Remnant mine workings are a legacy of localised mining activity. The mystery of mine void hazards has continued to challenge project feasibility for property development as subsidence risk and the associated remediation costs remain un-quantified.

But therein lies the opportunity. Do the voids beneath the city really matter?

It’s a million dollar question – and we might just have the answer.

Effective in-ground solutions

Infrastructure development in Newcastle has faltered recently due to cost uncertainty for underground mine void rectification. Risk from potential instability is low, but it can be quantified.Risk will be greater for larger and high rise developments that have a greater susceptibility to damage as they can tolerate less movement. Workings can become unstable if localised ground conditions change.

Rational ground modelling enables us to quantify the risks. Geology, geological development and mining history studies are merged with clever geotechnical evaluation to present innovative, costed solutions for planning application.

The solution

One remediation strategy is to fully grout mine workings within the zone of influence, which can cost millions. For these development projects to remain viable, finding other methods to reduce remediation costs is essential.

Voids underneath the city aren’t always an issue if we focus on the capacity of the overlying geology and pillars rather than the void space. Above the workings is generally a 20m thick sandstone layer that acts as a beam to distribute loads. And parts of the city are known to have large barriers of unmined coal.

Along the northern side of the NeW Space site exists one such barrier.

Coffey was engaged by the University of Newcastle to undertake geotechnical mine subsidence and environmental assessment for their NeW Space Development.

To assess the risk of a mine collapse on the development we developed a model in FLAC3D. This utilised finite difference methods to model the effect of the overlying strata, and then modelled the failure potential under various loading conditions.

Our assessment provided the Mine Subsidence Board with enough confidence to approve the mine rectification works for the NeW Space development. This was based on the grouting of one heading along the south western boundary of the site, allowing the sandstone layer to span to the edge of the workings.

How we can help

We can model the ground and provide an understanding of its behaviour. We can justify the case for cost effective, pinpointed remediation that offers huge savings in comparison to ‘traditional’ grouting, and we complement this with geotechnical investigation, contamination assessment and materials testing.

But the hazard from mine voids can be de-mystified with rational ground modelling that enables risk quantification. Innovative solutions can be priced with certainty, and success can be achieved in the development application process.

Effective management of in-ground risks such as mine subsidence, contamination and minimising soil waste can help save your time and your budget.

Modelling and remediation of mine subsidence – it’s just part of Coffey’s urban renewal consultancy service offering.

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