Funny that the Principal Geospatial Consultant didn't mention...

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Toastman

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25/08/20

15:35

Post #: 46803795
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Originally posted by tinnitus: ↑

https://www.ianvisits.co.uk/blog/2018/03/06/how-crossrail-was-affected-by-the-curvature-of-the-earth/

How Crossrail was affected by the curvature of the earth
How Crossrail was affected by the curvature of the earth

Crossrail’s tunnels under London are long, so long that when they were being planned, they were affected by something you might not expect — the curvature of the earth.

Knowing how the curvature of the earth is going to affect your new tunnels is quite important, otherwise the tunnels don’t line up when they meet. Worse, in some of the really tight spaces between older tunnels, you can end up drilling right into them. That would be embarrassing.When the current Crossrail scheme was developed in the 1990s, the planners used maps based on the Ordnance Survey National Grid reference system (BNG), but this turned out to be too crude a measure for the accuracy needed by Crossrail.
It’s not that Crossrail couldn’t have been dug using it, as obviously older tunnels were dug before modern maps, but there would have been risks of misalignment and a lot more time/money would have had to be spent surveying the tunnels to make sure they pointed in the right direction.In addition, interfaces between Crossrail and existing infrastructure as owned by Network Rail and London Underground would need to fit within tighter modern engineering tolerances.
Had they used normal “street maps”, then Crossrail tunnels could have been seen deviations of up to 20cm per kilometer of tunnel — due to the curvature of the earth. Maybe not a huge issue in some places, but that could have been catastrophic in central London as the Crossrail tunnels squeezed between gaps in other tube lines, sewers and modern foundations.

For example, Tottenham Court Road had a gap so tight that had they not adjusted for the curvature of the earth, the tunnel boring machine that left Paddington would have been sufficiently out of place by the time it arrived, that the cutting head might have drilled through the Northern line tunnels.

So Crossrails’s maps needed to adapt for the curvature of the planet.

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Funny that the Principal Geospatial Consultant didn't mention that in his award winning technical paper. Must have forgot.
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