Tracks on high ridges question

[richieb1971]

Quite a few tracks are on ridges exactly the width of how many tracks there are. I assume this is man made this way? And it does seem rather expensive to do that. So expensive I would imagine any new railways would ignore being high up.. so why did the old railways tend to be made higher up than the surroundings?

 

[bnm]

For a multitude of reasons.

Surrounding land not able to support a railway unless if has a sufficient 'bed'. The original Liverpool and Manchester Railway across Chat Moss being an example. (see attachment)

To raise the line to prevent flooding. Such as the lines to the north and east of Cogload Junction across the Somerset Levels.

To prevent steep gradients where there is a change in the level of the terrain.

As an alternative to a viaduct.

The opposite type of formation is a cutting.

The Victorian railway engineers tended, wherever possible, to follow the natural contours of the land to keep lines as level as possible. If that wasn't possible then it was an embankment, cutting, viaduct or tunnel. Sticking to contours is why we have so many lines that follow river valleys.

Modern builds tend actually to have more embankments, cuttings, viaducts and tunnels, not fewer, as they allow for straighter alignments and thus higher speeds. As opposed to following contours.

 

[PermitToTravel]

This type of formation is called an embankment.

 

[jopsuk]

in the Fens the embankments are often higher than they were when they were built, as the effect of draining the surrounding land has lowered the level.

But then, again in the Fens, the height also keeps the line clear of floods. When the line encounters a river it has to be a bit higher to ensure there's clearance below. If you're already building an embankment then the ramp the bridge may as well be as long and shallow as possible.

In other areas, this need for minimal gradient is often a factor. If a line is approaching a rise in the landscape, it may do so on an embankment that transitions into a cutting to keep the gradient shallow.

 

[Tomnick]

Engineers also usually tried (and continue to try, I'm sure) to design the formation such that the amount of excavated material from the cuttings along the route was roughly equal to the amount of material required for the embankments, to avoid the need to import or export vast quantities.

 

[Joseph_Locke]

Engineers also usually tried (and continue to try, I'm sure) to design the formation such that the amount of excavated material from the cuttings along the route was roughly equal to the amount of material required for the embankments, to avoid the need to import or export vast quantities.

Technical wordery - "balancing cut and fill".

Even if you built a railway on a flat surface the top of the sleepers would be 500mm above ground.

I can suggest another reason for low embankments - you very rarely lower the track, but you frequently lift and pack (or these days tamp) the track to maintain the track geometry. The net effect is that the track "floats" upward over time, making a low bank (common contraction of embankment) get taller.

 

[The Snap]

Engineers also usually tried (and continue to try, I'm sure) to design the formation such that the amount of excavated material from the cuttings along the route was roughly equal to the amount of material required for the embankments, to avoid the need to import or export vast quantities.

Technical wordery - "balancing cut and fill".

This is correct, still to this day.

Many projects have KPIs and KRAs to satisfy which require imported and exported materials to be balanced as much as possible, mainly to protect the environment and to reduce any environmental damage to the surrounding area.

A current example is the Norton Bridge flyover north of Stafford on the WCML. The chord being constructed there runs through a significant cutting for a large part of its length, then onto a large embankment to take it over the WCML. At the deepest point of excavation the dig reaches 15m below existing ground level. One million tonnes of muck will be excavated as part of the construction of the cutting, and every single tonne will be relocated on site to construct the embankment further north along the chord. Not a single tonne will leave site.

When HS2 starts, I have no doubt it will adopt a very similar model.

 

[LNW-GW Joint]

HS1 was built over the Essex marshes as a low piled viaduct rather than an embankment.
Must have been cheaper (using modern construction methods) or less environmentally damaging.
Modern high-speed electric lines use steeper gradients than the Victorians did, to reduce the length of cuttings/embankments/tunnels.
LGV (France) and NBS (Germany) lines have gradients up to 4% (1 in 25) compared to the typical UK main line gradient of 1% (1 in 100) or less.

 

[The Snap]

HS1 was built over the Essex marshes as a low piled viaduct rather than an embankment.
Must have been cheaper (using modern construction methods) or less environmentally damaging.

I suppose it depended where the nearest cutting construction was. Without a cutting, and therefore massive supply of material, I guess importing the material wasn't an option (not sure if there is a cutting nearby, I don't know the area!). Piles may well have offered a better solution in terms of stability of the railway - if the area is marshland, it could be that an embankment was not suitable due to settlement issues.

Modern high-speed electric lines use steeper gradients than the Victorians did, to reduce the length of cuttings/embankments/tunnels.
LGV (France) and NBS (Germany) lines have gradients up to 4% (1 in 25) compared to the typical UK main line gradient of 1% (1 in 100) or less.

I'd suggest the capability of electric trains nowadays in terms of tractive effort allows them to travel up a steeper gradient without being as affected in terms of deceleration as a steam loco might have been.

 

[HullMichael]

The mainline approach to Hull is from the west, so to reach the eastern docks and the Hornsea & Withernsea branches, the railway crossed the city at ground level, necessitating several level crossings which caused chaos every day. When the Hull & Barnsley Railway decided to build their own line (and dock) in 1885 they constructed it at a high level, essentially a four-mile long embankment around the city with underbridges for the roads and the river Hull. When Beeching closed the Hornsea and Withernsea branches in the 1960s, it was decided to remove the ground level line (and thus the level crossings) and use the high level line to reach the docks. This continues to this day with several freight trains a day using the high level "docks branch", but nowadays coal is imported and taken to Drax etc, not exported from the South Yorkshire mines as the Hull & Barnsley originally intended!