Soil Borings, New Home Planned, & Best Foundation

[Runway911]

My small home is being planned for a teardown in the Chicago area in favor of a larger one. The old home has cracks in two places in the foundation easily seen in the deep basement, and a Structural Engineer I hired checked it and said it would be too costly to repair. So, I had soil borings done (don't have the actual report yet-just was done yesterday) however, the drilling company said they found bearing soil at 3-4 feet deep on the front two corners of the house, however, on the back two, where settling had occured, was found way down at 14 feet and 19 feet. Seems that this is really weird to have that much differential in only 37 feet (width of house). However, for a new foundation, what are the best recommended ways of caring for the soil conditions. I've heard of excavating and backfilling with "3-inch gravel", or using caissons/piers. Are there any other solutions, and if not, which of these is more expnseive? Appreciate any help.

 

[VAD]

Hello Runway 911:

Rather than asking which would be the more expensive is which one of the solutions would prevent the previous problem of settlement from manifesting with the new structure.

The geotechnical report should provide you with the answers you are seeking. If not then you can discuss with the geotech company the merits and demrits of the solutions in mind. I trust, however, that you asked the geotech for this type of advise.

RE costs, if both solutions were deemed acceptably for the site then of course the one that is cheaper would be much preferred. In such a case one would have to determine the costs through solicitations from contractors local to the area. One needs to have a proper outline of the work to be done in each case for proper estimates.

 

[Runway911]

Thank you for the helpful information.

 

[sinkholeorg]

In Florida it is not unusual to find varied depths along the perimeter of the property. one house we were working on the depths varied for 99 to 156 ft from one side to the other of the property.

If the deepest depth encountered was only 14-19 ft the I would highly recommend auger cast piles or helicals to be installed prior to foundation work so that the newly poured foundation would have the additional support of that load bearing strata.

Mike Mosher
Ram Jack of West Florida
866-780-2222

 

[Grouser]

Runway911

Do you have a geotechnical engineer on board? You need one who is familiar with the local conditions and construction practices.

The rear of your house could be over a relic stream bed or a poorly backfilled ravine. There are many possible reasons for the variation. The geotech's job is to identify the condition and find a solution for it for your situation. (S)He will need to know the expected loading on the foundation. This information would come from the structural engineer or architect.

Local construction practices will affect the pricing of foundation alternatives. Unless some forum members have current knowledge about Chicago area foundation pricing, we can only give answers in relative terms. The obvious basics are: more labor and materials = more expensive. Some trade-offs are not direct. For example, a pile may be cheaper but there isn't any room for the installation equipment. Or, gravel is cheaper to install but it is more expensive to obtain. This is why the local knowledge is necessary.

Good luck.

 

[Runway911]

This is such a super form for us Computer dudes (Hey, if you need server/systems help, we're here for you!) I used everyone's comments. I found out from the soil boring GeoTech Engineer that a new home would require caissons around the entire foundation. It is suspect that the Du Page River ran through the yard many years ago necessitating this. A side note - I sold my home and bought an empty lot in town and will build a new home there instead. (Anyone want to guess whether or not I did soil borings there b4 buying???? Yes - soil is excellent. Cost of two borings = 2 x $450 - $900 - everyone wants a piece of the pie.) Thanks and keep the info flowing!

 

[Focht3]

[blue]VAD[/blue] is right - other posters, too.

If you think $900 is a lot for what you received, think again. The concrete in the piers will run more than $200 per cubic yard in place - so shaving just a few inches off of each pier will more than offset the cost of the study. In the big scheme of things, that's 'dirt' cheap.

Put another way, would you let a doctor perform surgery on you without performing appropriate tests? I wouldn't.



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