Bad news about N1 sinkhole

A large sinkhole next to the N1 in Centurion is now only expected to be fully repaired over three years after it formed, adding further frustration for many motorists.

The sinkhole appeared on the eastern side of the N1 southbound, near the Flying Saucer intersection with the R21, following heavy rain and flooding in January 2022.

To prevent the adjacent area from further collapse, the South African National Roads Agency (Sanral) was forced to close several car lanes, causing a traffic bottleneck during peak commuting hours.

Sanral reconfigured the lane layouts to accommodate the large volumes of cars using the road daily, including those of working residents of Pretoria who have offices in Johannesburg.

The closures have reduced the number of lanes on the main highway and offramp originating from the R21.

The location also makes it more difficult for motorists from the R21 northbound carriageway to enter the N1 south at speed.

The closed lanes cause a deviation from a normal gradual merge over a longer distance into a sharper and shorter entry into the N1.

The impacted part of the N1 shortly after the sinkhole formed in 2022.

Sanral told MyBroadband that the hole is only expected to be fully rehabilitated by the second quarter of 2025. Earlier this year, the agency said the estimated completion date was May 2024.

Both these timelines were far less optimistic than Sanral representatives’s early estimates that fixing could take four to six months.

In addition to an extensive investigation and rehabilitation of the area involving the Council for Geoscience in the first year following the collapse, the repair works by Jodan Construction have also encountered sophisticated challenges.

Sanral said that during project execution, the complex work required on the piling and soil anchoring proved to be difficult to complete due to the area’s potentially unstable sinkhole, worsened by additional rainfall during the summer.

“As a result, the engineering team focused on ensuring that workers remained safe during the execution of this work, and they paid special regard to ensuring that the sinkhole area remained stable while heavy machinery was in use.”

“This approach reduced the risk of further sinkhole collapse.”

Sanral said the piling work and soil anchoring had since been completed, and the appointed contractor was focusing on rebuilding the excavated layers.

The agency listed several steps taken by the contractor to ensure long-term stability after the repairs, including:

  • Drilling 278 holes and pumping grout into them.
  • Installed 55 no. 0.610m diameter piles, which are, on average, 25m deep.
  • Installing 161 no. 52/26 self-drilling anchors and a retaining wall

Sanral said although the entire project was now only estimated to be completed by Q2 2025, it was accelerating the work to ensure all lanes on the N1 were fully operational by the end of 2024.

The agency also previously revealed that the project cost was around R280 million.

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Bad news about N1 sinkhole