Block foundation failure 2

[Hammerslinger]

thread507-73922

I've been reading about block basement foundation failures and it seems the consensus is that concrete is better.

I have to disagree. Mostly the failure masonry occurs because of undersized block, lack of vertical and horizontal reinfocing along with improper backfilling.

I speak from experience having built masonry basements. Using 10 inch block with a #5 40ksi bar in a grouted core every 4-5 feet along with horizontal truss type galvanized steel every other course. I installed the vertical steel after the wall was built. Backfill with gravel up to the frost line. In Wisconsin that is usually 4 ft. below grade. Finish the backfill with soil, which acts as a frost insulator.

I remember building a home with my method of block wall construction while a neighboring builder was building with concrete. A few weeks after his house was framed and backfilled I went over and he showed me an ugly vertical crack from top to bottom in the concrete basement foundation.

I have to say I snickered. I could see that the span of that wall, even for reinforced concrete was too long.

As for my block foundations it's been 20 years for some and none have failed even with the heavy clay soil we have in Wisconsin.

I do see many foundation failures with block wall construction and it's usually due to no vertical reinforcement and improper backfilling.

My father-in-law had to have his block basement repaired with structural steel beams at the cost of $27,000. Before that one company installed the anchor system which failed. Most likely it failed due to soil and concrete slug shear.

My basement is built with 10 inch block. It is dry and there is not a crack in it.

Semi-retired builder--carpenter/mason
Structural engineering Tech.
Former building inspector

 

[oldestguy]

OG with a story. I once was called to a house under construction in Janesville, WI where the soil is the best one can find for filling to support a slab. A garage addition was near ready for a concrete slab, except the sand and gravel fill had just been dumped in. House part was done. However, the contractor hooked up a garden hose to a pipe and jetted the fill in the garage to "consolidate" it. He was about done when the basement wall to the house caved in and most of the saturated fill ended up in the basement. The contractor stated that this is the first time this has happened in the many years he has built houses. Well, we can bet it was the last time he jets again. So using a procedure that is not necessarily an engineered one, unpleasant things can happen.

 

[Hammerslinger]

Yea a lot of stuff happens. Take the pedestrian bridge collapse in Florida. I assume it was designed by competent engineers. Was that collapse due to under reinforcing or over reinforcement or untested concrete.

In today's world the calculations might have been produced with a computer software program. The designers should have at least did a by hand number crunch or thought hey wait a minute that thing just doesn't seem right.

The quest to make a quick buck today is usually the root of many construction projects.

I have spent my entire adult life building and that has always been the case. From Banks to owners. And the there are builders who have to justify every dollar and hour spent on the project. That extra just ain't in the budget!

 

[oldestguy]

Hey that is well stated. Short cuts can bite.

 

[oldestguy]

Here is a job in my neighborhood, next block north. The contractor is an experienced guy and the availability of excavators, concrete, etc has put him into winter. Today he is placing sand fill between a filled driveway area and the wall, now about 10 days old My hand held camera set at its zoom from my living room does not do the best, but here is the picture. Let's hope that filling doesn't overload the green concrete. Some tree branches in the way also.

 

[Hammerslinger]

I have seen better bracing jobs than that. Ouch!

 

[Hammerslinger]

That looks like the situation in which my neighbor's foundation cracked.

 

[chicopee]

Hammerslinger your statment "...Take the pedestrian bridge collapse in Florida..." Now I was not there in the determination of the collapse but from the news images and TV coverages, it appeared to be more of an improper erection procedure than design.

 

[Hammerslinger]

Sure that very well could be. I was merely throwing out an example of the unexpected.

It could have been a cumulation of things. A chain of events that nobody saw coming.

 

[BridgeSmith]

Regarding the pedestrian bridge that collapsed at FIU, the NTSB put out a preliminary report indicating errors in the design, although the designers are, of course, disputing that assertion. Also in that report, the materials tested all met their design specs.

 

[oldestguy]

Just finished my walk and stopped to see the builder. Says he is waiting on Menards for the lumber (big question) so is biding time. The walls are 7-1/2" thick with some (didn't say how many) horizontal bars. Didn't seem worried, but says many have questioned what is there. Using sand backfill. Could be frozen and not noticed due to very small water content. So with warmer weather predicted, let's see what happens. I'm surprised the local code does not require thicker walls. One large jog in the one main wall may be the saving thing.

 

[BridgeSmith]

...sometimes designers don't think things through.

In my experience, more often the problems arise when the builder/contractor makes changes to the designers plans, thinking they know better or just want to do it the 'easy' way.

It appears that fairly often in residential construction, the builder does their work without design, relying on experience. If they care about the end product, the worst is that they usually overbuild. If they're not conscientious, it can lead to an inadequate build, which may eventually (or immediately) fail. Having a well engineered design usually prevents both issues (assuming it's followed).

Anyway, to return to the subject of the OP and reiterate what I said before, block or concrete walls can fail and either one can be used successfully. It depends on whether it is built adequate to the applied loading. The success of your basement and the failure of your neighbor's were neither a result of the materials used, but the result of how the materials were used.

 

[charliealphabravo]

Those are some sketchy braces if they are just toe-nailed into the nailer. I get to look at a few of these that have fallen down but there must be hundreds that escape damage or aren't known if there are no casualties.

 

[oldestguy]

For what it is worth today Dec 10th. Contractor just filled the garage area. The earlier pix was before any filling there. I have some clear shots of that now and will keep an eye on it from my easy chair a block away. Full height of garage a reasonably clean sand just dumped in. Temp below freezing still. Sand likely fresh from pit, probably not frozen.

Edit: While typing I now see they removed those braces and are grading lower floor area out if front of wall. Wow.

 

[oldestguy]

Dec 12th situation. Wall backfilled a few days back. Still holding.

Garage is to the right in photo. Hopefully this not a "before" shot.

 

[XR250]

My guess is than an engineer will be coming back to the site to address the settled garage slab at some point.

 

[oldestguy]

Agreed, especially when the owner uses sand "because it doesn't settle"?? Notice the foot prints before it snowed. Also, those 2 bys somewhat attached maybe the "straws that hold it".

 

[Hammerslinger]

Concrete has a 28 day cure to full strength. Are those tarps on ground in basement area? It used to be when winter came construction shut down.

This time of year it'll be a constant struggle to get all that site work done.

 

[oldestguy]

Concrete has a 28 day cure to full strength.

Sorry Hammerslinger this site doesn't fit that ideal. The site has had only a few days with temp at freezing point for a short time those days. Most of the temps are at 25 degrees or lower since pouring.. The last I knew, water at a temp below freezing doesn't get used for curing, thus no curing improvement then. With no free water available, no strength gain. However frozen water in the mix (as ice) may have a temporary benefit in that it is pretty strong stuff then. Needless to say, I'll keep an eye on this and add any new stuff here.

 

[hokie66]

I haven't read all of this, but I won't be rubbishing reinforced masonry as a construction method. Provided the design is good, there is adequate reinforcement correctly placed, and the grouting is thorough, reinforced masonry walls work just fine. And they have the advantage of requiring no formwork.