Civil Engineering December 2021 | Vol 29 No 11

18 December 2021 Civil Engineering THE SOLUTION The designers made a different proposal: to preserve the existing underpass struc- ture, convert one of its abutments into a pier, and add a separate new second span. Reusing the existing bridge would be more sustainable, but the new span might be wasteful in a different way, by adding significantly more lane capacity than was necessary. And it would force the road levels at the adjacent intersections to be lower, which would have a knock-on effect throughout the neighbouring roads, more of which would need to be completely rebuilt in order to bring down their levels to tie in. One difficulty is that the interchange happens to be at the lowest point in the local road network, so reducing its levels reduced the global minimum road level. Another difficulty was the challengingly steep and constrained local topography, which already created an unusually tight radius on the existing highway. Existing roads had in some cases been unable to meet geometric design standards, and trucks were not able to use one of the ramps onto the highway. The designer’s proposal to reuse the existing bridge would deal with all the problems, and provide a much better re- sult, but it was a much more extensive so- lution than the planners had asked for and might be more expensive. There seemed limited room for compromise. Was it re- ally worth keeping the old bridge? Further analysis made it clear that the bigger solution was best. There was still room for more development in Westwood, with ongoing rezoning applications, and the municipality could be proactive in providing capacity for continued invest- ment. There were also numerous new growth opportunities, such as student accommodation for nearby University of KwaZulu-Natal’s Westville campus, which has an entrance accessed through the in- terchange. And the municipality would be upgrading well-located, well-serviced land. In addition, the designers managed to reduce costs below that of the original proposal, while also ensuring that as much value as possible would be created by the project. Compromise solutions like split carriageways and longer slip lanes were used to reduce the extent to which roads needed to be rebuilt to tie-in with the new levels, and the structural design to expand the underpass was innovatively optimised to provide a structure that is highly efficient in time, material, and construction costs. Bulk services through the area could also be upgraded with more capacity since they had previously been constrained by extensive hard rock material. Traffic flow and control was improved more widely in the neighbour- hood, providing a much safer, higher standard road network. STRUCTURAL INNOVATION A key concern was minimising construc- tion-related disruption and lane closures on the King Cetshwayo Highway (M13), an important arterial route that feeds traffic directly onto the N3 connecting to the Durban CBD and the N2. The new bridge span was built using a hybrid top-down, build-and-dig-out methodology. The top-down approach minimised traffic disruption because traffic could be moved onto the new deck superstructure before the substructure excavation and construction was complete. It also removed the need for expensive, time-consuming, and wasteful temporary lateral support structures be- tween the carriageways during the period when one carries traffic and the other is excavated for new foundations. The top-down approach led directly to the design of an extremely minimalist new abutment, with a bearing seat beam supported directly on piles, and a separate abutment retaining wall created by a sprayed concrete and soil nail lateral sup- port system to support the fill material. Another experiment to tighten the critical path was to not install expansion joint nosings for the bridge decks, which would normally have been the only op- tion with the 12% superelevation on the highway and could only be done after the final asphalt layers were in place. Instead, the tops of the expansion gaps were simply sealed off, and layers of fibreglass reinforcing grids installed within the overlying asphalt to distribute the strains of deck expansion and contraction. All six ‘jointless joints’ have performed even better than expected with no cracking in the asphalt after 18 months and produce a pleasantly smooth riding surface for vehicles travelling over the bridge. It provides a valuable case study for other designers wanting to eliminate expansion joints from small span bridges, or older structures where time-related creep and shrinkage is mostly complete. RADICAL ECONOMIC EMPOWERMENT The project was a pilot for a cutting-edge new specification to ensure maximum, equitable distribution of employment, sub-contracting and skills develop- ment opportunities among emerging contractors and workers in surrounding communities, with detailed technical requirements for this participation. The Go!Durban Radical Economic Transformation Specification (GRETS) was originally developed for construction of bus infrastructure projects, which require an unusually high level of stake- holder and community buy-in if they are to be successful. The effective application in those projects meant the approach was now being tested for the first time in a less controversial situation. More management was required because it was not enough to spend 30% of the contract value on community participation. Packages of sub-contracting work were also split up into many smaller packages to increase the number of participants, and a ‘business desk’ was set up to provide fair and transparent facilitation of GRETS. 22 very small Grade CE1 sub-contractors with minimal The asymmetry of the underpass was sustained in stylised facebrick façade panels on only one of the bridge’s four wall faces