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N1 sinkhole repairs hit massive roadblock

The repairs to the N1 sinkhole in Centurion that formed in January 2022 will take far longer than previously expected following several hiccups during the construction process.

Initially, the South African National Roads Agency (Sanral) optimistically said the sinkhole would be fixed in four to six months – i.e. no later than July 2022.

In May 2023 the hazard was still there, and Sanral subsequently said it will be a thing of the past by April 2024, if all goes according to plan.

Now in May 2024, Sanral confirmed to MyBroadband that all did not go according to plan and that the rehabilitation is only anticipated to be completed in the second quarter of 2025 – approximately three years and three months after the sinkhole first materialised.

The agency previously said that the repairs would cost in the region of R280 million, though it’s unclear whether the additional year of construction will add to this already enormous bill.

Ensuring long-term stability

The N1 sinkhole appeared in the first days of 2022 next to the Flying Saucer Interchange in Centurion following sustained rainfall in the area.

The region in which it formed is fraught with dolomite rock leading to the N1 sinkhole being one of many across the Centurion-Lyttelton-Valhalla area.

Sanral responded to the incident with haste and immediately closed off the affected lane to keep motorists out of harm’s way and repainted the road markings to retain three lanes and keep traffic disruption to a minimum.

However, due to the size of the N1 sinkhole and unfortunate placement thereof – being on one of the nation’s busiest roads where it merges with another freeway – there was no quick fix on the table.

The roads agency approached the Council for Geoscience (CFG) to conduct extensive gravity survey testing across both sides of the freeway and determine the best possible repairs, and thereafter it opened a tender for the remedial work based on CFG’s recommendations.

During this time, Sanral also built a temporary anchored pile retaining wall that allows portions of the road to remain open while the construction takes place.

Jodan Construction was awarded the tender in June 2023 and in short order started construction on-site to meet the estimated repair timeline of nine months.

Soon after this, the remedial work hit a series of roadblocks.

The piling and soil anchoring already proved especially difficult due to the instability of the dolomite-rich area, though the complexity was exacerbated by heavy rainfalls during the first few months of the year.

“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,” said Sanral.

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

To ensure long-term stability, Jodan Construction additionally took the following measures:

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

The good news is that while construction is only expected to cease in Q2 2025, Sanral said that all lanes of the freeway should be open once again by the end of 2024.

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