French Drain Specifications

[altor]

Do civil engineering handbooks have basic french drain specifications? I would like to create a drawing to submit to San Diego City with a section view of the elements of a french drain. Any documentation available or a pointer to where I can find one would be greatly appreciated.
Cheers

 

[dicksewerrat]

Just dream it up. Trench, geotextile fabric, drain rock, perforated pipe. Size and slope is up to you.

 

[Ron]

altor...dicksewerat is right, but go to the Florida Department of Transportation website and look at the french drain detail to help you visualize your dreams!

I specify a "socked" perforated pipe, AND lining the trench with filter fabric.

 

[GeoPaveTraffic]

dicksewerrat and Ron are both right, to a point. While size and slope are generally not that important in French drain design, you must pay careful attention to the gradation of the rock/sand that is around your drain pipe and the gradation of the natural soil that you are draining.

If you can avoid using filter fabric the French drain will perform better for a longer period of time. Ideally you want to use a sand/rock that will serve as a filter for the natural soil that you are draining. The permeability of the sand/rock should be at least double that of the natural soil. Second the holes in the pipe must be small enough not to allow the sand/rock to pass into the pipe.

With all of that said, yes you can just use a non-woven filter fabric between the natural soil and the sand/rock and between the sand/rock and the pipe. Good Luck.

 

[jheidt2543]

Here in the upper midwest US, french drains are pretty common in areas not serviced by storm sewers or where surface drainage is a problem. One thing to let your Owner know is that french drains require annual maintenence if they are to continue to perform. The top layer of the drains filter must be kept free of debris and silt or the top will become "sealed" and not allow drainage.

On one of my parking lot projects we installed six (6)large french drains made from perforated precast pipe with a manhole cone section on top. Each drain is approximately 5' in diameter and 15'deep. They have been working for 20 years now and with some annual maintenence should continue to do so.

 

[boo1]

jheidt2543 showing your age

 

[boo1]

check specification at:

http://www.transit.govt.nz/technical_information/content_files/Specification8_pdfFile.pdf

 

[altor]

Thanks for the input. I check the DOT of Fla website but didn't find anything that related to the specification. The New Zealand web link did provide me with adequate info however. If you know the direct link Ron, drop me a message.
Thanks for the help.
Al