[HN Gopher] The Weight of New York City: Subsidence from Anthrop...
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The Weight of New York City: Subsidence from Anthropogenic Sources
Author : jaboutboul
Score : 53 points
Date : 2023-11-26 13:31 UTC (1 days ago)
(HTM) web link (agupubs.onlinelibrary.wiley.com)
(TXT) w3m dump (agupubs.onlinelibrary.wiley.com)
| gcanyon wrote:
| Fun fact: the Empire State building weighs almost exactly the
| same as the rock excavated to make its basement. So that
| building, at least, is not contributing to the island sinking.
|
| It also makes an interesting way point to solving the Fermi
| problem of estimating the building's weight: first estimate the
| footprint, then estimate the depth of the basement, then
| calculate the mass of that much rock at 3-4 metric tons per cubic
| meter.
| brk wrote:
| Where did the excavated rock go? If it's still on island, just
| someplace else, then the ESB is additive weight.
| gcanyon wrote:
| Ha, fair point. I don't know where it went.
| pmayrgundter wrote:
| As a longtime NYC resident, the conventional wisdom is that
| much of the landfill for the buildings of the city went to
| expand shoreline of Lower Manhattan.
|
| This was well reported for major digs like WTC/WFC, which
| created Northwest Battery Park City.
|
| It's also seen in local landmarks like the Ear Inn on West
| Spring (one of the oldest bars in the city) which has an old
| painting inside showing the shoreline being not far outside
| the building, whereas it is currently a full block or two
|
| For more:
| https://en.wikipedia.org/wiki/Lower_Manhattan_expansion
| Spooky23 wrote:
| Another NYC trivia fact is that the FDR drive around
| Bellevue and NYU (20th-34th st iirc) is built on the rubble
| of Bristol, England. There may be another section up around
| MSK/Cornell as well but I don't recall.
|
| The ships returning from England would load up with rubble
| to use as ballast.
| JumpCrisscross wrote:
| > _may be another section up around MSK /Cornell_
|
| Yup, all along the East Side. This is why you'll find
| English weeds growing on Manhattan.
| istjohn wrote:
| What cargo were they delivering to England?
| bobthepanda wrote:
| Into the river, so next to the island.
| abduhl wrote:
| FYI most rocks come in at less than 3 tonnes per cubic meter,
| around 2.5-3. It's quite rare for in situ rock to have a unit
| weight (density I guess?) higher than this.
|
| I don't know where you're getting this fun fact either. It's
| very rare for a building to weigh as much as its excavated
| footprint absent an intentional design. The Empire State
| Building uses deep foundations as far as I'm aware, indicating
| that it weighed more than its excavated footprint.
|
| The prevalence of deep foundations throughout New York also
| explains why this paper is not good: it assumes and applies a
| uniform surface pressure across the city, without consideration
| for foundation system.
| ghc wrote:
| Based on publicly available information:
|
| The estimated weight of the building is: 365,000 tons
|
| The foundation area of the building is: 79,288 sq. ft.
|
| The foundation was laid at a depth of: 55.66 ft.
|
| The estimated density of removed rock: 165 lbs / cu. ft.
|
| The calculated weight of removed rock: 364086.5 tons
|
| It's very close actually!
| abduhl wrote:
| This is footprint. It's unclear whether the full footprint
| was sunk to your depth. Regardless, that's much closer than
| I anticipated it would be, which is pleasantly surprising.
|
| We can refine the estimate as well: surface soils probably
| make up half of the depth (25 ft) and granite rock the
| other half (30 ft). Blended unit weight would then be ~150
| pcf. About 327,000 short ton.
| ghc wrote:
| I based my estimate on photos of the foundation work
| like: https://keithyorkcity.files.wordpress.com/2013/02/1
| 930-march...
|
| I couldn't find actual blueprints.
| SoftTalker wrote:
| I'm not sure that surface soil is that deep. I seem to
| recall that in parts of central park the granite is
| exposed.
| saalweachter wrote:
| Yeah, NY throughout the Hudson Valley has shallow soil.
| The glaciers swept everything clean 21k years ago,
| dropped it all to form Long Island, and barely any of it
| has come back.
|
| (Looking it up, the first result says that soil for at a
| rate of about 0.5-1 inch/millennia, which sounds about
| right for how much has re-accumulated, on average.)
| 082349872349872 wrote:
| An anecdote that I've heard is that the NYC skyline and
| underlying geologic map correlate pretty closely; the
| skyscrapers were apparently built where the bedrock was
| conveniently close to the surface.
| Scoundreller wrote:
| Hrmmmmm, there's a bigger and bigger push to reduce parking in
| new buildings (largely supported by developers, because it's
| expensive to build down instead of up, and the real estate is
| worth less), so I wonder what effect this will have.
| AlbertCory wrote:
| Now do the Three Gorges Dam.
| UIUC_06 wrote:
| According to Snopes, the mass of the water held back by the dam
| (39 trillion kilograms, or 42 billion tons) is sufficient to
| change the rotation of the earth:
|
| https://www.snopes.com/fact-check/china-three-gorges-dam/
|
| https://interestingengineering.com/innovation/13-facts-about...
|
| So why is this being downvoted, when the subject is ground
| subsidence from man-made structures?
| Animats wrote:
| Oh, that silly paper. Discussed previously, although I can't find
| the reference. This is a non-problem for Manhattan, where bedrock
| is close to the surface and it's hard New York Rock. It's a
| problem for some buildings built with on friction piles, like
| that tower in San Francisco. It's also a problem for low-lying
| areas where there's been too much oil extraction, such as parts
| of Louisiana.
| bobthepanda wrote:
| The thing is that ground subsidence measured in single-digit mm
| is normal of any building.
|
| Your real issues are in places like Mexico City or Jakarta that
| are sinking at tens of centimeters a year.
| ejb999 wrote:
| Wow, didn't realize Mexico City was sinking so fast - this
| article says it could sink another 65 feet! Yikes!
|
| https://www.wired.com/story/mexico-city-could-sink-up-
| to-65-...
| aidenn0 wrote:
| Too much underground water extraction can do it too; see the
| San Joaquin valley.
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(page generated 2023-11-27 23:00 UTC)