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Safe to dig beside foundation for drain tile placement

Safe to dig beside foundation for drain tile placement

(OP)
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.

RE: Safe to dig beside foundation for drain tile placement

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

RE: Safe to dig beside foundation for drain tile placement

(OP)
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.

RE: Safe to dig beside foundation for drain tile placement

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

Dik

RE: Safe to dig beside foundation for drain tile placement

(OP)
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 ?

RE: Safe to dig beside foundation for drain tile placement

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

RE: Safe to dig beside foundation for drain tile placement

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

RE: Safe to dig beside foundation for drain tile placement

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.

RE: Safe to dig beside foundation for drain tile placement

(OP)
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.

RE: Safe to dig beside foundation for drain tile placement

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

RE: Safe to dig beside foundation for drain tile placement

(OP)
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

RE: Safe to dig beside foundation for drain tile placement

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

Dik

RE: Safe to dig beside foundation for drain tile placement

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.

RE: Safe to dig beside foundation for drain tile placement

OG:

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

Dik

RE: Safe to dig beside foundation for drain tile placement

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.

RE: Safe to dig beside foundation for drain tile placement

(OP)
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.

RE: Safe to dig beside foundation for drain tile placement

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.

RE: Safe to dig beside foundation for drain tile placement

(OP)
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

RE: Safe to dig beside foundation for drain tile placement

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/journaloflig...

RE: Safe to dig beside foundation for drain tile placement

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.

RE: Safe to dig beside foundation for drain tile placement

(OP)
OG, It looks like all your applications were commercial-municipal grade. Do you still recommend the cement sand for residential use ? and please clarify if you recommend the sand and a filter or does the cement sand do the job. Thanks

RE: Safe to dig beside foundation for drain tile placement

We have a product called Pea Gravel that is often used.

Dik

RE: Safe to dig beside foundation for drain tile placement

Wow,

Dik: I'd like to know how pea gravel can filter out silt when the void spaces there are much large than silt particle sizes? IT AIN'T A FILTER! Go ahead and don't change, it's not for me. Pea gravel, or other materials with no filtering ability are allowed on my jobs because "well meaning workers" see those large voids and figure water flows faster. Fast rate of flow for seepage collection is not needed.

Lawrence: There is no distinction between highway subgrades and house basements when it comes to keeping water out. Hell, I use concrete sand and perforated pipes for stabilizing side hill earth slippage caused by excessive water. Same purpose. I showed the photo to illustrate how you can have holes on the bottom and leaves a smoother path down the center. It is not critical if the bottom also has holes. However, if the collecting water has to flow up into the pipe, it is more difficult for fine particles of sand to migrate in.

No point in making a simple job complicated.

RE: Safe to dig beside foundation for drain tile placement

It doesn't filter our silt... it provides relatively free drainage. I cannot imagine cement sand to behave any better. With time, the cement sand will simply 'clog' with the silt particles...

Dik

RE: Safe to dig beside foundation for drain tile placement

Dik:

Let's not confuse things. Here is your statement from way above.

use a nonwoven geotextile between existing soil and drainage layer

That's correct. But, without the fabric covering the open graded stuff, you can have plugging of tghe open graded as well as the pipe.

There is one job that I came across that says you need a large area of filter between soil and the collecting place. Using fabric covered slotted pipe and an open graded collecting zone between earth and it. Or, no open graded material at all. With spaced slots in the pipe silt and clay can build up on the fabric just there and plug everything. That's where fabric over the gravel or just concrete sand can do the job.

by the way it's not cement sand.

RE: Safe to dig beside foundation for drain tile placement

The drainage stone is totally encapsulated by protective.

Dik

RE: Safe to dig beside foundation for drain tile placement

Now that that is settled, what about settled footings? I'd recommend an experienced geotech, since some form of soil examination may be needed.

RE: Safe to dig beside foundation for drain tile placement

(OP)
Gentlemen, final dilemma hopefully. The floor of the crawl is anywhere from 28 inches to 45 inches below grade. We dug down at lowest level and found that the stone wall foundation actually has no true footer per say and the bottom of wall is around 48 inches below grade.

I think I'm going to pour a slab after I level it but now I'm concerned with an old stone wall and no footer how close I can get to the bottom of the wall with the french drain without running the risk of drawing water from under it and causing erosion under the wall.

RE: Safe to dig beside foundation for drain tile placement

Another subject here. I've run into very few erosion problems as related to water flow from under footings and slabs. Usually that is when there is significant water flow and the stuff that moves is fine sand. First off is that stone foundation just a bunch of loose stones, no mortar to amount to? That is not good, but not terrible. If so, I'd keep my excavation away some, leaving say a triangular shaped zone against the lower zone.

RE: Safe to dig beside foundation for drain tile placement

And here is a case where you don't want to erode any of that zone. So, in no way use an open graded stone against that without a filter. Of course using concrete sand you do have that as a filter.

Otherwise ,another main problem I have seen is vibrations in the are causing the sand, usually damp, to actually flow out from under. That can be running a vibrating roller nearby or a large industrial compressor operating about 40 feet away.

RE: Safe to dig beside foundation for drain tile placement

Another one. Around the old prison at Waupun, WI there is a high stone wall made many years ago. It is about 3 feet wide and down about 4 feet for "foundation. Quite obviously it was built by prisoners. It is well cemented together above grade, but not so below grade. Through the years the wall has tilted a little this way and that. A grouting firm was hired to straighten it by pumping grout into zones below it as "jacks". However first any voids in the "foundation" need filling to keep it intact. I was able to take a folding ruler and insert it easily far into the voids in that "foundation". The explanation is, the guards apparently didn't watch closely because that loose foundation would be no sweat to dig through by hand to escape some day. However, the weights imposed on that supporting soil were darn high from that stone wall, yet these spaced stones carried it pretty well. So maybe the subject house is in pretty good shape even if not the most solid foundation.

RE: Safe to dig beside foundation for drain tile placement

(OP)
I've heard of this 45 degree rule, looks like thats what your speaking of. I found the soil at 48 inches down to be cold and clumpy but not truly wet to the touch. Not being an expert in this field I'm not sure if this is expected at this elevation (degree of moisture in the dirt). But I didnt have visible water per say.

I'm leabing toward keeping french drain about 1 ft out from the wall.

RE: Safe to dig beside foundation for drain tile placement

Sounds great, since fine sand would not hold together. Since experience there says water sometimes inside, that likely is from rain and not permanent ground water. Where there is a slope in the area, I'd suppose the most likely entry comes from that slope side, thus not coming out of the foundation. Sometimes the water gets by that outside drain and comes up a ways inside the basement. That can be collected with a drain there that then leads to the outside drains. Hopefully you can run your collection system to a down hill surface discharge by gravity. In some cases we need a manhole near the building (made from 2' diameter culvert pipes) in which a sump pump sits that discharges away in a safe place.. If you have cold winters and these discharges may freeze, it takes some doing to work with that (next time here).

RE: Safe to dig beside foundation for drain tile placement

(OP)
Thanks very much OG, everything u described matches (down slope etc). I was just worried as that its been 3 days since rain and the soil is still showing signs of moisture

RE: Safe to dig beside foundation for drain tile placement

The 45 degree concept is recognized as acceptable for avoiding the loaded soil profile. It makes sense and is easy to apply. For drainage pipe along a strip footings, it is the most commonly accepted load distribution for most soils.

It also is easy to implement for new construction IF the builder has the desire to avoid foundation problems and install perforated drain tile.

I had a friend that was a builder and also a member of the state building code committee that made recommendations to the use and implementation to the building officials.

He built over 200 homes per year and vowed to never have wet basement complaint. He had very practical, efficient method that required some special block for the walls, drainage pipe and strict construction methods that were easy to implement when you are big enough control design, construction and sell/guarantee a home. This method was based on keeping the drain tile outside of the 45 degree spreading out from the bottom of the footing toes.

We had a 48" frost depth.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

RE: Safe to dig beside foundation for drain tile placement

(OP)
Thanks all, if my math is right though were only talking about just a few inches away from the footer. I was thinking of putting the drain tile out about 12 inches and just slightly (2-3 inches) above the base of the footer to be on the safe side. Does anyone see a major issue with this in theory

RE: Safe to dig beside foundation for drain tile placement

I'd not worry about undermining the foundation due to this excavation to footing grade if there is no major flow of water encountered. A reasonably intact wall and "foundation" likely will not displace soil. That is what is called a soil rupture or shear failure. Such a condition is only possible if the soil is near a soup condition, about never happening. The main settlement problems come from the soil just becoming more compact with the footing pushing down.

I'd set the pipe at footing grade. I'd fill the trench up to what might be called "highest water coming in". That fill would be concrete sand, the simplest technique, most rapid, fool proof and cheapest. Following the comments on pea gravel and fabric is labor intensive and easily can be done wrong, takes longer and can invite cave in due to time taken to lay fabric, then pipe, gravel, and fabric. Suppose you are partly done and get cave in or big storm before the gravel is in or covered? A holy mess. Dig out and start over. With concrete sand, you can cover with sand as soon as each section is laid. Cave-in on that sand likely might not hurt, or can be removed later.

Final fill to grade can be what was dug out.

In summary, the interior footing settled examination by geotech might also involve him for these walls, but don't go for something without roper filters. That part of geotgech education usually is missed. The detail I'm going into here is much more than what the operators of this web site like to have us do. About all I'd like to leave is "don't forget filters".

RE: Safe to dig beside foundation for drain tile placement

(OP)
My picture is only showing up as a link, not sure what I've done wrong

RE: Safe to dig beside foundation for drain tile placement

Picture is fine. which way is the camera pointing and what do those words mean? Perhaps a sketch of what is proposed will help. You can also insert a picture as a JPG file using the icon above with a circle at the lower right corner of the screen , about in the center of the Post Options icons above. Picture won't show as you insert it, but thereafter will show along with the text.

RE: Safe to dig beside foundation for drain tile placement

(OP)

RE: Safe to dig beside foundation for drain tile placement

(OP)

RE: Safe to dig beside foundation for drain tile placement

(OP)
So water comes off the tracks in droves (second picture) due to water that flows onto the tracks from the street. The local municipality isnt cooperating as far as putting in storm runoff drains (this would fix the entire issue). The 1st picture is the bottom of the hill about 20 yards down from the tracks.

Our initial thoughts were a retaining wall with a french drain behind, a curtain drain (this is red line on the markup) and then a french drain inside basement-crawl.

We are likely going to put in a large swale right next to the tracks to divert water from that erosion point to a storm runoff area on the property. I'm thinking that the curtain drain may not be needed then as that the drain behind a retaining wall should now catch most of the water coming down the hill.

RE: Safe to dig beside foundation for drain tile placement

This the first time I have seen any info on "the tracks". Now we see there is substantial surface water problem, perhaps the main culprit after all. You might not even need basement footing drains if the surface water thing can be corrected. Perhaps walls and drains might be needed, but the main job is changing the surface grades to divert surface water WAY away from the building. Look into the possibility of having a small trench at the location of that yellow line, at the base of a bank and hopefully it is within he property limits. Paving the surface with asphalt "pavement" will divert a lot. If necessary a ground surface left there can be waterproofed using a clay layer and I mean real clay. Elsewhere in these forums I have explained on how to waterproof that surface with a natural volcanic clay bentonite. It has to be done very carefully or a real mess results.

Then after sufficient outside grade is changed a cut-off drain can be installed next to the basement. Follow with grading the surface and placing that sloped paving, etc.

This post should have been done about when the original question was asked, but missing important information really has wasted a lot of time here.

RE: Safe to dig beside foundation for drain tile placement

(OP)
Sorry by a "Cut Off Drain" next to the basement do you mean something sub-surface or are you talking about gutter drainage. And sorry I didnt mean to waste anyones time, I figured whether the water that was coming from the hill was exasperated by the track water or just natural water flow from the hill that there was still water subsurface that needed to be drained away.

RE: Safe to dig beside foundation for drain tile placement

@oldestguy

Quote (This post should have been done about when the original question was asked, but missing important information really has wasted a lot of time here.)


But then we wouldn't have a true Back of The Envelope Sketch. bigsmile


Some great points raised by all!

Jeff
Pipe Stress Analysis
Finite Element Analysis

www.xceed-eng.com

RE: Safe to dig beside foundation for drain tile placement

My definition of Cut-off drain is a perforated pipe in a pervious fill in a former trench that collects seepage water from one direction in soil, so as to keep it from going in the other direction in soil. In this case the collected water that otherwise gets in the basement from nearby soil. That cut off trench (filled) is what I detailed with the drawing posted showing some protection for footing support soil.

RE: Safe to dig beside foundation for drain tile placement

(OP)
Thank you all for the help.

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