This sector of the municipality’s water pipe replacement program, the Asbestos Cement (AC) Pipe Replacement Project, started in April and will be complete by the end of the year. The WBHO INSITU PIPELINES joint venture is responsible for all construction activities associated with the replacement of the secondary AC Mains.

The work in the CBD is part of the 850 million Rand ($US109.8 million) AC Pipe Replacement Project, which has been underway throughout eThekwini since June 2007 – 2,800 kilometres of burst prone AC pipe, of up to 160 mm in dimension, is being replaced, over a three year period.

Aurecon Lead Program Manager for project managers Jochen Dedekind says that existing AC pipes are cracked open using a pneumatic hammer and hydrostatic winch. This process fractures the pipes from inside using a pipe cracking head. New HDPE pipe is then drawn into place behind the cracking device.

“To date 2.5 kilometres of new pipe has been laid in the CBD,” says eThekwini Project Executive Alan Kee.

“We decided to use Trenchless Technology because this method is quicker than the traditional method. Other advantages include less surface disruption, with the only excavations being entry and exit points and tie-ins for buildings. Restoration costs are minimised as are disruptions to traffic and pedestrians, in this busy area.”

In addition, the HDPE piping being used is flexible and will be laid in exactly the same place as the old pipeline. This means that there is less chance of damaging existing communication services such as Telkom and Eskom cables. HDPE piping has a 50 year life span and is laid in continuous lengths, without couplings, minimising the possibility of leaks.

The municipality is aware of the challenges of working in the CBD. Every effort is being made to ensure that disruptions to water supply are well advertised and where possible done outside of working hours. The posters bear the distinctive AC Pipe logo and are prominently displayed 48 hours before a water cut. Flyers advising of water cuts are distributed to affected buildings and residences, by project community liaison officers.

Safety is another primary project concern. Traffic control is strictly applied in areas where work on the AC project is in progress. The affected area is demarcated using traffic cones and delineators. Traffic is directed by flagmen, clad in white overalls and orange safety vests for increased visibility. Open excavations are barricaded with orange safety netting.

“We are satisfied with the way the project is progressing, especially in terms of social deliverables. Local labour is being used on all project sites and businesses within the communities where we work also benefit.”

“80 kilometres of pipe is being laid throughout eThekwini each month. This means that we are on track for our June 2010 completion date,” says Mr Kee.

The towing head attached to the winch that pulls the HDPE pipe through the old asbestos water pipes. Themba Maredi removes the 700 mm rods as the pipe is drawn through.

A team effort

Before the construction commenced, investigations had to take place for design purposes. GOBA Consulting Engineers and Project Managers were responsible for the principal design of the works based on information gathered by the contractor during the proving stages.

The contractor, the WBHO IPL joint venture, was responsible for all construction completed activities including:

* Excavation at predetermined positions to determine the pipeline material used as only the AC pipe needed to be replaced. * A physical inspection, along the route of the affected mains, was carried out to establish all connections made to the line being replaced. * Excavation at predetermined positions to determine the primary main dimensions. * Excavation at predetermined positions – 48 metre intervals – shut off the valves and cut the pipe for inserting the CCTV camera. * After the recording of the CCTV was complete, the AC mains were repaired and backfilled.

Replacement of watermains

Once all the preliminary activities for the replacement of the AC mains were completed; rehabilitation of the identified mains commenced.

The construction team then excavated, by hand, to fully expose the underground connections on the pipeline to be replaced, removed all connections to the pipeline and disposed of them, then excavated for the launch pit and the receiving pit either end of the pipeline.

In order to replace the AC watermains the team then positioned the winch of the pipe cracking machine in the receiving pit and pushed the connection rods through to the launch pit side. Following this the team attached the cracking head, the expander, as well as the new HDPE pipe to the rods (at the launch pit) and pull the head and pipe back towards the winch.

As the HDPE pipe coil length is 80 metres, if the pipeline to be replaced is longer than this, the next coil is butt welded to the end of the coil being pulled into position.

Once all the connections to the replaced secondary mains are made, the line was connected to the primary main.