# Frost heave



## tom h (Jan 2, 2008)

This winter was a disaster for my layout, I have concrete down 3" thick with rebar you get from highways(got it free, love the price) that 1" green rebar, drove rebar down 3-4 ft in the ground and tied the other rebar to it, then poured concrete. We did have a bad year with moisture/freezing temps/rain then freezing, had major heave, cracked the concrete in 5 different places, my bridge abutments took the most damage, and I drove 2 pieces of rebar in the ground to make sure they stayed firm. My project last fall when I drove 1.5 in PVC in the ground 24-30 in in the ground then put Trex around on the PVC(ladder method) came out fine, no heave at all, level as can be. My question is why? Is it because the PVC is hollow? Then the dirt can heave in the middle of PVC? Curious to hear you guys opionons. Then when I rebuild my layout, am thinking how do I do my abutments then? With PVC and concrete? I have to cut out sections of the concrete because its cracked so bad and does not align anymore. So I have to replace it, like the PVC way because it was easy and so far lasted a whole lot better than my concrete did. But I am not sure how to do the abutments of my 2 bridges, and more to come.

Look forward to some of your thoughts.

Tom h


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## JEFF RUNGE (Jan 2, 2008)

When the ground freezes around the rebar it grips the rebar and pulls it out of the ground, the concrete just helps with the process. With the PVC, the frozen ground just slides.


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## Madman (Jan 5, 2008)

Jeff is correct. The concrete acted like a lever, helping to pull the rebar right out of the ground. Since the concrete was only in the ground by 3", as you mentioned, the frost had plenty of surface area along the length of the concrete roadbed to push on. The rebar that you drove into the ground was no match for the pressure of the frozen ground against the underside of the concrete. Thats why building codes call for foundation bottoms to be below the frost line, why is not the same depth thoughout the country. 
I started out with some concrete roadbed 19 years ago when I started building my garden railway. I was not comfortable with letting the track float on a ballasted roadbed like the prototypes do. What really made me switch to the floating roadbed method very early on was when I went to make track changes. The work involved with removing and adding concrete was way too labor intensive and costly. I wouldn't consider any other method of laying track these days, other than possibly a raised bench type layout.


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## rpc7271 (Jan 2, 2008)

Ideally the concrete should be below the frost line. Practically that is expensive. Driving rebar into the ground doesn't do anything to help. If you want concrete roadbed I would suggest a minimum of 8" thick. Preferably 12". Depending on the roadbed width use a top and bottom layer of rebar with about 3" between them sideways and 3" clear top and bottom. The idea is to let the concrete roadbed "float" on top of the ground. The rebar reinforces the concrete so it is harder for it to crack and break. It also spreads the upheave forces over the length of the roadbed. Worst case the rebar holds the broken pieces together. Eventually all concrete is going to crack somewhat because of temperature and shrinkage. Incedentally the "green" rebar you are getting is epoxy coated rebar. It's coated to help prevenr rust.


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## Dougald (Jan 2, 2008)

In establishin any track roadbed, it is worth examining the local building code to see what it says about structures similar to what is being contemplated. A concrete roadbed is like a sidewalk for example ... a raised benchwork is like a deck ... and so on. I do not know the problems faced exactly in different parts of the continent but the building codes locally are framed with both soil and weather conditions in mind.

Here in the Ottawa Valley where the frost line runs to 42 inches, the building code is very specific. And it specifies first of all, well drained but compacted, undisturbed and stable soil. In other words, if you are building in a swamp, on sand or worse on leda clay, then real engineering is called for. Otherwise the code tells what experience has found will work. Sidewalks always require a deep base of stone dust or crushed stone along with a thick slab of reinforced concrete. If the code is followed rigourously, the sidewalk is unlikely to crack ... ditto the roadbed.

For raised ladder trackage here, a deck structure works well. The code says 4x4 pt lumber set in concrete deck blocks on 4 foot centres resting on top of fully compacted stable soil. It has worked for OVGRS members who all build elevated trackage (as well as decks for bar-be-ques and summer relaxing).

Frost heave is serious business as are snow and ice loading in those areas that get a real winter. Every time the local building code is violated, the risk is run for greater repair and replacement down the line.

Regards ... Doug


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## NTCGRR (Jan 2, 2008)

Tom 
I'd like to see some photos, boy its hard to believe . I have never had trouble. I drill 4" holes ,then fill with concrete at bridge abutments. I pour sidewalks with 3/8" rebar , which means i don't put any rebar into the ground. 
Wish I lived closer to look at it. 
Even my big bridge has a pair of tee post in a 6" hole filled with concrete as abutments. 
Did it heave right at where the 1" rebar was in the ground? I'm thinking that is what the problem was???


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## tom h (Jan 2, 2008)

Marty, actually they did heave right where I put the rebar down in the ground for my abutments, I will take some pics tonite.

tom h


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## rpc7271 (Jan 2, 2008)

I think most of the problem is caused by the rebar that is driven into the ground. Without that the concrete roadbed would have faired better. As for building codes, most of them are way above and beyond what is necessary and definately prohibitive when building a garden RR. Obviously you don't want to have to rebuild your track and roadber every year but if you built everything exactly to code no one would be able to afford it. Fortunately 1n my area there is a gray area as to just what garden trains are. Most cities consider them landscaping. I would be interested is seeing just how much heavy has been encountered. Unfortunately it doesn't take much to derail a train.


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## NTCGRR (Jan 2, 2008)

I need to draw it but when i say drill a hole or dig one as I do when building decks. At the bottom I flar it as a pyramid to a flat base plus it keeps from pulling up in small supports like my abutments. 
Our building inspector requires this on any post hole type footing. I agree with it. Plus we have to have one stick of 1/2" rebar incase it cracks. 
I have spots where water regularly floods the areas around my roadbed but in winter no heaving. 
My only cracks is cold joints. from one pour to the next.


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## GG (Jan 1, 2009)

Marty, are you able to draw a quick sketch and post? I'm trying to understand but am a bit thick here. 

gg


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## Totalwrecker (Feb 26, 2009)

All rebar should be completely encased by the concrete, none into the ground. Use rocks to hold the rebar above the soil, the rocks become part of the crete. Let it float and it will stay whole longer, Where ever the rebar sticks out it draws moisture in. Resulting in corrosion, rust as well as freeze cracks. Most rebar is cheap steel. The ladder flexed and settled, the rigid crete cracked. 

I don't think you need that though. A trough of crusher fines for drainage and rail clamps and the track will flex naturally with the seasons. I use stainless and trust the screws, until they need replacing and then one of the rail clamps goes on. For sub ballast I use 1/4" gravel I screen on my land. Finer screenings around the ties. My desert sand is rough, stay away from river sand, it's too smooth. For embankments I use cribbing or stones. Most of my troughs are above ground! Like mainline track on an embankment, hold the main line The V and TW is a mighty short line...but growing.... my grand nephews made me do it! 

Track on gravel/crushers is held in place by gravity and the reluctance of stones to move in a crowd. Sure stragglers on the edges drift away with time, but my toe sends them home swiftly. Notice a boxcar sway? Lift the track push in a little gravel and gently wiggle the track back down to the profile, sway gone. The only change the 1:1 boys have made to roadbeds in 150 years is now they add a layer of asphalt on the dirt under all the ballast. It keeps the ballast cleaner, dirt can't vibrate up and clog the rocks. We use landscape cloth, weed barriers. 

Out here I get summer monsoons; inches in minutes, some gravel washes out, but looks realistic as it becomes evidence of water in my dry washes. Scoop some gravel out of the bucket, pour it through the ties, lightly tamp it down and cover with top coat. Brush with a 2 1/2 " wide soft paintbrush to tidy it a tad and a wiggle to level, then Back to running. 
Near the points I let more tie show. 

Do you attach your track to the concrete or does it float? I've noticed minor kinks where it floats on a trestle,(with in tolerances) but nothing where buried to the tie tops. 

Marty's hole has the cross section of a dovetail, he's still working on the bit; the tip is wider than the shank! Turn a drinking glass upside down, the taper of the dirt holds the foot down. 

I'm working on the bit to drill a square hole... 

Good Luck when trickery fails, 

John


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