Sinking Foundation

[FishTheStructure]

Hello All,

My parent’s 40 year old house in Canborough, Ontario, Canada started to shift/ sink for the first noticeable time during the driest part of the summer this year. My assessment was that the large trees adjacent the house (approximately 30-40’ away) dried out the soil (very high clay content) by this end of the house more than the other soil in the vicinity causing uneven settlement due to drying shrinkage of the clay soil. The house has a full basement, strip footings, and CMU foundation walls.

A relative in the foundation repair business suggested helical screw piles or hydraulic push rods as a repair at the 2 corners and the chimney location to push the foundation back into position. I question whether this approach will create “hard points” which won’t move with the rest of the house during subsequent wetting/ drying movement of the rest of the foundations in the future and only create farther problems.

Have a look at the attached pictures. I welcome others suggestions regarding the root cause and any recommended repairs or experiences.

Much Appreciated!


Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein

 

[cvg]

tree roots generally extend to the drip line which is a significant distance from the foundation. the downspout appears to be directing water directly at the corner of the foundation. there is no downspout at all on the other corner. fix the drainage problems first.

scenario
a) the roof drains saturate the foundation near the corners during wet season
b) dry weather results in this saturated soil drying out and shrinking
c) foundation settles

 

[FishTheStructure]

cvg,

Thanks for the feedback. I fully intend to recommend fixing the downspouts and improving the grade to divert water away from the house. But at this point, the first step is repairing the foundation before water starts leaking through these cracks. Any suggestions in that regard?

Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein

 

[oldestguy]

No question about which trees are causing the grief. It's those to the west. However the southerly growth also may be causing trouble.

With that lower level apparently along the west end also, chances are its floor also is down.

I'd not do any of that planned installation of piers. You aren't solving the problem. The effect of drying can go farther horizontally and vertically than so far experienced. You well not be able to support the interior lower level floor without lot of added work. Then as added settlement affects other places, be prepared.

On solution. Cut down the trees within say 30 meters of the house. The effect of trees can extend well beyond the tree drip line, even if the roots are not there. The effect can be very deep also (easily 30 meters), possibly deeper than underpinning work. Underpinning will find hard clay at shallow depth. No place to bear the loads however.

I have had great success (I won't call it luck)by a simple treatment in Wisconsin and Iowa. Each summer feed water into a trench alongside the area that you know is drying. It may take just a continuous slow dribble to keep soil saturated some. Initially it may require lots of water, but eventually that will cure the problem. Be prepared for the settled area to rise and cracks to close. So don't fill them. Leave the downspouts where they are as an assist. This treatment worked at a high school auditorium in Menasha, WI, nursing homes and mullti-apartments in south-west WI and Eastern, Iowa.

If there is doubt about this, maybe a search in Eng-Tips for shrinkage and you will find some of my comments. Specifically you might check with the only nursing home in Lansing, IA. Last I heard (about year 2008) all was well. It has been over 40 years since the high school fix.

I suspect the cost for annual watering will be much less in time than underpinning and more positive as to results. Removing the trees will not totally solve things,

 

[FishTheStructure]

oldestguy,

Much thanks for your comments, they are truly respected - I have read some of your other posts on eng-tips previously in regards to these sort of issues and was aware that you recommended watering the soil. My father did apply water to the soil once observing the settlement but I am not sure how much or for how long of a period - I will follow up on this.

If I may, I have several follow up questions to draw from your experience:
- How long did the process of the soil rising and closing the cracks typically take for you? Several weeks or several years?
- Is the process of wetting the soil only beneficial in the summer when the soil is very dry or can this process be started now and continued until frost with good results?


One note: The wall has dam proofing but no waterproofing and it is likely that the dam proofing is also cracked given the cracks in the foundation wall. I would expect that since the idea is to leave the cracks alone and allow the soil to rise and close them up again, that there is no way to prevent leaking (especially during the process of encouraging water to wet the soil) therefore the best course of action would be to gut the interior space (a large rec room) and deal with the water as it comes in before it causes more problems (mold).

Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein

 

[oldestguy]

Fisherman:

Hopefully I can help. In each of the cases I mentioned and some others, I usually did not closely watch things, due to distance. I have heard back from the sites at times a month or so later as the earliest and corrective motion was taking place. Generally it was noted that things were back to normal surely within a year, but some times sooner. This is due to me not monitoring or checking back. At the Lansing nursing home I merely dropped a comment about other jobs, since I was not the hired engineer (as I visited with a friend). We returned a year later and the formerly unoccupied rooms were being used, but for how long not used I don't know.

To avoid running water into the basement walls I would be out from the wall with a trench about the depth of basement there, I'd shoot for the Probably shrinkage cracks in the soil to close up some early on,. but who knows how long that will take. Sometimes these get filled with topsoil and remain more porous than nearby non-cracked zones. I'd say it takes some early watching and then you may find some changes are needed, but the goal should be to get moisture to the zone under the house. The trench watering is more or less a 24 hour a day event, so doing it now and then is not as good. Aftr all those trees didn't stop needing water. And some of this will go to those trees. I'd keep it up until ground is frozen.

 

[oldestguy]

One more thought. I have never tried it, but in the interest of getting moisture down where the shrunken soil needs it, one might try extending down maybe 3 or 4 post holes down as far as feasible. There may be cave-in so filling the holes with sand as a "reverse-drain" may well speed things up. The Iwan type augers with extendible pipes is what I would use. In hard clay that will be a tough job however.

 

[oldestguy]

On my evening walk another item came up. Most of the time the backfill to foundations is shoved in from the adjacent higher ground. This results in layers of fill sloping towards the foundation. Water infiltrating at the surface readily flows towards the house. I don't think that is really what you want here. So, try to place your trench out far enough to avoid feeding that backfill, even though that will help get water near the supporting soil under the foundation..Seepage into the house won't be so good, especially if you are watering 24/7.

 

[oldestguy]

I'm still thinking about this situation. Being that it is late in the warmer weather and winter coming on, suppose you wish to continue the dosing of water to the soil. One thing to remember is that when water freezes it releases heat. Thus saturated soil which has high capacity for water does not freeze down as deeply as sandy soil. So the wet area near the trench won't freeze as deep. Here is an idea that may be considered for dosing for a considerable time into freeing weather.

Cover the trench with an insulating blanket. I'd use closed cell poly styrene (pink stuff) in full width sheets, anchor with weights (excess soil from trench) to keep it there. The water line should be wrapped with heat tape. Be sure plenty of coverage with that tape at the faucet also. 2 inch thickness is the least I'd use. Remember freezing goes in any direction, so a coverage of insulation well to the sides of trench is needed. It may help to know one trick that has been used for years to keep water pipes from freezing is allow a trickle to flow all the time.

 

[oldestguy]

Sorry, but this old guy (87 yrs) won't sleep until I can clear out one more item from my head.

Since the clay will be hard and difficult to drill my hand, consider hiring some outfit similar to us geotechs with a solid stem auger capable of drilling 4" diam. say to 4 meters, maybe a little more. One rig could follow the trench and drill a bunch of holes in short order. Fill them with clean sand. Look up "test boring" in the yellow pages. It would significantly speed up the job.

One more. That heat tape also can keep the trench from freezing. Monitor to make sure no fuses blow.

Good nite.

 

[BAretired]

Are there cracks visible in the CMU foundation walls?

BA

 

[dhengr]

FishTheStructure:
Why not use plastic perforated drain pipes with a geotextile sock for protection. Bury it just under the frost line in a layer of granular, well draining material, cap the ends and use it ‘in reverse’ to distribute, rather than collect water at that level. After a while, you could (should be able to) keep this pipe filled by filling a buried sump once a day or however often it is needed. Put the sump right near the house found. wall to keep it warm and high enough so it gravity feeds the drain tile. You could put a clear plastic sight tube through the found. wall and mounted to the inside of the found. wall so you could monitor the water level in the sump. Be careful how you fill this sump, you have to have a back-flow protector or a physical gap btwn. the hose or piping and the sump tank, to prevent any back-flow.

 

[FishTheStructure]

oldestguy,
Thanks for your many responses, especially in terms of how to implement a solution. Following up with my father regarding the wetting he did this summer, he added 750 gallons of water to the sump pit which then reverse fed the weeping tiles around the house. Taking the rest of your comments into consideration, I will have a discussion with him regarding how to move forward with additional wetting of the soil. Being the family farm, we have a bulldozer, a deep well with a jet pump, a couple ponds of water, irrigation pipes and pumps, water tanks, and various other equipment which may be beneficial to the design of a workable repair solution.


BAretired,
Yes, there are visible cracks in the CMU foundation wall. This can be seen in picture 2 on page 2 and picture 2 on page 4. The interior space is finished with the 70's favorite wood paneling so the foundation wall is not visible. Note that no water damage is visible at this point on the interior.

dhengr,
Thanks for your suggestions.


As I find this topic quite interesting, and perhaps because I am a little skeptical myself, I will try to keep the forum updated regarding the decision taken regarding how to proceed, the means and methods, and most importantly, the results of the watering.


Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein

 

[Gumpmaster]

The foundation for my house has similar problems. My neighbor's does too. My neighbor used the helical pier solution. It cost roughly $30,000 (perimeter piers only). I chose to water my foundation instead. That costs maybe $10/month in the summer. Watering the front door results in visible movement within a day. It's fascinating.

My neighbor still has problems with the interior foundations. It would probably be another $50,000 to fix all those.

 

[FishTheStructure]

Gumpmaster,

For reference,
- where are you located?
- did you cut down the trees in proximity to the damaged foundation?

Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein

 

[oldestguy]

Fisherman: Hey, expansion problems with clay are common in many parts of the world. Some ares have more montmorillonite in the clays, which makes them more active in the shrink swell properties. Montmorillonite (bentonite), commonly in a volcanic clay is really bad.

Check with your local agronomists and see what minerals are most common in your area. Some clays off from lake Ontario are pretty active. In

Wisconsin the clays from adjacent (Michigan and Superior Lakes) are pretty active, as are some residual glacial wind deposits.

 

[FishTheStructure]

oldestguy,

I found some information regarding the soil type in the reports here:

http://sis.agr.gc.ca/cansis/publications/surveys/on/on60/index.html

This report identified the house to be located within the Haldimand Clay Plain and classified the soil as Lacustrine Heavy Clay. The specific location was soil unit HIM (Haldimand); I have attached a few pages describing the composition of the soil unit HIM from this report.

Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein

 

[oldestguy]

OG again.

Sounds like the reverse drain may well work. Saves all that outside work. However, monitoring the wall is needed.
Cracks can be monitored by drawing a line across the crack. At fixed distance apart, place a cross mark. Periodically record the distance apart of the cross marks and any displacement of the main line. If you are seeing no motion, you may not be getting any water to the right places. However, that large quantity expended seems to show the drain is clear in the reverse direction. I'd stay with it for a while, but not just a periodic dosing.

Long term treatment ay well be remove the trees anyhow. The aim for these sites is keep the soil moisture content constant.

A common problem with footing drains is that clear stone has been used for the backfill around the pipe. With a flow of water towards the pipe in that stone, silt will come along and plug it. The best backfill around drain pipes is concrete fine aggregate, concrete sand.

 

[SAIL3]

oldestguy..that was an elegant solution...looks like those grey cells are still colliding...