One of the largest infrastructure developments in Gauteng, Waterfall City, has been supplied with 1 900 t of precast concrete stormwater pipes by precast concrete specialist Rocla to drain the area.

The progress of what is set to become Midrand’s new central business district is overseen by developers Atterbury Property and will comprise 800 000 m2 of rental space when the project is completed in 2018.

The stormwater piping project began in November last year and was initially planned for completion in November this year; how- ever, various additions to the project resulted in the completion date for the overall stormwater piping project being moved to early 2013.

Rocla was initially contracted to supply 1 550 t of stormwater piping, but was asked to provide an additional 350 t. The storm- water piping is also being extended to an adjacent housing development.

The installation of all piping at Waterfall City is well advanced. Other aspects of the project, such as the construction of roads, will be completed by early next year.

Construction company Labucon Resources is building the roads according to Johannesburg Roads Agency (JRA) standards.

Rocla sales executive Johann van Niekerk says the size of the interlocking joint pipes, which weigh up to 7.5 t each and vary in diameter from 450 mm to 1 950 mm, was a challenge, as large trenches had to be dug to accommodate their size and volume.

Labucon Resources project site manager Sias Swart adds, however, that the pipes posed no quality issues and the quick supply from Rocla allowed for swift installation.

“It was important that the material was supplied as quickly as possible so that we have enough time to start building the roads, which will start soon.”

Once the roads have been built, the JRA will take over responsibility for the stormwater and road infrastructure.

Meanwhile, Swart points out that one of the challenges experienced during the stormwater piping installation was groundwater, which produced a high water table in areas that were being excavated.

To manage and prevent structural problems between the trenches and the piping, bidem sheeting and 150 mm of stone bedding were placed around the piping.

The bidem sheeting was installed on embankments above the pipes to prevent ground- water from penetrating beneath the road surface material.

The stone bedding provides stability for the pipes and prevents soil movement from exert- ing stress on the pipe joints.

Groundwater was also pumped out of trenches and the area was laid with concrete.

The stormwater pipes will drain the site and release the water into three channels, all of which will eventually flow into the Juskei river.

To prevent soil erosion, Rocla supplied the precast wingwalls required for the project.

The wingwalls direct the water into and out of pipes, reducing turbulence and improving the hydraulic capacity of the conduit, says Rocla sales and marketing director Craig Waterson.

“Precast wingwalls are equipped with a separate concrete toe, which keys the entire unit to the ground and prevents any movement, which also reduces the risk of scouring the soil below or to the side of the toe,” he explains.

The wingwalls were introduced to the South African market in June, last year, and Waterfall City was one of the first projects in Gauteng where these have been used, says Van Niekerk.

Rocla will also supply manholes, which are installed at the points where the pipes change direction.

The stormwater pipes, wingwalls and manholes are manufactured at Rocla’s premises in Roodepoort.

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