Officials suspect work on a new 3.9-km metro line as the most likely cause of the early afternoon collapse of the city’s historical archive building in Cologne, Germany, on March 3. Buildings adjacent to the six-floor archive structure, which was erected in 1971, were demolished. By the morning of March 4, two people were thought missing, though no injuries had been reported. A Cologne city hall spokesman says the collapse occurred over a few minutes as ground beneath the archive caved in. The buildings were some 20 meters above new twin tunnels of Cologne Transport Company’s (KVB) North-South line, due
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.