Consolidation characteristics of Marine Clays Florida Gulf Coast

[UdayRB]

I am looking for consolidation data, particularly any preconsolidation history, for marine clay deposits in the Pensacola area. These soils are at a depth of about 100' to 145' below MSL. Any references or actual lab data information would be appreciated.

 

[Focht3]

Those clays are CH materials - I believe thet are Pleistocene in age. Preconsolidation pressure is on the order of 300 to 400 feet of water. I've seen Florida geology information on the Internet; I'll bet you can find good stuff with only a little digging -



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[UdayRB]

Thanks. Unfortunately, I was not very successful in finding much data of the consolidation properties of this clay on the internet. I'll keep digging.

 

[Focht3]

These same materials appear all along the Gulf Coast. In Texas, we refer to them as the Beaumont Formation. All of the high rises in Houston bear in these clays, so they have been well studied.

Why are you looking for consolidation properties in these soils? (Describe your project and problem - in some detail, please.) Do you have any soil borings (and samples) that can be tested? Have you contacted the local universities (with engineering schools)?



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[UdayRB]

This relates to foundation support conditions for a project. I was contacted by a client after the local geotech informed him that the site was unsuitable for foundation placement. They did 5 borings at the site. The summary is as follows:

Elev> +10 to -22' Medium to dense sands SPT 22 to 76 bpf
Elev> -22' to -50' Very soft CH/OH marine clays with WOR to 2 blf consistency
Elev> -50' to -75' Medium to very dense sands 20 to 50/4" Blf
Elev> -75' to -95' Mixture of loose SM to very soft clays with WOR consistency to 4 blf
Elev> -95' to -110' Very Dense sand 50/5" blf
Elev. -110' to -140' Stiff to Very stiff clay SPT 9 to 15 blf. PPQ of 1 to 2 tsf.
Elev -140'+ Dense to very dense sand.
The local geotech did not conduct any laboratory tests on the clay strata and is concerned that extending augercast pile foundation to elevation of about -95' (which is about 15' above the clay zone) will result in excessive settlements. I am asking the client that supplementary borings and laboratory testing be conducted including at least 3 consolidation tests within the deeper clay strata. In the mean time, we wanted to get a feel for likely settlements based on the maximum foundation loading. This is in the coastal area so the minimum foundation bearing depth is -12'. The largest foundation has a load of about 9500 kips. Looking at the load transfer mechanism, the load transmitted to the deeper clay will be in the range of about 2500 psf from the pile group. So we were looking for any current data on the preconsolidation characteristics of this clay that may allow us to estimate settlements and also compare the actual laboratory data to other recorded information. Thanks for your comments.

 

[Focht3]

I participated in a study about 8 years ago on one of the barrier islands in the Pensacola area. I'm not licensed in Florida, so I didn't sign/seal the work, but I was heavily involved. (I was the chief engineer of that firm.) The strarigraphy looks very similar to what I recall - right down to the OH clays and SP sands, even the elevations. And we were coming behind a local geotech...

The principal problem that I observed was the type of drilling technology that was used: hollow stem auger. The SP sands below El. -80 ft MSL (+) were severely disturbed. Those upper sands were damn competent, and while settlement was an issue, we were able to deal with it.

Give me an email address, and I'll be happy to discuss the "characters" involved in your case off this forum. Perhaps I know some of the players -



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[UdayRB]

Focht3,
E-mail to uday@bhate-eng.com. Thanks.

 

[BigH]

UdayRB: Are you going to raise grade at the site? Other than the heavy foundation of 9500 kips, what are the typical other foundation loads - the heavy load - is it a boiler or compressor?

 

[UdayRB]

BigH: This is for a highrise building project. The load is at the shear wall foundation. The bottom of the pile cap is at about +4'MSL. Augercast piles are being considered for the project. These piles will terminate in very dense sand 50+blf SPT at either about
-60'(below the upper very soft clay layer) or go below the 2nd layer of clay to about -95'. The third layer of clay is at elevation of about -110' to -115'.

 

[BigH]

UdayRB:
Thanks for the information - I guess you can't found lighter foundations in the upper zone.
In Atlantic City, NJ, they found most of the very high rise casinos on Franki-piles (expanded base piles) for very high loadings - if I remember correctly - in excess of 250 tons. You might consider such foundations in the -95ft sand layer. You could possible get away with 20 piles or so. As this is about 100ft in length, it might be, though, at the "limit" of such piling. Contact a piling contractor to get his thoughts.

 

[UdayRB]

BigH, Thanks for your comments