EXPLAINED: Why repaired sinkholes reappear and how to fix them correctly the first time

The Johannesburg Roads Agency (JRA) has yet to repair a massive sinkhole on Loch Avenue in Parktown and the hole is growing in size.

A geotechnical engineering senior lecturer at Stellenbosch University, Dr Talia da Silva Burke, said if sinkholes are left open for an extended time, the sidewalls start collapsing and the void will ncrease in size as material washes away and falls into the hole.

This has been the case with the sinkhole on Loch Avenue, which started about a year ago as a small hole on the side of the road close to Alison Gaylard's property. The JRA previously filled the hole but it returned. Since then it has expanded to block most of her driveway.

After TimesLIVE Premium's report on the sinkhole in February, and the promise the issue would be escalated for repair, Gaylard's family continue to battle to access their home.

"It's worse. It's bigger and growing more tricky getting in and out. I scraped my car last week. It's very scary. People drive past and can't believe what they're seeing," she said.

It is negatively impacting their lives, Gaylard said.

"Not only can we not have visitors because of the risk factor, we can only use one part of our driveway with lots of maneuvering, and our pavement is being destroyed."

The JRA said the sinkhole was about 5m x 1m x 1.5m when it was reported. However, the extent of the damage to the masonry stormwater channel necessitated an excavation of 10m x 3m x 2.5m.

Da Silva Burke said sinkholes like this can be caused by leaking pipelines, either bulk water, sewer or stormwater networks.

It is important for the full extent of the collapsed void and any remaining underground voids to be identified so the repair can be properly completed. Where appropriate, grouting of the remaining underground void spaces can be used to ensure pathways for underground water erosion are plugged
— Dr Talia da Silva Burke, geotechnical engineering senior lecturer at Stellenbosch University

She said the water erodes the soil supporting the road, forming an underground cavity that eventually collapses once the cavity becomes big enough and the road surface cannot support itself over the void.

To repair it properly and ensure it doesn't reoccur a few months later, the cause of the sinkhole needs to be identified and fixed before the void can be filled.

"If the source of the water leak is not adequately repaired, it is likely the sinkhole will reappear or new sinkholes will form in the area," she said.

When repairing sinkholes, the collapsed material needs to be removed, and the void needs to be refilled in compacted layers that are constructed to the same standards and specifications used in the construction of the road.

"It is important for the full extent of the collapsed void and any remaining underground voids to be identified so the repair can be properly completed.

"Where appropriate, grouting of the remaining underground void spaces can be used to ensure pathways for underground water erosion are plugged," said Da Silva Burke.

JRA said it has identified 48 sinkholes across six regions in the city. The repair cost of the Loch Avenue sinkhole would only be established once repairs are completed, it said. The entity expected to work on it in the week of February 24. It has not explained why the repair has not been done.