Raised level track construction method

[Les RileyParticipant @lesriley75593]

Happy New Year.

Our club are deliberating an extension to our existing raised level 5″ / 3.5″ track layout.

The existing track is built on concrete “tank teeth” plinths with steel strip rails joined by spacer tubes and studding.

This obviously involves casting a lot of plinths (about 300).

Existing track

We have a supply of scaffolding tubes and the adjustable feet for same and are considering whether they could be used instead. Pole driven into the ground around 3 to 4 feet and foot upside down on top for fine level adjustment.

No concrete involved.

We have recently built a Gauge 1 layout using this method but passenger trains weigh a bit more!

Gauge 1 Method

Obviously the track posts would be a lot lower in the ground than this.

So, does anyone know of a club track that has something similar? We are interested in the stability aspects of a single pole. I suspect there maybe tracks that have similar single pole but maybe concreted in the ground?

Thanks,

Les

[duncan webster 1Participant @duncanwebster1]

Some of our signal posts are just driven into the clay ground. Different levels of water logging affect how wobbly they are, never fallen over yet. They are not driven that far in, maybe a couple of feet.

[Nigel Graham 2Participant @nigelgraham2]

You could do that, using a pair of poles per pier, but the poles will soon and quite rapidly corrode, whether galvanised-steel or aluminium. Especially in what look like quite impermeable, water-retaining soil. Naked pipes simply sunk into the ground will also want to sink further if they can, especially when the soil is as wet as seems possible.

A better solution would be concrete ground pads with the pipes held to those by appropriate galvanised-steel sockets – all commercial items.

 

Our club’s main track is ground-level but the raised 16mm-scale circuit is held on plastic drain-pipe columns in concrete footings. If you do that, note that the PVC pipe intended for buried services is attacked by sunlight, and we have keep ours painted. Not suitable for passenger-carrying trains just on PVC pipes of course, but it might be feasible to use large-diameter pipes filled with concrete, preferably reinforced. Then the tube is just a mould/covering.

Really, concrete is about the most reliable material for such ground-works but yes, it is heavy and time-consuming to use. One option is to cast in-situ: make, say, 10 timber moulds, fill each with concrete on its location on prepared ground, the mix with carefully gauged water and properly tamped so self-supporting after about two days (but not fully load-bearing for at least two weeks); release and move the moulds to the next set. So no handling of tank-traps themselves.

Is that ground heavy clay? Ours is, and it does give weather-related expansion and contraction problems; by both ground-water and the sun’s heat. So being able to adjust the rail’s bearings on the supports is a wise idea.

 

Your existing raised track looks much the same construction as my club’s first one; built on reclaimed quarry land. It was generally stable but the plinths, about 18″ square on their bases, did sometimes subside slightly.

An alternative may be to install concrete foundation pads to carry piers built from standard concrete blocks, with adjustable pads under the rails. One raised track I have seen, looks as if on a continuous wall partially embanked for appearance – but that’s a lot of material and work!

 

[BazyleParticipant @bazyle]

Newton Abbott track uses scaffold poles for a raised track including 7 1/4″.

[Les RileyParticipant @lesriley75593]

Thanks both.

Sadly the NA website doesn’t show much but I will enquire with them.

[brickyParticipant @bricky]

Hi Les,Look at trench blocks they may do the job.

Frank

 

[duncan webster 1Participant @duncanwebster1]

We use 9″ dense hollow concrete blocks as supports. Either a solid 4″ on its side or a cut piece of 2″paving flag on top to give a flat top. Some of our pillars are very tall to get the track level and give something to screw down to, then an embankment made of polystyrene blocks covered in soil to make alighting safe.

[Les RileyParticipant @lesriley75593]

Thanks gents but I am only looking for info about anyone using scaffolding poles (or similar).

We have a pile of poles and screw adjusters in stock that were free. Obviously if we can use them it saves us a load of cash.

[noel shelleyParticipant @noelshelley55608]

A single pole will be unstable, will need 2 poles per stand. If the material is galvanized then that will help, but the real problem will be at the ground level where stress cracking will occur, followed by corrosion and finally failure. Use them but maintain a close inspection regime to detect any sign of the above from 3″ below ground to 3″ above. Noel.

[noel shelley]

On noel shelley Said:

A single pole will be unstable, will need 2 poles per stand. …

Or more!

In addition to the problems mentioned by others, my concern with poles is rigidity.   Trains require a firm bed that won’t move much, which is why railways never use suspension bridges.  They’re too bouncy and it doesn’t take much movement to derail a train.

Scaffold poles are springs and there’s nothing to stop the single poles shown in Les’ prototype photo, bending and recovering with a flipping action.  The track won’t break when a heavy train takes that curve at speed, but the poles will bend and release the energy when the loco hits the straight, or brakes, risking derailment.

Les says the poles will be shorter, which will reduce spring considerably, but it’s still dodgy, and might resonate.   I think the posts have to be cross-braced and stayed as well.  Wood has a similar bendy problem, so elaborately braced ‘A’ frames are typical in railway bridges.  They resist sideways and fore-aft movement.

Speed limit likely too, and ideally no tight curves!

I’m sure scaffolding will work, but single poles are risky.   The existing raised track on concrete blocks is much less bendy design.  Scaffolding needs more thought – what could possibly go wrong?  Building a test track is a really good idea, but it needs to be long enough to run a heavier than normal train at double speed.

Dave

[duncan webster 1Participant @duncanwebster1]

Before launching into a test track, which would have to be quite long to allow train to get up to speed and stop again, some sums might help. If we take 4 off 14st passengers per truck, the mass on 2 adjacent bogies is 356 kg. Assume 10 mph (4.5 m/s) and 40ft (12.2 m) radius curve and you get 583 N (~130 lbf) sideways force. Then you can drive a pole into the ground leaving whatever height the tallest will be and repeatedly apply the force, probably needs the local tug-o-war team, and see what happens. You’re still not sure, because if it’s clay soil, as it dries out it shrinks, our signal posts are definately more wobbly in summer.

[Nigel Graham 2Participant @nigelgraham2]

I am sure two scaffolding-poles driven to some depth and firmly cross-connected (perhaps by tube and tubular-socket fittings, e.g. “Kee-Klamps”) will be strong enough and exhibit none of that springing Dave worries about, as the height above ground is pretty minimal; but I still think corrosion will prove a problem in future. Wet soil is not the place for either steel or aluminium.

[Dave HalfordParticipant @davehalford22513]

It depends on how soft your land gets. I can’t keep a linen line vertical even with an 18″ slab buried end on to stop it. Our winter water table is only 4″ down even though there’s a 2 foot deep field ditch 20ft away.

[Nigel Graham 2Participant @nigelgraham2]

Deep clay ground can be as bad when very dry. Though it takes a lot of wet weather to soak it, it takes enough water to shrink on drying, distorting structures based on it.

As we found at my club’s track, though that is ground-level. We also have a raised 16mm-scale layout built on tubular piers, and such ground movement has given it an undulating profile and some lateral distortion, although it is still useable.

[Nigel Graham 2]

On Nigel Graham 2 Said:

…. will be strong enough and exhibit none of that springing Dave worries about,….

Try it and see!   Hold a 750mm length of scaffold pole in a lathe chuck, put a DTI on the far end and press with a thumb.  No danger of the pole breaking, but it will deflect and return when released.  It’s a spring that obeys Hooke’s Law.

The deflection is proportional to the forces applied, and on a raised track they depend on the mass of the train, how fast it’s moving, is it on a curve, and how quickly it accelerates / decelerates.   The forces are significant and not just the weight, see Duncan’s post.

In a concrete block track the forces are grounded, getting rid of the energy.  Not so in a line of single scaffold poles: they will deflect, storing energy as they do so, and then return it to the track as the train passes over, possibly derailing it.   For the same reason it’s unwise to pressure test boilers with compressed air.  Air is a spring, and pumping energy into a boiler that might fail is unwise.

Possible to manage springy materials by adding cross-bracing, but that’s not what Les described.

Dave

[NealebParticipant @nealeb]

Speaking as chairman of the Newton Abbot club, and despite comments above to the contrary, you can build a 3.5/5/7.25 raised track sitting on single scaffold poles. Ours has been sitting there happily without moving for longer than the 12 years or so that I have been a member. I understand that the poles were originally inserted by pushing with a large bucket on the end of a JCB arm!

Les – if you would care to send me PM via this site with an email address, I would be happy to discuss details.

Is this another triumph of experience over armchair theory? Said strictly tongue-in-cheek…

[Author]

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