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SteveHen (Civil/Environmental)
19 May 09 4:34
How do I calculate the frost depth in a concrete slab? What formula should i use?

I am working in an area where typical frost depth is around 6 feet. But as concrete is a worse insulator than typical soils, is the frost depth greater? how do i calculate this?

We have a 2m thick reinforced concrete base slab for a highway tunnel. Initial ideas were to put surface water drainage pipes within the slab but these would then be above the frost depth.

Should the drainage pipe therefore be placed below the concrete slab? And would we need to provide a layer of insulation board?

We don't want the drainage pipes to freeze, block up and the area to flood!
 
GeoPaveTraffic (Geotechnical)
19 May 09 7:43
You need to hire an engineer who practices in that part of the world.  They will be able to help you determine how the pipes should be placed.
CarlB (Civil/Environmental)
19 May 09 13:44
The "frost depth" concept doesn't work well in this application. A tunnel would not have a "frost blanket" of uniform thicknesss in ceiling, walls & floors.  At floor the ground (earth)temperatures would not be the same as at outside surface. Initial ground temperatures (before freezing onset) will vary, temps in tunnel will vary, etc.

To be (somewhat) safe you could heat trace the pipes from inlet to non-freezing outlet. Placing pipes under the slab, and with some insulation over them would provide pretty good protection.

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