Seismic Load for Design Underground Concrete PIT for Water Retaining Structure

[Notch08]

Hi Every one,

Doe any one have any input regarding Hydrodynamic considerations for underground concrete pit during seismic activity? Is is an additive from the lateral earth pressure or does it lessen the lateral earth pressure for wall design?

 

[r13]

Externally, hydrodynamic pressure is in addition to the hydrostatic and soil pressure on the pushing side, and it reduces resistance force because of suction.

 

[JedClampett]

It might do either, but from someone who does water bearing structures for a living, we don't consider anything that reduces loads. We consider the case of soil without water pressure and water pressure without soil. Seismic is a little less cut and dried, but I'm sure I have colleagues that don't use the soil pressure to resist seismic sloshing.

 

[r13]

You should check USACE engineering manual on design of hydraulic structures for seismic loadings. Pay attention to structural stability.

 

[Notch08]

Thanks for your inputs, so in summary we dont apply these loads simultaneously under the same load combination?
Im pertaining to hydrodynamic loads induced by liquid inside, the pit by the way.

 

[Notch08]

@r13 do you mean that we can add the hydrodynamic force by the inside liquid from the lateral soil pressure from the outside due to suction?

 

[r13]

No. Keep internal empty. Sketch below shows hydrodynamic pressure and suction.

 

[Notch08]

So this is pertaining to Hydrodynamic loads by liquids outside of the pit. How about the liquid inside? Does it contribute any stress together with lateral earth pressure, or are they not applied simultaneously under the same load combination?

 

[r13]

You can add internal case, especially if you are certain there is always have presence of water. However, no matter in view of structural stability, or design, the internal empty case will always govern. Check me out on this, I could be wrong though.

 

[Notch08]

Ok. Thanks for your inputs

 

[r13]

You are welcome. Owing to the complexity of hydrodynamic soil water interaction, and the consideration of devastating consequence of failure, we can only hope we are err on the conservative side. Good luck.