Concrete Pit Design

[Slaze]

Consider designing a four walled concrete pit with a concrete bottom and open top. The walls are 9 ft wide inside. The top of concrete at pit floor is 8 ft below grade with another 2 ft projecting above grade. Would the pit walls be like a retaining wall and size for vertical flexural reinforcement? Or would the main flexural reinforcing be horizontal, spanning between the two perpendicular pit walls?

 

[dik]

What are the plan dimensions? and the soil type? do you have a sump within the pit? or is the pit drained somewhere else? Is there a cover over the pit?

Dik

 

[hokie66]

For a small pit like this, 9' square in plan (I think that is what you mean), I would design it as spanning horizontally, then probably use the same reinforcement vertically. Put the horizontal bars in the outer reinforcing layer to facilitate concrete placement.

 

[Slaze]

Yes, it is 9 ft square (inside)in plan. The pit will have a sump.
There is no cover over the pit.

 

[dik]

You would likely be looking at 8" concrete walls and possibly sitting on an 8" concrete floor slab (maybe your code dictates 10" min). Reinforcing as per design can be relatvely small, ie. temperature steel plus a bit maybe... care to detail at corners.

Do you require provisions for a temporary guard at the top?

Dik

 

[dcarr82775]

PCA has a handy book that gives you moment and shear coefficient for two way action given various boundary/loading/geometric ratios. Very handy book for tank design. I would think controlling moments will be horizontal at the corners for what you described.

 

[dik]

and also loading from surcharge and restraint at the top can have a significant effect.

Dik