Mount Marrow Trial - Mount Marrow, QLD

The Mount Marrow trial investigated abandoned underground mine workings (Caledonian No.3 Colliery) beneath a proposed residential development at 433 and 435 Thagoona Haigslea Road, Queensland. The site sits over a historical bord-and-pillar coal mine, with depths to the seam ranging from 15 to 27 metres below ground level.

DGSA was engaged to perform a field investigation and a grout block construction trial. The primary goal was to assess subsurface conditions—specifically the height of remaining void spaces and the volume of grout required—to determine the viability of full remediation.

Six boreholes were drilled using a dual rotary drill rig. Following drilling, CCTV camera inspections confirmed open void conditions in three boreholes. A trial placement of 6 m³ of 5 MPa readymix grout was conducted at BH4, which accepted the full volume without pressure increase, indicating significant unfilled void space.

The site posed significant risks due to the unknown condition of historical workings and the absence of competent rock cover, which increased subsidence sensitivity. DGSA resolved these uncertainties by executing a targeted drilling and CCTV program that provided the precise field data required to inform future remediation design, including treatment grid spacing and expected grout volumes.

The trial confirmed that the mine workings are predominantly collapsed with significant residual voids. DGSA successfully demonstrated that grout cone construction is a viable treatment methodology for this site, providing Atrio Property with the necessary data to proceed with a comprehensive remediation strategy.