I haven't seen the job yet but the customer said that he has a large slab that lifted about an inch due to the harsh winter but then went down again. He wants to know what can be done to prevent if from happening again. My first thought that the lack of a footing was the problem. However, he would like to know what other solutions exist.

 

No solution exists beyond ripping it out and re pouring it. That is one of the consequences of floating a slab on grade.

Heaving due to frost can be mitigated if the base under the slab is prepared right to allow for good drainage and runoff.

Is this a slab for a building or just a patio or walkway? There usually is no issue if it is not supporting a stucture because as he learned, the slab will generally return to its original position once the frost is gone.

 

1, hire the 5 biggest folks in the county & have 'em sit on the slab every winter might need 6 or 7 if it gets real cold; OR 2, don't let the ground under the slab freeze !

you already know what to do, pulp - if the ground's going to expand from freezes, slabs move - same w/conc highways - they also move,,, eventually the slab won't return to its original position then it may be an issue for repair,,, footings below the frost line, properly compacted base of suitable mtl under the slab, steel tieing in slab to foundation would have prevented this problem,,, but you know that too.

good luck !

 

LOL You guys are funny. The customer was hoping that there was an easier solution & I told him that I would ask. The slab is just a walkway but he also mentioned that a fence around it was removed & replaced at a later date. In his mind, that's how water may have gotten under the slab. I'll give him the news if & when he calls or maybe I will at least look at it.

 

Here in Vermont, the frost gets into the ground pretty deep. Often, 4' footings isn't enough.

People will tell me that the "frost pushes things up every year; but they come back down".

They may come back down, but never quite as much as they went up; because of varying amounts of sand and silt that fall down below whatever the moving object was. Each year, a deck or a drain pipe, a side walk, or a camp's toilet . . . . may go up 7" but it may only come back down 5½". After a few years or a decade, that difference can add up to some serious heaving. And the Sun can play a big role in how crooked that heaving is.

I'm in Real Estate and often encounter buildings, camps, barns, sheds, docks, retaining walls, et cetera that present optical illusions . . . . as if they were constructed that way as a joke because they can make you dizzy just looking at them. Holding a plumb bob up to one can be an eye-opener.

That's one of the reasons that Banks now loan on Double-Wide Mobile Homes ONLY if they're set on deeply footed and reinforced continuous concrete pads. Too often in the past, frost heaving would send one half of the mobile going one way and the other half going the other . . . . until the Unit was split and irreparably damaged. Not something you'd want to be holding a mortgage on !

What goes up must come down . . . . but sometimes not all the way (or in unison).