The immediate damage caused by the sink hole in Oxford Road has been repaired, and the integrity of the Gautrain tunnels "has been maintained".

The sinkhole that appeared along Oxford Road filled with water very quickly

OXFORD Road should be re-opened to traffic in a week's time, after a substantial sinkhole appeared in the road this week, say Gautrain officials.

A huge hole - 12 metres by 7 metres in size - formed on Tuesday, 8 July, just 12 metres above the tunnel boring machine (TBM), which is creating a tunnel to Park Station in the CBD, for the Gautrain.

But officials were confident that the road would be repaired and open to traffic by next week. The hole appeared about 1.30pm between North Close and 8th Avenue, and traffic is being diverted along 11th Avenue and Riviera Road.

Provincial MEC for transport Ignatius Jacobs said: "We were very happy that there was no loss of life or injury. We wish to apologise to residents in the area for any inconvenience caused."

He said that the immediate damage had been repaired, and that "the integrity of our tunnels has been maintained".

It had been noticed that more soil than normal was being processed by the TBM while boring, which is "symptomatic of a void being formed above the TBM". A cavity above the machine's cutter head was detected, and it was switched off. The cavity appears to have been formed by water seepage from service pipes.

The road was cordoned off as a precaution in the morning, while monitoring continued. When the sinkhole appeared the water mains burst, causing the initial hole of 6 metres by 4 metres rapidly to grow to 12 metres by 7 metres, as the water washed the soil into the tunnel.

Water seepage
"Preliminary investigations carried out by Bombela after the event suggests that water seepage from the utilities above the tunnel alignment led to a weakening of the soil being excavated, causing ground loss directly above the TBM," says a Gautrain statement.

The pavement, a street pole and the garden wall of a nearby house collapsed when the sinkhole developed.

The TBM is being used because the ground along Oxford Road is "a mixed zone of soil, with very soft ground and very strong rocks".

Joburg's emergency management services was alerted and the area was made safe. Work continued throughout the night, with a level of gravel laid down to cushion a 1m thick layer of concrete. The hole has been completely covered, but there is access on the pavement for the City to repairs the service pipes.

"I can't stress enough: the different soil conditions make the ground unstable, particularly in contact with water," said Chris Andrews, the civil construction director of Bombela, the turnkey contractor for the Gautrain.

There were procedures in place to ensure that incidents like these did not happen; but when they did contingency plans kicked in immediately. "Hourly and daily monitoring will continue," he added.

Jack van der Merwe, the chief executive of the Gautrain Management Agency, said that cameras would be sent down water and sewer pipes to assess whether there were any further seepage problems.

The Department of Minerals and Energy will be the final authority on when drilling can resume along Oxford Road.

In all, 15 kilometres of tunnels will be dug under the suburbs of Joburg for the 80km railway line. So far 7,5 kilometres of tunnels have been excavated, at 10 tunnelling sites. The sinkhole appeared some 617 metres from the Rosebank Station site. Work on the Gautrain is ongoing at 50 sites.

First trains
Meanwhile, also on Tuesday, the first four-car train set was handed over to Gauteng Premier Mbhazima Shilowa at the Bombardier assembly plant, in Derby, England.

"Bearing the pride of the nation, Gautrain has reached a major milestone in its delivery of world-class public transport to South Africa," Shilowa said.

The stock of 96 rail cars is based on the Bombardier Electrostar series, known for its "state-of-the-art technology and reliable, high performance standards". The cars are made of lightweight aluminium, chosen for "increased energy efficiency and reduced maintenance requirements".

Canadian company Bombardier is a 17 percent shareholder in the Bombela Concession Company, which holds a 20-year concession agreement with the Gauteng government, based on the public private partnership to design, build, operate and maintain the Gautrain.

The Gautrain will be supplemented with a fleet of 125 buses, enabling it to transport more than 100 000 passengers each day in each direction between Johannesburg and Tshwane.

More information can be obtained from the Gautrain website or from the Gautrain toll free number 0800 Gautrain (0800 428 87246).

Related stories:

• Oxford Road collapse
• Gautrain will 'make electricity'
• Gautrain rock arrives for duty