Technical excellence recognised in South Africa’s largest interchange project

SMEC South Africa won the Technical Excellence category in the 2018 SAICE Durban Branch Awards for the Mount Edgecombe Interchange Upgrade project.

SMEC South Africa won the Technical Excellence category in the 2018 SAICE Durban Branch Awards for the Mount Edgecombe Interchange Upgrade project.

Currently considered to be the largest interchange project in South Africa, the Mt Edgecombe Interchange boasts one of the longest incrementally launched bridges in the southern hemisphere at 947 m long. In total there are six new bridges, three existing bridges widened or lengthened, and a total of 12.4km of ramps on this project. A total of 1.8Km of mechanically stabilised earth walls, some as high as 17m, were constructed. These walls required extensive geotechnical ground improvements by way of a grid of rock columns at foundation level.

The team has had to overcome numerous challenges throughout the nearly decade-long project, which was launched in 2009. Some of the major design considerations included physical space constraints due to current and future developments, road reserve boundaries, traffic congestion, future traffic demands, proximity of the Gateway Theatre of Shopping offramp from the M41, existing stormwater attenuation areas, and accommodation of future development access and future capacity.

These constraints were overcome using a four-level free-flow interchange configuration. This provides for full-width free-flow directional ramps in all directions whilst keeping the geographical footprint of the interchange as small as possible and largely within the constraints of the road reserve.

The main feature of this Project is the two upper level ramp viaducts. Bridge B0214 has a deck length of 443 metres long and Bridge B0215 has a deck length of 947 metres, which makes it the longest incrementally launched bridge in the Southern hemisphere, as well as the longest bridge structure to ever be built in South Africa. What sets B0215 apart however is that the bridge is constructed in two decks, which were both incrementally launched but from opposite sides, and designed to meet in the centre. Ensuring that the two decks would meet up within dimension tolerances required innovative design, precision survey work, and sound construction management.

The final position of the decks was 7mm from the design position transversely and 0mm from the design level vertically. Given the size of the decks and the fact these decks were launched from opposite ends, this accurate final position is a testimony of the workmanship and world class engineering capabilities in South Africa.