Mine subsidence assessments and review of selected grouting remediation projects in the Newcastle area

Widespread mining has been undertaken beneath developed areas of Newcastle and it’s surrounds since the early 1800s, and continues to the present day.

Local geotechnical consultants are regularly asked to assess the risk of mine subsidence for proposed developments, and to provide ‘worst credible case’ subsidence parameters in the event of a future subsidence event. Where the risk of subsidence is considered too high for the proposed structure, ground improvement is usually adopted which includes remedial grouting works, in order to limit the risk of future subsidence to acceptable levels.

The uncertainties associated with grouting of the old mine workings beneath sites in and around Newcastle has in the past been seen as a big risk for prospective developers, with the potential for expensive overruns associated with grout volumes making them reluctant to commit to developments underlain by mine workings. The introduction of a Government backed Newcastle Mines Grouting Fund has now provided a safety net to developers in the event that grout costs are more than anticipated. This safety net has provided developers and financiers more confidence to proceed with developments, but the need to understand the likely quantities of grout required to remediate sites continues to be an important consideration for both Government and developers alike.

This paper presents data for numerous local projects where remedial grouting works have been undertaken for large developments. Common methods of investigation and assessment of the condition of the mine workings are discussed. The focus of the paper, however, was to compare the volume of grout required to remediate selected projects with knowledge of the mine conditions to develop an empirical approach to evaluate the quantities of grout for future projects in the Newcastle Coalfields.