FLashfill/CDF

[wnwniner]

I work for a local government where we see flashfill being used for utility repairs under pavement. We seem to be experiencing "heaving" in these areas, especially in the winter months (midwestern climate). In the summer these areas actually settle a little closer to level, but in the winter there are bumps in the road and concrete sidewalk panels that are heaved up. Has anyone else experienced this, and does anyone know why? We beleive that the fill is freezing and expanding, lifting the surface above. If this is true, would keeping flashfill below the frost line prevent this from happening?

 

[msquared48]

A stab in the dark here...

Maybe the CDF is transmitting cold to the underlying soil causing that to freeze if it is at or below the seasonal water table? The soil above the bottom of the CDF may be above the water table and more of an insulator to the material below. Thus, you may see the heave in the winter over the CDF.

Mike McCann
MMC Engineering

 

[cvg]

I'm not sure that CDF is considered an adequate alternative to non-frost susceptible backfill. And if the trench does not go below the frost penetration depth, then it may behave similar to a shallow footing that will heave. And Msquared48 also hit on another factor that frost depth is always greater in roadways and the CDF may even aggravate this by transmitting the cold better than earth backfill.

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