Caution Against Perforated, Corrugated Pipe with French Drain via Trencher

[the44chris]

Hi,

Researching my own terrible drainage problems in a newly purchased home, I stumbled upon several threads located at this forum and thought I would add my own 2 cents as a newbie finishing up my semi-large installation.

I rented a 36" deep, 6" wide trencher thinking it would be plenty wide to surround corrugated, perforated 4" pipe with an adequate amount of the C-33 sand spec'ed by oldestguy. I feel this is typically what someone would rent as it's on the larger size of what you can readily find. The corrugated style of pipe is surrounded by fabric and I planned on surrounding it with sand to filter out my clay-rich ground. This proved challenging due to a combination of the pipe snaking around and the trench walls just not being wide enough. It also required several more trips to my local materials yard for sand than anticipated.

If I ever have to do this again I will instead use the 2-hole style triple wall pipe available from the big box stores, throw a sock over it, and plunk the holes straight on top of a healthy sand bed. No need to worry about the proper amount of sand completely encasing the pipe, and the cost is very comparable even after considering PVC fittings added in (and likely cheaper when considering the extra sand). Back-fill and done.

Lesson learned.

 

[emmgjld]

What went wrong? What were your expectations. Details would be appreciated.

 

[oldestguy]

Draw us a sketch. Explain why a 36" deep trench and not deeper. What are you trying to protect? Was this trench getting water in it already? I can't figure how the very simplest form of sub-drainage construction can go wrong. It's usually fool-proof.

My thought is that narrow trench was a major mistake. It should have been at least 10" wide or more. I'd opt for s small back-hoe in a small tractor. Trench width then at least a foot wold be possible and deeper.

I'd put the blame on the choice of excavation, not the drain design. With a drain with slots at 1/16" or so, no sock is needed if concrete sand backfill is used.

 

[cvg]

more trips to the store for sand sounds like you didnt estimate the amount of sand required very accurately. reducing the amount of sand in the trench will reduce the effectiveness of the drain in capturing subsurface water. if this is handling surface drainage like it sounds like it is - than a french drain is the wrong solution and you should install a catch basin to capture the surface water flow.

 

[oldestguy]

My guess this is for a wet basement. If so, a deeper trench is required to cut off the flow at an elevation lower than the floor. My suggestion is check with Kubota dealers for persons that bought their BX tractor with a backhoe attachment. Many of these guys got it for one or two jobs and after that it sits idle. I had one of these, but no back-hoe. Only problem is a small fuel filter, requiring frequent changing. Also I see some for sale on line. It is ideal for a small estate.

just one link of many.

http://www.tractor-review.com/kubota-bx25.html

 

[fattdad]

what problem are you solving?

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

One more from OG. As to getting the pipe fully encased with filter sand, that would be nice, but not necessarily required. Those slots against the trench walls at some places will clog, but as long as most of the pipe perimeter has a sand cover, it will work OK. Of course being fussy is fine and using a small cover at a time, followed by tamping from above along side the pipe will do the job, Tamp with a narrow board so as to get alongside the pipe. Of those I've been involved with I recognized the non-perfect situation is likely in places, but they all worked fine anyhow. That even comes for some cave-in before the pipe is laid, or even some cave in on the pipe.

 

[the44chris]

Thanks for the responses. My back yard is split between one neighbor towards the side, and two neighbors on the back... all whose properties are 5-10ft above mine and sloping towards it. The back yard also sort of "bowls" overall, with some sections near the slab(I don't have a basement or crawl space) also poorly graded. The downspouts just had old concrete blocks under them. Some sections are highly clay as well.

All this combined to make a soupy mess of my backyard when it rained even lightly. There was pooling on top of the ground, and in some sections you'd have water swelling the ground below to the point you could "pop" the surface. I wasn't as concerned with the deep water resting against the slab (I should have) as I was with just wanting to walk around without trudging through water to my ankles. I was also planting a new lawn that I didn't want to get flooded out, and was abruptly scheduled to travel long term. This had to be done in 6 days.

I do not do this professionally but enjoy tackling projects myself as a learning experience. Using a backhoe in my narrow pathway to street near all the utilities was a bit daunting. A trencher was more precise and much easier for me to get going on. I did not estimate the amount of sand accurately. It was a large job for me to do myself, but seemed a little ridiculous to start figuring out different cross sections of the trench with all the other variables in place that tend to render that kind of thing a waste of time.

I split and capped two separate perforated lines running from the back yard around different sides of the house, and then started (running on top of the french drain) with the downspout extensions. Spread(for grass) and regraded with 5 tons of topsoil, and ended all 4 runs with mitered drains.

My concern with not completely encasing the perforated pipe with ~1" of sand was not with the slits clogging, but more so clay finding it's way into the pipe and then rendering the whole thing useless. If the clay will just clog the slits (because of the fabric sock?) then that's great... it should function for a very, very long time.

I still think it would have been much easier, used less sand, and gave a thicker layer of filtering to use triple-wall pipe with downward facing holes. This has been recommended over the corrugated type by most of you elsewhere in other threads and I should have followed that. I went with the corrugated pipe because of a initial perceived savings and ease of use that just wasn't there. I think the setup will work pretty good overall, it just could have been a little better.

I'll put up pictures of everything shortly, and would appreciate anything you think I should have done differently.

 

[oldestguy]

OG again. Nice to have a more thorough explanation, although a bit confusing at times with undefined wording, etc. One thing lacking however is house and more lot information. Does the house have a basement and if so any problems???. How does the ground slope now? Ideally a contour map of the site or at least some elevations (as ? feet below main floor elevation at house and elsewhere would help us. Other than bad yard surface drainage, are there any other reasons for the drain. Normally if it is only bad surface elevations and slopes, there is no need for any underground drainage. Also, what does this installed drain system drain to and at what elevation? If the drain system is to help dry the back yard only, be prepared for it to clog up where surface water enters, unless that siltation is cleaned away every few years.