58-Story Luxury Condo Tower: sinking & tilting

[Lee Hixson]

Built in 2008. So far it has sunk 16". And depending on your source, it's tilting to the NW by at least 2", possibly 6".

That got me to wondering: how would one accurately determine the amount of tilt? Drop a plumb bob?

Suppose your firm was hired to measure the tilt. How would you do it?

http://www.sfchronicle.com/bayarea/mati ... abb4fbbd34

[pls7809]

Easy peasy. Reflectorless shots. ;)

[Jim Frame]

The technical approach would likely depend a lot on sight line availability, both optical and satellite. Urban canyons can make both kinds of measurements maddeningly difficult, but I think I'd probably combine both GNSS and total station observations if practical.

[Lee Hixson]

This is in the thick of downtown SF. Given that it's 58 stories tall, I'd be nervous shooting a vertical angle from a block away. The closer to the building you are the harder it is to see straight up, or even close to straight up. And even if you could--and considering the multi-million (billion?) dollar lawsuits that are sure to transpire--would you really trust your ability to definitively give an offset distance from vertical?

I'm sure there's a way. But it is way outside my area of expertise.

[Steve Martin]

Lee,

With the kind of dollars involved in a big project like that, likely they are using a specialty monitoring firm managing fixed infrastructure, similar to the Robotic Total Stations we have at San Pablo Dam, with automated software, co-located with GNSS where feasible, and likely an inclinometer in the building.

Leica has some information/examples on their website:

http://leica-geosystems.com/industries/ ... monitoring

Look for the link to "TruStories"

http://leica-geosystems.com/products/to ... eica-geomo

[mpallamary]

I have had to testify in a big case involving a CALTRANS subcontractor who had to locate the underside of an interstate highway. I will not bore you with the details but, as we proved in court, the best way to approach this is by setting up a series of control stations that maintain mathematical strength of figure elements and involve a number of redundant measurements. if you have a problem with reflectorless, you can do it by a precise triangulation network. The trick is redundancy and a tight control network.

It would also appear advisable to set up a monitoring system to detect movement and start off at one week intervals and if no movement is detected go to a monthly interval, etc.

http://www.newagepublishers.com/samplec ... 001033.pdf

Good luck!

[Lee Hixson]

"Good luck"? I wouldn't touch this one with a 10-foot range pole.

[mpallamary]

Send it to me.

[Lee Hixson]

Sorry. Guess I didn't make it clear: I'm only curious about the mechanics involved; I haven't been contacted to actually do the survey.

[Warren Smith]

"Sorry. Guess I didn't make it clear: I'm only curious about the mechanics involved; I haven't been contacted to actually do the survey."

Yeah, Lee, you don't look like you're dressed for the field anyway ...

[LS_8750]

That is a sticky one. They definitely have geotech issues to deal with, plus the potential of undermining the Millennium Towers building with the rail terminal next door. Nobody is walking away from this one with clean shorts.

Mr. Pallamary is of course correct, it is all about a having a tight triangulation network and knowing that your off site occupation points are not moving. Then you shoot targets on key structural components of the building, at key intervals, and report the differential movement. You could put sensors on the buildings as well, which would detect the vibration of a fly hitting a 44th floor window, but that data is often not necessary - depending on what you are monitoring.

The rail transit terminal contractor should have been monitoring the adjacent buildings, including the Millennium Towers building, for months prior to excavation in order to develop a baseline so that they could either defend themselves against future (now present) claims, or determine the impacts of the construction activities and take precautionary steps as necessary.

I'm starting up a monitoring program for a new construction job next week, at sea level, on beach sand, with adjacent high tower amusement rides and buildings and a railroad. It gets interesting when you see tidal influences affecting your elevation measurements, until the dewatering operation balances the groundwater pressures.

[Anthony Maffia]

The contractor claims to have monitored it before excavation, and the sinking occurred beforehand. The initial news report stated the building is all concrete construction, not steel, and is therefore "heavier" than it had to be, and they didn't drive the piles down to bedrock, but "just far enough". Of course, the builder says all is fine, it was designed to sink, but a half billion dollar lawsuit was filed yesterday by an attorney representing 400 owners of multi-million dollar condos. That is a lot of money in a neuvo Leaning Tower of Pisa.

[land butcher]

if the side is flat columninator (sp) vertical only scope I used one to run up control on a high rise. Or vertical laser which the glass bracket installers used.