7 feet of soft soil

[kansascity]

A 500 foot long by 50 foot wide area has approx 7 feet deep soft saturated fat clay. It is set to receive 13 ft of fill and hold up some small structures and possibly a parking lot. Our preliminary recommendation is to over excavate and replace the 7 feet of soft material. Any other cost effective ideas?

Thanks

kansascity

 

[civilperson]

6500 cubic yards to remove and replace seems a rather modest cost element even at $7/yd, (91,000 dollars for half acre site). Dirt is cheap compared to repair of foundation failure!

 

[MikeDB]

With 13' of fill, will the clay even be a factor?. That is deep enought that the moisture content may not vary too much. I would think that it would depend on the foundation loads and estimated settlement.

 

[Drumchaser]

With the limited info on what this loc. will be, structures being a very broad term, I would not undercut 7 ft. ...... with a proposed 13 ft. fill. Some times the deeper you get the worse it gets....water etc.

I am assuming your "soft matl." is a lower P.I. soils? If the heavy fatty clay is a big worry, you could Lime treat it about a foot thick, then begin your fill.

I have seen 10+ ft. of fill bridge a multitude of bad stuff. Once you start your fill,I would not over compact or vibrate too much until at least a few feet of new material is in place ( you might pump up some moisture etc.)Shoving a 3-5 ft lift across this area initially might be the way to go before you begin to compacting.

Good Luck

 

[civilman72]

Do you have time to surcharge the area with extra fill, and allow any settlement to take place prior to constructing the structures? If it works, it's certainly less expensive than overexcavating.

 

[Melzar]

Possibly geopiers

 

[TDAA]

I see this is somwhat old at this point, but . . . Since no one else asked: What is your concern? Is it a constructability issue, or are you concerned about long term performance, such as consolidation issues? Both?

I assume the soft material is at/near the surface. What is below? Where is ground water? Is the material suitable for reuse? Can it be properly conditioned during the construction period?