The Western Cape Department of Transport and Public Works identified two sections of Trunk Road 31, totaling a 13.4-kilometers, between the towns of Ashton and Montague for rehabilitation. This was needed to improve traffic and pedestrian safety, as well as enhance the flood capacity of bridges along the route.
The road is also the start of the strategically important tourist Route 62, on which 4,000 vehicles travel through Cogmanskloof Pass towards Montagu everyday.
The upgrade of Cogmanskloof Pass presented several challenges due to significant ecological and heritage constraints, and extensive rock cutting required to realign the narrow gorges. These were overcome through considerate design and landscaping, and the preservation and reinstatement of indigenous vegetation.
The Cogmanskloof River flows adjacent to much of the route and crosses the road at four locations by means of existing bridge structures, which did not have adequate hydraulic capacity. The greater Ashton-Montagu region, and Cogmanskloof Pass in particular, had experienced substantial flood damage that resulted in multiple road closures and significant operational disruptions, with adverse impact on the local economy.
Three new bridges crossing the Cogmanskloof River were constructed during the project, the most iconic of which is the New Ashton Arch Bridge, which had been repeatedly damaged by floods and no longer fulfilled its functional purpose. Sediment build-up had significantly reduced the bridge’s freeboard height. During flooding it became clogged with debris and was overtopped by the river, cutting off the town.
To replace Ashton Bridge, we designed a single span, 100-meter, concrete tied-arch solution with a suspended deck. It accommodates four traffic lanes and walkways for pedestrians. To minimize traffic disruption, the new structure was constructed adjacent to the pre-existing bridge. After completion the new bridge was used as temporary bypass while the existing bridge was demolished, and new abutments built. The new concrete tied arch bridge was then jacked transversely into its final position in less than 12 hours. This was the first application of this bridge engineering technique for a concrete tied-arch bridge in South Africa.
Local manufacturers, with support from overseas specialists, were used to manufacture and supply specialized components such as post tensioning systems, arch stay cables, anchor plates and support bearings. On completion of the project, 42 per cent of the contract value had been allocated to the creation of economic opportunities and entrepreneurial capacity in the surrounding areas over five years.