Drain Pipe Perforations - Up or Down?
Drain Pipe Perforations - Up or Down?
(OP)
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!
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!





RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?
Cheers
RE: Drain Pipe Perforations - Up or Down?
You are carrying the water away. Invert should be beloww level desired to drain. Most black courragated pipe has drain holes in an array in the upper 270 degree quadrant.
However, when all else fails, check with the manufactuerer of the pipe.
RE: Drain Pipe Perforations - Up or Down?
If your French drain is an interceptor and you want to limit the uptake of water from below, then the faster route would be with the holes down, but still requires hydraulic gradient to push water into the pipe.
In my humble opinion, having the holes on top is the better of the choices.
RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?
This one makes me chuckle! Good job, BigH!
I have two answers - one theoretical, the other practical.
Theoretical:
The holes are on the bottom - see boo1's excellent arguments.
Practical:
It doesn't really matter (unless BigH left out some critical concern.) The 150 mm distance (about 6 inches) appears insignificant in the scale of the problem. (Only about 8 percent of trench depth.) I didn't run the calculations, but if the head in the trench between the manholes is above the perforated pipe, it will drain into the pipe either way. You could get a slight increase in the phreatic surface at the mid-point, but I doubt that it is significant. (This would only occur if the influx into the trench exceeded the perforated pipe's capacity. Highly unlikely.)
A question for BigH:
Any problems with the holes clogging that might affect the choice of hole orientation?
RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?
Something gave me the impression that this was a "tempest in a teapot" question. Please elaborate on the "if water ever does get into the pipe!! . . . oops" comment at the end of your last posting.
RE: Drain Pipe Perforations - Up or Down?
However, on my home projects, with perimeter footing drains, I turn the drain holes upward, and than grab my chordless drill....and methodically punch some 3/8" holes at the mfr's req'ed spacing...about 1" above the bottom...on either side. I'm partial to believing that water runs downhill, and likes a little trough to travel in....even with the help of a hydraulic gradient/head.
RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?
Cheers
RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?
Pipe also conveys water faster than stone alone (there's a poem in here somewhere!)
The best way to solve this for all of us to meet, drink lots of beer and test the capacity of the pipe.
RE: Drain Pipe Perforations - Up or Down?
(with all due respect to the staff spelling expert... Just typing in the ver-nack-u-lar. :)
I'll start collecting the supplies for the experiment, someone will have to write the procedure and post it in the ASTM forum... :0!
RE: Drain Pipe Perforations - Up or Down?
I trying to imagine a pipe sitting on top of a sloped ground with the perforations aligned perfectly UP. If I take a hose and spray water along the length of the pipe, I can't imagine much water getting in. Then imagine the contractor has perforations a few degrees off. Even less water gets in the pipe. Doesn't seem too effective.
I always viewed the pipe as a second line of defense (a preferential flow channel) - a redundancy if you will. Thus, the rock carries all the flow until such time as the water level reaches the bottom of the pipe. Therefore, for me its perforations DOWN.
DRT
RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?
http://www.nrcs.usda.gov/feature/backyard/watercon.html
A nice link
http://www.ecy.wa.gov/programs/sea/pubs/95-107/groundwater.html
Pipe
4" = 0.087 sqin area
100 lft 4" = 8.7 cuft volume
100' = $33
1 cuft = $3.79
Stone
1.4 ton=1 cuyd = 27 cuft
$40 /ton
27cuft=$56
1 cuft= $2.07 *****cheaper******
RE: Drain Pipe Perforations - Up or Down?
I still think the better solution is to drink the beer and then "performance test" the system.
RE: Drain Pipe Perforations - Up or Down?
If it intended to remove water from under a roadway build on, say 1.3 feet of OGB [Open Graded Base] wouldn't we want the water to infiltrate up into the pipe so as not to leave a 'wedge' of water 1/2 pipe dia X slope length?
RE: Drain Pipe Perforations - Up or Down?
But what an interesting topic, something simple but different opinions exist!
RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?
RE: Drain Pipe Perforations - Up or Down?