Unconsolidated Fill

FYI - The attached drawing was developed for a settlement/cracked foundation issue for one of my clients. Free for anyone to use if needed.

Randy,

Looked at a commercial building with CMU construction 2 story built in 1992, last week. No basement. 4’ footings. They did know about bad soil in one area. They thought it was corrected before construction.
Expansion joints every 20 feet. The back wall (about 30 feet wide) has a separation of the expansion joint and adjacent attached window second floor of almost 1 inch. The corner of building is sloooowly sinking.
Your illustration brought that settling to mind. Good pic.

Thanks Randy. Nice graphic.

Marc

The photos attached, from one of my clients, shows the foundation of a house that was jacked up with push piers to correct for settlement on unconsolidated fill. The house was raised about 1.5 inches.

Randy,
What is the next step, to fill the void created? What method is used?
Jeff

Jeff

The excavated soil was replaced and compacted. No attempt was made to fill the gap. The push piers are now supporting the entire weight. The interior slab was floating independent of the footing and stem wall. This end wall now acts like a grade beam and pier foundation.

That would be something to see first hand. Really interesting.

Thanks for sharing the 2 photo’s. That is a lot of weight.

I often specify/design either push piers or helical piles, and sometimes underpinning in certain circumstances, for settlement on cut-and-fill construction if it hasn’t stabelized (tough call sometimes).

Attached is an old NACHI TOD graphic on cut and fill settlement and some repair graphics … :wink:

NACHI TOD Cut & Fill.jpg

Foundation Repair - Underpinning.gif

Great info. Thanks guys.

Once a building is determined that in fact there is a footing or soil issue. You determine these devices are to be used. How do you determine the depth of the pier or pile? Bore testing? Is there a typical building age that warrants a pier or pile? Is it more to do with storm or water washout around footings and slabs? Or?
If you can suggest a good read on the subject can you forward a link.
Thanks

Try here … Roy

http://www.pieuvistech.com/html/en/about.php

I do not see any electric wires to help control the steel Posts from decaying .

I expect they were added before closing … Roy C

http://www.caproco.com/catalog/pdf/Related-Equipment/Cathodic-Protection-Pipeline-Supplies.pdf

Roy,

Thanks for the links.

Just read a few things on them. Makes sense in Canada. You can use them all year round weather conditions. Indicates they can be removable. Why would you want to remove them?

What would be interesting is what was seen to cause recommendation for repair. Cracks…? Someone notice XXX in home?

Any access to pics Randy?

Nice pics BTW… you’ve posted a few over the last year or so… do you make yourself or have a library?

Tim

This house was inspected by another home inspector that noticed a 1/4" crack in the drywall at one corner in a basement bedroom. Plus he performed a crude floor level survey on the main floor showing some elevation differences that turned out not to be structural. The buyer backed out because of his report and I was called in by the owner to give an over all structural evaluation. In general the concrete workmanship in the basement/foundation was among the worst I have seen. Nothing was square or level…so I spent more than the normal amount of time figuring out what was settlement and what was just poor workmanship. For example the foundation wall that was jacked up was about 3 inches out of square in 40 feet. Plus the basement floor slab has poured as much as one inch high and one inch low in spots. The original floor level survey elevation differences was just a reflection of a poorly finished basement floor slab and not any structural issue. So without knowing the “as built” elevations I was forced to have some of the drywall in the basement removed to expose the stem wall and lower half of the stud wall. Once exposed the problem became apparent, the stem wall had obviously rotated. The rotation was confirmed by the gap between the slab and the stem wall and the rotation of the stud wall that was on top of the stem wall. The root of all the problems was poor exterior water management which saturated the unconsolidated fill.

The answer to your second question, I do all my graphics in Corel Designer.

On a fairly new construction I see whole corners drop off foundations. Some foundation contractors claim that piering just that corner will not cause any future problems. I am always leery of that idea because the other three corners will settle and the new pier will not or not enough, causing other breaks in the foundation. Does anybody have any info on this?

James

You have a valid point that needs to be considered when using helical or push piers to lift part of a foundation. Working with soils is as much an art as a science in my opinion. Here in southern Missouri soil types, composition and depths vary significantly from house to house making each project unique. A house sitting completely on fill is most likely to have a problem with only part of the foundation supported on steel piers. Consolidation of the soils under the footings takes place over time with the majority of the settlement occurring within the first 3 to 5 years. In the case of a basement foundation sitting 6 feet below the original soil surface the foundation loading on the soil causes less consolidation then the same house sitting on a crawlspace foundation. The soil 6 foot down has been compressed by 6 foot of soil (approximately 700 psf) for thousands of years. So in theory further consolidation would not take place until your soil loading exceeds 700 psf. Depending on the size of the project soil borings could be taken and consolidations tests performed in the lab to help determine how much more settlement is expected. The cost for these test could not be justified for this $250,000 house. Only high end residential or commercial buildings would justify the cost of the tests IMO. As a side note the piers bracket can be adjusted at a later date if necessary.

Very Interesting. Randy, in your evaluation can we assume poor site preparation at the start?

Marc

It was a combination of poor compaction and poor surface water management. I didn’t go in to detail but this house also had some drainage issues that were fixed about a year before. This extra water may have accelerated the settlement problem…we will never know for sure.

Randy, is there another name for “push piers”?