Unconsolidated Fill

[James E. Braun, CMI]

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?

[Randy L. Mayo, PE]

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.

[mstankiewicz]

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

[Randy L. Mayo, PE]

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.

[Kenton H. Shepard, CMI]

Originally Posted by rmayo

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, is there another name for "push piers"?

[Randy L. Mayo, PE]

Ken

Push Pier, Resistance Pier are the two most common names used by the biggest manufacturers of these piers. I recommend companies that use the push pier or helical piers manufactured by Foundation Supportworks. In my opinion they are superior to the others I have researched.