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Environment / Climate change

Is a Seoul skyscraper causing sinkholes?

The Lotte World Tower is a skyscraper currently under construction in Seoul, South Korea, which, when finished, will be the sixth tallest building in the world. As you can imagine, construction of a 123-storey tower comes with its fair share of difficulties: getting approval, ticking health and safety boxes, and squashing the sneaking suspicion that the building’s tapered top sort of looks like it might house the eye of Sauron. The planned tip of the Lotte World Tower

But the Lotte World Tower’s developers have another, rather more pressing problem to contend with. The Associated Press reported on Friday that, since June, “small sinkholes” have been appearing in residential neighbourhoods near the tower. One, just 500m from the construction site, was 500cm in diameter and 20cm deep. In other news, the water levels of the nearby Seokchon Lake have in recent months fallen from 5m to 4.3m.

Despite the fact that the sinkholes aren’t exactly swallowing cars, these occurrences have prompted the city government to ask lawyers, engineers, environmentalists and other experts to submit their thoughts on the affair. They’ve also put Lotte’s plans to open a shopping centre next to the tower on hold.

So could the tower really be causing falling water levels and holes in the ground? Sinkholes can be caused by a range of different factors: rock under the ground’s surface dissolving, say, or a torrent of groundwater washing away material. Park Chung-Son, a professor of civil engineering at Kwandong University and a member of the team giving feedback on the construction site, said he saw water pooling in the tower’s sixth basement level. He suspected it of coming from the nearby lake. If he’s right, that could mean that groundwater is flowing from the lake to the building’s basements, depleting the water levels and possibly washing away underground material in the process.

Dr Philip Collins, a lecturer in geotechnical engineering and geology at Brunel University, said by email:

“The geology of Seoul is mainly made up of an insoluble rock called gneiss which is less likely to have collapsed. It is possible that the deep excavations for the tower (it has a deep basement) could have drawn down the groundwater table… theoretically, this could have caused some subsidence in the surrounding area.”

However, he added, it could be caused by something else entirely:

“It is very possible, however, that the sinkholes are nothing to do with the Seoul Tower. Seoul has expanded very rapidly, and it is possible that some of the infrastructure, such as drainage, was poorly built.”

If all goes to plan, the building should stretch to 555m, and should open in 2016.

Image: Kohn Pederson Fox Associates/CTBUH
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