Safe to dig beside foundation for drain tile placement 2

[Lawrence P]

Helping a relative install drain tile beside a leaking basement (and partial crawl). Intention is to dig directly beside the wall, cover in a waterproof membrane then place a French drain beside the footer. I'm a bit concerned (for them) about soil compaction and shifting once we disturb the soil near the footer. Looking for any insight.

 

[dik]

With careful work, this is often done. Excavate adjacent to existing foundation, put a membrane on the wall, install new drain tiles to free drainage, backfill with a clean granular drainage layer, use a nonwoven geotextile between existing soil and drainage layer, and add topsoil (sometimes an impervious soil cap). I often use miradrain dimpled plastic drainage adjacent to the foundation wall.

Dik

 

[Lawrence P]

Thanks very much, the house has been subjected to years of poor water management and there is evidence that some settlement has already occurred. My plans were to use a dimpled membrane against the foundation then place the drain tile; I had been advised (warned) by a local contractor that I could damage the foundation however I did find that warning odd as that "B-dry" type interior drain tiles essentially do the same this when they dig beside the foundation from inside.

 

[dik]

Check carefully for Brown Rot (aka Dry-Rot)... often occurs with moisture issues.

Dik

 

[Lawrence P]

I neglected to mention that this is a stone house (1935) I'm not sure if a footer is even present. Does this fact cause any unforeseeable issues ?

 

[dik]

Only if the mortar lacked hydraulic properties and has turned to 'sand'. If the mortar is sound, you should have no issues, and if you parge the outer stone wythe so it is flat, you can still add the Miradrain material... used that with the Lindsay town hall where the mortar had turned to sand.

Check with SlideRuleEra's website for a paper I wrote on Historic Brickwork for some background information. Written for brickwork, but a lot of the information is applicable to stonework.

Added: Don't repoint with high strength mortars.

Dik

 

[thaidavid40]

Be sure to adhere to OSHA guidelines for how to safely trench excavations over 4 feet deep, if that is true in your case. This is to prevent injury or death from collapsing soil walls.
Good luck - Dave

Thaidavid

 

[oldestguy]

Pay attention to this from above: nonwoven geotextile between existing soil and drainage layer,

Just covering the clean gravel with the fabric is not enough. You lay it down, place pipe and gravel and then wrap over it. All possible entry places for water so all possible water routes must be filtered. It can come from all directions.

An alternative is to use a tile with entry holes in the bottom third about 1/4" diam. or so. Slotted corrugated plastic pipe also is fine with 1/16" slots. The backfill that collects the water should be clean coarse sand, such as ASTM C-33 concrete fine aggregate. Probably costs less and is easier. In this alternative no gravel is needed on the job. I usually spec that NONE IS ALLOWED. Most gravel is not a filter and easily plugs.

 

[Lawrence P]

I have been doing some pretty extensive reading on the fabric placement (or need for it). On a sidenote ThaiDavid40 thanks very much, I had already briefed all parties involved that we wouldnt be entering any trenches that werent "cut back" to osha guidelines.

Back to the fabric; in addition to reading multiple studies I also had a conversation today with Tim from "Ask a Builder" I know others on this site have spoken about him. Its his recommendation to use no fabric at all in any french drain as that laterally moving water is almost always clear (he gave a cold spring as an example), and that if were relying on fabric to filter sand then what stops the fabric from clogging. Any thoughts on this ? I am quite curious about the cement sand youve mentioned.

 

[dik]

Over time, the geotextile prevents any fines from migrating through the clean crush... It could take decades, depending on the soil, but, it's a relatively inexpensive prevention. Contrary to the other dude... I'd recommend the use of it. Added: I've seen too many foundation drains that have silted up and caused major water problems.

Dik

 

[Lawrence P]

Thanks Dik, to say I'm torn on this is an understatement. My original plans were to do a fabric cover and then I was swayed by Tim and other sites. Now I'm back on the fence as that I dont want to have to dig this thing up in 5 years when it stops working

 

[dik]

Not 5 years, but, depending on your soil, maybe 20 years... It's your call...

Dik

 

[oldestguy]

OG here. As background, my Master's thesis back in 1956 was on underdrains for highways, a similar situation to buildings. Been at the subject ever since. Anyhow, one never knows when a non filtering system will plug. I've seen them plugged in one year. As to builders giving advice, go ahead, but don't come back here when it plugs up and ask "Now what do I do?". Answer, tear it out and do it right. See below.

I can point to an extreme. A small office building was to go on a site south some miles off lake Michigan that used to have high ground water, but when the basement was dug, no water. Knowing the history the basement floor and backfill to footings was filled with clear stone layer, not a filter. Sump pump was installed also. A year or so later the groundwater came up and now and then the sump pump ran. Our firm was called about 6 years later, because the interior footings had settled and the basement floor was badly cracked and settled. The sump pump discharge was in the open next to the road. A significant delta was present there having been soil carried along with the pumped water. Major failure. Enuff said.

 

[dik]

OG:

I haven't seen one plug that soon... my earliest is about 10 years with large amounts of silt...

Dik

 

[oldestguy]

Another point. Wisconsin plumbing code committee consists only of plumbers. The code specs a backfill to footing drains of open graded gravel. I've given up trying to get it changed because the plumbers say: "We don't see a problem here". Likely they are not those that have to go back and fix the plugged ones. No engineers on the committee. Possibly that "builder" was one of those plumbers. When I have had a chance to get the proper backfill on a job and the inspector objects. I say "I stake my reputation on this" and it goes like I spec. There are many highway sub-drain jobs and building jobs I have been associated with using concrete sand as backfill. Not one has ever failed to my knowledge.

 

[Lawrence P]

OG just want to clarify then, your saying to use concrete sand and a filter ? or just the sand. Also after reviewing your top post you say as an "alternative". My plans were to use the PVC with larger holes and not the black ribbed tube. I was also going to do clean outs so I could flush the pipe a few times per year. Just wanted to clarify if my alternate you meant that no filter is needed if I use a pipe with larger holes.

 

[oldestguy]

OG here. My research on drain pipes used Armco pipe (furnished free to this study)and concrete sand. I got the highway departments to install this "free" pipe and had 5 different sites with shallow ground water, measured water table and soil moisture with nuclear gage to see how well the installations worked. It did tell you do best when you cut off the flow, rather than depend on draw down. I also tested the filtering ability of concrete sand in several cases, seeing absolutely no penetration of silt, etc. I based e design of the tests on US Army Corps of
Engineers investigations at Vicksburg. That pipe had 3/8" diameter holes and they were in the lower third. A small amount of the finer fraction from the concrete sand came in but the larger sand sizes bridged over. Since you have holes all around, then you need some means for keeping sand out. That's where I'd go for plastic drain pipe (hole sizes unknown) inside a sock made of the non woven fabric. Of course you can manually wrap the pipe with the fabric also.

As to clean-outs I used to call for that, but never had an occasion to use them. With a means to keep the sand out this system is very simple and can't be goofed up. You place the pipe, dump in the sand and be done with it. Maybe place clay and topsoil on top to grow plants, etc. For deep trenches you don't even have to enter the trench.

If one wants to he can take the sieve sizes of the stuff naturally there and the gradation of concrete sand and use a few formulas to see what range of soil sizes it will filter out. However, I have noted that real fine clay (doesn't fit this) usually is so fine and cohesive that it doesn't migrate with water, even though theoretically it might get through the sand filter.

 

[Lawrence P]

To clarify I do plan on using rigid (PVC) pipe with holes only on the lower side, I feel the ribbed black pipe is too susceptible to clogging as that the slits are much smaller and by nature the interior texture of the tube will not mitigate as effectively

 

[oldestguy]

OK, that's your opinion, not mine. For the heck of it look at Form a Drain that is now being pushed as doing two jobs. I'd guess the slots are 1/4" or less. Note the use of open graded gravel and a fabric covering. Means extra work. However, some testing with concrete sand may show that will work, who knows.

https://www.certainteed.com/resources/journaloflightconstructionmarch2005.pdf

 

[oldestguy]

Here is a photo of the Armco drainage pipe, not made any more. However, look at the position of the holes, leaving a flow path without holes.
While they were 3/8", I would think 1/4" would work fine for a typical footing drain not carrying a lot of water. Then even the finer fractions of sand would likely stay put.