tremie slab/foundation 2

[L775]

we are building a 17 story building with 2 story underground parking. the average water table elevation is at +/-12' above the proposed top of foundation elevation. what is the best scheme the foundation system in a condition as this. what is the interaction between the tremie slab and the foundation?

thanks

 

[Lutfi]

Did you consider any of the following:

1. Dewatering
2. Coffer dams (using sheet piles)

Good luck

 

[L775]

is anyone familiar with building foundation over a tremie slab? or how does the building foundation work with the tremie slab from the design and construction point of view.
Thanks

 

[SlideRuleEra]

The tremie slab is not considered to be part of the foundation since there is a cold joint between the two and the tremie concrete is unreinforced. A typical assumption is that the foundation is sitting on the equivalent of rock.

An exception would be a pile supported foundation (piling driven inside a cofferdam before the tremie seal is placed). Then the weight of the tremie concrete is often assumed to be supported by the pile - by skin friction between the pile surface and the tremie concrete. However the foundation is still considered a separate entity.

 

[L775]

well said,
what can be done if the foundation for the building shearwalls require resistance or anchorage to prevent uplift. How can that uplift force due to wind can be transfered thru the cold joint to the piles?
Thanks

 

[TTK]

When piles are used with a tremie seal they typically project up past the top of the seal where they can tie into the rest of the foundation system

 

[L775]

Thanks, for all the responses.

1. How can that be accomplished construction wise.

2. It seems to be a complicated construction process that may require special equipment and well knowlegable, experienced, and specialized FOUNDATION CONTRACTOR.
This obviously, is not a run of the mill achivement. I do not know if it is possible for someone here who can recommend sucha contractor or company in general. Or what is the best way to find this contractor? This is not very common practice where this project is located, South Florida.
Thanks again,

 

[SlideRuleEra]

This type work is more common in bridge construction than buildings. If you make inquiries about experienced coastal bridge contractors you will be able to find the needed expertise.

 

[L775]

Thanks

 

[Prepakt1]

You can build such a foundation using fabric formwork as used for bridges. Basically a large flat bag
attached to vertical formwork for columns or walls with the required rebar extending into the bag.Holes can be cut in the bag so that the base and the first part of your columns can poured at the same time.

 

[L775]

how does the large bag look like? and what is it made of?
excuse my questions, I am not familiar with marine structures. is there a web site where I could check them out?

 

[Prepakt1]

You can go to marineconcrete.com there are several different bag details. They can be customized to a variety of shapes. Bags can be made of nylon , polypropelene or some of the other polys but nylon is by far the strongest material about twice the strength of polypropelene.Strength
of material is aconsideration as bags will burst if overpressured when pumping. For high pressures ballistic nylon is sometimes used. This is nylon in a basketweave pattern which will not tear or rip because of the cross weave.
Nylon does not float ,poly does. This makes positioning nylon underwater a lot easier.

 

[PEinc]

L775,

Don't ignore what Lutfi asked. If you have that much water, you eventually have to temporarily dewater the site to build the basement slab and foundation walls. So, you will need sheeting (essentially, a cofferdam). If the sheeting can be driven deep enough, you may not need a tremie seal. Since you have to control the flow of water from all directions (a tremie only controls the vertical flow), you will need sheet piling or some other more expensive cut-off wall (deep soil mix walls or slurry walls) around the perimeter to control the horizontal flow of water. You could also install a dewatering system such as deep wells or well points. The proper solution to your problem depends greatly on the subsurface conditions (soil layer types? rock?) and on the closeness of any adjacent structures. Also, investigate the need for underpinning any adjacent buildings, if any.

Make sure that the building's basement floor slab is properly attached to the tremie concrete or that the slab is held down some other way (tiedown anchors?) to prevent uplift from water pressure.

For a job in Florida, call Moretrench American Corporation, 973-627-2100, in New Jersey. Moretrench has a Tampa office but I would start with their office in New Jersey. They specialize in dewatering, earth support systems, and ground anchors (tiebacks and tiedowns).

 

[BK123]

L775,

I just built something very similer in Miami, Florida. You can see it at

http://www.downtowndadeland.com.

It is a +/- 7 acre 2 story underground parking garage with 7-7 story buildings on top of it. We poured 1700+ Auger Piles (both 36" and 16" for compression and tension. We excavated to -14 ft NGVD (-25 ft from ground level). We poured a 4 ft tremie seal. We then pumped down the building, plugged the small holes, cut the auger piles down to expose the steel. You bend the steel into the structural slab, placed gravel, and waterproofing. The last part was placing steel/structural slab. The tremie holds no structural value other than a plug for the water table. Columns on 36" piles and that's it. It is more complicated than this, but there is an outline of it. I don't know if it helped or not.

Here is a website that gives a little tutoral if you are interested.

http://www.pdhcenter.com/courses/g113/g113.htm