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Concrete Slab Cracking

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Allan Yango wrote:

. > According to the Project Manager, they have attained a more than 95%
. > compaction (Modified Proctor Test). 

and

. > the soil is expansive in nature 

which may be the cause of your problem.  Contrary to normal procedures, 
compaction of expansive soils is more likely to **cause** problems than to 
prevent them.

An example is cited in the Civil Engineering Magazine, August, 1987, article, 
"Treating Expansive Soils" (by D. Earl Jones, Jr. and Karen A. Jones) as 
follows:

   "The problems that may arise ... were exemplified in a 2,487-home 
subdivision built 30 years ago in Thornton, Colo.  Site preparation involved 
massive regrading in virtually dry expansive clays and shales.

   The Federal Housing Administration denied mortgage insurance on all homes 
built on fill in the development, because the fills were simply end-dumped 
without any moisture or density control.  The agency granted mortgage 
insurance on homes sited on cuts as deep as 30 ft.

   Within five years after construction, many homes on the cut areas were 
seriously damaged or destroyed by heaves of up to 2 ft and more.  Few homes 
on the loose uncontrolled fills have yet been appreciably damaged."

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona