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Transforming an informal settlement into a fully-fledged urban development requires extensive planning and integration of infrastructure, and civil engineering consultant Hatch was tasked with this job at the Elias Motsoaledi settlement in Johannesburg. The company was tasked with the design and construction supervision of about 7 km of internal road and storm water infrastructure in the conversion of the informal settlement to an urban housing development, as well as the construction of a bridge.

Elias Motsoaledi bridge

Named after ANC veteran and Rivonia trialist Elias Motsoaledi, who served 25 years on Robben Island, the project is located near Bara Mall in Region D. The existing informal settlement has been rocked by violent service-delivery protests, due in part to the fact that unscrupulous landlords rent out shacks to over ten inhabitants, according to Housing Department Assistant Director Bubu Xuba.

When completed, the two-phase housing development will contain 1 424 low-cost houses, five blocks of medium-density units, and associated amenities such as schools and churches. The project was given the go-ahead by the City of Johannesburg in 2010, with construction beginning the following year.

A stipulation of the project was that 30% of the work had to be carried out by the local community. Following an intensive screening process, two local subcontractors and about 20 local residents were employed, tasked with the construction of concrete kerbs, block paving, brick manholes, and general labour. To facilitate this, a dedicated Community Liaison Officer (CLO) was appointed by Hatch to be the main interface with the local community.

The work allocated to local contractors was always carried out under the supervision of the experienced main contractor for quality control reasons. It was critical to have clear lines of communication between all the professional teams, main contractors and sub-contractors to ensure proper logistics management and co-ordination, says Hatch Project Leader Leon Mbongwa.

The central portion of the project was the construction of the bridge, as it provides an important link between the two areas of the informal settlement, which are separated by a river. The project site is located in a valley divided by the river, with the housing being developed in two areas that needed to be linked together.

The bridge, designed for a 1:50-year flood event, comprises a five-span, 65m-long, 13.5m-wide continuous composite deck, supported on two reinforced concrete abutment walls and four piers on spread footing. The central three spans are 15m long, while the end spans are 10 m long.

The bridge project location posed a challenge in terms of the presence of a high water table and poor founding material, which affected the foundation design. Six test pits were excavated and suitable material was only reached at about 3.5m. Samples taken to classify the type of material on-site resulted in the geotechnical and structural engineer recommending a mass concrete foundation, using a high-strength mix.

Apart from the foundation design, the bridge itself had to cater for specific community requirements such as walkways for pedestrian traffic. Future street lighting requirements also had to be catered for, while service ducts for utilities such as electricity and fibre optic cables were provided for ease of installation without disturbing the bridge structure itself.

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