Civil Engineering April 2022 | Vol 30 No 3

Civil Engineering April 2022 1 B efore I provide you with my views on civil engineering silos in South Africa, I must express my devastation about the human suffering and infrastructure destruction currently underway in Ukraine. I grew up in Europe about 2 000 km from Kyiv – a mere 21.5-hour drive. What has been built over centuries has been decimated in a week. Rebuilding what is gone will take decades. As the dust has not settled and the full extent of the damage cannot be assessed yet, this article will attend to local infrastructure issues. In the meantime, my thoughts and prayers are with the inhabitants of the Ukraine. BACKGROUND In the 18 th century the term civil engi- neering was coined to incorporate all things civilian as opposed to military engineering, i.e. in the beginning civil engineering included all engineers that did not practice military engineering. Due to the large scope of civil engi- neering, the discipline has been further divided into 13 sub-branches. I believe that specialised fields of engi- neering should be promoted, as specialists are able to explore engineering branches in more depth. However, in practice, there is a risk associated with specialists working in silos. SINKHOLES We read about the appearance of unex- pected sinkholes in the media. In 2001, the collapse of a mine shaft caused a large sinkhole to appear in the middle of the night in Waihi (New Zealand). The sinkhole in São Paulo (Brazil) in 2007 was triggered by the construction of an underground train tunnel, while the 2010 sinkhole in Schmalkalden (Germany) can only be explained by natural erosion 1 . In 2013 five people died when a 10-metre-wide sinkhole opened at the gates of an industrial estate in Shenzhen (China), while at least three people fell into a huge sinkhole in central Henan (China) in 2016. More recently, an enormous sinkhole swallowed a bus and pedestrians in northwest China, sparking an explosion and killing nine people 2 . Such media reports are not exclusive to the international media. There were reports of road closures due to sinkholes on the East Rand 3 in 2019, and a car swallowed completely in George 4 in 2021. About 200 sinkholes have been reported in Gauteng over the past five years, according to WillemMeintjies from the Council for Geoscience 5 . The Daily Maverick reports that “at least 38 people are known to have died in South Africa over the past 50 years, due to sinkhole formation”. 5 THE CAUSE OF SINKHOLES Land surfaces are generally hard, sup- porting heavy loads including buildings and traffic. At times, however, some surfaces become unstable, either due to natural or human causes, and can sink several metres into the ground. With them, anything on top may be swallowed, as illustrated by the examples above. These cavities or pits appear when water erodes the geotechnical layers that support the hard land surfaces. The world’s deepest recorded sinkhole is in Chongqing, China, reaching down 662 metres 6 and illustrating the danger of sinkholes to mankind. The causes of sinkholes are three-fold: water, human activities (such as the mining and rail tunnel examples above) and earthquakes. In the remainder of this article, I focus on water induced sink- holes, which account for 90% of events. 6 Certain materials are water soluble, and the presence of water may cause weathering leading to cavities under the surface. Materials can also be granular, providing an opportunity for water, either ground or surface water, to carry them away. The latter is also influenced by the interlocking of (the same or different) ground materials. Heavy rainstorms, floods, burst water pipes and long-term leakage from a sewer or storm- water pipe can all cause granular erosion. Seasonal changes in the groundwater table, From the Pres ident ’ s desk Are silos exacerbating the infrastructure maintenance backlog? Prof. Marianne Vanderschuren SAICE President 2022 marianne.vanderschuren@uct.ac.za as well as extreme precipitation when there are heavy rains following droughts, exacer- bate the situation. This can cause sudden changes to the hydrologic system, potentially causing the geotechnical systems to become (temporarily) unstable, resulting in sinkholes. In a country such as South Africa, where droughts and floods are common climate occurrences, should our geotechnical and water engineers not work more closely with our transport and structural engineers to improve the monitoring of already fragile building, road, water, and sewer infrastruc- ture? The monitoring of infrastructure alone creates risks that have already led to the loss of South African lives. For more information, I invite you to read the 2022 Infrastructure Report Card, which will be available during the second half of this year. Finally, as a specialist myself, I look forward to working together with my colleagues to minimise the risks of sinkholes occurring and avoid potential catastrophes. I encourage you to collabo- rate and, at the same time, become part of the CARE movement. Give 67 minutes of your engineering time to the South African society, every month. REFERENCES 1. https://www.bbc.com/news/av/ science-environment-31602248 2. https://www.sciencealert.com/a-huge- sinkhole-opened-up-in-china-and- swallowed-a-bus-and-pedestrians 3. https://www.sowetanlive.co.za/news/ south-africa/2019-11-03-giant-sinkhole- forces-road-closure-on-east-rand/ 4. https://www.thesouthafrican.com/news/ george-sinkhole-video-13-march-2021/ 5. https://www.dailymaverick.co.za/ article/2022-01-17-new-centurion- sinkhole-is-one-of-about-200-recorded- across-gauteng-in-past-five-years/ 6. https://www.conserve-energy-future. com/causes-effects-and-types-of- sinkholes.php