KwaZulu-Natal’s North Coast has grown over the past few years, with the uMhlanga and La Lucia Ridge areas having been expanded substantially. As a result, the highway interchange feeding the region has been operating at capacity, with vehicles backing up on the M41 and onto the N2 in peak hours.

SAs longest incrementally launched bridge completed

According to Corne’ Roux, project manager for SANRAL Eastern Region, an additional 40 000 vehicles enter or leave the N2 from the M41 daily, resulting in substantial queuing of vehicles during the day. This, together with expected future expansions and anticipated development of the Cornubia area, required the existing interchange to be upgraded in order to improve the flow to and from the N2 and M41 to the supporting road network.

This expansion is now nearing completion with the north and south decks of the one-kilometre ramp of the Mt Edgecombe Interchange having been joined. Connecting Phoenix and uMhlanga with Durban and the North Coast of KwaZulu-Natal, this is the longest incrementally launched bridge in the Southern hemisphere.

Incremental launching involves casting 12m-30m long sections of the bridge superstructure in a stationary formwork behind an abutment and pushing a completed section forward along the bridge axis. The sections are cast contiguously and then stressed together.

The Mt Edgecombe Interchange bridge has a deck length of 947 metres, a total number of 23 piers – of which the highest is 26 metres – with typical spans of 42 metres. The longest span is 50.5 metres.

“Constructing one of the longest structures ever built in South Africa over one of the busiest intersections in KwaZulu-Natal successfully, without ever closing any of the roads permanently, bears testimony to the success of the selected construction methods and materials,” Roux told a local newspaper.

Gert van Schalkwyk, resident engineer (structures) for the main consulting engineers SMEC South Africa, says that ensuring that the two decks would meet up after each individual deck was launched was a challenging exercise and took innovative engineering and design. “The deck was modelled on AutoCAD in 3D to accurately plot the launching path of the deck during construction. This model was used by the surveyors to set out and track the bridge within 1mm of its design trajectory, alignment and level,” he explains.

“A total of three surveyors were present during each of the launching operations to ensure live tracking of the front and back of the deck as well as provide constant verification of their surveys. Both decks were successfully launched to within five metres from each other: the last five metres of deck was cast in situ and is referred to as the ‘stitch’ which neatly and monolithically joins the decks together.”

Image credit: http://www.smec.com/en_au/newsroom/current-news/success-fulton-awards-south-africa


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