When infrastructural developments are underlain by dolomitic ground, there is an increased risk of subsidence and sinkholes; this demands the early involvement of geotechnical professionals by developers, ideally during a project’s design stages.
South African National Standards (SANS) 1936 require a detailed assessment of geological stability before any development on dolomitic ground commences. Dolomite is a common feature of the geological landscape in many parts of South Africa, particularly in Gauteng and the Northern Cape. There are particular concerns related to mining activities, as the extensive dewatering conducted by mines has tended to increase risk levels.
Groundwater commonly fills cavities within dolomite rock, exerting hydrostatic pressure that helps to stabilise these voids. When groundwater is removed during dewatering, this pressure is reduced, making the ground more prone to internal erosion and the migration of cavities to the surface. Dewatering can also result in desaturation of weak horizons present in the profile, triggering their consolidation and causing surface sinkholes and subsidence.
Evolution of Standards
Risk related to dolomite is not limited to mining areas; it is equally prevalent where the presence of water concentrations leads to internal erosion within the ground profile. Developments in areas of Gauteng that are underlain by dolomite - such as Soweto, West Rand, East Rand and Centurion - have been plagued by sinkholes and subsidence, leading to significant damage and potential risk to life.
