MEDIA RELEASE
SANRAL CEO leads site visit to the newly completed N1 sinkhole in Centurion
From right: SANRAL CEO Reginald Demana with Design and Construction Manager, Tsakane Mathebula, during the site inspection of the N1 sinkhole in Centurion, Gauteng.
Pretoria, 13 December 2023 – The South African National Roads Agency SOC Limited (SANRAL) has announced that construction to repair the sinkhole on the N1 near the Flying Saucer Interchange in Centurion has been completed, easing the flow of heavy traffic ahead of the festive season.
The repairs to the sinkhole on the N1 come shortly after another sinkhole on the nearby R21 was completed last month. The total cost of repairs to the two sinkholes was R424 million, with R280 million spent on the N1 and R144 million on the R21, respectively.
SANRAL CEO Reginald Demana said the N1 sinkhole project, which started in September 2023, was 99.9% complete and commended the construction team for working hard to ensure all lanes were open on the N1 in both directions between Pretoria and Centurion.
Speaking alongside the N1 during a site visit to the construction site, Demana said: “We have good news for motorists travelling on the N1, especially at the start of the Reconciliation Day long weekend and, of course, ahead of the festive season.
There was a massive sinkhole cavity underground along the N1 between Pretoria and Centurion, which caused significant damage to the road.
“Given the importance of the N1 and R21 to the economy of Pretoria, South Africa’s Capital city, the construction work undertaken here was very important. The Flying Saucer is a major interchange, which connects the N1 and R21, so it was critically important to ensure we minimised congestion in morning and afternoon peak traffic.
“One of our major concerns here was the extent of the damage due to the rains at the end of 2021 and early in 2022, and whether the sinkhole might extend further under the N1, which could have led to a total collapse of the road.
“For SANRAL, the repair of this sinkhole is a major achievement, especially with the peak traffic expected ahead of this long weekend and the peak festive season traffic on this key route to the northern parts of South Africa. I’m very happy that today it is 99.9% complete. The sinkhole has been rehabilitated and a wall built to ensure the road will stand the test of time.
“I have inspected the site today along with some of our executive team and I am very excited that they have managed and completed this project successfully, especially the quality of work and the fact that they were able to accelerate the work to get it done ahead of the festive season peak traffic,” said Demana.
Regarding the management of traffic during construction over the last 15 months, Demana said: “We are impressed that the team managed to repair both the southbound and northbound lanes without having to stop traffic. One of the critical things we said to the team was, ‘whatever happens, the road must remain open at all times’.
He added, “Although there were constraints at certain times where we had to reduce the number of lanes from four to two, we are now complete and that is why we are here today to witness that for ourselves.”
Demana congratulated the SANRAL Northern Region engineering team, the Zutari engineering consultants team and JODAN construction team for their work on the project.
“This was a very complex piece of geotechnical work. Pretoria is a dolomitic area so when it rains a lot, sinkholes develop in certain parts of the city and this was one such case,” he said.
“The sinkhole led to depressions of sections of the N1 and cracks developing on the entire route, so we immediately took measures to assess the damage and start the repair work. With sinkholes you never know the extent of the damage until you start excavating and drilling holes and piling in with concrete.”
SANRAL was made aware of the sinkhole along the N1 in Centurion at the beginning of January 2022. To prioritise the safety of road users, SANRAL immediately closed off the affected lanes and redirected traffic.
Demana said SANRAL deployed a team of specialist engineers to work on the project. “It took some time to start the project, mainly due to extensive research to find the best solution to fix the problem. Natural phenomena such as sinkholes are difficult to prevent because they are mostly unexpected. However, through state-of-the-art technology, SANRAL engineers were able to pre-emptively diagnose, assess and then provide the correct remedy.”
The newly rehabilitated N1 sinkhole situated near the Flying Saucer Interchange in Centurion.
The scope of works for the project included:
• Stabilisation of the area for works to begin using dynamic compaction
• Installation of an 83m long by 15m deep piled and anchored retaining wall in the carriageway
• Excavation of 27 000m3 of material from the sinkhole area
• Stabilisation of the sinkhole with 4 500m3 of grout and several layers of geogrids
• Backfill of the affected sinkhole area with 28 000m3 of crushed material
• Compaction grouting of the surround area with 18 000m3 of grout pumped into 27km of drilled and cased holes
• Replacement of all layer works directly around the sinkhole
• Replacement of all base and surfacing layers in the surrounding area
• Drainage works
As part of the roads agency’s empowerment policies, close to R50 million was allocated to targeted enterprises. A further R3.2 million was spent on targeted labour for locals.
Employment breakdown
Click on link for audio to the story: SANRAL CEO visit to N1 Sinkhole
ALL YOU NEED TO KNOW ABOUT SINKHOLES
What is a sinkhole?
A sinkhole is a depression in the ground that has no natural external surface drainage. This simply means that when it rains, all the water stays inside the sinkhole and typically drains into the subsurface.
Where do they occur?
Sinkholes can appear anywhere, usually in karst terrain where the types of rocks below the land surface can be naturally dissolved by groundwater circulating through them. When water from rainfall moves down through the soil, these types of rock begin to dissolve, creating underground spaces and caves. The land around the affected areas often stays intact for a period until the underground spaces get too big, and if there is not enough support for the land above the spaces, a sudden collapse occurs.
Can sinkholes spread?
Although some may be big enough to swallow entire buildings, sinkholes do not spread beyond the area where the bedrock is eroded.
Can a sinkhole be repaired?
Once a sinkhole is discovered and examined, the repair method depends on the size, stability, location, geological context and its immediate cause. Generally, a hole that’s very small and stable in an open area can simply be filled with dirt and restored with ground cover.
//Ends
Issued by FTI Consulting on behalf of SANRAL. For editorial content or additional information contact: Lwando Mahlasela on 082 440 5305 or pressoffice@nra.co.za