Pervious Driveway Infiltration Rate

[XR250]

Does anyone have a table of washed stone infiltration rates?
I designed a pervious driveway for a customer which was basically 4 inches of surge stone over geotextile fabric topped with 1 inch of #67 stone . Apparently, the new state standard in our area is 4 inches of #57 stone alone (they used to allow any washed stone above .08 inches in diameter. That was changed without me knowing about it). They want me to prove that my design meets or exceeds the state standard. Intuitively, I don’t see how it can’t and also it has to be better than pervious concrete that is also allowed.

Yea, yea, I know it ain't a great path to drive on but the customer is actually happy that they didn't have to spend tens of thousands on pervious concrete.

Thanks!

 

[nackra]

Pervious pavement will require maintenance to remain "pervious"

About 15-years ago city installed an "innovative" infiltration drain system for a storm drain (aka, storm sewers in the Midwest) under a street. I learned about the installation after working for the city a couple of years. Street department staff complained about a catch basin (with no access lid) holding water and creating a mosquito haven. I pulled the plans and found that the catch basin outlet drained to this infiltration drain system. The system was plugged by fines and organics which blinded the pervious aggregate (relatively coarse if I recall). There was no access point to use a vacuum truck to clean the aggregate.

Long story short, the maintenance crews vacuum out the upstream catch basin periodically and dose the stagnant water with chlorine granules.

Like a gravity sand filter, the driveway will require periodic maintenance to perform.

 

[XR250]

How was this supposed to be helpful?

 

[SwinnyGG]

Obviously you did it wrong, XR.

Code compliance, customer satisfaction, and cost efficient construction methods be damned since they'll have to rake their gravel once a year.

RE: maintenance.. it will silt up. I have a gravel driveway (6" of 57 stone for the record) which collects fines and whatnot. It has geotextile under it, and a weed barrier, which so far has been very effective at keeping the stone from migrating downward. All I do is run out 300 feet of garden hose, and flush it out on a hot day using a spray nozzle and pushing the trapped dirt towards the sides (since it can't go down). Takes 2-3 hours once a year, I usually try to pick the hottest day of the year so the water will dry up quickly and since working in 100 degree heat isn't so bad when you can mist yourself down every so often.

Also, I agree, not helpful to your main question - but if your client brings up maintenance as an issue, that's what I'd tell them. 2 hours of maintenance per year is the tradeoff for the 20k you saved by not using concrete.

 

[XR250]

I honestly don't care how long it maintains its permeability. It will always outperform the pervious concrete that the town uses in some of its parking areas. I'm honestly thinking of getting a 5 gallon bucket of water and shooting a video of me pouring it on their pervious concrete and on the driveway and showing which drains better.

 

[SwinnyGG]

Random chart on page 4 below

http://www.mncompostingcouncil.org/...ment_2-eor_gravel_road_pad_imperviousness.pdf

Don't know if that helps at all, not a lot to go on here.


One more - specifically for subsurface filter layers, not sure if that helps

https://scholars.unh.edu/cgi/viewcontent.cgi?article=2311&context=thesis

 

[XR250]

The first one was actually pretty helpful. The second one makes my brain hurt.
Looks like they feel any washed stone has similar drainage characteristics..

Thanks!

 

[XR250]

Also, I agree, not helpful to your main question - but if your client brings up maintenance as an issue, that's what I'd tell them. 2 hours of maintenance per year is the tradeoff for the 20k you saved by not using concrete.

Pervious concrete also requires similar maintenance.

 

[cvg]

is it really infiltration rate that you need to prove? or is it the retention volume? pretty much all gravel or crushed will have relatively high infiltration rates.

your chart above does not apply to washed or crushed rock, it applies to unwashed mixtures of gravel and sands which probably have lower infiltration rates than any sort of crushed rock.

 

[XR250]

is it really infiltration rate that you need to prove?

The infiltration. The whole thing is a pretty dumb exercise if you ask me.
The town planner does not really understand things.

 

[TigerGuy]

Best not to confuse the planner with facts and information.

 

[swazimatt]

If this has already been constructed (which it must be otherwise why not just change the stone requirement in the design) I would suggest you do an infiltration test on site. There are numerous methods, but i would suggest using a cylinder that is not too big, infiltration will be to ground so cylinder will need to "seal" against the base filter fabric and measure the rate of water depth drop mm/hr (inches/hour glass) and keep topping it up until your drop rate becomes constant. This would be your base soakage rate which you would probably factor by 0.25 based on the fact that it is very likely to silt up over time

 

[XR250]

I thought about that. I'm gonna try arguing logic first.