This may be a dumb question, but I’m struggling to understand how drain tile works.
It’s a perforated pipe. So…what keeps water from simply passing through it and soaking into whatever is below it? Should a water barrier be placed underneath the drain tile?
Also, we’re putting in a drain tile behind a new retaining wall. I purchased a few end-caps to cover the pipe as it exits the wall (keep the mice out). The cap is 4″ in diameter with about 6 holes in the center. does that make any sense? The pipe would have to fill at least half way before water drains. I’m just going to drill a bunch of holes in it but looking at it, it got me scratching my head.
Replies
The idea is to give the water a path to follow. The perforations allow water below the pipe to well up into it also, the open pathway being an easier transit away from where it is than through the soil.
Excellence is its own reward!
Read this url.
http://www.builderswebsource.com/techbriefs/drainage.htm#Perimeter
If you put the drain tile lower then the footing the tile will fill with water. The water in tile will run to the sump. So even if the water soaks in and goes down into the ground away from the foundation. You got what you want.
That makes sense, Fred, but in the case of retaining walls, they recommend placing it behind the second course of block. So, technically, water seems to still be able to get behind the base of the wall...hence my confusion. ;)
they may be making that recommendation so teh perf pipe will not fill with sediment. but there are other ways to overcome that .. like filter fabric and crushed stoneMike Smith Rhode Island : Design / Build / Repair / Restore
The only dumb question is the one that goes unasked. The purpose of drain tile is to prevent the buildup of water- not to completely drain away all water. Behind a retaining wall for instance, you want to drain away excess water so that the ground doesn't end up reaching saturation. In additition to producing muddy ground, saturated soils are weaker than drained soils and may pose a stability problem with the wall because the weakened soils will exert more outward pressure on the wall. The drain tile works by providing the majority of the water a place to go. You're correct in that not all of the water will get into the drain tile and that's OK. Soil can absorb a certain amount of water without causing problems such as the stability problems I just mentioned or, in the case of foundations, wet basements.
Installing end caps is probably a good idea to prevent animals from nesting in the pipes but make sure at least some of the holes you drilled are at the very bottom of the pipe so that any water in the pipe can drain away.
One other thing, the best way to insure a perforated drain pipe functions as intended is to use what is referred to as a "burrito." Basically, it consists of crushed stone surrounded with geotextile on all sides with the pipe in the center. Avoid the pipe socks put out by the manufacturers to slip over perforated pipe. They are easier to use than burritos but are much more prone to clogging by fine grain soils.
Edited 8/7/2003 12:35:28 PM ET by stonebm