Construction Joints in Small Clarifiers (WWTP) 1

[jjezmarlo3]

Hi everyone,

I have a small clarifier (20ft ID, 12" walls, 66ft wall circumference) I am designing for a WWTP and I am looking at the wall/slab construction joint layout (with waterstops of course). Usually in the water tanks we design, we limit the maximum wall length between vertical construction joints to 30ft or 40ft, and locate a horizontal construction joint in the slab at the same location as the vertical wall joint. For clarifiers, we generally pour a round portion of slab at the center of the tank, and then pour slab segments outside of this that line up with the vertical wall joints. For a small tank like this, I would like to break up the walls into two 33ft long pours, but only use one pour for the base slab, as for such a small slab I don't know if breaking it up into separate pours is reasonable. However, this arrangement creates a condition where a vertical wall construction joint is not located over a horizontal slab construction joint. Has anyone ever had this condition for a water-tight structure?

 

[JedClampett]

If you don't have the joints match, there's a possiblity that a crack will transmit from the wall to the slab. Also note that the perimeter of the slab is the same 66 ft length as the walls. I'd add a joint in the slab and two in the walls.
Seems like a pretty small clarifier.

 

[hokie66]

I would eliminate the joints, both in the slab and walls. 66' of wall should be easily cast at one time.

 

[jrfroe]

I would pour both the slab and the walls in one pour each. Look at it as a structure with a maximum horizontal dimension of around 22' instead of 66' of linear wall. The shrinkage forces in the wall would act uniformly on the entire three dimensional structure, so I don't see any reason to base the joint spacing on the circumferential length of the wall.