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jddoe (Structural) (OP)
22 Jan 06 14:55
To All:

I am dealing with a garage floor in the midwest.  Garage is 24x24 attached to home.  There is a post dead center that carries a floor beam above.  There is a footing under this post.  The garage floor (concrete slab on grade) has heaved and cracked considerably.  The doors in the rooms above the garage have stuck at times.  Some where cut off in order to close.  The movement seems to have settled down (10 year old home) but the garage floor looks like a road map.  It appears to me that that slab has heaved up enough to pull the footing (20"x20" x depth??) up off the soil.  There is a trench footing under the wall where the overhead doors are located. The slab is poured over the top of this footing.  The slab has lifted off of this footing, up to one inch +/-.  One bearing wall, 8ft away from the garage, (that rests at the same level as the garage floor) in the home, has also heaved up some, it is noticable in the floor directly above this wall.   The builder's engineer said there is expansive soil in some parts of the town and suggested that I don't plant any trees nearby (don't want to add water) and that I don't let the soil dry out too much.  Great advice..??

I have consulted a university professor who has been involved with similar situations.  His remedy is to bore 6"diam. (+/-) holes on a 2ft grid throughout the garage foor,(keeping 2ft away from the exterior walls) remove soil from each hole to a depth of 4ft+/-, fill hole with quick lime (keep away from water and lime, explosive results..) to 6-8" below the slab, fill the remainder with gravel and cover for 8 to 12 months.  The lime will interact with the soil particles to stop the expansion.  After this time the holes could be grouted and the cracks repaired and some top coat applied.  Probably would live with the heaved interior bearing wall.  This wall would be close to the lime columns in the garage, may migrate enough to help..??

My quesion(s):  What is the interaction?  Does the lime change the affinity of the soils desire for water?  Change the pH?  Is water causing the expansion? Would this fix cause any settlement of the expansion or just stop/slow future expansion?

Any insight, advice, remedies, experience, etc...would be appreciated.

JedClampett (Structural)
24 Jan 06 10:53
The chemical reaction is pretty complicated involving ions and stuff like that.  I don't understand it.  I'm sure you can do an internet search and get some references.  But the bottom line is that the lime reacts with swelling clays to form a cementatious like substance that is pretty inert.  It won't swell or absorb water.  One of the many uses of lime treatment is to build temporary construction roads in wet environments.  They lime treat the grade and a "crust" is formed that can be driven on.  We use it a lot in Texas to improve soils under roadways.
Iv'e never heard of it used the way your professor recommended, but it seems to make sense.

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