Spillway Loads 2

[bpstruct]

I am working on a spillway project for a pretty big dam. I am struggling with rationalizing some of the loads that will be present on the spillway channel bottom. The dam is clay (an "impervious" layer of soil covered by concrete slab), and I do not believe that we will have uplift due to unbalanced head despite the fact that we have a weir on top of the spillway set at normal water surface elevation. But, I do think there is potential for cavitation on the slab during storm events at the downstream face of the weir as water flows over. No way to calculate that though - at least not that I can find. Not really sure that there is a good way - I believe that cavitation is an abrasive force. I am also struggling to find a reference that quantifies uplift on the channel bottom due to water flowing over the slab. I can find equations for the tractive force, but nothing on uplift. Seems there would be some uplift, much like we have uplift on a roof as wind flows over the top. I have checked out "Design of Gravity Dams" and "Design of Small Dams"....no luck.

Any help would be appreciated!

 

[WARose]

There are a lot of different types of spillways. If you have anything in the flow (i.e. to break it, or edges) the drag on it will typically be the critical (net) loads. I think there is some (hydrodynamic) uplift......but IIRC it is almost always offset by the wight of the water involved in the flow. I'll check on the uplift in a couple of references I have.

 

[jayrod12]

Might want to look into bridge pier design for scour information (the abrasion you mention).

 

[ishvaaag]

By searching

Link

I found this

Link

Look 4.3 there.

I also read in another found item that uplift may exceed the head.

Hope this helps.

 

[Ingenuity]

Sorry for the thread hijack...

ishvaaag - welcome back to Eng-Tips

 

[dhengr]

Ishvaaag:
Highjacking or not, I second that welcome back.

 

[JedClampett]

Welcome back ishvaaag!
Get USACE HYDRAULIC DESIGN OF SPILLWAYS Engineer Manual No. 1110-2-1603 and
STRUCTURAL DESIGN AND EVALUATION OF OUTLET WORKS Engineer Manual No. 1110-2-2400
They should be on line.

 

[ishvaaag]

Thank you all and best wishes to everyone. Not that I can spare much time as of now, but it has always been and is a pleasure to be here.