct.
• The superstructure for Viaduct V5c was constructed using the ‘match cast segmental construction method’ widely used for the construction of long viaducts in other parts of the world. The Gautrain project was the first project to implement this method of construction in South Africa.
• The majority of the Centurion Station buildings (including the ticket offices and foyer) are located underneath the viaduct with elevators providing access to the station platforms above. The standard viaduct segments were modified by the addition of external propped extensions (precast struts) to the cantilevers. These provide support to the precast station platforms, parapets and station canopy.
• Four different foundation types were used to support Viaduct V5c, mainly due to construction restraints and the complex nature of the geology associated with the viaduct.
• The majority of the Viaduct V5c route is urbanised and congested with existing infrastructure. A large number of existing services had to be moved or relocated to enable works for the viaduct construction. These services included telecommunication, bulk water and sewerage, power supply, road infrastructure and buildings, to name but a few.
• Aurecon’s design had to conform to strict aesthetic and environmental parameters, which were predetermined by the master architect and environmentalists.
• Although not unique to this viaduct, the design also had to accommodate aesthetic features, including the implementation of an African woven basket pattern to the parapets along the viaduct and tree-shaped standard concrete piers.

It is these solutions that distinguish this viaduct from others on the Gautrain project, even though V5c is similar in appearance to the standardised viaducts.

The Gautrain project is set to play a pivotal role in the economic development of the Gauteng Province. Through ensuring the longest viaduct on the project met stringent safety, design and aesthetic requirements, Aurecon’s bridge, geotechnical and road experts have helped devise a cost-effective, efficient and environmentally friendly transport solution for the most densely developed area in Gauteng.