The Weight of New York City: Subsidence from Anthropogenic Sources | Hacker News Reader

The Weight of New York City: Subsidence from Anthropogenic Sources

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61 pointsjaboutboul30 comments

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.

Where did the excavated rock go? If it's still on island, just someplace else, then the ESB is additive weight.

Ha, fair point. I don't know where it went.

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

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.

> 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.

What cargo were they delivering to England?

Raw materials. Wool, tobacco, furs etc. The economy of the British Empire was based on extracting raw materials from the colonies and manufacturing finished goods in England.

I'm not sure of a legitimate record, but searching for "Bristol Basin" suggests that it was supplies/weapons to assist with the German attacks on Bristol, England.

Edit to include text from the plaque commemorating the basin: BENEATH THIS EAST RIVER DRIVE OF THE CITY OF NEW YORK LIE STONES, BRICKS AND RUBBLE FROM THE BOMBED CITY OF BRISTOL IN ENGLAND... BROUGHT HERE IN BALLAST FROM OVERSEAS, THESE FRAGMENTS THAT WERE ONCE HOMES SHALL TESTIFY WHILE MEN LOVE FREEDOM TO THE RESOLUTION AND FORTITUDE OF THE PEOPLE OF BRITAIN. THE SAW THEIR HOME STRUCK DOWN WITHOUT WARNING.... IT WAS NOT THEIR WALLS BUT THEIR VALOR THAT KEPT THEM FREE ......

And broad-based under all Is planted England's oaken-hearted mood, As rich in fortitude As e'er went worldward from the island-wall.

ERECTED BY THE ENGLISH-SPEAKING UNION OF THE UNITED STATES * 1942 *

Given that they had an excess of rubble, I'd guess that they sufferred bombings and had to be rebuilt, so, bricks steel and oil I suspect.

Weapons, tanks, cars, materials.

Into the river, so next to the island.

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.

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!

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.

I based my estimate on photos of the foundation work like: https://keithyorkcity.files.wordpress.com/2013/02/1930-march...

I couldn't find actual blueprints.

I'm not sure that surface soil is that deep. I seem to recall that in parts of central park the granite is exposed.

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.)

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.

Thanks for this; I read this a long time ago and have no clue where, so it’s nice to have the backup of some math.

I don’t know where I’m getting this fun fact either; I read this <somewhere> at least twenty years ago, used it to succeed at the Fermi problem maybe ten years ago.

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.

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.

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.

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-...

I didn't know this until recently that Mexico City was built on top of a lake

https://youtu.be/f8JVdpWCKeM

Look up digital reconstructions of pre-colonial Tenochtitlan and the huge lago de Texcoco that surrounded it. The colossal metropolis of Greater Mexico City, with its roughly 23 million people, was started over a series of swampy islands that were barely fit for 250,000 people and then grew to consume the entire lake that used to fill the Valle de Mexico. Doing that is bound to have repercussions that stretch across centuries, particularly as the city in question grows to megalopolis proportions.

Today's Mexico City is a water distribution and ground water control disaster that only keeps getting worse. For many people who don't know its geographical history, it's hard to believe that the city periodically floods catastrophically. After all it's in the middle of a broad high mountain valley with generally dry conditions surrounding it, but flood it does, and sometimes terribly during the annual rain seasons, causing incredible levels of gridlock for a place with already bad general traffic problems.

One curious lesson from this is about how adaptable humans are even in especially disastrous situations once they've already invested in maintaining their place there. Mexico city continues to be a desirable living destination and through a mix of improvisations, new technologies and creative uses of established engineering methods, the city's residents and government keep finding ways to mediate against their problems.

You could extrapolate this to many human-caused problems that people think insurmountable.

Too much underground water extraction can do it too; see the San Joaquin valley.

Now do the Three Gorges Dam.

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?

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