Bad news about N1 sinkhole

The large sinkhole that formed next to the N1 in Centurion, Gauteng, is only expected to be completely repaired two years after it first formed.

The sinkhole appeared in January 2022 after heavy rain and flooding hammered the dolomite-underlain area.

Since then, the emergency and two left lanes of the N1 southbound have been closed as a safety measure, and to allow for initial steps in the rehabilitation process.

That included gravity survey testing on both the southbound and northbound carriageways to establish the real size of the sinkhole and conducting temporary repairs.

The South African National Roads Agency (Sanral) previously told Top Auto in August 2022 that it had completed these processes and would start the tendering process for the project’s construction phase “soon”.

The agency has now confirmed to MyBroadband that the project was awarded to Jodan Construction (Pty) Ltd on 26 June 2023.

The rehabilitation of the sinkhole officially started on 11 July 2023 and is estimated to take nine months.

Jodan’s website lists several major roadworks projects worth hundreds of millions of rand. However, it does not appear to have been updated since July 2020.

Its most valuable listed contract before that date was worth R131.44 million and involved work at the Rietkuil Coal Loading Facility. It counts Eskom among its major clients.

Section of the N1 that was closed off soon after the sinkhole formed.

Sanral warned that motorists should expect initial disruptions due to lane reconfiguration and temporary traffic barrier placements that will eventually facilitate the start of initial piling operations.

“Some lanes will be kept open to traffic during the contract — outside of temporary lane closures for ad hoc works executions that will be notified in advance, as per the contract.”

While Sanral has adapted the two lanes on the section into three to ease traffic flow, the section’s proximity to an off-ramp from the R21 Flying Saucer Interchange has continued to cause regular traffic pile-ups.

Sanral Northern Region Regional Manager Progress Hlahla advised motorists to be patient during initial traffic disruptions for the first phase of the work and to plan their trips accordingly.

“They should consider alternative routes and use caution when making use of the roads,” said Hlahla.

No comment on costs

Sanral previously estimated the repairs could cost “tens of millions” of rand.

MyBroadband again asked the agency for an estimation of costs for the repair, but the agency did not elaborate on this point.

Sanral worked with the Council for Geosciences (CGS) to fix the hole.

While not a rare phenomenon in South Africa, CGS told MyBroadband it had observed an increase in sinkholes in the past few years.

Although no fatalities were recorded as a direct result of the N1 Centurion sinkhole, several others were to blame for the deaths of an estimated 38 people in the past 50 years.

Roughly 25% of Gauteng is underlain by dolomitic rock, a type of limestone that is particularly susceptible to sinkhole formation.

Sinkholes typically occur for one of two reasons — concentrated water ingress due to leaking underground water and sewerage pipes, stormwater ingress, leaking swimming pools, or extensive groundwater abstraction.

CGS told MyBroadband that the remedial work and duration of appropriate construction and its associated costs would depend on the complexity of the geological profile where the sinkhole formed and the affected infrastructure.

“Generally speaking, the cost is determined by the extent of the area requiring remedial work and the strategic importance of the infrastructure affected or damaged by sinkhole-induced ground movement,” CGS said.

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Bad news about N1 sinkhole