My intro to Materials Science class at Cal had a couple of days or so on soil mechanics. One topic was settling in the Bay fill where the settling progresses logarithmically, i.e. fast at first and slowing as time goes on. A specific example was the Toll Plaza for the Bay Bridge, which had been completed in the late 1930’s and was still measurably settling when I was taking that course in 1973. The settling of the tower seems to be following this rule.
With 20/20 hindsight, it does sound like sinking some pilings to bedrock would have been a good idea. That would have likely required that the entire weight be born on the pilings as the settling process would eventually transfer most/all of the weight to the pilings.
Sinking concrete pilings to bedrock is standard practice for high-rises in Chicago. Some go down about 150 feet or more below grade level. I’m not sure why this wasn’t used in this case.
When the Fed’s replaced the old Chicago Post Office building in downtown Chicago (Between Clark & Dearborn, and Adams & Jackson) they started excavating the basement space and before they put shoring in, Jackson St started sinking.The new buildings on the site did have cassions down to bedrock but the 'BLUE CLAY" that constitutes most of the top fifty feet of the soil in downtown Chicago is like playdough. It squeezes and flows like braunswager out of its tube when under pressure. So when the land under Jackson Blvd no longer had any side support, it sank. Slowly but traffic pushed and the pavement over weeks sagged and cracked. After it was noticed, sheet pilings were driven down at the property line and strong support tubes were used to brace the the sheet pilings. The buildings constructed after the Federal Buildings (like the Sears {Willits} tower) were built all included the sheet pilings when excavation started and all also are built with cassions to bedrock. It looks like they use old tank cars as “sleeves” to line the cassion holes as they drill them.
Most houses are supported on footings on stable soil. Some buildings are supported on floating foundations such as Frank Lloyd Wright used for the Imperial Hotel in Japan which was designed to support the hotel and survive (it did) an earthquake. The San Francisco case looks like the designer was using a floating foundation design but overloaded it. The soil could not support the load and the building weight caused the soil to be displaced allowing the slow sinking of the building. I wonder what soil tests were done before the design and why the engineer didn’t realize the problem.
No, more like compressed concrete and fill. [D] The Millennium Tower developers need to plan for the current second floor to be the new lobby. The cost of the Tower was about $350M (at least until now).
Not sure if it will scale, but the actual Leaning Tower Of Pisa had its foundation stabilized successfully by removing soil from the opposite corner. If all else fails, one of the sfgate commentors suggested building flying buttresses across Mission St. [:D] The web site of the design firm (DeSimone Consulting Engineers) shows selected details. Hope DeSimone has a good ‘Pearl Harbor’ file on this project.
The TJPA response to the Millennium Tower lawsuit has a good timeline of events and TJPA proactions, hope that the trial jury makes note of that. Per the above link in order to protect the Tower, a $58M buttress was built that "consists of 181
Not much new except unding is being held up for additional engineering for the tunnel from the terminal to the present Caltrain terminal. Still a lot of wealthy persons are going to sue every body. But most likely the builder who used concrete instead of steel making it twice as heavy and not sinking piling to bedrock.
Wonder if ther would be some way to retro active instal bedrock pilings ? Probably some demo to get access ?
Ah, yet another city/county commission involved in this cluster*; it’s a wonder anything gets done in SF. IMO it is another distraction ploy away from someones brainless approval of the TTC platform design which currently has Caltrain and HSR use completely separated. This is grossly inadequate to support existing and future Caltrain service. Hopefully someone will rediscover crossovers.
The big losers, of course, are local transit patrons; construction of the planned pedestrian tunnel from the TTC to BART (which passes alongside the Millennium Tower) will not proceed until some resolution is agreed upon.
That’s an interesting problem. The progress of one of the stations being built for Phase Two of the WMATA Silver Line has fallen behind the other stations. The contractor had soil problems and they had to drive a whole bunch of piles. It went on for a few months. Now they’re drilling these large tubes into the ground.
The pile driver looked like it had steam and smoke coming out of it. I wonder what kind it was.
I believe Pile Drivers these days are diesel powered. The moving head coming down to strike the pile forms a piston that is fed properly timed fuel to ignite the compressed air created by the falling head at the point of impact - what is seen as ‘steam & smoke’ is the diesel exhaust from what is in effect a single cylinder diesel engine.
Per the latest article “Millennium Partners says they are identifying the best experts” (to mitigate the settling). Waiting to see what solution they come up with, popcorn in hand. Meanwhile, I’m not visiting anywhere in the fall zone.
Pile driving along side the existing building seems a bit dicey, and I’d like to see the compact driver that would fit in the basement. [:O] Perhaps some plentiful, deep grouting through a drilled hole under the NE corner (the leaning direction) would slow the tilting; experts, please weigh in.
The new Transit Center has been open since August 2018, but I’m not sure about the interruption due to the steel defect found and since corrected.
The Millennium Tower spokespersons are not telling all of the history. The tower was originally designed as a conventional steel frame building but was later changed to concrete/steel to ‘reduce costs’ (hah). Approval of the change is still suspect IMO since the building is on the ocean side of the former shoreline. This area is mostly rubble from the 1906 earthquake cleanup, not sure how that compares to south Florida sand / limestone. The foundation steel pile ‘fix’ sounds good, but I still wouldn’t live in a highrise building with that much concrete structure.
OTOH those buildings in Miami Beach look like more disasters waiting to happen. Concrete and steel rebar in a salt fog environment, now with added rising sea level issues. Color me out of there !!
Throw in Florida’s lax to corrupt politically inspired building inspections or the lack thereof - and anything above ground level is suspect for its structural integrity.
not a place I would ever want to live, fear of heights, but that is creepy. Just like the Hard Rock collapse in New Orleans, shoddy construction work. Have a friend who works in construction and he said they did not give time to dry concrete out and not enough piers to hold the building together. No thanks, I will stay on ground level. San Francisco used to never build high rises because of earthquakes and saw the Trans-America Needle on my last trip and earthquake proofed or so they said
The Millennium is a puzzle. Everyone says it has sunk 16 inches or whatever, but before they started the recent work on it you could walk into it, and you didn’t step down 16 inches as you went thru the front door. You probably didn’t step down at all. So has it pulled the surrounding sidewalk down with it? The sidewalk is still higher than the street, so has it pulled Mission St and Fremont St down too?
When I checked in late 2016, it seemed the sidewalk at the east corner of Mission and Fremont was 6 or 6-1/2 inches lower than it was circa 1990.
The confusion continues. Appears that tower took a “sudden” extra tilt. Pilig are scheduledtobe installed to bedrock. However 4 days lasped from piling excavation and grout installed. Was supposed to be done immediately. The though is soil may have migrated into the piling?