The long-term impact of illegal mining is becoming an increasing concern for engineers and infrastructure experts, with warnings that continued underground excavation could threaten roads, buildings and critical public infrastructure across Johannesburg and other parts of South Africa.
Mining specialists say illegal mining extends far beyond criminal activity, describing it as a growing engineering and public safety challenge linked to the country’s extensive mining legacy.
Professor Hennie Grobler, Head of the Department of Mining Engineering and Mine Surveying at the University of Johannesburg, warned that decades-old underground workings are being further destabilised as illegal miners remove support pillars that were intentionally left in place to protect the surface above.
He said some areas have already been extensively undermined, although the full extent of the underground damage remains unknown.
Historic mining areas face growing risks
According to Grobler, Johannesburg’s development has always been closely linked to gold mining, with major transport routes such as Main Reef Road following the historic gold-bearing reef stretching from Springs to Krugersdorp over a distance of approximately 77 kilometres.
Many roads, buildings and public facilities were designed with underground mining excavations in mind, while support pillars were deliberately left untouched to maintain ground stability.
Those remaining pillars, however, are now increasingly becoming targets for illegal miners seeking small quantities of gold.
Grobler explained that these sections were never abandoned because mining companies overlooked valuable resources. Instead, the remaining ore was left in place because extracting it would have been economically inefficient while also compromising the structural support required to protect surface infrastructure.
He stressed that the challenge extends well beyond Johannesburg.
Former mining regions in Mpumalanga, Limpopo and other provinces are experiencing similar problems, with some villages built above historic mining areas now facing potential risks from illegal extraction involving gold, chrome, platinum and coal.
Beneath many of these communities lies an extensive network of fuel pipelines, water infrastructure and sewer systems that rely on stable underground conditions.
Calls for government-led monitoring
Grobler said technology capable of detecting and monitoring illegal underground mining already exists, but implementing large-scale monitoring programmes would require sustained government funding.
Mining companies are unlikely to finance such initiatives unless they directly benefit their own operations, leaving public authorities responsible for protecting broader infrastructure.
He argued that municipalities and national government need to establish comprehensive monitoring systems capable of identifying areas where underground stability is deteriorating before serious damage occurs.
However, he acknowledged that funding remains a major obstacle.
South African municipalities already face significant financial pressure in maintaining existing infrastructure, including routine road repairs, making it difficult to allocate additional resources for sophisticated underground monitoring programmes.
As illegal mining continues to expand across former mining regions, experts warn that protecting underground support structures will become increasingly important for safeguarding roads, bridges, pipelines and residential communities.
They argue that stronger enforcement, improved monitoring and coordinated government intervention will be essential to prevent mining-related legacy risks from developing into larger infrastructure challenges in the years ahead.
Source: University of Johannesburg / Professor Hennie Grobler