Briswest Precinct 4, Swanbank Ipswich

Briswest Precinct 4 at Swanbank, Ipswich, required comprehensive ground engineering to support industrial development. The site presented complex ground conditions, including abandoned underground mine workings and areas of uncontrolled fill within an open pit.

To address the dual geotechnical challenges, we deployed a two-fold approach: Grout Cone Construction to mitigate underground mine subsidence, and Dynamic Compaction to densify the uncontrolled fill within the open pit area.

Mine Remediation: We utilised cased drilling to reach the base of the mine workings. Each location was assessed via borehole camera before pumping high-strength grout while retrieving the casing to form a structural cone, ensuring direct contact with the mine roof.

Ground Improvement: Dynamic compaction was achieved by dropping a 25t pounder from 20m using a crane on 7m grids. Following compaction, the surface was ironed with a specialised pounder and levelled with a dozer. Final verification was conducted via CPT testing.

The primary challenge involved drilling cased holes within the complex mine environment and ensuring strict adherence to the grout cone design. These were resolved through rigorous QA/QC protocols. For the fill pit, potential variability in soil density was mitigated by conducting extensive dynamic compaction trials in advance to ascertain the exact parameters required for optimal ground improvement.

The project successfully removed the risk of subsidence and sinkholes associated with past mining activities. Furthermore, the dynamic compaction significantly increased the bearing capacity of the uncontrolled fill, allowing the client to proceed with safe, permanent industrial lot development.