SF Tower settlement Part II 18

[1503-44]

"Appreciation has dropped to 2%"
Well that's less than inflation, but more than interest rates.

Although as I said, probably nobody bought in for either of those reasons.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[dik]

Funny... that's why I 'laughed'... I noticed the same similarity, and my earlier comment about the hamburger being 'done'...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[epoxybot]

This photo from ENR on Sep. 29 2021, somewhat suggests that revision of the number of piles from 52 to 42, resulted in abandonment of work in progress at the southern limit of the Perimeter Pile Upgrade.

 

[hamjohn]

Shimmick ceo

https://www.bizjournals.com/sanfran...himmick-president-talks-millennium-tower.html

 

[hamjohn]

Troubled Millennium Tower Gets Green Light for Key Test Tuesday

https://www.msn.com/en-us/news/us/t...for-key-test-tuesday/ar-AAPiNqx?ocid=msedgntp

 

[epoxybot]

John Egan’s report of June 23, 2021 stated the sum of 36” casings on Fremont St. would be completed by June 25, 2021. Why risk another 36” pile on Fremont St., which is the most problematic source of settlement?

 

[Walnuts]

epoxybot, location 33 where they are going to do the test 36-inch casing is the third pile on Mission Street. They did finish the 36-inch casings on Fremont back in June. If they keep the water level up, settlement of the corner should be minimal unless there is "heave" into the tip of the casing of the OBC. They have dismissed that as a cause of the increased rate of settlement but questions in the comment log suggest that Shah Vahdani likes it. He may be right. Almost certainly it is not vibration. That makes no sense for several reasons.

 

[dik]

There are better mimes than ours at work...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[epoxybot]

Walnuts, I would hope so but the text of the NBC report states Fremont Street.

 

[Walnuts]

epoxybot, good catch! I had seen / heard that report but did not catch the error. I am pretty sure that Jaxon knows it is on Mission, but he just misspoke. I have seen the letter from SGH to Patrick O'Riordan with the final "protocol" and it has an error saying they will stop if the settlement of the north-east corner exceeds 1/4 inch (increased from 1/8 inch in the draft). I am pretty sure they mean the north-west corner. Not their worst mistake! I don't think that they will come close to 1/4 inch for a single 36-inch casing so this might just be a "false flag" which will allow them to claim great success. But SGH stick to saying their expectation is that settlement will not exceed 1/8 inch (reasonable) and lateral deflection of the roof will not exceed 1/4 inch (ratio of 2 - other work near the north-west corner has shown tilt to settlement ratios of more like 4 or 5.) I am not sure that the test will prove anything!

 

[dik]

It may seem silly, but can they put 'well points' down on the side opposite the tilt and draw ground water off to maybe 'right' the tilt?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[apper.42]

...but can they put well points down...

Rather than lowering the high side I think it would be better to try and raise the low side by trying to recharge the water table on the low side to replace all the water removed when wet sand was removed from the 36" casings. They also removed considerable weight of overburden. Any increase in the water table would increase the buoyant force on the bottom of the raft on the low side. Most of the conductivity in the sand is in the horizontal direction. Slight excess pressure of 5 to 10' of head on the injection system might be effective without liquifying the sand layers.

 

[epoxybot]

Until they investigate the cause of the southeast corner of the tower driveway's 'phenomenon', as to why this area defies settlement; I think they are just asking for trouble. The southeast corner must have a lot of Young Bay mud under pressure. The current tilt tends to confine the mud on the east side, while squishing mud out the west side.

When I look at Slates ground profile, showing the Colma sand hump, I wonder if the sand hump and the even larger Young Bay Mud 'bulge' are the result of the tower's southeast behavior.

The Marine sands and the Colma sands are both aquifers. The lower Young Bay Mud is only 10 feet thick & very plastic.

This, from John Egan's June 18, 2021 report of piezometer readings...
Piezometers
Several sharp increases of piezometric head have been observed in the PB-1 piezometer at a depth of 85 feet bgs (located in the Marine/Colma Sands). [highlight #FCE94F]The spike on May 15, 2021[/highlight], between 6AM-12PM corresponds to a known influx of water onto the crane mat/sidewalk during installation of the 36" casing as the auger is retracted and soil is removed. The Building Engineer for the Tower also noted water infiltration into the basement. Similar increases were not observed in SB-1 and PB-2, as these piezometers are not situated close to the source of this water influx.

Additional spikes were observed on May 28, 2021, June 1, 2021, and June 7, 2021, all between 6AM and 12PM, and on June 11, 2021, between 6AM-9AM. The cause of the May 28 and June 1 spikes is not known, but likely is similarly due to an influx of water as described above. The spike on June 7 corresponds to advancement of the 36-inch casing for Pile #27 to a depth of ≈89 feet feet bgs and on June 11, the spike corresponds to advancement of the 36-inch casing for Pile #28 similarly to a depth of ≈89 feet feet bgs and observed water addition; both Piles #27 and #28 are located in close proximity to Piezometer PB-1.

For the piezometers in the Old Bay Clay (OBC), piezometric head at the PB-1 piezometers was influenced (increased) by the installation of the nearby Indicator Piles and has exhibited a general trend of decrease (dissipation) since then. Small increases of the head in the PB-1 piezometers at depths of 105 feet bgs, 120 feet bgs, and 135 feet bgs was observed on May 17, 2021, but piezometers at greater depths were not noticeably affected. Advancement of the 36-inch casing for nearby Pile #25 achieved its tip depth of ≈102 feet bgs on that day. Sharp decreases in the PB-1 piezometer at 105 feet bgs was observed on June 7, 2021, between 3PM-6PM and on June 11, 2021, between 6AM-9AM and 12PM-3PM. The decrease on June 7 corresponds to advancement of the 36-inch casing for nearby Pile #27 to a depth of ≈101 feet bgs and the decreases on June 11 correspond to advancement of the 36-inch casing for nearby Pile #28 to depths of ≈89 feet bgs and then ≈103 feet bgs. The decreases may be result of release of water from OBC into the casing, as the length over which the head loss occurs is much shorter after removing the soil inside the casing. [END]

Serendipity would have it that LB Karp was on-site taking pictures on June 15th and you can see the results of the water influx, on hat date. Photo 1 & Photo 2

Post from SF tower settlement (Part 1)

BUGGAR (Structural) 23 Sep 18 00:56
Bay Mud really is interesting stuff. The contractor approaching the Lower Market Street Station used a tunnel shield in the Bay Mud and the muck (mud) was routed through the face of the shield through a large tube like so much cookie dough. Of course it was referred to as elephant shi*

My questions, is whether the Lower Young Bay Mud is leaking water from the Colma Sand aquifer, upwards into the Marine Sands, during drilling operations, where the horizontal conductivity is greater and the water more readily disperses over a wider area, resulting in volume loss. This would be around the outside of the casing. Subsequently the Lower Young Bay Mud 'heals' around the casing, shutting off the water leak from the Colma Sands.

 

[dik]

It might be a tad easier to remove water than to add it...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[apper.42]

Hamburger and his group appear to have done a great job in removing groundwater and overburden and relieving pressure at the sand OBC layer and possibly between the sand and Young Bay Clay. This is why I think that probably overburden pressure should be restored and possibly increased depending on competent geotechnicaL assessment or review and that the water table should be raised if possible. Perhaps a verification is needed to see if the SE corner is actually hung up on the adjacent basement, which I personally doubt just because of the force that would require it to hang up would breach the basement

 

[spsalso]

If the Leaning Tower is "hung up" on an adjacent basement, that implies construction on someone else's property. By someone.

If the adjacent basement was there first, as it would have to be, it's interesting that the new builders either decided to build on top of the intruding structure, or did not actually know it was intruding. Or even built on someone else's property themselves.

"The required construction is neither complex nor unusual." Ronald O. Hamburger


spsalso

 

[apper.42]

They only talk about vertical settlements and lean at the top in N and West directions, not sure if they have monitored any lateral movement of the entire building in any direction. With the soft bay clay is it possible that the piles are slightly S shaped and the building has moved laterally. So far I have assumed that measurements are relative to some fixed vertical datum and some horizontal fixed coordinate system but have not seen any lateral measure to some fixed point. Oh, right is anything really fixed sitting on this geological formation if piles do not go to rock.

 

[dik]

...and what sort of P-delta effect would that have?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[apper.42]

If the tops of the piles are fixed at the 10' thick slab the tilt of the building would tend to bend the tops of the piles so that they curve slightly out to the East. If the piles are not fixed the tilt would tend to crush the edge of the pile tops. Since the tilt of the building is at about 0.3% ie .003 ft/ft this would mean that no matter if fixed or pinned the strain in the piles at the top would be .003 in/in which just happens to be the strain limit for ultimate design. Since the base slab is apparently dished this could mean that the slope on the East side of the building could be greater than 0.3%. So some of the building settlement could be from failure in the tops of the concrete piles to various degrees across the building. There certainly could be a lot going on here at once; enough to confuse the engineers.

 

[apper.42]

Dug up this picture from a 2016 article written by Alex Weinberg P.E. then of NY. The included photo clearly show the 14" square pile tops protruding into the 10' thick pad with dowels already coming out of the tops to transfer load to the base slab. It would thus appear to me that the piles are virtually fixed at the slab which means that the building tilt will be transferred as moment into the piles. Since the piles are designed for axial load it is possible that the combined bending and axial load would overstress the piles. Since there are no details of the pile reinforcing it is not possible to check this theory but the tilt of the building would result in about 0.003 in/in of strain in bending only without axial load.

 

[spsalso]

Since it's been asserted that there is some sort of basement structure holding up the "uphill" part of the building, might it not be wise to search for a corresponding basement on the "downhill" or "sinking" side? Say, across the street. And rest that side of the building on it.

Clever minds will note that there is a street (just previously mentioned) between the tilting building and the needed basement.

FLYING BUTTRESSES!

Yup. Works for cathedrals. Mostly.

Best part is you could keep using the street. After construction.

No. There's something even BETTER. It would make the building actually visually interesting.



spsalso