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It’s Always Water

March 16, 2014

A prolonged cold spell is just coming to an end in Winnipeg, with water main breaks every day.   Over a thousand houses are without water because of frozen water lines.  These effects of frost reminded me of something a professor had told me years ago about his garage.

Even though it was built on piles, one corner of his garage was rising a bit every year.  Buildings on piles are not supposed to move like that.  His garage had three piles on each side.  These were poured-in-place piles that went below the frost line.  First they drilled the holes with a large auger.  They belled out each hole at the bottom by spinning the auger.  Then they lowered reinforcing steel into each hole and filled them with concrete.  They also poured a grade beam along each side, tying in the reinforcing steel in the grade beam.  The garage itself rose on top of the grade beams.  That seems to be the typical way garages were built in his area.

Now this professor was a soil scientist.  He got out his shovel and excavated along side the grade beam where the garage was rising.  There he found alternating layers of clay soil and ice under the grade beam.  It was the ice, of course, that had pushed the garage up.  One pile had separated from the grade beam.  Another pile stayed attached but had been pulled up.  These things are not supposed to happen.  The professor described this situation to several Civil Engineering professors at the university.  They were interested to hear the story, but couldn’t offer much advice.  He also talked to contractors to get answers to his questions.  One contractor told him that they attempt to bell out the hole for the pile, to prevent it being pulled up, but they can’t really tell what is happening at the bottm of the hole.  He also stated that they do put a layer of gravel below the grade beam to provide drainage, but that it sometimes gets incorporated into the clay soil.

The cause of this problem must have been water getting into the soil under the grade beam and then freezing over the winter.  In fact, one of the evestrough downspouts from the house discharged beside the garage.  That would have kept the soil waterlogged in that area.  Surface water might even have run down underneath the grade beam.  I learned a long time ago that nothing can resist the force of water when it freezes.  If freezing water can split rock, it can certainly raise concrete.

I recalled this incident a few years ago when I had a new garage built behind my house.  My garage isn’t built on piles, though.  It’s on a concrete pad that’s poured over a layer of gravel.  I knew it was critical to prevent water getting into the gravel under the pad.  One thing I did was to build the soil up to half way up the concrete and to slope it away from the garage.  The other was to make sure that evestrough downspouts from the garage had extensions so they discharged water a couple of metres away from the garage walls.  I’m hoping that those measures are sufficient.  Water is always the problem when it meets concrete here.  Time will tell.

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