Massive R21 sinkholes repair cost revealed

It will cost over R144 million to repair two large sinkholes that formed next to the R21 highway just after the Olifantsfontein interchange in Gauteng in February 2022.

The South African National Roads Agency (Sanral) revealed the figure in recent feedback to MyBroadband on progress about fixing the sinkholes, which formed after heavy downpours and flooding.

The sinkholes’ proximity to the road forced the closure of multiple lanes on the R21 northbound toward and one of the R21 offramps to avoid potential further collapse.

That has resulted in a bottleneck of traffic during peak commuting periods, with Sanral advising motorists to use alternative routes such as the M18 and M57, which run parallel to the west of the R21.

Their appearance came just a month after another large sinkhole formed next the N1 highway and R21 offramp northbound.

The screenshot below from Google Maps shows the typical traffic flow that section of the highway experiences from around 07:00 on a weekday.

The section of highway affected by the sinkhole is maintained by Sanral, which is a state-owned agency funded through toll fees and allocations from the National Treasury.

It has now been nearly two years since the sinkhole formed.

In addition to revealing the total amount of R144,245,942.80 that will be spent on the repairs, Sanral also said the estimated completion date for the project was August 2024.

Sanral Northern Region project manager Oakley van Eyk said a joint venture between Raubex and Esor was fixing the sinkhole and started their work in December 2023.

Van Eyk explained that fixing a sinkhole in an area underlain with dolomitic rock — and a large portion of the adjacent highway — presented a complex engineering problem.

The impacted area falls within a large dolomite area that is highly susceptible to sinkholes.

Over time, rainwater and groundwater can dissolve dolomite as it flows through joints and fractures in the rock.

This creates underground cave systems and voids, which makes the surface above unstable and prone to movement or collapse.

This Google Maps satellite view shows the location of the two sinkholes next to the R21 northbound carriageway. Credit: Imagery ©2024 Airbus, CNES/Airbus, Maxar Technologies, Map data ©2024

Before the rehabilitation of the sinkhole could begin, experts had to be brought in to assess the situation.

Van Eyk said a specialist geotechnical engineering company, Jones & Wagener, was appointed to investigate the sinkhole.

“Subsequently, geophysical testing and extensive percussion drilling had to be conducted to establish the extent of the poor dolomitic conditions and provide input into the design of remedial measures,” he said.

“Thereafter, results from the various testing procedures had to be interpreted and remedial actions formulated through a formal design process to ensure the design was both technically appropriate and the most cost-effective solution.”

Van Eyk said another major issue in the project has been limited access due to power lines running through this section of the R21.

Sanral again warned that road users should expect traffic delays and disruptions during the project, as some lanes would be reduced to carry out work.

“To minimise delays, work will also be carried out at night, outside of peak traffic hours, between the hours of 19:00 and 05:00,” Sanral stated.

Editor’s note:

A previous version of this article said that the cost and timelines for completion of the repairs were for the large sinkhole next to the N1.

This was due to an error from Sanral in its original response to MyBroadband and was corrected.

It should be noted that this sinkhole’s repair started in July 2023 and is planned for completion by April 2024.

Sanral previously said this sinkhole’s repair would cost “tens of millions” of rand.

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Massive R21 sinkholes repair cost revealed