A Lifted (Heaved) Basement Floor Slab

Posted by in Basements, Concrete, Unusual, Water Sources, Weather Events | August 08, 2016

What would cause a concrete basement floor slab to lift in this fashion?

Figure 1 Basement floor slab heaved and cracked.

Figure 1 Basement floor slab heaved and cracked.

The basement floor slab was lifted up about eight inches or so.  The area of floor slab over the sanitary sewer lines was lifted more than the other areas.

Figure 2 Basement floor slab heaved and cracked.

Figure 2 Basement floor slab heaved and cracked.

The home owner reported that he observed water gushing up through the cracking in the floor to a height of approximately 1½ feet during a heavy rain storm.  He further reported that there had been flooding in the streets.

The report of water gushing up through the cracks indicated that the lifting was due to excessive water pressures.  The greater lifting of the floor slab over the sanitary sewer lines indicated that the water under the floor came from a broken or separated sanitary line and/or through the gravel filled excavation for the sanitary sewers, storm sewer lines, and water supply lines.

The heavy rainfall and flooding in the street indicate that the water in the sanitary lines or the gravel filled excavation was from the excessive accumulation of storm runoff in the storm sewers and on the streets.

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