The $US205 million Asbestos Cement (AC) Pipe Replacement Project is a major scheme to replace 1,750 km of ageing water pipe throughout Durban, a city on the east coast of South Africa and part of the eThekwini Municipality.

Project management was provided by Aurecon, an international engineering and project management company, and work commenced in July 2007. Approximately 60 km of pipe has been laid per month, and so far 1,600 km has been installed. At this rate, the project is on schedule for completion in June 2010.

The ageing asbestos cement water pipes, measuring 160 mm in diameter, are being replaced with modified polyvinyl chloride (mPVC) and high density polyethylene (HDPE) pipe.

“The old pipes were desperately in need of replacement,” said eThekwini Project Executive Alan Kee.

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“Bursts were occurring on a daily basis and the effective life span of the pipes had come to an end. We had to devise a way to replace the pipes whilst keeping disruption to service to a minimum,” he said.

The project has relied heavily on moling and pipe cracking. These technologies were chosen as they are modern, cost-effective and environmentally friendly.

Moling was used in the suburbs of Kingsburgh and Amanzimtoti, and in parts of Hillcrest and Kloof. This process involves using a moling machine to excavate under the existing surface of a road or driveway. The rocket shaped, pneumatically driven machine is placed in a specially prepared launch pit on either side of the road. Then, directed by an internal telescope, the machine digs the required bore.

“As moling helps to minimise the surface excavation required, it is an ideal technology to use on busy roads in built-up areas. It is also useful when working in the suburbs, as the necessity for costly driveway reinstatements is avoided,” said Project Manager Jochen Dedekind.

However, moling can only be used in soft soil conditions, and when hard rock is encountered hand excavation is required.

Another No-Dig technology, pipe cracking, also known as pipe bursting, was extensively used in the city centre of Durban, where 15,000 m of AC pipe was successfully replaced with HDPE pipe. This process involved shutting down the main to be replaced, excavating and removing a small section of pipe and inserting a hydraulically powered cracking head.

“The head is drawn through the old pipe by means of a winch. As it moves forward, by hydraulic action, it expands and bursts the pipe and at the same time pulls through a new HDPE pipe, of similar or larger dimension,” Mr Kee said.

In some cases CCTV cameras were placed into the old pipes prior to pipe cracking to ensure that the new pipe was smoothly pulled through the old AC pipe.

With the project on the verge of completion, the project managers were full of praise for the successful repairs, particularly the use of no-dig techniques.

“eThekwini Municipality is to be commended on the innovative approach taken in combining traditional and trenchless technologies on this massive project,” said Mr Dedekind.

Now that the new pipes have been successfully installed, citizens and local government will start reaping the benefits. The new pipes have a fifty year lifespan and should significantly reduce the number of bursts, saving the municipality $US31.8 million per year.