Drain Pipe Perforations - Up or Down? 1

[BigH]

Hey all! Am putting this out for your learned opinions. I have mine, of course, but would like to see how others view the following. We have had a lot of discussions on the site in the last while over this issue – some are strongly one way, others opposite. Hope this piques some interest.

Scenario. French drain installation in median of two lane each dual carriageway super-elevated section. Approximately 1.8m deep, 600 wide, surrounded with geotextile. We are installing a 150mm diameter perforated pipe within the French drain. Perforations of 8mm diameter; 4 rows of holes all in same half section of pipe. Infill is +10 to –20mm stone although contractor will ask soon to put in 20-40mm stone above the drainage pipe - availabiity of materials. Pipe will tap into a manhole at 75m spacing which will also collect water from depressed median drain. Then water goes out from manhole in a 200mm pvc pipe to daylight at embankment slope. Opinions sought !! Do you put the pipe perforations down, or up??? Up – reasons why! Down – reasons why! Look forward to some interesting dialogue.

Best regards. And the best of the holiday seasons to all - somewhat belated to some, ahead for others!

 

[boo1]

Ron there is no got me. I enjoy all you guys teaching me, a few simple things.

But what an interesting topic, something simple but different opinions exist!

 

[MikeDB]

I am a little confused by the pipe vs. rock comparison of 1--3-03. Looks like one would want to compare the area of the pipe to an equivilent void area of the rock. Wouldn't it take at least 2 or 3 times the volume of rock to get the same void area? If so, the pipe would appear less expensive.

 

[boo1]

Mike should you compare the void areas?

 

[Ron]

boo/Mike...no, the void area is already there. The only difference is the exit velocity....will be higher with the pipe, but probably not a big deal since these are low volume, low flow propositions.