Sinkholes near Olifantsfontein offramp finally being fixed

Two sinkholes on the northbound side of the R21 close to the Olifantsfontein turnoff in Gauteng have been causing headaches for the past two years. Their appearance in February 2022 led to the closure of traffic lanes, disrupting traffic and causing congestion at peak hours.

Construction to repair the sinkholes has now started, following the award of a tender valued at R144.24 million to a joint venture (JV) comprising JSE-listed construction and engineering group Raubex and former JSE-listed civil engineering and geotechnical construction group Esor.

South African National Roads Agency (Sanral) spokesperson Vusi Mona said this week the tender for the repair of the sinkholes on the R21 was awarded in October 2023 and has a duration of nine months, including a one-month site mobilisation period.

Mona said the project is expected to be completed by the end of August 2024.

“Road users can expect traffic delays and disruptions during the project, as some lanes will be reduced in order to carry out work.

“To minimise delays, work will as far as possible be carried out at night, outside of peak traffic periods, between the hours of 19h00 and 05h00,” he said.

‘Complex engineering challenge’

Explaining why it has taken so long to start work to fix the sinkhole, Mona said fixing these dolomitic sinkholes, and a large portion of adjacent freeway, is a complex engineering challenge, particularly given the limited access due to the power lines that cross this section of the R21.

Mona said a specialist geotechnical engineering company, Jones & Wagener, was appointed to investigate the R21 sinkholes.

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 added.

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.

“As a state-owned company, Sanral has to adhere to instructions from National Treasury in terms of all of its procurement processes,” said Mona.

“As such, following the above, a formal tender process for invited specialist contractors had to be followed, whereby the contractor Raubex Esor joint venture was appointed.”

Mona said the scope of work entails the filling of two sinkholes within Sanral’s road reserve, using grout and soilcrete, as well as the treatment of the surrounding area to mitigate the risk of future sinkholes forming.

He said this would be done by drilling percussion holes in a grid pattern and pumping a low viscosity grout into these holes to form a grout-soil-mattress.

“Approximately 1 400 to 1 500 primary, secondary and tertiary percussion holes are currently expected.

“It is also expected of the contractor to observe high levels of occupational health and safety (OHS) standards, due to the sensitive nature of the work.”

Mona added that a specific challenge with the project is that work will be carried out underneath Eskom’s high voltage transmission and distribution lines.

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He said the contractor therefore has to ensure that the drilling rigs and equipment are within the prescribed Eskom wayleave conditions, which include height specifications.

Tender process

Mona said the Raubex Esor JV was the lowest bidder for the tender.

He said a closed invitation was conducted in terms of Sanral’s policies for emergency procurement.

Five specialist contractors with a Construction Industry Development Board (CIDB) grading of 8CE and higher were invited to tender.

These contractors were selected based on previous experience in handling complex repairs including sinkholes, he said.

“Sinkholes pose a major risk and the strategy is to use experienced contractors to minimise the potential risk to life when working in an area with an active sinkhole.

“At close of tender, three bidders submitted an offer,” he said.

Update on Pretoria’s ‘Flying Saucer’ sinkhole

Repairs to the sinkhole near the Flying Saucer interchange on the N1 in Pretoria are progressing according to schedule and expected to be completed in April.

Mona said work on the project began on 11 July 2023, with a contract duration of nine months.

He said this tender was awarded to Jodan Construction (Pty) Ltd and is valued at about R280 million.

It has taken so long to fix this sinkhole because the rehabilitation work is “highly complex”, but the project is on schedule. “Sanral is assessing the contractor’s performance against the tendered programme.”