cracks in launder of water retaining structures

huangyhg

cracks in launder of water retaining structures
a launder wall of height 1.5 m is taken  cantilever from the base slab of launder. the thickness o launder is 150 mm and the grade of concrete is m25 (ready mix concrete). the steel provided is 10 tor @ 150 mm c/c.
the vertical through cracks are generated in the launder at a approximate spacing of 4 to 6 m.
as far as design & detailing is concerned it is absolutely perfect, but the cracks are developed in the wall, what may be the possible reason ?????
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pray tell:  what is a launder wall??  is it a local term?
punnarkar,
what is the size and spacing of the horizontal steel?
do the cracks start at the top of the wall?  how far do they go down?
how long is the wall?
is the wall affected  by temperature changes?
to bigh:  the term launder in water and wastewater treatment is used to describe a channel at the top of a basin used to decant the surface liquid from the top of a basin.  they are commonly used in clarifiers to separate the heavier solids from the liquid.  in a round clarifier they are "l" shaped ledges near the top of the basin with the vertical leg acting as a weir and the horizontal leg attached to the wall acting as a collector channel.
to punnarkar:  when a wall is attached to a slab, sometimes shrinkage cracks appear in the wall.  this is because the slab is poured first and drying shrinkage occurs.  when the wall is poured, it is restrained by the slab, so horizontal stresses are created by shrinkage forces.  the solution is to add extra circumferential steel in the wall to control these cracks.  
thanks - i've seen them but never knew their name.