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SF Tower settlement Part III 18
- Thread starter dik
- Start date
To the Geotech's.
I have reviewed the drilling logs, and it seems that there is not a consistent nor stable strata that is capable of transferring a 2,000kip load via friction, and that most of the load will be a point load at a rather weak shale base. Can the shale (1) actually support a 4.4 kip sq in static load and (2) support the "live" load that occurs in the jacking processes?
This is way beyond any field condition that I have ever encountered, perhaps I'am just overwhelmed by the concept of the transfer of a 2,ooo kip load to a 24" pile.
In my experience a good Geotech/Civil Engineer is the vital key to building any large building.
I have reviewed the drilling logs, and it seems that there is not a consistent nor stable strata that is capable of transferring a 2,000kip load via friction, and that most of the load will be a point load at a rather weak shale base. Can the shale (1) actually support a 4.4 kip sq in static load and (2) support the "live" load that occurs in the jacking processes?
This is way beyond any field condition that I have ever encountered, perhaps I'am just overwhelmed by the concept of the transfer of a 2,ooo kip load to a 24" pile.
In my experience a good Geotech/Civil Engineer is the vital key to building any large building.
Keith 1, which boring logs did you review? I think the best and possibly the only reliable log is of boring PB-1 drilled by Slate near the two indicator pile locations on Fremont Street. It shows Franciscan Melange from 256 feet down to 323 feet. The melange is described by Slate as "generally consists of pervasively sheared shale matrix supporting blocks of siltstone, sandstone, chert, serpentinite, and volcanics; blocks vary from 1/2 to 3 inches; local serpentinite and quartz veins." There is no indication of even a rather weak shale base. The melange is known to be a tricky material that can vary quite widely over short distances. Not what I would want to support a 600-foot tall, concrete-framed building. Ron Hamburger, a structural engineer, keeps on referring to piles drilled into rock, but this is not what most geotechnical engineering would regard as rock for this purpose. It is instructive to see what Slate wrote about the first indicator pile, which they abandoned because they could not keep the hole open: "leaving the uncased rock socket hole open for any significant amount of time, as well as repeated extraction and re-insertion of the drilling tooling and flushing with water, seems to be detrimental to the stability of the hole [which should not have been a surprise!]. The Franciscan Complex bedrock materials are quite variable ..."
Thank you for your support of good geotechnical / civil engineering!
But also, the one and only "pile load test” was done on the second indicator pile which had three Osterberg load cells embedded in the rock socket plus other devices to measure deformation. They do some tricky stuff to come up with “unit side shear resistances”. That is all they report, but I added up the shear forces around a 2-foot diameter pile and got 663 kips in the Lower Alameda formation and 2060 kips in the Franciscan. These are not capacities of any kind – just what was developed when the load cells reached their limit of 800+ kips. So, if you believe this, you could safely apply 1000 kips as a permanent load. But I think there is something funny about these numbers. The loads cells, when tested one at a time maxed out pushing a bit over 800 kips in both directions, up and down, 1600 kips total. I am not sure how they then get interpreted resistances that add up to 2723 kips (not my expertise and I don't have time to read all the relevant literature). Also, the capacity for a downwards load might be different because of a different pattern of deformation and the long-term capacity of the Franciscan Melange might be different from the short-term capacity. Basically a lot of unknowns. To rely on just one pile load test and some input from adjacent sites (which John Egan mentioned in his remarks to the Board of Supes hearing) seems like more than a bit of a gamble for a high-profile fix and building.
Thank you for your support of good geotechnical / civil engineering!
But also, the one and only "pile load test” was done on the second indicator pile which had three Osterberg load cells embedded in the rock socket plus other devices to measure deformation. They do some tricky stuff to come up with “unit side shear resistances”. That is all they report, but I added up the shear forces around a 2-foot diameter pile and got 663 kips in the Lower Alameda formation and 2060 kips in the Franciscan. These are not capacities of any kind – just what was developed when the load cells reached their limit of 800+ kips. So, if you believe this, you could safely apply 1000 kips as a permanent load. But I think there is something funny about these numbers. The loads cells, when tested one at a time maxed out pushing a bit over 800 kips in both directions, up and down, 1600 kips total. I am not sure how they then get interpreted resistances that add up to 2723 kips (not my expertise and I don't have time to read all the relevant literature). Also, the capacity for a downwards load might be different because of a different pattern of deformation and the long-term capacity of the Franciscan Melange might be different from the short-term capacity. Basically a lot of unknowns. To rely on just one pile load test and some input from adjacent sites (which John Egan mentioned in his remarks to the Board of Supes hearing) seems like more than a bit of a gamble for a high-profile fix and building.
Thanks Walnut, that was a very informative post, and I greatly appreciate it.
I apologize for the use of the term "weak shale" as I lack the vocabulary or knowledge to properly characterize the substrate as you have correctly done so.
The logs that I saw were posted on this thread and consisted of site specific and local surveys that contained hammer #'s and soil characterizations, and to be honest the use a rotary drill left me with nothing more than a best guess, because I have only ever dealt with test results from bore holes taken with a spoon bill.
My observation was that the strata varied dramatically every 10' or so, and I did not see anything that offered much soil sheer strength to carry anything close to the applied loads via friction, and that the terminal strata was nothing like a granite or a 6,500 psi consolidated clay layer to carry the point loads at the socket.
The only thing that makes possible sense to me, and that would give them a fighting chance would be to bell the bottom out above the socket to distribute the load, but again I have never seen a pile that was loaded anything near what they are attempting.
Foundations, dewatering, sewer/water and storm water management are vital to construction, and in my opinion a good Geotech/Civil is the best investment you could ever make.
I apologize for the use of the term "weak shale" as I lack the vocabulary or knowledge to properly characterize the substrate as you have correctly done so.
The logs that I saw were posted on this thread and consisted of site specific and local surveys that contained hammer #'s and soil characterizations, and to be honest the use a rotary drill left me with nothing more than a best guess, because I have only ever dealt with test results from bore holes taken with a spoon bill.
My observation was that the strata varied dramatically every 10' or so, and I did not see anything that offered much soil sheer strength to carry anything close to the applied loads via friction, and that the terminal strata was nothing like a granite or a 6,500 psi consolidated clay layer to carry the point loads at the socket.
The only thing that makes possible sense to me, and that would give them a fighting chance would be to bell the bottom out above the socket to distribute the load, but again I have never seen a pile that was loaded anything near what they are attempting.
Foundations, dewatering, sewer/water and storm water management are vital to construction, and in my opinion a good Geotech/Civil is the best investment you could ever make.
JStructsteel
Structural
With all the legal beagles looking at this, why would any engineer take on this project?
- Thread starter
- #66
I like challenges... but, this one is a little more than that. I still don't have a warm fuzzy feeling about any of the proposed solutions. You would think they would be getting the best, world wide, geotekkies involved.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
I agree, I don't really get any warm fuzzies about what they are doing. On the other hand, I'm not sure what else could be done short of tearing the building down. They really don't have a lot of room to work in while doing remediation and they've already shown that additional excavation just causes more problems.dik said:
- Thread starter
- #68
That's why they have to quickly sit down and talk to all the experts... they may have time now, but maybe not in a couple of years... an old expression one of my colleagues that was a pilot used to say, "There's nothing more useless than runway behind you."
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
- Thread starter
- #69
One of the main tenets of professional associations (engineering ones, at least) is looking after the safety of the public. SEAOC is strangely quiet about this structure (with the exception of a past member). A seismic event, with the precarious foundatons, could kill or injure many. I don't know what it would take for the association to 'really' be interested in public safety? Maybe it a 'catch all' that all associations use to make themselves feel important.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
Red Corona
Computer
If they're overloading the capacity of that clay and sand to support the building then the only safe options are to reduce the load (i.e. remove some of the building) or get the piles down to bedrock. And then because that's so far down, you have to worry about bending of the piles too. So yeah they look to be in some serious trouble to me.
Maybe, instead of driving piles on the shady side of the building, they should be pumping water out from under the other side.
Let the building sink, but keep it vertical. Then there'll be some new basement apartments that will rent out at a substantial discount. Or maybe just an extra parking floor or two. But most of the owners will just have a slightly less wonderful view.
Otherwise, the buildings got to come down. One way or another.
spsalso
Let the building sink, but keep it vertical. Then there'll be some new basement apartments that will rent out at a substantial discount. Or maybe just an extra parking floor or two. But most of the owners will just have a slightly less wonderful view.
Otherwise, the buildings got to come down. One way or another.
spsalso
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1
- #74
hpaircraft
Member
In Part II I asked:
I wonder if the situation is grave enough for this yet?
One of the responses to my original query is that such contingency planning might be seen as an admission of failure. I think what it would be, an act of concern for public safety, is more important than what it would look like.
hpaircraft said:
I wonder if the situation is grave enough for this yet?
One of the responses to my original query is that such contingency planning might be seen as an admission of failure. I think what it would be, an act of concern for public safety, is more important than what it would look like.
- Thread starter
- #75
If the video by Josh Porter is correct, it's something they should be looking at predicated on the repair efforts to date. SEAOC is strangely silent.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
- Thread starter
- #76
Dik - From the "Structural Evaluation of the Millennium Tower, 301 Mission Street, San Francisco, CA; Revised Supplemental Report" July 26, 2017
BEGIN Page 12: We used an in-house computer program to calculate a group factor for the piles based on the empirical method outlined in Reese6 et al. We obtained a group factor of 0.6 and assigned it to LPile as a modifier. END
6) Reese, LC., Isenhower, W.M., and Wang, S-T, Analysis and Design of Shallow and Deep Foundations,
Dec 2007
ti89t - The items that are now broken links can now mostly be found on LBKarp's Millennium Debacle page.
In addition there are the SF Gov. Audit & Oversight Committee "Communication Packets" that comprise everything SF Supervisor Aaron Peskin has requested be made public. File Destinations: 160975 & 210954
Apart from a plan view of the piling and an elevation view of the tower podium shoring wall, there aren't any structuaral drawings of the mat foundation or basement. There is a original floor plan of the basement in some of the documents linked above.
BEGIN Page 12: We used an in-house computer program to calculate a group factor for the piles based on the empirical method outlined in Reese6 et al. We obtained a group factor of 0.6 and assigned it to LPile as a modifier. END
6) Reese, LC., Isenhower, W.M., and Wang, S-T, Analysis and Design of Shallow and Deep Foundations,
Dec 2007
ti89t - The items that are now broken links can now mostly be found on LBKarp's Millennium Debacle page.
In addition there are the SF Gov. Audit & Oversight Committee "Communication Packets" that comprise everything SF Supervisor Aaron Peskin has requested be made public. File Destinations: 160975 & 210954
Apart from a plan view of the piling and an elevation view of the tower podium shoring wall, there aren't any structuaral drawings of the mat foundation or basement. There is a original floor plan of the basement in some of the documents linked above.
- Thread starter
- #78
It as a WAG, with fictitious numbers, just to get an inkling of the reduction... I've never done this type of calc before, but the 0.61 calculated is close to the 0.6. I wouldn't do this sort of design myself; I'd rely on a geotekkie. I just didn't realise that there could be that much of a difference... I was thinking maybe 80% or something of that ilk. It's just nice to know the sort of methodology that goes into this type of calc. Thanks, epoxy...
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
AutisticBez
Computer
How many inches before the building becomes unstable?
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