The "Ballroom" of Dread: A Tragic Tale of Underground Failure

Whenever I come across underground development called a “ballroom” it gives me an instant feeling of dread.

Especially when there are mined out voids surrounding it.

Especially when it’s in the upper levels of the mine.

Especially when the groundwater is highly corrosive.

Especially when the ground support was installed in the previous decade.

Especially when there’s a plan to go back in.

This article will explain why.

This article will explain how two people met their deaths as a result of all these factors.

The Coroner’s Inquests Touching the Deaths of Jarrod Keith Jones, Matthew David Lister and Sidney Thomas Pearce heard that in 2001, two miners tragically lost their lives in just such a "ballroom." The ground support, consisting of cablebolts and chemical bolts, had been installed seven years prior. While the area saw occasional scaling, a critical, unknown factor was at play: highly corrosive groundwater. Despite no previous incidents of fully grouted cable bolt corrosion at the mine, this hidden threat was silently at work. Geotechnical assessments of existing travelways weren't common practice then.

The incident itself was swift and devastating. As the two victims were scaling the drive, a 117m³, 450-tonne wedge of ore suddenly released from the roof. Investigations revealed that while the cable bolts were long enough to anchor the wedge, severe localised corrosion had drastically reduced their tensile strength. A change in local stress from adjacent mining had cracked the grout, allowing acidic water to corrode the bolts, rendering them almost useless. The low-stress environment meant minimal lateral compression, turning the wedge into a dead weight on the compromised cablebolts.

The Coroner's findings highlighted systemic failures: a lack of coordination in checking re-entry areas, no formal systems for assessing these areas (especially for geotechnical review or updating to new ground support guidelines), inadequate record-keeping, and a general breakdown in communication. While the Coroner concluded the rock fall likely couldn't have been "reasonably anticipated" by the mine owner, this tragic case serves as a stark reminder of what can materialise when a systemic approach to accessing previously worked areas is absent.