Tunnelling

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Oswyntail

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Could anyone explain to me how engineers in the 19th century managed to "navigate" tunnels correctly. Was it as simple as having a compass and saying "dig in that direction"? Did they ever dig tunnels from both ends, and, if so, how? This question has been inspired by the East end of Standedge Tunnel, where the immediate sharp bend often makes me wonder if the portal was quite where it was originally intended.
 
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Wasnt it something to do with candles and string and some really basic stuff like that?


I dont know why I thought that but its sticking in my mind for some reason
 

eastwestdivide

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The line of Standedge might well have been influenced by the adjacent canal tunnel. They dug cross-passages to take out the spoil by canal boat apparently.
More generally, it's not that hard to survey a straight line with unsophisticated equipment - Roman roads anyone?
 

Tomnick

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Theodolites were around by then - I'd be surprised if they didn't play a part. Once you've established an accurate position and heading at each end of the proposed tunnel (either relative to existing benchmarks or by going over the top to relate the two portals directly), it's fairly straightforward to maintain that heading as the tunnel progresses, by establishing new 'stations' at regular intervals and sighting back to the previous station to then determine the heading going forward. Curved tunnels were more of a challenge, I'm sure!
 
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Pinnock tunnel on the old Par to Fowey branch (now a private clay lorry road) is like a S.
In hard rock tunnel builders made a small pilot tunnel first. They tunneled from both ends and met in the middle!
 

LE Greys

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The line of Standedge might well have been influenced by the adjacent canal tunnel. They dug cross-passages to take out the spoil by canal boat apparently.
More generally, it's not that hard to survey a straight line with unsophisticated equipment - Roman roads anyone?

Wasn't the original Standedge (the canal tunnel) started in about five places at once, the two ends and three shafts sunk in the middle?

I know that's what they did with Bramhope and Box tunnels.
 

michael769

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The answer is by employing basic trigonometry, combined with onsite surveyors.

When you have two landmarks at a known locations you can accurately plot the precise position (in 3 dimensions!) of anywhere where the two landmarks are visible by measuring your angle and distance to them using either a sextant or a theodolite, the latter was available since at least the 18th century.

In tunnels where there are no landmarks you simply create your own by placing two posts at locations you have already surveyed and then use them to survey 2 points further in (and so on).

Even today - as GPS signals do not penetrate very far underground, the same basic mathematics and techniques are used, albeit lasers and optical receivers are used to measure angles and distances and the points are plotted virtually in a computer model
 

John55

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Could anyone explain to me how engineers in the 19th century managed to "navigate" tunnels correctly. Was it as simple as having a compass and saying "dig in that direction"? Did they ever dig tunnels from both ends, and, if so, how? This question has been inspired by the East end of Standedge Tunnel, where the immediate sharp bend often makes me wonder if the portal was quite where it was originally intended.

Well one answer is they didn't always! There are several early tunnels with kinks in the middle were things didn't go quite to plan. Penmanshiel was one where it was dug from each end and when the tunnels met the line up was not exact, hence the kink.

However it should be remembered the canal builders did get there first and amongst others Telford had worked on several long tunnels which enabled the railway engineers to build on their original techniques.

Having read about the construction of the Mersey Tunnel in the 1880s it was remarked by the engineers that being able to see the top of Liverpool workshaft from Birkenhead and vice versa made life much easier when lining up the tunnelling headings. If there is a hill in the way it is harder!
 

bolli

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If I remember correctly, theres a tunnel on the IR Kalka-Shimla Line that was partly dug before they realised that it wasn't going to meet properly.
 

Kentish Paul

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People, as a qualified mines and tunnel surveyor (Cornish Tin Mines, Channel Tunnel, Jubilee Line etc.) I can tell you its really quite simple. It is basicaly simple triganometry transfered by theodelite and tape. (19th century here). I will try and put together a post which trys to keep things simple but explains how its done. By knowing where you start from and where you are going to (previous overland survey) you can set out the line and gradient of the tunnel. Please remember I am talking 19th century here. It is basic Mathematics measured by Theodelite, Level and Tape.
 

LE Greys

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People, as a qualified mines and tunnel surveyor (Cornish Tin Mines, Channel Tunnel, Jubilee Line etc.) I can tell you its really quite simple. It is basicaly simple triganometry transfered by theodelite and tape. (19th century here). I will try and put together a post which trys to keep things simple but explains how its done. By knowing where you start from and where you are going to (previous overland survey) you can set out the line and gradient of the tunnel. Please remember I am talking 19th century here. It is basic Mathematics measured by Theodelite, Level and Tape.

A version of the same thing was used in Stalag Luft III, described well in The Great Escape. Basically, it involved rough triganometry, pieces of string and primitive spirit levels, close checks done by holding a fat-lamp against the walls and sighting along it. They had a lot of trouble maintaining a straight line, and of course slipped up with the trig, finishing 10ft too short and almost surfacing too early in broad daylight (the ground fell away outside the wires, and doing trig without the Germans spotting it must have been hard). Still, if you ever go there, it they laid out the line of the tunnel on the ground and it was astonishingly close to a straight line.
 

Weary Walker

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Standedge Canal Tunnel is not straight either - from memory of what I was told on the guided trip through it, they made a mistake and had to get a new contractor (Thomas Telford) to complete it. To get the two ends to meet he had an S bend inserted.
Aha found a site with some details:Standedge Canal Tunnel
 

AndyHudds

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The line of Standedge might well have been influenced by the adjacent canal tunnel. They dug cross-passages to take out the spoil by canal boat apparently.
More generally, it's not that hard to survey a straight line with unsophisticated equipment - Roman roads anyone?

Correct,the two tunnels are connected at regular intervals and the spoil was removed by canal boat. There are also 2 further disused rail tunnels which are proposed to be brought back into use eventually.
 

pablo

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S L III. My Dad was there. According to him the tunnel emerged on the wrong side of the road just outside the peri wire instead of the other side of the road in the woods. Rather more the 10' out. Only c75 escaped instead of c250 because of the patrolling guard interupting the flow as they skipped across the road. Discovery was before dawn.

I suspect the pressure to go overcame the accuracy of the trig. Triangulation isn't a difficult task.
 

LE Greys

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S L III. My Dad was there. According to him the tunnel emerged on the wrong side of the road just outside the peri wire instead of the other side of the road in the woods. Rather more the 10' out. Only c75 escaped instead of c250 because of the patrolling guard interupting the flow as they skipped across the road. Discovery was before dawn.

I suspect the pressure to go overcame the accuracy of the trig. Triangulation isn't a difficult task.

That's interesing, my grandad was also a POW, although in Italy rather than Germany. He escaped during the Italian-German handover and eventually made his way to Switzerland. That's one of the things that sparked my interest in the area.

Going through Paul Brickhill's book, they couldn't find out what had gone wrong until the night of the escape itself, and by then all the papers were date-stamped and so they had to go no matter what.
 

pablo

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Great big thread drift......

I think they were running out of bed-boards to line the tunnel with amongst other necessities.

Next escape tunnel was rather more accurate. Wooden Horse. cf Brickhill also.

Reckons he jumped over the box each day and spread the spoil via hidden trouser bags.
 

Bill EWS

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Due to an error the old Dundee & Newtyle tunneat the top of the the incline up on the Law (Hill) at Dundee finished up with a kink to get back in line for the straight outside the north end.

http://theatreorgans.com/hammond/keng/kenhtml/Dundee Newtyle Railway/Dundee & Newtyle Rlwy (Index).htm
 

dalmahoyhill

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King horn tunnel on the edinburgh dundee line on the north side of the forth has a kink and 40mph limit in it.i did surveying the old fashioned way with theodilite and chain s at college if you are meticulous the accuracy is mms.......but I wasnt!
 

Tiny Tim

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Most early tunnels weren't dug just from the ends inwards, but also from a series of vertical shafts outwards. This was necessary to allow enough working faces to get the job done on time. It also meant that it was easier to keep on an accurate heading. Even so, many canal tunnels have unplanned kinks. Wast Hill tunnel on the Worcester & Birmingham Canal has a distinct dog-leg in the middle.
 

185

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If I remember correctly, theres a tunnel on the IR Kalka-Shimla Line that was partly dug before they realised that it wasn't going to meet properly.

The mile-long Barog's Tunnel, next to Barog Station.... the engineer shot himself after the two ends, bored from either side of the hill didn't meet. The disused tunnel portal is still visible.
 

SussexMan

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According to the Network Rail Archive...

Work on the tunnel had begun from both the east and west sides of Box Hill in 1836; Brunel’s calculations, and the skills of the contractors and navvies were such that when the two ends met in 1841 the difference in their alignment was less than 2 inches (5cm).

It still amazes me how that sort of accuracy could be obtained.
 

michael769

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Fascinating stuff - so what is the simple trig underpinning it?

Basically if you know the precise location of two points (which you will have already surveyed), and have measured the distance between them you can then use the cosine rule to calculate the angle to one of the next points you wish to mark and the tangent rule to calculate the angle to the other (or you can use the cosine rule for both if you are able and willing to move between the two reference points).

Once you have calculated the angle and distances you then use a thodolyte to measure both the angle and the distance with the help of your assistant, who you guide to the locations where he will place markers that become the known points from which you will calculate the next steps.

The maths is fairly straight forwards however accuracy is critically important as even a small error (especially near the start) can accumulate as you go. To reduce the risk it was normal practice to remeasure from the new points back to the reference point to make sure the angles were also correct in that direction. The skill of the surveyor was not in his maths skills but in his accuracy and attention to detail.

With a tunnel - typically the navvies would try to dig in a straight a line as possible, after a certain distance they would pause and the surveyor would place new markers in the freshly dug section which the navvies would use to realign their digging to correct the inevitable tendency to drift off track.
 
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Most tunnels are not level, either a 'summit' near the middle, or a slight slope. This helps with drainage, as water can pose problems.
A straight tunnel would be fairly easy. Something like two candles placed on poles 50 feet apart behind the diggers would keep a straight line.
 
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