french drain behind raised beam wall?

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T

TomCa

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Sep 28, 2015
16
Roseville, Ca
A new discovery for a rookie is that carving the pool into slope at rear of yard means
I will need a french drain and the PB doesn't do that nor did we discuss addressing the slope
runoff prior to my questioning the ditch they are planning to leave for me.
1a) PB carted off a ton of dirt yet now I am looking for it to fill in the ditch after I address drain.
There seems to be plenty of free dirt on Craig's list but shouldn't they have offered to save some
of my dirt for this issue?
1b) Can I request/demand that they bring back enough dirt to backfill trench?

2) I have not done a lot of DIY and no experience in landscaping.
Can a guy like me lay a french drain on Saturday morning ?
32ft of Perforated pipe, wrap in landscape material and lay/connect/install pipe 12-18" deep, leading
away from pool to my side yard drain? Is that what it takes?

3) I read in another thread that I should water proof back of wall with sealer - is that a must?

thanks
Tom
 
I would backfill with rock. You want all the porosity you can get. sealing the backside may help with calcium deposits weeping out the front.

If you are not familiar with this work, get someone to do it for you.......I would not let them backfill with dirt, regardless.
 
Tom,

I'm not sure I understand the problem, but here are a couple of thoughts..

1. French drains generally get rid of ground water, not surface water. So if you are building a wall at the bottom of a slope, a French drain is often installed behind the wall to divert the ground water away from the back of the wall. A French drain is not just a piece of perforated pipe wrapped with cloth... for the drain to work, the pipe is normally in the center of a gravel/small rock filled trench about a foot or so square. This is normally something the builder of the wall does.

2. If the problem is surface water, French drains might help, but only slightly. Maybe that is why your PB is wanting to install a ditch..

3. Anything I have ever planned to do on a Saturday morning has always ended up taking me three days.. :D

If you can post a pic of the area we might be able to better understand the problem.

Thanks,

Jim R
 
The PB stated that because the slope is modest and the land above it is flat and graded
that he doesnt think a french drain is necessary. While we are clear, he is not responsible for
a french drain install , he did acknowldge that the trench is deep, some exposed pipes and he
would bring some dirt and gravel and fill it in. Here is a pic of current trench. Thoughts on how to
proceed are appreciated.
Thanks Tom.
View attachment 44179
 
Tom,

Normally French drains are installed where there is ground water that you need to get rid of. I don't see a ground water problem in your picture, but they may be just because it hasn't rained in California in the last few years.. :cool:

My gut says that a French drain is not necessary but it would not hurt anything to put one in if you think that you might have an issue once it starts to rain. Obviously, if you are going to do it, now is the time. Did you ask your PB what it would cost for him to do it? I would not think it would be too expensive since he is going to have to fill the trench anyway.

Jim R.
 
I too do not see a Pressing need for a French drain system. Hydrostatisc pressure would be troublesome only if there is an appreciable slope on the otherside of your fence - if so, hydrostatic pressure picks up quite exponentially. If that is the case (steeper slope on other side of fence), I would consider a French drain. Try to get a proper install of the French drain. Seen a lot of improper installs: drain pipe laid with perforated holes facing up, no filter/fabric sleeve for the pipe, inadequate amount/size of gravel, improper placement of pipe in gravel, wrong diameter pipe, etc.).

In any case, would coat the back side of your wall with some heavy duty sealer...Asphalt based, applied in multiple coats (can't tell from pic if a portion of the wall is already getting that treatment). This will minimize efflorescence.

A simple surface swale for diverting surface water during a heavy downpour is a good way to go, given that it looks like your soil is poor draining clay...once saturated, water runoff can be quite abundant.
 
Guessing a bit, but it seems to me that without a french or surface drain. ALL the water off that hill is either gonna' settle into the soil behind it or come over the wall. Personally, I would put a drain there.

I put one around the base of my pool (it's pretty flat) and ten years later it still removes thousands of gallons of groundwater during a major storm.....I am a big fan.
 
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