Lean­ing San Fran­cisco tower seen sink­ing from space

Kuwait Times - - HEALTH & SCIENCE -

Engi­neers in San Fran­cisco have tun­neled un­der­ground to try and un­der­stand the sink­ing of the 58-storey Mil­len­nium Tower. Now comes an anal­y­sis from space. The Euro­pean Space Agency has re­leased de­tailed data from satellite im­agery that shows the sky­scraper in San Fran­cisco’s fi­nan­cial dis­trict is con­tin­u­ing to sink at a steady rate - and per­haps faster than pre­vi­ously known.

The lux­ury high-rise that opened its doors in 2009 has been dubbed the Lean­ing Tower of San Fran­cisco. It has sunk about 16 inches into land­fill and is tilt­ing sev­eral inches to the north­west. A dis­pute over the build­ing’s con­struc­tion in the seis­mi­cally ac­tive city has spurred nu­mer­ous law­suits in­volv­ing the de­vel­oper, the city and own­ers of its mul­ti­mil­lion dol­lar apart­ments.

Engi­neers have es­ti­mated the build­ing is sink­ing at a rate of about 1-inch per year. The Sen­tinel-1 twin satel­lites show al­most dou­ble that rate based on data col­lected from April 2015 to Septem­ber 2016.

What the data shows

The satellite data shows the Mil­len­nium Tower sunk 40 to 45 mil­lime­ters - or 1.6 to 1.8 inches - over a re­cent one-year pe­riod and al­most dou­ble that amount - 70 to 75 mm (2.6 to 2.9 inches) - over its 17-month ob­ser­va­tion pe­riod, said Pe­tar Marinkovic, founder and chief sci­en­tist of PPO Labs which an­a­lyzed the satellite’s radar im­agery for the ESA along with Nor­way-based re­search in­sti­tute Norut. “What can be con­cluded from our data, is that the Mil­len­nium Tower is sink­ing at a steady rate,” Marinkovic said in a tele­phone in­ter­view Mon­day from The Hague, Nether­lands.

The data de­tected a small slow­down this sum­mer but one that needs fur­ther anal­y­sis, he said, and does not change the over­all data. “There is quite a steady sub­si­dence.”

The Sen­tinel-1 study is not fo­cused on the Mil­len­nium Tower but is part of a larger mission by the Euro­pean Space Agency track­ing ur­ban ground move­ment around the world, and par­tic­u­larly sub­si­dence “hotspots” in Europe, said Pierre Potin, Sen­tinel-1 mission man­ager for the ESA.

The ESA de­cided to con­duct reg­u­lar ob­ser­va­tions of the San Fran­cisco Bay Area, in­clud­ing the Hay­ward Fault, since it is prone to tec­tonic move­ment and earth­quakes, said Potin, who is based in Italy. Data from the satellite, which is or­bit­ing about 400 miles (700 kilo­me­ters) from the earth’s sur­face, was recorded ev­ery 24 days.

The build­ing’s de­vel­oper, Mil­len­nium Part­ners, in­sists the build­ing is safe for oc­cu­pancy and could with­stand an earth­quake. The de­vel­oper’s spokesman PJ John­ston said he had no di­rect com­ment on the satellite data but is­sued a state­ment say­ing that the Mil­len­nium Tower is a state-of-the-art build­ing that was “de­signed and con­structed to the ex­traor­di­nar­ily high stan­dards” man­dated by San Fran­cisco.

He re­it­er­ated the de­vel­op­ers’ blame for the tower’s prob­lems on the city’s con­struc­tion of an ad­ja­cent rail­way sta­tion, which they say re­moved ground wa­ter from be­neath the Mil­len­nium Tower that caused it to sink and tilt.

The city agency, the Trans­bay Joint Pow­ers Au­thor­ity, blames the build­ing’s “in­ad­e­quate foun­da­tion” which is not an­chored to bedrock. The tower is sup­ported by piles driven 60 to 90 feet into land­fill.

Engi­neers hired by the build­ing and its de­vel­op­ers have drilled deep holes around the build­ing to test soil sam­ples to de­ter­mine if the build­ing has stopped sink­ing, and if there’s a way to fix it.

One of the build­ing’s ten­ants, Jerry Dod­son, says that de­vel­op­ers have given ten­ants the im­pres­sion that the sink­ing was slow­ing and stop­ping. “To have the space agency look­ing at it de­bunks what (de­vel­op­ers) have put out there. Now we know it’s con­tin­u­ing to sink at an ac­cel­er­ated rate,” said Dod­son, an at­tor­ney who has helped or­ga­nize home­own­ers law­suits. “I can tell you that satellite data is way more ac­cu­rate that dig­ging in the dirt.” — AP

SAN FRAN­CISCO: The im­age pro­vided by the Euro­pean Space Agency ESA on Thursday, Nov. 24, 2016, shows the Mil­len­nium Tower on the base of mod­i­fied Coper­ni­cus Sen­tinel satellite data. — AP

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