Building collapse

A Matter of Time

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“As Iraqi forces continue their military operation to take Mosul from the Islamic State of Iraq and the Levant (ISIL, also known as ISIS), another equally important battle to save the Mosul Dam, located 60km north of Mosul, is under way. After six months of frantic security and logistical preparations, an Italian company has kicked off the repair works to beef up the dam, under the protection of five hundred Italian soldiers and Kurdish Peshmerga forces.

“The Italian company,TREVI, will have about 18 months to prevent the foundations of the dam from plunging deeper underground, averting an impending catastrophe. Experts warn that if the dam collapses, up to 11.11 billion cubic-metres of water known as Lake Dahuk, will submerge Mosul and create an inundation that will affect the lives of millionsof people living along the banks of the Tigris river.

“I don’t know if it’s a race against time, but we have the know-how and the technology to make the dam safe for the time-being,” said a company source on the phone, on condition of anonymity for security reasons…

[…]

“But scientists say the repairs are just a temporary solution and that the Iraqi population should get ready to evacuate the Tigris’ banks. “No matter how much grouting and maintenance the company will do, it may expand the life span of the dam, but it is just going to delay the disaster,” said Nadhir al-Ansari, professor of water resources and environmental engineering at Lulea University in Sweden and a published expert on the Mosul Dam.

“Speaking to Al Jazeera, Ansari said the 3.4km-long dam, the fourth largest in the Middle East, is built on unstable grounds and its collapse is inevitable. “It is just a matter of time. It will be worse than throwing a nuclear bomb on Iraq,” Ansari said.”

Text: Mosul Dam collapse ‘will be worse than a nuclear bomb’, Al Jazeera.

Image: Thomas Hart Benton, Flood Disaster, 1951

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Displacement Hotspots

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Data from the Sentinel-1 satellites acquired between 22 February 2015 and 20 September 2016 show that Millennium Tower in San Francisco is sinking by about 40 mm a year in the ‘line of sight’ – the direction that the satellite is ‘looking’ at the building. This translates into a vertical subsidence of almost 50 mm a year, assuming no tilting. The coloured dots represent targets observed by the radar. The colour scale ranges from 40 mm a year away from radar (red) to 40 mm a year towards radar (blue). Green represents stable targets. Credit: Contains modified Copernicus Sentinel data (2015–16) / ESA SEOM INSARAP study / PPO.labs / Norut / NGU

“The Sentinel-1 satellites have shown that the Millennium Tower skyscraper in the centre of San Francisco is sinking by a few centimetres a year. Studying the city is helping scientists to improve the monitoring of urban ground movements, particularly for subsidence hotspots in Europe.

“Completed in 2009, the 58-storey Millennium Tower has recently been showing signs of sinking and tilting. Although the cause has not been pinpointed, it is believed that the movements are connected to the supporting piles not firmly resting on bedrock.

“To probe these subtle shifts, scientists combined multiple radar scans from the Copernicus Sentinel-1 twin satellites of the same area to detect subtle surface changes – down to millimetres. The technique works well with buildings because they better reflect the radar beam.

“It is also useful for pinpointing displacement hotspots over large areas, thanks to Sentinel-1’s broad coverage and frequent visits.

“Working with ESA, the team from Norut, PPO.labs and Geological Survey of Norway have also mapped other areas in the wider San Francisco Bay Area that are moving. These include buildings along the earthquake-prone Hayward Fault, as well as subsidence of the newly reclaimed land in the San Rafael Bay.

“An uplift of the land was detected around the city of Pleasanton, possibly from the replenishment of groundwater following a four-year drought that ended in 2015.
Text and Pic: Satellites confirm sinking of San Francisco tower, Physics.org