Client name: JML Group

Duration: June 2014 - February 2016

Location: Newcastle, NSW, Australia

Coffey developed and supervised an innovative and cost-effective grouting strategy, which used less than 50% of the grout previously assessed whilst reducing residual movement predicted for the development.

Proposed high-rise development above old mine-site was cause for concern

Once constructed, Icon Central will be Newcastle’s highest development to date rising 18 storeys. This development is positioned over mine workings at a depth of 70m. 

Mine workings within the Borehole Seam have historically hindered the development of sites within Newcastle. Development above five stories generally requires grouting of large portions of the mine workings before the Mine Subsidence Board would give approval.

Historically grouting was only carried out under the site. This allowed significant residual movement to still be possible at the boundaries.

3-D modelling to find the solution

Using FLAC3D, a three-dimensional explicit finite-difference program, Coffey was able to demonstrate remaining coal pillars under the site could resist collapse providing barrier grout locations were installed around the site. 

Innovative and cost-effective grouting strategy

Coffey was able to demonstrate the rock overburden could span approximately 50m to 70m. This allowed the grout barriers to be located away from the building, ensuring the pillars under the site would always remain in their elastic range, reducing the residual movements the building would need to be designed, while also reducing the cost of grouting work.

After completing the assessment, Coffey carried out supervision work of the grouting work completed allowing Coffey to verify the mine workings were as drawn on record tracing (survey of mine workings) and that the workings were grouted as proposed by Coffey. 

This work was approved by the Mine Subsidence Board with construction now underway.