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Frost Damage

Frost Damage

Frost Damage

(OP)
A friend of mine is building a house and he recently noticed his foundation walls have started to push inward. I looked at the walls, which had cracked badly and he showed me the line he had strung to measure the deflection of the wall. Three of the four corners of the house have cracks starting in the bottom intersection of the foundation walls and extend diagonally upward the top of the wall. Pictures are attached (left and right referenced from standing in the driveway and looking at the front). The right side wall has moved over 1.5". I don't think the file names are coming through with the link...most of the pictures are along the back right corner and the right side wall.

I told him that the wall can be fixed/braced, whatever needs to be done. But first he needs to determine the cause. I recommended he talk to a Geotechnical Engineer to determine the cause and then I could help with the structural fix.

I have attached a few pictures, a grading plan and the basement plan. Some other relevant information:

•Local Frost Line is 4 feet.
•He described the native soil as a heavy clay.
•The foundation was poured in the fall, it set for 1 week and then was backfilled. He said he took precautions to prevent frost from getting into the ground when he poured the footings and the foundation.
•Shortly after backfilling the ponywalls and first floor were built along with the rest of the house. No significant variations in the foundation noted.
•We have had a couple stints of unseasonably warm and cold temperatures this winter. The mean temperature in the weeks leading up to the noticeable damage was about -6C to -7C.
•The walls are 8" thick poured concrete. He says they put a few bars into the walls but nothing that you could call reinforced.
•Basement has been unheated until he noticed the movement in the walls (a few days ago). The excavator operator said it was likely frost and he should keep the basement heated. He has had a propane heater in the basement since.
•When I was on site, it was around 0C and the previous day was above 0C for most of the day. The ground was very wet.

I wasn't sure if it would be a waste of money for him to talk to the geotech, it seems likely the damage is from the frost. I don't know much about clay and thought that might complicate the problem/fix. I figured at the very least the problem would be properly documented.

I am looking for opinions on what you think could be the likely cause. I would also like to know if anyone knows how the lateral force produced from frost compares to the vertical force.

https://dl.dropboxusercontent.com/u/29304000/ENGTI...
https://dl.dropboxusercontent.com/u/29304000/ENGTI...
https://dl.dropboxusercontent.com/u/29304000/ENGTI...
https://dl.dropboxusercontent.com/u/29304000/ENGTI...
https://dl.dropboxusercontent.com/u/29304000/ENGTI...
https://dl.dropboxusercontent.com/u/29304000/ENGTI...
https://dl.dropboxusercontent.com/u/29304000/ENGTI...
https://dl.dropboxusercontent.com/u/29304000/ENGTI...

RE: Frost Damage

Why do you have a 6-8 ft high wall that retains soil with no reinforcement? Makes no sense. Of course the wall will crack and particularly so with potentially active clay soils under high moisture being retained by the wall. Someone didn't think this one through.

RE: Frost Damage

(OP)
Its times like this I wonder why they don't require minimum steel for residential foundations. I really don't think it adds that much expense. Overall it seems like a great investment.

Unfortunately, no one thought this detail through. This is the first I saw of his plans and even without seeing the tall walls, I would have recommended min reinforcing. At this point, I'm just trying to help him with the next step.

RE: Frost Damage

The top of wall elevations are all different. This, plus your mention of pony walls and the excessive deflection at the top of wall leads me to believe the floor is not bracing the top of wall. Is the footing big enough for cantilevered walls?

RE: Frost Damage

Drainage is the number one thing I would look at, and is the chief cause of cantilever retaining wall failure. Obviously, the more water in the soil when it freezes, the greater the risk of frost damage (actually, the pressure exerted by the freezing of water in the soil.)

Unless it is a fairly thick section, unreinforced may be common, but is not a great practice.

RE: Frost Damage

Sounds to me like the walls may have been backfilled before the wood framed floor system was in place. While contractors do this all the time, it is very risky and not recommended.

Is there a wood framed pony wall on top of the concrete foundation wall? If so, this creates a hinge and is a bad detail for basement walls this height ... no lateral support at top of wall. The soil pressure would have pushed the wall in at the top.

Frost could also be an issue. Once backfilled, the interior of the footings either need to be insulated or heated to prevent frost heave during winter construction. The interior footings typically only have a few inches of soil cover on the interior.

Based upon the Canadian/Ontario Building Codes, one should be able to construct an 8'2" high, 8" thick foundation wall, retaining about 7'-7" of drained backfill without any problem, it's done all the time, provided it is laterally supported top and bottom. Beyond the parameters in the code, this becomes an engineered design.

RE: Frost Damage

Since its new construction, have him contact the original engineer that stamped it for his advice...oh wait...it was more than likely not stamped.

RE: Frost Damage

Also consider if the floor joists run parallel to the top of wall, there is still effectively nothing bracing it.

RE: Frost Damage

I can't see the pictures(gov. computer doesn't like dropbox) but would guess frost action. I would guess you likely have a frost susceptible soil, more than likely a silt. Heavy clays tend to be too impermeable for frost action. Keep in mind there is a difference between freezing water and frost. Freezing water alone doesn't expand enought to cause the displacements that frost(formation of ice lenses in soil) does. It takes 3 things for frost action; extreme cold for many days, frost susceptible soils and a water table below. The water that causes these ices lenses to develop is actually drawn up from below by capillary action. To prevent frost, you have to remove one of the three.

Unreinforced basement walls are the norm. Regardless, you can't reinforce (not economically anyways) against frost. Remove the soil and or install a capillary break.

RE: Frost Damage

SkillsAndBikes:

I'm no Part 9 memory wizard (and I don't really feel like looking it up), but isn't the 8" thick wall at 8' height reinforced? It is a 10" wall that the OBC/NBCC permits to be unreinforced.

RE: Frost Damage

so has anything been done correctly?
backfill with heavy clay against unbraced, partially cured, un-reinforced concrete walls in an unheated and un-insulated structure. pictures also tend to indicate that grading for drainage away from the building was not done, it appears the ground slopes towards the building.

The cause is not frost heave or expansive clay, it is design error and construction fubar. It is likely expansive clay or possibly heavy equipment and lateral loading during the backfilling operation that cracked the walls. The cracks might not have shown up right away.

RE: Frost Damage

CEL,

OBC Part 9 - No reinforcement in an 8" wall, to 8'-2" wall height. 15MPa/20MPa concrete is permitted. The only reinforcement specified in 2006 edition is for masonry foundation walls and icf walls.

RE: Frost Damage

Wow... Learn something shocking every day. OBC Div B Table 9.15.4.2.A. (2012) Propped top and bottom, 15MPa Concrete, Height of 2.5m and less, 8"thick unreinforced wall may retain not more than 2.15m (7 feet) of free draining backfill.

I had to look it up to believe it... *sigh*

Better complete the propping of the top before the wall is ever backfilled. Crazy...

RE: Frost Damage

If it is clay soil it could be it had enough cohesion that it was more or less self supporting. Then something changed and the soil got weaker so it loaded the unreinforced/unbraced wall and broke the wall. I have seen failure cracks like that before, but that wall had reinforcing.

I don't think it is frost or expansive soils. Bad design/construction

RE: Frost Damage

(OP)
Thanks for the replies. I agree with the bad design/construction opinion, if the problem didn't show up now from the frost it would have showed itself over time. I think this was a case of multiple trades and designers doing things that aren't 100% proper but will get away with 99% of the time.

I was also surprised with how much retained soil was allowed by unreinforced concrete in the NBCC. Its interesting that the Ontario code specifies free draining backfill because I did not see that in the National code...seems like a fairly obvious requirement that they should have in there. I will have to look into my provincial building code.

I know nothing of the person who prepared the plans, there weren't likely reviewed by an engineer and did not have a stamp (prepared by a drafting company). I'm interested to hear opinions on the attached wall section. This is fairly typical around here and is routinely approved by the City. As stated already, part 9 of the code allows more than 7 feet of soil to be retained by an unreinforced wall if it is braced top and bottom. In order for the wall to be considered braced at the top, it needs to have a floor system fastened directly to the foundation (it even says parallel framing is acceptable). If the foundation wall is not braced at the top, it can only retain 1.2m of soil. The attached wall section clearly shows no acceptable means of lateral support at the top of the wall and they show a MINIMUM of 1.22m of retained soil. Of course their first note is that all work must conform to the NBCC 2010. It seems to me that they should be on the hook for the cost of repairs.

http://files.engineering.com/getfile.aspx?folder=1...

RE: Frost Damage

Appears to be both a code violation (failure to require effective lateral bracing to the top of the wall) as well as a negligent design (failure to exercise due care and skill expected of a reasonable and competent person operating in your field of endeavour).

I'd use the term "profession" rather than the obviously linguistically painful "field of endeavour", but as per ztengguy's barb there is no professional involved here.

Oh, and since you're new to our profession I'll spell one more thing out to you: The drawings must be constructable, and must include any and all details typically provided by your peers. That means that slapping "All work shall comply with (INSERT)" is never, ever, going to provide you anything more than a minor negotiation point. It won't save your license, and I certainly won't save you from liability.

Time for your friend to lawyer up, mind you they may want to start with a licensed and appropriately trained and qualified P.Eng's forensic report. I'm pretty confident you've got the right answer here, but no one can give you a professional opinion online.

RE: Frost Damage

I just love how horrible that detail is... So many things wrong! *sigh*

If I had an intern bring me that, I'd make them draw it correctly from scratch every day before they'd be allowed to go on lunch break, for at least a week.

I've not had a reputation for being a patient or forgiving mentor.

RE: Frost Damage

(OP)
CEL, I appreciate your input. I think you may be misunderstanding my position in all of this. I saw the plans for the first time when I was on site looking at the cracks in his foundation. I am just trying to help him clean up the mess. Structurally, I know very well why the walls failed...that's pretty obvious. I originally posted because I wasn't sure what loaded the wall to failure. FYI - I removed a lot of the detail from that wall section so that it would be more generic.

RE: Frost Damage

I agree the detail is poor. No engineering required when working within the confines of the prescriptive requirements of the NBCC (part 9).

As per 'code' (NBCC), this detail is permitted in certain situations. For an 8" wall, you are allowed something like 3'-11" of backfill height against a fdn wall that is laterally unsupported at the top. Not my idea of a good detail, but it does meet 'code'. Note that the backfill height is measured starting from the top of the slab-on-grade on the interior. The height of the concrete wall can be higher, its only the backfill height that is limited.

Of course, the detail is devoid of any limiting dimensions.

RE: Frost Damage

Hi CANEIT,

I think you're trying to help your friend, which I respect, and obviously this provides a learning opportunity... Just be careful not to do anything that would constitute the practice of engineering without a licensed P.Eng. supervising. Many an Engineer has regretted doing a favour for a friend.

As to the detail, this is typical of a disease rampant in the Construction industry. It seems like we are seeing more and more "detail" in drawings and less and less meaning... There is something about the human mind that makes us think we're doing a more complete job when we put more information in, whether that information is pertinent or not. I half expect to pick up a drawing in a few years and have it contain something akin to Galileo's cantilever. Just sad.

I have been, however, potentially unfair here. If the wall had been properly limited in height, and if the soil had been suitable, construction sequence monitored and correct, etc, etc, etc, this would have likely been another "fine" residential construction.

But I still don't think the designer has the faintest clue why this failed or what they could have done to prevent the failure. I'd like to ask them where they would put reinforcing bars to try to make this detail better. $50 says they'd want them on the inside face of the wall, because that's what they've always seen in foundation walls.

Just sad how little our skills are valued this day and age.

RE: Frost Damage

@SkillsAndBikes- I always wonder why the code defines the height based on the interior slab when it should be measured from top of footing. Due to shrinkage or expansion joint material, the slab provide little, if any, restraint to the wall.

RE: Frost Damage

Excel,

I don't agree. A pretty small amount of movement you can respectable restraint from the slab on grade. The expansion joint material does need to compress a little, but takes real load. The only other things you have are sliding on the bottom of the footing and passive to resist the loads at the base. You will load up the s.o.g./joint filler long before you get anything resembling passive resistance. The s.o.g. shrinkage is spread out over the area of the slab, but again, you need much more movement to get any passive resistance so the slab is going to do the work anyway. Just my opinion of course

RE: Frost Damage

Quote:

...the slab provide little, if any, restraint...
more importantly, due to construction sequencing, the interior slab on grade that is supposed to provide some lateral bracing may not have been poured or cured yet when the foundation wall was backfilled. Also, no idea of what type of material or compaction that was provided on the interior side of the footing, below the slab. So the deflection and cracking could still could have started during construction and then made worse by crappy backfill and poor drainage management

RE: Frost Damage

@Dcarr

I have never seen a slab tight against a basement wall.
As such, friction and passive pressure must be taking care of it.
I always specify a 6 mil poly bond breaker in lieu of expansion joint material.
That way I only have to worry about approximately 1/8" of movement before the slab hits the wall. (Maybe 1/4" if they added a ton of water to the concrete)
Between slab shrinkage and expansion joint material compression, you are asking for a lot of potential movement.

RE: Frost Damage

(OP)
CEL, I wouldn't go as far to say that the foundation was designed, it was drawn by a CAD technician. Unfortunately for my friend, I think this turned into a "perfect storm" of "we've always done it this way".

I understand where you were coming from with your previous comments, I've been reading this forum for a few years now and it is fairly common for people to come here looking for detailed solutions rather than a discussion of the problem. And it often seems that these people are in over their heads without much support. I'm fortunate enough to have great mentorship at work and I ran this problem by a few people knowing I would have to the solution approved by them eventually anyway. I came here for some other perspectives. Coincidentally, the same night I was out talking to my friend about this problem my application was finalized and I became a fully licensed Engineer.

I would still be interested in hearing where people think the CAD company's liability is in all of this, since as far as I can tell they clearly show a wall section that has no chance of meeting code.

RE: Frost Damage

Excel,

The expansion material doesn't flatten completely, so it takes some load pretty early on. Friction/cohesion may be doing work, but passive is not. You can't mobilize passive resistance without movement. I would agree I have never seen a joint fully closed either, but I have also seen that joint material in hundreds of buildings without ever a problem.

The problem with the 6 mil is due to roughness in walls due to forms and such the slabs are interlocked to a degree that can lead to cracking. In my neck of the woods, that type of separation doesn't work well with expansive soils. But like most engineering there are different ways to skin the cat and they all work about the same.

RE: Frost Damage

Congratulations CanPRO! Well done!!!

I used this site extensively while in my internship, and continue to learn as much from it as I contribute to it... I never had my handle changed, however, I just signed up under the new one. My previous account was YoungStructural, just didn't seem right to keep using it after ten years of doing this work.

As to the liability of the CAD company, that depends on their scope. Were they just drawing this under directions, or are they the designer of record under Part 9 and with the Building Authority? First is nearly no liability unless they erred, second case is nearly complete liability.

RE: Frost Damage

CEL,
I thought your posts looked familiar, and now I know why. I think you should amalgamate your contributions to the forums. Management can do that, by bringing your YS postings into your new identity.

How is life treating you back in Canada?

RE: Frost Damage

Heh, I had wondered if anyone would remember or recognize... It is a funny thing being away for so long and then coming back.

Life in Canada is... Odd. I've been doing some fairly specific structural work for the Canadian Federal Government (which one cannot discuss on a forum, hence the long time away) and then followed that up with a few years working principally as a Senior Project Manager. Effectively that's a glorified paper pusher, as the majority of you will know well.

I actually miss New Zealand very much, but Canada is quickly becoming home once again. As for work, while the money is very good in the day job, I missed designing too much and have started a Structural Engineering business on the side.

I'll think about amalgamating the posts; I hadn't really thought about bothering until now...

How's Aussie? You still keep in touch with the (now defunct) Connell Wagner gang at Aurecon?

RE: Frost Damage

Not much. I'm retired now, and I think they have forgotten me. All good here. Don't know how I had time to work. My golf has even improved.

RE: Frost Damage

@Dcarr

How much movement is required to achieve passive resistance?

RE: Frost Damage

We have highly plastic clays to a dept of about 40'. Lateral design soil pressures usually use a Ka=0.35 to 0.4... actual pressures can be quite a bit higher given the right circumstances. Typical foundation wall construction for the excavated part is to use a perforated geotextile covered drainage tile bedded in Pea Gravel. The backfill area is filled with lightly compacted clean granular material nearly to grade. A 6" cap of clay is placed over the granular material and 6" of topsoil is placed over this. Clay is generally separated from the clean granular material by a geotextile. The foundation wall is also dampproofed and sometimes a Miraffi drainage layer is placed on the foundation wall. Seems to work really well and there are no excessive soil pressures on the wall. Grade is well drained from the wall. Often foundation walls are supported on piles in lieu of strip footings.

I notice in the photos that the surrounding grade slopes towards the house and it may require a drainage swale.

Dik

RE: Frost Damage

(OP)
I think the CAD company was probably given the floor plan, but the wall section would have just been one of their typical details.

Thanks Dik, I've given him a similar suggestion. The final grade has not been set, there will be a retaining wall in the back corner and a swale along the back.

CEL, nothing makes you feel more at home than watching the Canadian hockey teams beat the Americans in a couple big games. Sweden is next!!

RE: Frost Damage

In Manitoba, they're allowing the bars to open at 4 AM, tomorrow for the hockey game...

Dik

RE: Frost Damage

so, do they close at 2am the nigh before, or just stay open all night?

RE: Frost Damage

I found the Finnish - USA game a good one to watch... Sorry for our US friends, but what a win for Finland!

RE: Frost Damage

CEL... you'll be happier now... When the Swedes trounced the Fins, I was a little concerned... got up early to watch the game.

Dik

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