A sinkhole approximately 8 meters wide and 5 meters deep appeared at AJ Burkitt Oval in Heidelberg, Melbourne, on Tuesday. This event prompted discussion regarding the formation, detection, and repair of sinkholes.
Sinkhole Formation
Sinkholes develop from subsurface cavities that can form over periods ranging from years to centuries due to factors such as erosion and human activity. A surface layer initially covers these cavities; collapse occurs when this layer weakens sufficiently.
Causes of sinkhole formation include:
- Suffosion: A chemical process where groundwater dissolves carbonate rocks like limestone, creating underground voids over thousands of years. The ancient limestone sinkholes in Mount Gambier, South Australia, exemplify this process.
- Soil Liquefaction: Rapid sinkhole formation can occur when excessive water saturation weakens soil, leading to collapse. Flowing groundwater can also transport soil particles, forming subsurface cavities.
- Infrastructure Failure: Broken stormwater pipes or burst water mains can contribute to sinkhole development. Examples include a sinkhole in Kew in 2020 due to a broken stormwater pipe and a car-swallowing sinkhole in Port Melbourne in 2014 caused by a burst water main.
- Human Activity: Excavation and construction, particularly tunneling, can induce sinkholes in water-weakened soil. Tunnel boring operations near Heidelberg are considered a likely factor in the recent sinkhole. Similarly, tunneling through saturated sandy soil at the Snowy 2.0 project in 2023 caused a sinkhole, halting work.
- Disused Mineshafts: In areas like Ballarat, which contain old mineshafts, sinkholes are a recurrent phenomenon, as evidenced by a 2007 incident in Ballarat East.
Detection Challenges
Detecting sinkholes before they collapse is challenging because subsurface cavities are hidden. Francois Guillard, a senior lecturer in geotechnical engineering at the University of Sydney, notes that predicting sinkhole formation is difficult because it requires assessing underground soil conditions, which are hard to determine broadly.
Current detection methods include soil sampling, satellite imagery analysis, and seismic wave analysis to identify subsurface weaknesses. While localized assessments are possible, broad-area modeling remains a challenge, and research efforts are ongoing to improve these tools. A sinkhole in Tokyo in January 2025 illustrates the impact of such events.
Remediation
Sinkhole remediation typically involves filling the cavity, often with materials such as resins or concrete, to stabilize the soil. Dr. Guillard emphasizes that identifying and addressing the root cause, particularly controlling underground water flow and drainage, is crucial to prevent recurrence. Repair work for the Heidelberg sinkhole is scheduled.