A peek into the history of engineering on Chapman’s Peak Drive

Date:8 December 2021 Author: Micayla Vellai Tags:, , ,

Chapman’s Peak boasts breathtaking views, and is one of the world’s most scenic drives, but how much do you actually know about the history of this spectacular gem?

According to the Chapman’s Peak Drive website, Sir Frederic De Waal, who was the first administrator of the Cape, ordered the construction of the Hout Bay-Noordhoek Road in the early 1900s.

The route was opened in 1922 and took seven years to complete, but this extraordinary drive is not without danger as rock falls and mudslides have always been a hazard for motorists. However, suitable rock fall protection measures had been implemented in 2000 after a few fatal occurrences.

“The rock fall protection measures implemented at Chapman’s Peak Drive were selected on the basis of what is considered to be best international practice and consists of a half tunnel, catch fences, slope stabilisation and canopy structures. In 2004, Chapman’s Peak Drive received an excellence award for rock fall protection,” the website explains.

Project Engineering Solutions are outlined as followed:

Rock Fall Protection Measures

The design of rockfall protection measures involved sophisticated, three-dimensional computer modelling of the topography assessment of mountain and location of boulders on the slopes and cliffs above the road to predict the associated rockfall patterns.

It predicted the location, trajectory, frequency, bounce height and energy of falling rocks along route on a statistical basis, while working conditions were challenging with up to 11 different mobile cranes being deployed. Helicopters and abseilers were also used to complete the work in inaccessible locations.

Terrain Modelling

Engineers, along with Swiss specialists utilised a digital terrain model to generate three-dimensional simulations of rockfalls.

Half Tunnel

The 155m half tunnel was built at the base of Chapman’s Peak, while the overhanging rock-mass is supported by 95t rock anchors. The soffit and side walls are supported by 150mm thick steel reinforced shotcrete lining.

Rock Shelters

Building a concrete canopy ensured that any rocks that do fall off the mountain will land close to the old rock-faced guard wall, as traffic moves safely under the canopy.

Concrete impact protection canopies were constructed at two locations where sandstone cliffs extend to more than 400m above the road. These structures arch over the road and protect it by intercepting rock fall.

A 40m long curved cantilever canopy, arching over both lanes was built on a tight bend at the confluence of three gullies.

In addition, a portal canopy coincides with the highest predicted rockfall energies and the structure is free of the cliff face, which is supported from behind by tapered columns.

Catch Fences

The website explains that catch fences is a new, sophisticated Swiss design which consists of interlocking rings of high tensile wire designed to trap rocks as they fall, and are anchored into the rock with steel wire ropes.

The 21st-century cutting-edge construction processes, together with the determination of the early 1920s when the original drive was built, has resulted in this project showcasing the amazing expertise of South African engineering.

Picture: Unsplash

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