Subgrade Stabilization

[LausDeo]

In a 50 feet continuous footing, if we encountered with 12 feet length of sand fill (SW/SP) in the center of the subgrade, what would be your recommendation to stabilize the subgrade in this location.
The depth of the sand fill is not sure, but it is approximately around 10 feet deep.

Suggestions are greatly appreciated.

Thank you.

 

[civilperson]

Vibrating plate or jumping jack compaction for the length of the footing prior to setting forms.

 

[Riggly]

What is the problem with the sand? Can you give some more info? What kinds of loads are we looking at? Have you done borings? What kind of structure? How wide is the footing? (In strip footing the effective depth is about 4B unlike 2B for retangular and square footing). Will immediate settlement be a big problem?

Civilperson, I don't think jumping jack is good for compacting sand on a subgrade. And if he needs deep compacting, the vibrating plate would not do.

 

[fattdad]

I'm with Riggly - what's the problem? What's to either side of the sand, I mean is it soft fat clay? While not likely the case, there are plenty of foundations that are supported on clean sand, heck just go to the beach for a week!

f-d

¡papá gordo ain’t no madre flaca!

 

[escrowe]

Maybe it's quick sand...

 

[Bluefoot]

If this just for constructibility, and if the fill is relatively stable and workable, e.g. compact or dense condition, groundwater controllable,etc., and your construction equipment is able to reach the bottom of fill, you may have options as:
1. Engineered fill: dig it out and relay it with engineered fill (check with a geotech engr for local specs).
2. Extended footing: construct a steepsided trench down to contact competent native soil, fill up with flowable, lean mix concrete (unshrinkable fill) to the underside of the footing. Due to the different supporting characteristics undercross the footing, transitions in subgrade or structure strengthening should be provided in the footing unit.
3. Piers or short piles.
Again, as others indicated, if data shows the fill is engineered, you do not have to remove it, get a geotechnical firm assess the condition (compactness) and if it is considered competent, you may revise you footing design based on a different soil condition and just leave it there and build your foundation over it, provided that no utilities buried within it and surface improvement carried.
Anyway, a geotechnical engineer should be involved for the site condition.