Tunnelling through a Mountain - Numberphile

Featuring Professor Hannah Fry - more details on her work below.
More links & stuff in full description below ↓↓↓

NUMBERPHILE

Video by Brady Haran and Pete McPartlan

[joaquinclavijo]

Another interesting fact is that the meeting point in the middle isn't perfectly straight, Eupalinos was afraid they wouldn't intersect if they had done the math wrong, so to make sure he instructed to bend both tunnels to the same side so that a crossing point was guaranteed, even if both tunnels were originally parallel to each other.

[martinepstein]

0:47 "So let's say you want to go in here, doo doo dooo ♫♩
and you want to come out here" _squeak_ _squeak_ _squeak_ ♫♩

[luisdaumas]

I believe the main reason to excavate from both ends is to gain time. When opening a tunnel, you are limited by the number of people that can work at the same time. To increase the number of workers you need a bigger tunnel, so you gain nothing. But working both ends you half the time for a given tunnel size 😊

[PlateTechTony]

Hannah Fry's voice gives me a warm feeling

[bonecanoe]

I found the best technique is using F3 to get the coords of both ends.

[TheJensahlgrd]

As an old tunnel surveyor I know how difficult this is, even with modern equipment! Impressive. Great video as always.
And no, GPS won’t work in a tunnel. We use modern total stations that measures angles and distances very accurate. For very long tunnels we also use gyro theodolites to help find the correct direction. :)

[nordicexile]

My grandfather was a civil engineer on the team that built the tunnel through Zion National Park (in Utah). The story I heard was that using only slide rulers to calculate, they dug from both ends and were only an inch or two apart when they met. The "Mt Carmel Tunnel" is 1.1 miles long (1.6 km) and is not a straight path through the mountain, which I always thought was a pretty impressive feat.

[isaacbenrubi]

As a Greek person, I can tell you that"Polycrates'" name means, "a whole lotta crates."

[ethancheung]

when doing those right angle steps around, because the steps are relatively small, we could possibly build planks between the marking poles and use the water level test.

[johnchessant]

It's because of that 60 cm mismatch that we even know that they used this ingenious method. If they had gotten it perfectly then the "likely" explanation would've been that they dug it from one side all the way through

[variousthings]

That pronunciation of "Polycrates" reminds me of the way Bill & Ted said "Socrates".

(Watching Bill & Ted's Excellent Adventure as a child spoiled my mental pronunciation of Greek names ending "-es" for life.)

[axelBr]

Brady "as long as you can see the opening you know you are digging in a straight line". Hannah "they had to dig around hard rock at the entrance".

Recently I saw a YT about the Roman Roads in Britain that raised the point that I had never thought of, "how do you create a straight road to a town you can't see?"

[Krekkertje]

OMG numberphile with Hannah Fry. Christmas came very early!

[cconnors]

It's just nice to hear Brady's voice in a video once in awhile.

[Zveebo]

Looking forward to a future video where Matt Parker and Hannah Fry build a kilometre long stick to dangle from a mountain 😅

[RobertoTifi]

She is fantastic! She speaks so clearly! I'm a non-native English speaker but she's so easy to follow... Love her!

[someknave]

The stick thing sounds like a misunderstanding. A stick going from a point on top of a mountain to the base of the mountain, while being impractical in general, also won't necessarily generate the same height if the different sides have different steepnesses. More plausable is having a stick going straight up and noticing when this is level with a structure on top of the hill.

[asthmen]

Oh this is one of my favourite facts about Ancient Greek engineering! Thank you so much for covering this, I think Ancient Greek uses of maths are wild

[whitslack]

Solution to the level problem: temporarily build a trough around the mountain, filling it with water as you build it. The water level in the trough at the tunnel entrance will always be at the same altitude as the level at the tunnel exit. The trough could be as simple as a clay-lined ditch in the ground.

[rickinielsen]

With a plum line and a right angle attachment, you could just sight out points of same elevation around the mountain, until you get to the other side.