Thousands of cubic metres worth of grout will be injected into abandoned mine voids under the Newcastle Art Gallery site, before the facility's $40 million expansion takes place.
Fencing was erected this week and a specialist drill rig installed at the site, ready for the work to begin.
The Newcastle Herald reported previously that the work was initially expected to start in June but wet weather in recent months caused a delay.
Newcastle lord mayor Nuatali Nelmes said it was a crucial step to ensure the safety of the area ahead of the main expansion project, which is expected to begin in mid-2023. Shortlisted applicants from the expression of interest process will be invited to tender for the main construction job later this year.
Cr Nelmes said the expansion, which would double the size of the gallery, was 16 years in the making.
"Newcastle's long coal mining heritage means that much of the city centre sits on top of a number of historical underground mine workings, which date back as far as the early 1800s," she said.
"Remediating these coal seams in the early stages of this project will ensure the long-term stability and protection of the expanded art gallery and its nationally significant $126 million collection, which has been relocated into secure off-site storage for the duration of the work."
The remediation is expected to be completed in the first half of 2023, subject to weather, and will target the 6.5 metre thick Borehole coal seam - which sits about 75 metres below ground - and the one metre thick Dudley coal seam - about 27 metres under the surface.
More than 100 bores will be drilled throughout the site to allow about 15,000 cubic metres of grout to be injected into the seams.
State government funding will help the council pay for the mine remediation work.
The gallery expansion is expected to create an extra 1600 square metres of space to display the city's collection on the lower level and temporary exhibitions upstairs.
A new cafe, retail store, multi-purpose and educational program space and secure loading dock will also be included.
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