Underwater Angle of Repose

[jreece]

Does anyone have any reference information (preferably published) on determining the underwater angle of repose?

Thanks

 

[ItsOnlyDirt]

Hi

Are you considering a material tipped into water? or are you considering a slope under water which has been placed/compacted under engineering control ??

They are very different things, so best to clear it up.

 

[fattdad]

this is an impossible question. "Angle of Repose" is really not an engineering term. In it's common vernacular (dry stuff falling into a pile, it's closely related to friction angle, which is an engineering term. It's typically related to the friction angle for "loosely" placed materials (i.e., nobody requests an angle of repose for compacted materials, eh?).

Fundamentally, the friction angle is not affected by pore-water pressure. So, whether your pile of material is submerged, the friction angle would not be affected. The placement density as the grains "fall" to the bottom and the instantaneous pore-water pressure may lead to some "liquefaction" which would in tern "flatten" the pile. I just don't know if this has been quantified. I'd rather think not.

There may be something, but I've never heard of it, for what that's worth. . .

Good luck.

f-d

¡papá gordo ain’t no madre flaca!

 

[dgillette]

http://140.194.76.129/publications/eng-manuals/

You might start with the Corps coastal engineering manuals. If you are interested in sand or finer material, the tailings literature might help.

A priori, I would expect coarse, free-draining material (say, clean +3/4" gravel and larger) to dump at the same angle below water as above it. From experience, finer-grained material, like sand, will run out to very flat slopes if dumped into water, because of the pore pressure issue fattdad talks about. If you place it a spoonful at a time, it would probably be free-draining on that time scale and pile up at 30 degrees or steeper.

DRG

 

[BigH]

remember infinite slope analyses? The slope angle of Saturated (submerged) slopes for SF=1 are approximately 1/2 of the slope angle for dry slopes.

 

[dgillette]

True BigH, but that's for a saturated slope under air, not one under standing water, where you could say the effects of pore pressure and bouyancy - is that spelled right? - cancel each other (eff stress is ~half, but bouyancy cuts driving force ~half).

However, drain the pond too fast and the steep slope will ravel back to about half the original slope, or flatter (Wachusett Dam).