Margaret Street sinkhole update

The City of Mount Gambier is working with a local concreter to fill the sinkhole in the walkway between Margaret Street and the Railway Lands.

The cavity first appeared when the bitumen collapsed following heavy rain in June last year. Since then, an independent geotechnical investigation has been undertaken by engineering consultants, providing recommendations to fill the void that has a footprint of about 30 square metres.

City of Mount Gambier city infrastructure general manager Barbara Cernovskis said due diligence on this solution had taken some time.

“Following independent advice, we are filling the cavity with stabilised sand, a mixture of soil and four to six per cent concrete,” she said.

Site access in the vicinity of the sinkhole on Margaret Street is limited and a traffic management plan is in place during the drilling and filling process.

Heavy machinery was on site on January 17 to drill down to the void, which was identified using a camera and a torch lowered down on a rope at two locations.

“We have now filled the augured holes with concrete which is an extra wet mix so it flowed into the voids in the underground cavity.” Ms Cernovskis said. “We built up the base of the sinkhole with 30 cubic metres of stabilised sand to 2.5 metres below ground level. The filled material will now be left to set.

This week work continued with the addition of 90 cubic metres of engineered fill, similar to road fill material and then reseal the top so the walkway surface is reinstated.

“We are confident that once works to stablilise the site are complete, it will be safe to return the thoroughfare to the community,” Ms Cernovskis said.

Walkway access to the Railway Lands will be reviewed once the work is complete. Council continues to work with adjoining property owners to ensure safety within the vicinity of the impacted area.

“We will install a crack monitoring system on the wall of the neighbouring business to monitor any further ground movement or settlement during the next 12 months,” Ms Cernovskis said.

Total remediation work costs for the project are sitting at approximately $160,000.