Construction of the Gauteng Nerve Centre (GNC), which will control all commuter rail traffic in Gauteng, is well under way, with the roof scheduled for completion next month.

The centre is located in Kaalfontein, near Kempton Park, in Johannesburg.

Multidisciplined turnkey rail engineering company Mehleketo director David van der Merwe notes that about eleven 25 m lattice trusses will be used in the construction of the roof, which started earlier this month.

Electronics and electrical engineering group Siemens Southern Africa infrastructure and cities senior project manager Lucio Lefebvre adds that construction of the offices and the GNC crisis centre is also well under way.

The power transformer and the medium- and low-voltage switchgears have also been installed in the nearby service building, which will also house two 800 kVA rotary uninterrupted power supplies (UPSes).

“The UPSes will be powered by two V16 Cummins diesel engines, which have been delivered to our supplier, diesel generator supplier Diesel Electric Services, by the Belgium manufacturer Euro-Diesel,” Lefebvre says, adding that the UPSes were tested in Europe in February.

There have been several delays to construction of the GNC, as three separate sites, owned by State-owned commuter rail operator the Passenger Rail Association of South Africa (Prasa), had to be consolidated.

More delays followed after an environmental- impact study by consulting engineering firm MottMacDonald PDNA had been concluded and approved in December 2011. It was found that there were high levels of dolomite in the soil of the construction site, which has strict legislative requirements concerning construction and water drainage methods.

Dolomite dissolves when exposed to water and combined with carbon dioxide, resulting in sinkholes.

Mehleketo director Niren Singh notes that an independent dolomite specialist, as well as geological, geophysical and palaeontological research organisation the Council for Geoscience had to be contracted to assist in resolving the problem.

“The project’s foundations had to be changed from normal foundations to raft foundations,” he explains, adding that the dolomite issue was the most significant engineering hurdle in the project to date.

Singh notes that dynamic impact compaction methods were employed to address the poor soil conditions encountered, which resulted in certain areas achieving a soil subsidence of up to 600 mm. These areas required additional backfilling as a result.

He highlights that the dolomite conditions also affected other facets of the project, including the structural design of the building and the subsurface drainage, water and wastewater systems.

Following the successful compaction of the soil, first concrete was poured in October 2013.

The GNC forms part of Prasa’s national resignalling project, with Siemens being the lead contractor for the Gauteng portion of the project. Gauteng holds 60% of Prasa’s rail infrastructure assets.

Lefebvre notes that Midway station, in Soweto, and Lenz station, in Lenasia, are currently in the testing phase. Siemens and independent tester consulting engineering firm Hatch Goba are conducting testing of the signalling at the two stations.

“Towards the end of June, all the equipment will go to site, which will be followed by final on-site testing. Once the safety validation for the software has been completed, we will proceed with installing it at the two stations.”

He notes that the Gauteng resignalling project comprises two projects, Gauteng Phase 1 and Phase 2, which, once completed, will result in eight sites being transformed into centralised satellite traffic control (CTC) centres. The CTC centres will be responsible for rail traffic within the surrounding areas of a given station.

“These satellite CTC centres will come into operation during various phases of the project and will be transferred to the GNC in a phased approach once each satellite CTC centre is complete,” Lefebvre explains.

For business continuity, should the GNC for some reason not be able to operate, control can be reverted back to the satellite CTC centres in order to maintain operation of the train service.

The first CTC centre, Midway station, is scheduled for completion in April next year, with the final CTC centre scheduled for completion near the end of the resignalling project, in October 2018.

Lefebvre notes that outdoor signalling work is currently under way at nine different stations, five of which will soon be completed following the connection of all the necessary electronic interlocking. Outdoor work includes trenching, recabling, installation of signalling, axle counters, points machines, overhead track electrification and track works.

He notes that points machines are currently installed at only two sites because changing the points machines too soon could impact on rail operations, as these would need to interface with existing interlockings.

Singh adds that installing new signalling while keeping train services running is particularly challenging, as extensive preparation and planning are required to change the system while lowering the impact on train operations.

“There are also safety aspects involved, as Prasa needs to maintain the integrity of its services while the signalling is being changed. This requires a lot of additional staff to perform manual operations, which will be ongoing for the duration of the project,” Lefebvre concludes.