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Megabridge construction on N2 highway project to start later this year

The construction of two megabridges, as part of the South African National Roads Agency Limited’s (Sanral’s) N2 Wild Coast Toll Road (N2WCTR) project, is expected to begin between August and October this year, says Sanral’s bridge network manager Edwin Kruger.

“The tenders for the two bridges – the Msikaba and Mtentu bridges – are in the adjudication phase, which means we cannot comment on the value of the bridges and to which tenderer they will be awarded.

“With that said, the estimated construction cost of the bridges is in the range of R1.5-billion to R1.8-billion each.”

“Local contractors have not built bridges such as the Msikaba and Mtentu structures before,” adds Kruger. “As such, their skills will be supplemented by international contractors with the requisite experience. All the tenders received have large South African contractors, who of their own accord, have created joint ventures with international contractors.”

The last time a megabridge was constructed in South Africa was in the early 1980s, with the construction of the N2 Tsitsikamma toll road along the Garden Route.

“This project included the Bloukrans arch bridge, which today would probably cost in excess of R1-billion,” says Kruger.

The two new bridges will be funded from Sanral’s non-toll portfolio.

“All funding for national roads – except for toll roads – comes from national government,” explains Kruger.

“National Treasury allocates money towards this portfolio and has specifically allocated funds for the Msikaba and Mtentu bridges in the current three-year funding cycle.

“In the case of the N2 Wild Coast Toll Road greenfields section, as is the case for the Gauteng Freeway Improvement Project, money for the bridges will come from a combination of national government funding and borrowing. Only the portion of the project funded from borrowing will be repaid through toll fees.”

The Msikaba and Mtentu bridges form the backbone of the greenfields portion of the N2WCTR. The toll road project is one of government’s 18 Strategic Integrated Projects, which were identified to support economic development and boost service delivery in the country’s poorest provinces.

“The greenfields section of the Wild Coast highway project extends from Port Edward through Port St. Johns. This section is a brand new road and without the bridges we cannot complete the highway,” notes Kruger.

The first phase of the project has already started with the construction of haul roads to the bridge sites, he adds.

“The N2WCTR project has full environmental approval and has been given the green light by national government.”

The first megabridge will cross the Mtentu river, just outside of Xolobeni, and the second will cross the Msikaba river, near Lusikisiki – hence the bridge names.

As the first of its magnitude in South Africa, the Mtentu bridge will be one of the longest main span balanced cantilever bridges in the world, says Kruger.

Reaching heights of around 220 m, it will take over the title as the highest bridge in Southern Africa from the Bloukrans Bridge, with its 217 m deck height.

The construction of the 1.13-km-long bridge in a remote location is a major undertaking that requires specialised engineering skills and building techniques.

“The 580-m-long Msikaba bridge will cross the spectacular and pristine Msikaba river gorge and will be the longest span cable-stayed suspension bridge in South Africa – and possibly Africa,” says Kruger.

“Cable-stayed bridges are distinct in their use of towers and cables to support the bridge deck. This single span bridge will be anchored back into rock on either side of the gorge.”

One of the environmental requirements in building this bridge is that Sanral does not touch the unspoiled Msikaba gorge.

The cable-stayed design will ensure that the construction of the bridge will have no direct impact on the environment in the gorge almost 200 m below, notes Kruger.

“Since both bridges have a large concrete component, labour will be needed for fixing steel and placing the concrete for the bridges. Semi-skilled and unskilled labour will be sourced locally,” he adds.

Tourist Attractions
Pedestrian sidewalks will be constructed on either side of both bridges and view sites off the bridges will provide special viewing points for tourists.

These sidewalks will also serve to connect communities on either side of the gorges.

“The Msikaba and Mtentu bridges will become tourist attractions in their own right, and will offer opportunities for the associated tourism industry in the area,” says Kruger.

He adds that the term ‘megabridge’ – coined by the media – refers to a single bridge that costs more than R800-million to build.

“However, it should be noted that what we in South Africa call a mega structure, may be regarded as a medium structure internationally.”

It will take around three to four years to build the two bridges.

As the new route will be substantially shorter and flatter than the current route, it is estimated the N2WCTR will improve heavy freight travel time between Durban and East London by up to three hours, significantly lowering transport costs and carbon emissions, says Sanral.

The road will also increase mobility through an area that is currently isolated from the rest of South Africa.

Source : Engineering News