size of stone in a retention pond. 4

[escoline]

Hole in ground holding water. Requirement is to maximise the volume of water in hole. Stone added for safety. What size stone should be used. No filtration requirement.

 

[gbam]

escoline, the porosity is more important than the size fraction. Make sure that your specification requires the appropriate porosity. Then you need to determine whether you plan on storing the entire design volume within the rock/gravel. Then your hole size will need to be the correct size accounting for the porosity of the stone.

 

[beej67]

What determines void ratio in stone isn't necessarily the size, it's the gradation.

Imagine you've got a bag full of marbles, and you dump it into an aquarium. You're looking at around 35% voids, 65% marbles. (I've seen some designers assume 40%, but I like to check with the aggregate specifications before I assume that) Now imagine you mix in a bag of marbles half the diameter of the first bag. The second bag fits in the gaps, and reduces your void ratio. Now imagine another bag of very tiny glass beads mixed in. Void ratio goes down further.

What you want is "uniformly graded" aggregate, which means it's mostly one size. Typically people use "washed #5 stone" for stuff like this.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

question the "safety" aspect. explain how the stone increases it? riprap is usually used for erosion protecton and perhaps also to control vegetation.

 

[fattdad]

aggregates of one gradation are called, "poorly graded," or, "open-graded." I'm not sure what uniformly graded means, but I do know what poorly graded means.

Clay typically has the highest void ratio. That said, it's clearly not appropriate for this project.

I'd be perfectly o.k. using #5s though. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[beej67]

http://en.wikipedia.org/wiki/Soil_gradation#Poorly_Graded

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[fattdad]

Just using ASTM and AASHTO vernacular. Never thought to check Wiki. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[civilman72]

I thought you were both right (poorly=uniformly), but I just checked Wiki and could not confirm... Wiki has purposely shut down. Here's the reason:

"Right now, the U.S. Congress is considering legislation that could fatally damage the free and open Internet. For 24 hours, to raise awareness, we are blacking out Wikipedia."

Wow. Haven't heard anything about this.

 

[beej67]

Wow. Haven't heard anything about this.

Wow, really? It's quite a big deal. At the risk of derailing the thread, SOPA/PIPA would mean that the government, with no trial and no judge and no due process, could shut down a site such as Wikipedia or Youtube or EngTips simply because one of the *links* on it, posted by a user and not the site itself, linked to another site they thought was "dangerous," or because a competing company claimed (with no burden of proof) that the site in question had violated copyright. It's horribly worded, and being ramrodded through by some very rich players in the media who want to use it as a weapon. Further, it doesn't really do anything to "Stop Online Piracy" or any of the things it intends to do. Quite a boondoggle. It would easily shut Wikipedia down, or EngTips, or any site that relies on user generated content, simply because they don't have the manpower to actively patrol every link on their site.

To add fuel to the fire, the congressman who wrote the SOPA legislation is actually in violation of his own legislation on his own website, because he doesn't even realize the scope to which his legislation was drawn.

So yeah, politics as usual.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com