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Re: Water Retaining Concrete

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"Chance, Acie P." wrote:

>I am designing retaining walls which will form the edges of a lagoon.
>The first two walls we poured have cracks which go completely
>through the wall.  The cracks appear to be shrinkage cracks. The mix
>design uses 4000 psi concrete with flyash, super P and well graded
>aggregate. The walls are between 10 and 20 ft. high and 2 ft. thick.
>Vertical steel is # 7 @ 12 back side and  #5 at 12 water side. Horz.
>steel is # 5 @ 12 both faces. Crack control joints are located at 25 ft.
>O/C. This follows ACI 350 recommendations. I am worried about the
>damage to the rebar from the chlorinated water moving through the
>cracks. We do not intend to waterproof the lagoon but we do need to
>insure the structural integrity of the wall.  The existing cracks are from
>.002" wide to .035" wide and will be injected but I have a lot of wall left
>to pour. If any one knows of a good authority on cast in place concrete
>for water retention I would be interested. 

Probably your best source would be the Corps of Engineers, since they
have extensive experience with water retaining structures.  Call your
local district office or visit their web site (if they have one) and ask for a
copy of their Engineer Manual "EM 1110-2-2104", which is called,
"Strength Design for Reinforced-Concrete Hydraulic Structures", dated
June 30, 1992.  It essentially refers to ACI 318 with several important
modifications to help control cracking.  One modification is the use of a
hydraulic loading factor of 1.3 in the design in addition to the other
loading factors.   This will increase the amount of reinforcing in the wall
resulting in lower stresses in the steel and better crack control.  The 
code also requires a four inch concrete cover on walls 24 inches thick
and greater.  I hope this helps.

Michael S. Davis, P.E.